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C: Spectroscopy and Dynamics of Nano, Hybrid, and Low-Dimensional Materials

Fluorescent Probe of Aminopolymer Mobility in Bulk and in Nanoconfined Direct Air CO2 Capture Supports
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  • Helen Correll
    Helen Correll
    Department of Chemistry, Colorado School of Mines, 1012 14th Street, Golden, Colorado 80401, United States
    National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
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  • Noemi Leick
    Noemi Leick
    National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
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    Orcidhttps://orcid.org/0000-0002-2014-6264
  • Rachel E. Mow
    Rachel E. Mow
    Department of Chemistry, Colorado School of Mines, 1012 14th Street, Golden, Colorado 80401, United States
    National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
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  • Glory A. Russell-Parks
    Glory A. Russell-Parks
    Department of Chemistry, Colorado School of Mines, 1012 14th Street, Golden, Colorado 80401, United States
    National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
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    Orcidhttps://orcid.org/0000-0001-9059-1681
  • Simon H. Pang
    Simon H. Pang
    Materials Science Division, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, United States
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    Orcidhttps://orcid.org/0000-0003-2913-1648
  • Thomas Gennett
    Thomas Gennett
    Department of Chemistry, Colorado School of Mines, 1012 14th Street, Golden, Colorado 80401, United States
    National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
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  • Wade A. Braunecker*
    Wade A. Braunecker
    Department of Chemistry, Colorado School of Mines, 1012 14th Street, Golden, Colorado 80401, United States
    National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0003-0773-9580
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The Journal of Physical Chemistry C

Cite this: J. Phys. Chem. C 2022, 126, 25, 10419–10428
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https://doi.org/10.1021/acs.jpcc.2c01099
Published June 14, 2022

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Abstract

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Poly(ethylenimine) (PEI) is widely recognized as an efficient carbon capture medium. When loaded onto mesoporous oxide supports, the polymer becomes particularly attractive for direct air capture (DAC) applications given the high surface area of the composites, the low volatility of the polymer, and the excellent cyclability of the system. As polymer segmental mobility is coupled with CO2 uptake and diffusion, understanding how that mobility is influenced by nanoconfinement will ultimately be critical to the development of more efficient DAC systems. Here, we discuss our development of a fluorescent probe molecule based on tetrakis(4-hydroxyphenyl)ethylene. As the fluorescence intensity of this molecule and the shape of the emission spectra are strongly dependent on the viscosity of the supporting medium, doping PEI-composites with this fluorescent probe can provide sensitive indication of polymer glass transition and/or melting temperatures across a wide range of temperatures (−100 to +100 °C). Herein, we demonstrate how this molecule can be used as a ratiometric probe to study bulk PEI dynamics and confinement effects in mesoporous silica as influenced by pore functionality, polymer fill fraction, and polymer architecture.

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1. Introduction

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As countries around the world work to reduce their carbon footprint, numerous reports (1,2) and reviews (3−5) anticipate that direct air capture (DAC) systems will play an increasingly important role in curbing net global greenhouse gas emissions through CO2 removal. Among the different types of capture systems being studied for DAC, (6) chemisorbent amines, such as poly(ethylenimine) (PEI) supported in solid mesoporous oxide composites, are receiving extensive attention. (7−17) In addition to having CO2 adsorption enthalpies in an ideal range to perform separations at the low partial pressure of CO2 in air, (18) the low volatility, commercial availability, and high cyclability of PEI in combination with the high surface area of the support leave these composites well suited for DAC applications.
Understanding aminopolymer mobility plays an important, but often overlooked, role in the optimization of these DAC systems. In general, gas diffusion through any polymeric material is coupled with polymer segmental mobility. Rubbery polymers, or polymers that are employed above their glass transition temperature (Tg), are able to promote more efficient gas diffusion than glassy polymers. (19) Thus, aminopolymers with a low Tg/high mobility are attractive for promoting efficient gas diffusion in DAC. However, their segmental mobility is also dramatically influenced by the dynamic uptake and release of CO2 upon cycling, as electrostatic cross-links develop throughout the polymer when amine and CO2 react to produce carbamate species. This phenomenon significantly rigidifies the aminopolymer and can in turn create a barrier for subsequent gas diffusion. (20) For this reason, inert plasticizers and additives such as poly(ethylene glycol) (PEG) (20) have been blended with aminopolymers in an effort to decrease their rigidity and promote more optimal uptake kinetics. Additionally, polymer mobility can be influenced by a variety of surface, interface, and confinement effects (21−23) that vary quite dramatically from the bulk when loaded into nanocomposites. For example, the thermal transitions of PEG loaded into various framework supports can shift by as much as 100 °C due to different polymer–support interactions. (24) Given the myriad factors that can influence the mobility of aminopolymers and polymeric additives in DAC, the design of more efficient DAC processes would benefit from a thorough fundamental understanding of mobility.
Conventional techniques for probing generic thermal transitions and mobility of bulk polymers include viscometry, thermal or dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC). However, these techniques are often either not sensitive enough to determine transitions in thin films or at low polymer loadings in composites or they are of limited application for probing polymer properties within nanoconfined pores. Several specialized techniques have been developed to study the mechanical properties of ultrathin films, including so-called bubble inflation and buckling measurements, which have been used to characterize unique behavior induced by substrate interactions, including glassy softening (25,26) and rubbery stiffening. (27,28) Broadband dielectric spectroscopy was recently used in conjunction with NMR (29) to infer information about the mobility of specific regions of PEI under different conditions, i.e., backbone, side chain, and chain end mobility in the bulk vs in confined composites. Neutron scattering has also been employed to provide particularly rich information about the nature of PEI mobility within different mesoporous composites as a function of polymer loading and pore functionality. (30−32) However, given the vast number of parameters that can influence aminopolymer mobility in DAC systems, the development of sensitive benchtop techniques that can provide additional or complementary information to the aforementioned methods concerning mobility in nanoconfinement would be of significant value for advancing the field.
The recent development of several fluorescence techniques for characterizing glass-forming polymers (33) offers some intriguing opportunities for evaluating DAC-based systems. While fluorescence can be used to characterize the Tg of bulk polymers, (34,35) the sensitivity of this benchtop technique and its ability to provide location-specific information through the tethering of probe molecules make fluorescence particularly powerful for studying polymer properties at the nanoscale. In addition to studying glass transitions, fluorescence measurements can also aid in the physical characterization of polymeric properties such as mobility and diffusion, (36,37) physical aging, (38,39) and mechanical response. (40,41) These measurements can further be utilized to study the effects of complex geometries, including capped films, (23) multilayer films, (39,42) polymer–polymer interfaces, (43,44) and nanocomposites. (23,45) While fluorescent probes have also been tethered to PEI (46) and to the walls of mesoporous silicas (47) for various applications, to our knowledge, there are no reports on the use and development of a fluorescent probe designed specifically to study PEI thermal transitions, much less in nanoconfined systems employed in DAC.
Herein, we report our efforts to develop such a probe whereby we identified a suitable fluorogen compatible with PEI and benchmarked its response in different environments across a wide swath of temperatures. We then studied fluorescence in a series of PEI samples with different molecular weights and architectures and probed relative PEI mobility in confined mesoporous silicas as a function of different polymer loadings and pore functionalities. The results were then verified through a comparison with literature studies using other techniques to probe PEI dynamics.

2. Experimental Section

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2.1. Materials

Tetraphenylethylene (TPE) derivatives were purchased from TCI. 2,6-Dimethylbenzonitrile (DMB) was purchased from Fischer Scientific. All other reagents, chemicals, and polymers were purchased from Aldrich and used without purification, unless otherwise noted. SBA15-OH (30) and SBA15-CH3 (31) were synthesized according to literature procedures.

2.2. Fluorescent Doping Procedure

Bulk polymers and small molecules were doped with tetrakis(4-hydroxyphenyl)ethylene (THPE) (0.02–1 wt %) by stirring the mixtures under a N2 atmosphere in the dark well above the mp/glass transition temperature of a given matrix (e.g., 50 °C for branched PEI, 100 °C for linear PEI). Composites were prepared by first stirring pre-doped PEI and SBA15 in separate methanol solutions (∼10 mg/mL) for 1 h and then combining and further stirring for 3 h. The combined mixture was then placed on a rotary evaporator to remove the methanol. Final degassing was performed on a Schlenk line under vacuum (∼100 mTorr) at 110 °C for 48 h in the dark to remove any CO2, moisture, and residual solvent. Samples were left under vacuum and taken directly into an inert atmosphere for further handling.

2.3. Differential Scanning Calorimeter (DSC)

The phase changes of the samples were compared with data obtained from a TA Instruments DSC 25 equipped with a Discovery liquid N2 pump allowing a minimum sampling temperature of −150 °C. Samples were prepared under an inert He atmosphere. The system was calibrated at the temperature ramp of choice using an indium reference sample prior to the measurements. The samples were heated at a 10 °C/min ramp rate with a 50 mL/min N2 flow through the cell and a 307 mL/min base purge.

2.4. Isotherms

N2 physisorption isotherms at 77 K performed in a Micromeritics TriStar 3020 were collected with 45 s equilibration time in the p/p0 range of 0–0.001, which was decreased to 10 s for p/p0 > 0.001. From these isotherms, the specific surface area and pore volume of the samples were extracted through the Brunauer–Emmett–Teller (BET) in the range of p/p0 from 0.05 to 0.2 and the Barrett–Joyner–Halenda (BJH) method from the total N2 adsorbed at p/p0 0.95, respectively.

2.5. Thermogravimetric Analysis (TGA)

PEI content in the composites was estimated using a TA Instrument Q600 TGA apparatus and a literature procedure. (48) Weight loss from 120 to 900 °C under a 100 mL/min flow of N2 diluted air was recorded at 10 °C/min and normalized by the residual mass at 900 °C.

2.6. Photoluminescence (PL) Spectroscopy

PL experiments were conducted on a custom-built Princeton Instruments spectrometer using a liquid N2-cooled Si CCD (PyLoN) array for collecting visible–near-infrared (NIR) spectra (400–900 nm). Intensity calibration was performed daily using an IntelliCal USB-LSVN (9000-410) calibration lamp. Samples were placed in a 2 mm quartz cuvette and excited with a 365 nm light-emitting diode (LED) (7.5 nm full width at half-maximum (FWHM)). A 400 nm longpass filter was employed between the sample and collection fiber. Emission spectra were collected from 200 to 800 nm using a 150 g/mm grating with an 800 nm blaze and a 3 mm slit; 20 spectra were averaged with an overall exposure time of ∼5 s. Temperature control was achieved with an Oxford Instruments OptistatDN sample-in-N2-vapor cryostat. Unless otherwise specified, polymer samples were both cooled and heated at a rate of ∼1 °C/min. The standard error was calculated by dividing the standard deviation by the square root of the sample size, typically attained from three different independent samples.

3. Results and Discussion

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3.1. Tetraphenylethylene Derivatives as Ratiometric Fluorescent Probes

A wide variety of fluorescent probe molecules and techniques have recently been employed to study diffusion and mobility phenomena in polymer systems. (33) Among these probe techniques, aggregation-induced emission luminogens (AIEgens) are particularly sensitive to minute changes in the viscosity of their supporting matrix. AIEgens have high photoluminescent quantum yield (PLQY) when aggregated or suspended in a frozen or glassy matrix, but PLQY decreases substantially when dissolved in a fluid system. (49) Tetraphenylethylene (TPE) is an archetypal AIEgen whose derivatives have been widely used for sensing applications ranging from biomolecular science (50,51) to mechanoresponsive systems. (52) The viscosity-dependent PLQY of TPE has also recently been employed to study glass transition dynamics of amorphous polymer films. (35,53)
The fluorescence of TPE is largely governed by intramolecular rotations. (49) In a fluid matrix, rotation of the phenyl groups around their single bond axes in photoexcited TPE molecules contributes to nonradiative decay from their photoexcited state. Furthermore, the central olefinic double bond of TPE can open in the photoexcited state, leading to torsional rotation around the central C–C bond that creates significant additional friction with solvating molecules and subsequent thermal relaxation. Hence, TPE becomes virtually nonemissive when well solvated in low or nonviscous fluids. The shape of the TPE emission spectra can also be highly dependent on the viscosity of the supporting matrix, emitting a photon of one wavelength when rotational motion is restricted, but emitting at a longer wavelength when the excited state molecule can rotate into a more energetically favorable conformation with a smaller highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) transition. (54) The dependence of the shape of the emission spectrum on viscosity affords an opportunity to employ TPE derivatives as ratiometric fluorescent probes, whereby the ratios of intensities at two or more wavelengths are recorded. In this way, the technique is effectively self-referencing and allows for the comparison of samples with different geometries, light-scattering properties, concentrations of the fluorescent probe, and even loss of fluorescence intensity with time due to photobleaching. (55)
In principle, TPE derivatives can be introduced into a polymer matrix to probe mobility via several different strategies, each with its own nuanced advantages. If the probe molecule has good miscibility with the matrix over the full range of temperatures being studied, it has been demonstrated that simply doping the probe into the system can provide a reliable indicator of polymer Tg. (35) When miscibility/solubility is a concern, TPE derivatives can also be covalently tethered to aminopolymers. (35,46) For nanocomposite systems (i.e., mesoporous silica impregnated with aminopolymer), TPE can also in principle be tethered to the pore wall. (47) While we found that TPE itself is not soluble in branched PEI, the commercially available analogue tetrakis(4-hydroxyphenyl)ethylene (THPE) could be well dispersed in bulk aminopolymers (Figure 1). We thus opted to first consider simple doping strategies in this initial fluorescence investigation of PEI mobility.

Figure 1

Figure 1. Chemical structures of tetrakis(4-hydroxyphenyl)ethylene (THPE) as well as linear and branched poly(ethylenimine) (PEI) are used in this work.

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3.2. Tetrakis(4-hydroxyphenyl)ethylene (THPE) Fluorescence in Small-Molecule Matrices

As discussed, even aminopolymers with very low glass transition temperatures can effectively become glassy at higher temperatures upon CO2 uptake; thus, a fluorescent probe developed to study mobility in aminopolymer-based DAC systems would ideally operate in a predictable fashion over a wide range of temperatures. Here, we begin to benchmark the fluorescence response of THPE in several different small-molecule organic solvents, namely, tetrahydrofuran (THF), naphthalene, and 2,6-dimethylbenzonitrile (DMB), with corresponding mp values of −109, 80, and 89 °C, respectively. Small-molecule matrices were attractive for this initial study because they tend to have well-defined thermal transitions as well as tunable melting point (mp) values and polarities.
While THPE is essentially nonemissive in THF at room temperature (rt), the fluorescence spectrum of a 0.02 wt % solution of THPE in frozen THF at −180 °C showed intense emission at a λmax of 458 nm (Figure 2, top panel). This observation agrees well with previous reports citing an emission λmax near 450 nm, depending on the nature of the solid-state matrix. (56) Both the emission λmax and PLQY stayed essentially constant between −180 and −140 °C, changing less than 2%. However, between −120 and −100 °C, the relative fluorescence intensity dropped by a factor of 20 (Figure 2, middle panel), and λmax red-shifted with increasing temperature. Above −100 °C, λmax stayed essentially constant at ∼525 nm, though the signal-to-noise ratio became very poor under these conditions. Overall, the results are highly consistent with the behavior of TPE in 3-methylpentane, (54) which similarly displayed three temperature-dependent “regions” with differing fluorescence responses and emission λmax shifting from 460 to 525 nm. In the lower panel of Figure 2, we plot the change in ratiometric intensity as a function of temperature; 530 and 460 nm were selected as representative of λmax at the relatively warm and cold temperatures, respectively, for the different samples studied throughout this manuscript. From the plots in Figure 2, both fluorescence intensity at 460 nm and the change in ratiometric intensity appear to be good indicators of the mp of THF (−109 °C).

Figure 2

Figure 2. (Top) Emission spectra of tetrahydrofuran doped with 0.02 wt % THPE as it is heated through its melting point at −109 °C. Excitation at 365 nm. (Middle) Normalized fluorescence intensity at 460 nm as a function of temperature for 0.02 wt % THPE solutions in tetrahydrofuran (red circles), naphthalene (black triangles), and 2,6-dimethylbenzonitrile (blue squares). (Bottom) Ratiometric fluorescence intensity (530/460 nm) for the same data set. Dashed vertical lines indicate literature mp values.

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The same general trend in fluorescence behavior of THPE was observed for a 0.02 wt % sample doped into DMB, albeit shifted at 200 °C. This sample was prepared by stirring THPE and DMB at 110 °C for 1 h under a N2 atmosphere in the dark and then cooling to rt. The ratiometric fluorescence intensity (530/460 nm) of this sample remained relatively constant between 20 and 80 °C but then undergoes dramatic change above the mp of DMB (89 °C). While the fluorescence intensity at 460 nm drops ∼30% between 20 and 80 °C, there is a marked decrease above the mp of DMB, and the solution was only weakly emissive above 110 °C.
In contrast to the THF and DMB solutions, the ratiometric fluorescence response of THPE was markedly different when the molecule was dispersed into a matrix where it was poorly miscible, such as naphthalene. While THPE would fully dissolve in the former two solutions, rapid stirring in liquid naphthalene at 110 °C for 1 h produced a very fine suspension that scattered light, indicative of THPE aggregation. Upon heating a 0.02 wt % suspension from rt through its mp (80 °C) up to 120 °C, the emission maximum remained essentially constant near 450 nm, and no dramatic increase in ratiometric intensity near the mp of the solvent was observed as in the other two solvents. The results were consistent with our observation that THPE aggregates in liquid naphthalene, which would restrict intramolecular rotation, even above the melting temperature of the matrix. We note that while the shape of the emission spectra does not change, the absolute fluorescence intensity of THPE in naphthalene does start to drop significantly above 90 °C (Figure 2, middle panel); taken as a whole, the results suggest that THPE can be employed as a reliable indicator of small-molecule phase changes over a range of nearly 200 °C, and furthermore, the molecule is an excellent ratiometric probe over this range when well solvated in its matrix (THF and DMB).

3.3. Polymer Mobility and Thermal Transitions

3.3.1. DSC Data

Prior to investigating polymer thermal transitions with our fluorescent probe, we first used DSC to determine the effect of doping up to 1 wt % of the probe molecule into a series of PEI samples with different molecular weights and architectures. A fundamental requirement of using any probe molecule to investigate the mobility of a medium is that the presence of the probe should have a minimal effect on the medium. In Table 1, thermal transitions of the bulk polymer recorded by DSC are compared with fluorogen-doped polymer transitions for branched PEI samples with weight average molecular weights (Mw) of 800 and 25,000 g/mol and a linear PEI sample with Mw ∼ 2500 g/mol. The traces are illustrated in Figure S3 and were recorded at a heating rate of 10 °C/min. Values of Tg for the branched PEI samples were estimated at −65 and −52 °C for low- and high-molecular-weight samples, respectively. The onset of Tm for the linear PEI sample occurred at 54 °C. The values for both the branched (57) and linear (58) samples were fully consistent with literature values that employed the same heating rates. As seen in Table 1, fluorogen-doped polymer samples differed by only 1–2 °C when compared with the neat sample. Although doping at lower concentrations of a fluorogen (0.02 wt %) made these already small differences completely negligible, employing a 1 wt % fluorogen gave a substantially better signal-to-noise ratio during fluorescence measurements with polymer systems. An improved signal-to-noise ratio allowed spectra to be collected with an overall lower intensity of excitation light and/or with a shorter duration of light exposure, both of which lead to less artifacts in the mobility data (vide infra).
Table 1. Thermal Transitions Recorded with DSC (°C)a
polymerneat1 wt % TPHE
L-PEI 2500b5453
B-PEI 800c–65–64
B-PEI 25,000c–52–50
a

Heating rate = 10 °C/min.

b

Onset temperature of melting (°C).

c

Estimation of the polymer glass transition temperature (°C).

3.3.2. Photostability and Cycling

In the presence of oxygen, TPE and its derivatives can be photo-oxidized to a diphenylphenanthrene derivative within minutes of UV exposure at irradiances used in this work (∼1 mW/cm2), both in solution and in the solid state. (59) However, under an inert N2 atmosphere, we observed THPE to generally be photostable toward any degradation on the timescale of our experiments. We performed a photostability study on a 40 wt % composite of branched PEI 800 and commercial grade mesoporous silica (MCM-41). The latter parent compound had a surface area of ∼1020 m2/g, an average pore-size distribution of 2.5 nm, and a pore volume of 0.8 cm3/g. PEI was doped with 1 wt % THPE relative to the polymer. The stability of the probe was then investigated over a wide range of temperatures (−120 to 100 °C) by holding the sample at a given temperature under an inert atmosphere, exciting the sample for 5 s at ∼1 mW/cm2 of 365 nm light to collect an emission spectrum, and then performing four subsequent measurements over the course of 10 min. Emission spectra from each of these five measurements were compared and monitored for changes due to photobleaching or degradation. We found that below rt, the first and fifth emission spectra were virtually indistinguishable, implying excellent photostability under these conditions. At rt, the intensity of the first and fifth emission spectra varied only 1%. At 100 °C, the intensity of the fifth emission spectra was ∼5% lower than that of the first spectrum, though the ratiometric intensity (530/460 nm) remained essentially constant. The results suggest that the probe is more than sufficiently photostable during the collection of a typical emission spectrum to infer reliable mobility information at all temperatures employed in this manuscript.
We note that at temperatures above the Tg of the polymer, where both the polymer matrix and the THPE molecule are more mobile, longer durations of light excitation/exposure (on the order of minutes) can result in a red shift in the recorded emission spectrum as compared to a spectrum collected over 5 s. Presumably, this is the result of localized heating that can be attributed to the excited state THPE molecule rotating more freely and dissipating more energy to the matrix through nonradiative (thermal) decay mechanisms. If allowed to re-equilibrate for several minutes after longer light exposures, the spectrum will blue-shift back to its original shape. We note this as a word of caution when inferring differences in polymer mobility across samples at a given temperature; we found it is critical that light exposure is both minimized and held constant across samples. Below the polymer Tg where TPHE rotation is restricted, this reversible red–blue shift phenomenon was not observed.
We also cycled THPE-doped PEI above and below its Tg to ensure that THPE was not aggregating with time at colder temperatures and that the measurements were fully reproducible upon cycling. In Figure 3, ratiometric fluorescence intensity is illustrated for a 50 wt % composite of branched PEI 800 and mesoporous silica (SBA15-OH). PEI was doped with 1 wt % THPE and the sample was cycled six times above and below its Tg (−65 °C) for a total of 12 measurements. Figure 3 illustrates how constant the ratio remains at a given temperature, particularly for cycles 2–6. The subtle difference in ratiometric intensities between corresponding data points in cycles 1 and 2 is likely due to the uncontrolled thermal history of the first cycle (see the discussion in Section 3.3.3). Overall, the cycling experiment provides additional evidence for the reliability and reproducibility of these measurements.

Figure 3

Figure 3. Ratiometric fluorescence intensity (530/460 nm) for SBA15-OH with 50 wt % PEI doped with 1 wt % THPE. The sample was cycled 6 times between −80 and −20 °C, above and below the Tg of −65 °C.

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3.3.3. Thermal History

For most fluorescence measurements conducted in this manuscript, the intensity of the emission spectrum changes more than an order of magnitude across the temperatures investigated, dropping in intensity as the temperature is increased. As a high-fluorescence signal-to-noise ratio is typically achieved by optimizing several different light acquisition parameters for a given sample, it is desirable to optimize those parameters at the temperature where the signal is most intense so as not to risk saturating the detector midway through a series of temperature-dependent measurements with the increasing signal. For this reason, the fluorescence signal-to-noise ratio was optimized at low temperatures for most of our measurements, at which point it was pragmatic to collect spectra upon heating.
We acknowledge that measurements probing polymer mobility as a function of heating (vs cooling) are technically estimating the so-called fictive temperature of a material rather than the glass transition; the latter can only be attained upon cooling. (60) We provide several references here discussing the nuances of these parameters and perspectives on the kinetics of glass-forming polymers. (61−63) We note that it has also been proposed (64) and observed (60) that when the thermal history of a given sample is well controlled and rates of cooling and heating are equivalent, values of fictive and glass transition temperatures vary by only ∼1 °C and are thus close approximations of each other. When the rates of heating and cooling are not equivalent, volumetric changes associated with thermal expansion are complicated by the kinetics of structural recovery. The phenomenology is, however, generally well understood. (62) For example, if cooling is relatively rapid, the polymer can be kinetically arrested far from its equilibrium state. A slow heating following rapid cooling can initially result in negative thermal expansion as arrested chains are effectively afforded more time to approach their equilibrium state at a given temperature. (60) Here, we study the fluorescence response of THPE-doped PEI as a function of thermal history to gauge the sensitivity of our technique in detecting and studying such phenomena.
In Figure 4, we illustrate the fluorescence response of two samples with different thermal histories. The first was cooled slowly at 1 °C/min from 20 to −120 °C, while the second sample was quenched to −120 °C one order of magnitude more quickly (within ∼15 min). Emission spectra were then collected for both samples at a heating rate of 1 °C/min (representative spectra are illustrated in Figure S2). A comparison of the two data sets in Figure 4 reveals differences in the fluorescence response as a function of their cooling rate/thermal history. Those responses begin deviating from each other at approximately −70 °C (near Tg estimated from DSC). For the sample with equivalent rates of heating and cooling, the smooth increase in ratiometric fluorescence intensity is consistent with a general increase in mobility and/or thermal expansion of the polymer matrix. In contrast, we observed that the ratiometric response of the rapidly cooled sample initially decreased upon heating from −70 to −50 °C before increasing again at higher temperatures (see Figure 4). The results are consistent with literature examples of systems that experience negative thermal expansivity upon slow heating after rapid cooling. (60) In addition to illustrating the importance of controlling the thermal history of a sample, we believe that these results also highlight the power of the probe to detect and study sensitive changes in glass-forming kinetic phenomena, such as polymer fragility, (65) which we are currently evaluating.

Figure 4

Figure 4. Temperature dependence of the ratiometric fluorescence intensity (530/460 nm) of bulk PEI 800 doped with 1 wt % TPHE upon heating at 1 °C/min. The cooling rate of one sample was controlled at 1 °C/min (purple), while the other sample (blue) was flash-cooled to −120 °C in 15 min.

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3.3.4. PEI Molecular Weights and Architecture

The fluorescence responses of bulk linear PEI 2500 as well as branched PEI 800 and 25,000 doped with THPE are illustrated in Figure 5. The dashed lines on the plot indicate values of Tg and the onset of Tm estimated from DSC. As can be seen in this figure, there is a sharp transition in the ratiometric fluorescence response of THPE-doped linear PEI between 50 and 60 °C, which corresponds well to the onset of Tm determined by DSC as 53 °C for this sample (Table 1). The rapid change in fluorescence response is similar to that observed in the melt transitions of the small-molecule matrices discussed earlier. In the branched PEI samples, the ratiometric fluorescence response is also pronounced as the material passes through a glass transition; however, changes in fluorescence response are generally more gradual in these amorphous polymers than in systems that experience formal melting. The behavior can be rationalized by considering that glass transitions are pseudo-second-order transitions characterized by a change in the slope of a specific volume at Tg rather than a large stepwise change in specific volume at Tm (see Figure 3 in Burroughs et al. (33)).

Figure 5

Figure 5. Temperature dependence of the ratiometric fluorescence intensity (530/460 nm) of branched PEI 800 (green), branched PEI 25,000 (blue), and linear PEI 2500 (black). Dashed lines illustrate Tg and onset of Tm estimated from DSC.

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We note that certain techniques (e.g., dielectric spectroscopy) are sensitive to sub-Tg molecular motions. While the glass transition is generally believed to be associated with the coordinated motion of 50–100 carbon atoms (often labeled the α-relaxation), (66) dielectric spectroscopy has been used to identify independent movements in the side chains of PEI associated with 4–8 carbon atoms (a.k.a. β-relaxation) and terminal amino group motion (γ-relaxation) at temperatures well below Tg of branched PEI. (57) Both of these motions are believed to facilitate the physical aging phenomenon in polymers held below their Tg. (67) They have also been invoked to explain penetrant transport into glassy polymers, including diffusivity of CO2 through glassy poly(vinyl acetate) as a function of polymer aging. (68) However, it does not appear from the data illustrated in Figure 5 collected down to −150 °C that sub-Tg molecular motions can be detected with this probe molecule. The results suggest that the probe is much more adept at detecting so-called α-relaxations than β- or γ-relaxations.

3.3.5. Mobility of PEI in Confinement

Having studied the fluorescence response of THPE in bulk polymer and small-molecule matrices, we turn now to investigate the probe response in more accurate models of DAC operating systems, namely, PEI loaded mesoporous oxide composites. Interactions between the polymer and support in these composite gas sorbents are well known to influence performance in these materials; e.g., pore wall functionalization and polymer fill fraction have been correlated with CO2 sorption kinetics and capacities. (30,31) Due to the well-defined and tunable nature of mesoporous silicas such as SBA15, aminopolymer-loaded SBA15 composites are often employed in both fundamental and applied systematic DAC studies. (3) Here, we probe the mobility of PEI 800 in composites with native silanol-terminated silica (SBA15-OH) as well as hydrophobic-functionalized silica (SBA15-CH3), where silanol functional groups are capped via reaction with hexamethyldisilazane. The effect of the polymer fill fraction in both composites is also investigated.
Details of the preparation of the fluorescent-doped composites are provided in the experimental section. The surface area and pore volumes of the parent materials and composites were characterized by nitrogen-physisorption isotherms, and the PEI content was determined via TGA. Nominal polymer fill fractions of 40 and 50 wt % were targeted for SBA15-CH3 and SBA15-OH, respectively, as these values are near the theoretical loading limit for each composite. The 5 wt % composites were also used for each system for comparison to literature data concerning polymer mobility at specific fill fractions. Data characterizing these composites are summarized in Table 2. Pore-size distributions are illustrated in Figure S5.
Table 2. Characterization of PEI 800-Mesoporous Composites
samplepore volume (cm3/g)organic content (wt %)a
SBA15-OH0.994.3b
5 wt % PEI/SBA15-OH0.7511
50 wt % PEI/SBA15-OH0.0856
SBA15-CH30.668.1
5 wt % PEI/SBA15-CH30.6412
40 wt % PEI/SBA15-CH30.1645
a

Estimated from mass loss between 150 and 895 °C via TGA.

b

Partially attributed to decomposition of silanol surface groups.

Figure 6 illustrates the ratiometric fluorescence data measured for the SBA15 composites alongside bulk PEI. The data indicates that confinement of PEI in mesoporous silica in all cases significantly lowers its mobility relative to the bulk. A comparison of the fluorescence response for the two samples near their theoretical loading suggests that PEI in the SBA15-CH3 composite has higher mobility than PEI in SBA15-OH. The results are consistent with previous literature investigations using quasielastic neutron scattering (QENS) and molecular dynamics (MD) simulations to establish the nature of polymer–support interactions and polymer chain dynamics. (31) Those studies determined that hydrophobic functionalization of silica weakens the silica–PEI interactions and results in greater mobility of the PEI than in composites where more extensive hydrogen bonding with silanol surface groups existed. Furthermore, the fluorescence data suggests that PEI in both 5 wt % samples is significantly less mobile than that in the higher fill fraction composites, which is also consistent with the literature QENS studies.

Figure 6

Figure 6. Temperature dependence of the ratiometric fluorescence intensity (530/460 nm) of bulk PEI 800 as well as mesoporous silica composites with different PEI 800 loadings and surface functional groups (−OH vs −CH3).

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To reduce or eliminate the possibility that THPE may migrate as a function of temperature in the composites and begin interacting with the pore walls, we synthesized a TPE-based probe that was covalently tethered to PEI. Details of the synthesis and characterization are recorded in the Supporting Information. In Figure S9, we compare the ratiometric fluorescence intensity of a composite where THPE was doped into the system vs a composite with tethered TPE. The fluorescence responses of these two systems are remarkably similar. The results provide additional support that the polymer mobility we believe we are probing is not an artifact of temperature-dependent probe migration.
Finally, we note that thermal transitions could be detected with DSC in all composites near their theoretical loading; a shift in PEI 800 Tg was recorded from −65 °C in the bulk to between −58 and −56 °C in confinement (Figure S4). However, no thermal transitions were detected for the 5 wt % composites. In the latter samples, a relatively high fraction of the material could be present both at the polymer–support and polymer–air interfaces. This can result in a large mobility gradient across the thin supported films that can be difficult to disentangle. (69,70) Indeed it has been argued that the field needs to look beyond simple Tg measurements to characterize the dynamics of thin supported polymer films. (71) As such, this fluorescence technique allows for powerful qualitative comparisons of relative mobilities across different samples over a range of temperatures that few other benchtop techniques can provide.

4. Conclusions

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This work represents an effort to develop a suitable fluorescent probe for extracting information about aminopolymer chain dynamics in confinement that can otherwise be difficult to ascertain. After benchmarking the response of our probe in different bulk environments across a wide swath of temperatures, we determined the photo and cycling stability of the probe and established its ability to detect subtle polymer aging phenomena based on the thermal histories of the sample. We then demonstrated that these fluorescence measurements could be used to study chain dynamics across a series of PEI samples with different molecular weights and architectures. We further probed PEI chain dynamics in confined mesoporous silicas as a function of different polymer loadings and pore functionalities. The results highlight the power of the technique to detect subtle changes to polymer dynamics induced by different microenvironments in nanoporous supports using a benchtop technique. As composites with faster PEI dynamics have been found to be more efficient for CO2 capture, the results are also particularly relevant for carbon capture applications. We believe that understanding how the aminopolymer mobility is influenced by nanoconfinement and other environmental factors and conditions will ultimately be critical to the development of more efficient DAC systems employing these materials, and we contend that this technique is a powerful means for advancing that understanding.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.2c01099.

  • DSC traces, TGA data, nitrogen isotherms, emission spectra (PDF)

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Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Author
    • Wade A. Braunecker - Department of Chemistry, Colorado School of Mines, 1012 14th Street, Golden, Colorado 80401, United States;  National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States;  Orcidhttps://orcid.org/0000-0003-0773-9580;  Email: [email protected]
  • Authors
    • Helen Correll - Department of Chemistry, Colorado School of Mines, 1012 14th Street, Golden, Colorado 80401, United States;  National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
    • Noemi Leick - National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States;  Orcidhttps://orcid.org/0000-0002-2014-6264
    • Rachel E. Mow - Department of Chemistry, Colorado School of Mines, 1012 14th Street, Golden, Colorado 80401, United States;  National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
    • Glory A. Russell-Parks - Department of Chemistry, Colorado School of Mines, 1012 14th Street, Golden, Colorado 80401, United States;  National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States;  Orcidhttps://orcid.org/0000-0001-9059-1681
    • Simon H. Pang - Materials Science Division, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, United States;  Orcidhttps://orcid.org/0000-0003-2913-1648
    • Thomas Gennett - Department of Chemistry, Colorado School of Mines, 1012 14th Street, Golden, Colorado 80401, United States;  National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was authored in part by Alliance for Sustainable Energy, LLC, the manager and operator of the National Renewable Energy Laboratory for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Work at the Lawrence Livermore National Laboratory was performed under the auspices of the U.S. DOE under Contract DE-AC52-07NA27344. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

References

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This article references 71 other publications.

  1. 1
    National Academies of Sciences, Engineering, and Medicine. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda; The National Academies Press, 2019.
    Google Scholar
    There is no corresponding record for this reference.
  2. 2
    Baker, S. E.; Stolaroff, J. K.; Peridas, G.; Pang, S. H.; Goldstein, H. M.; Lucci, F. R.; Li, W.; Slessarev, E. W.; Pett-Ridge, J.; Ryerson, F. J. Getting to Neutral: Options for Negative Carbon Emissions in California, LLNL-TR-796100; Lawrence Livermore National Laboratory: Livermore, CA, 2020.
    Google Scholar
    There is no corresponding record for this reference.
  3. 3
    Sanz-Pérez, E. S.; Murdock, C. R.; Didas, S. A.; Jones, C. W. Direct Capture of CO2 from Ambient Air. Chem. Rev. 2016, 116, 11840– 11876,  DOI: 10.1021/acs.chemrev.6b00173
    Google Scholar
    3
    Direct Capture of CO2 from Ambient Air
    Sanz-Perez, Eloy S.; Murdock, Christopher R.; Didas, Stephanie A.; Jones, Christopher W.
    Chemical Reviews (Washington, DC, United States) (2016), 116 (19), 11840-11876CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review providing a historical overview of direct air capture (DAC; direct removal of CO2 from air), including an exhaustive description of the use of chem. sorbents targeted for this application, is given. Topics discussed include: introduction (CO2 emissions and related problems, processes to reduct CO2 emissions [pre-combustion, capture during combustion, post-combustion], reducing CO2 emissions vs. neg. C technologies); capturing CO2 from air (rationale and role in atm. CO2 redn., C utilization, DAC via sorbent-based processes); aq. hydroxide solvents (causticization with alkali and alkali-earth hydroxides, alternative causticization processes); solid alkali carbonates (bulk and supported alkali carbonates); org./inorg. hybrid sorbents (amines phys. adsorbed to oxide supports [temp. and moisture effects], amines covalently tethered to oxide supports [moisture effect], amines supported by solid org. material, using metal-org. frameworks (MOF) and their high degree of tunability [amines tethered to MOF]); alternative DAC approaches; feasibility, economics, and design considerations for DAC processes (thermodn. anal. of feasibility, DAC design considerations and cost ests. [aq. alk. and solid sorbent systems]); and conclusions.
  4. 4
    Beuttler, C.; Charles, L.; Wurzbacher, J. The Role of Direct Air Capture in Mitigation of Anthropogenic Greenhouse Gas Emissions. Front. Clim. 2019, 1, 10  DOI: 10.3389/fclim.2019.00010
    Google Scholar
    There is no corresponding record for this reference.
  5. 5
    Shi, X.; Xiao, H.; Azarabadi, H.; Song, J.; Wu, X.; Chen, X.; Lackner, K. S. Sorbents for the Direct Capture of CO2 from Ambient Air. Angew. Chem., Int. Ed. 2020, 59, 6984– 7006,  DOI: 10.1002/anie.201906756
    Google Scholar
    5
    Sorbents for the Direct Capture of CO2 from Ambient Air
    Shi, Xiaoyang; Xiao, Hang; Azarabadi, Habib; Song, Juzheng; Wu, Xiaolong; Chen, Xi; Lackner, Klaus S.
    Angewandte Chemie, International Edition (2020), 59 (18), 6984-7006CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. The urgency to address global climate change induced by greenhouse gas emissions is increasing. In particular, the rise in atm. CO2 levels is generating alarm. Technologies to remove CO2 from ambient air, or "direct air capture" (DAC), have recently demonstrated that they can contribute to "neg. carbon emission." Recent advances in surface chem. and material synthesis have resulted in new generations of CO2 sorbents, which may drive the future of DAC and its large-scale deployment. This Review describes major types of sorbents designed to capture CO2 from ambient air and they are categorized by the sorption mechanism: physisorption, chemisorption, and moisture-swing sorption.
  6. 6
    McQueen, N.; Gomes, K. V.; McCormick, C.; Blumanthal, K.; Pisciotta, M.; Wilcox, J. A review of direct air capture (DAC): scaling up commercial technologies and innovating for the future. Prog. Energy 2021, 3, 032001  DOI: 10.1088/2516-1083/abf1ce
    Google Scholar
    There is no corresponding record for this reference.
  7. 7
    Xu, X.; Song, C.; Andresen, J. M.; Miller, B. G.; Scaroni, A. W. Novel Polyethylenimine-Modified Mesoporous Molecular Sieve of MCM-41 Type as High-Capacity Adsorbent for CO2 Capture. Energy Fuels 2002, 16, 1463– 1469,  DOI: 10.1021/ef020058u
    Google Scholar
    7
    Novel Polyethylenimine-Modified Mesoporous Molecular Sieve of MCM-41 Type as High-Capacity Adsorbent for CO2 Capture
    Xu, Xiaochun; Song, Chunshan; Andresen, John M.; Miller, Bruce G.; Scaroni, Alan W.
    Energy & Fuels (2002), 16 (6), 1463-1469CODEN: ENFUEM; ISSN:0887-0624. (American Chemical Society)
    A nanoporous solid adsorbent suitable for "mol. basket-type" adsorption of CO2 in the condensed form was prepd. by impregnation of polyethylenimine (PEI) onto MCM-41 mesoporous mol. sieve. The phys. properties of the adsorbents were characterized by x-ray powder diffraction, N2 adsorption/desorption, and thermogravimetric anal. The structure of the MCM-41 was preserved after loading the PEI, and the PEI was uniformly dispersed into the channels of the mol. sieve. The CO2 adsorption/desorption performance was tested in a flow system using a microbalance to track the wt. change. The mesoporous mol. sieve had a synergetic effect on the adsorption of CO2 by PEI. A CO2 adsorption capacity as high as 215 mg-CO2/g-PEI was obtained with MCM-41-PEI-50 at 75°, which is 24 times higher than that of the MCM-41 and is even 2 times that of the pure PEI. With an increase in the CO2 concn. in the CO2/N2 gas mixt., the CO2 adsorption capacity increased. The cyclic adsorption/desorption operation indicated that the performance of the adsorbent was stable. The adsorbent has interest in the sequestration and storage of CO2 from combustion processes.
  8. 8
    Son, W.-J.; Choi, J.-S.; Ahn, W.-S. Adsorptive removal of carbon dioxide using polyethyleneimine-loaded mesoporous silica materials. Microporous Mesoporous Mater. 2008, 113, 31– 40,  DOI: 10.1016/j.micromeso.2007.10.049
    Google Scholar
    8
    Adsorptive removal of carbon dioxide using polyethyleneimine-loaded mesoporous silica materials
    Son, Won-Jin; Choi, Jung-Sik; Ahn, Wha-Seung
    Microporous and Mesoporous Materials (2008), 113 (1-3), 31-40CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier)
    Mesoporous silica materials, MCM-41, MCM-48, SBA-15, SBA-16, and KIT-6, were synthesized and impregnated with 50% polyethyleneimine (PEI) in methanol to evaluate the performances of the materials in terms of CO2 adsorption (adsorption-desorption in 150 min cycle each at 75°). These PEI-loaded mesoporous silica materials were characterized by XRD, N2 adsorption isotherm, TGA, and TEM/SEM to monitor their textural properties before and after PEI-impregnation. All the PEI-loaded mesoporous silica samples exhibited reversible CO2 adsorption-desorption behaviors with >99% recovery. The CO2 adsorption capacities of the materials were substantially higher than that of pure PEI (79 mg CO2/g-adsorbent), and varied in the order of KIT-6 > SBA-16 ≈ SBA-15 > MCM-48 > MCM-41. The PEI-loaded mesoporous silica samples also showed faster adsorption kinetics than pure-PEI, and the performance of these materials as a CO2 adsorbent was influenced primarily by their pore size. KIT-6 with the largest pores in 3-dimensional arrangement was impregnated with 50% PEI, and showed the highest CO2 adsorption capacity (135 mg/g-adsorbent) in the fastest response time. It also exhibited stable adsorption-desorption behavior in three consecutive test cycles in 900 min.
  9. 9
    Goeppert, A.; Czaun, M.; May, R. B.; Prakash, G. K. S.; Olah, G. A.; Narayanan, S. R. Carbon Dioxide Capture from the Air Using a Polyamine Based Regenerable Solid Adsorbent. J. Am. Chem. Soc. 2011, 133, 20164– 20167,  DOI: 10.1021/ja2100005
    Google Scholar
    9
    Carbon Dioxide Capture from the Air Using a Polyamine Based Regenerable Solid Adsorbent
    Goeppert, Alain; Czaun, Miklos; May, Robert B.; Prakash, G. K. Surya; Olah, George A.; Narayanan, S. R.
    Journal of the American Chemical Society (2011), 133 (50), 20164-20167CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Easy-to-prep. solid materials based on polyethylenimine-impregnated fumed SiO2 were superior adsorbents for direct CO2 capture from air. During the initial hours of expts., these adsorbents effectively scrubbed all CO2 from air despite its occurrence at very low concns. The effect of moisture on adsorption characteristics and capacity was examd. at room temp. Regenerative ability was also detd. in a short series of adsorption/desorption cycles.
  10. 10
    Chaikittisilp, W.; Kim, H.-J.; Jones, C. W. Mesoporous Alumina-Supported Amines as Potential Steam-Stable Adsorbents for Capturing CO2 from Simulated Flue Gas and Ambient Air. Energy Fuels 2011, 25, 5528– 5537,  DOI: 10.1021/ef201224v
    Google Scholar
    10
    Mesoporous Alumina-Supported Amines as Potential Steam-Stable Adsorbents for Capturing CO2 from Simulated Flue Gas and Ambient Air
    Chaikittisilp, Watcharop; Kim, Hyung-Ju; Jones, Christopher W.
    Energy & Fuels (2011), 25 (11), 5528-5537CODEN: ENFUEM; ISSN:0887-0624. (American Chemical Society)
    Carbon management by a means of CO2 capture from large stationary sources such as coal-fired power plants or from ambient air is a significant global issue. In the context of steam-stripping as a regeneration process for solid CO2 adsorbents, new adsorbent materials robust enough for direct contact with low temp. steam are needed. Here, mesoporous γ-alumina-supported poly(ethyleneimine) composite materials are prepd. and evaluated as effective CO2 adsorbents, using dil. CO2 streams such as simulated flue gas (10% CO2) and ultradilute streams such as simulated ambient air (400 ppm CO2). In comparison to the silica-supported amine adsorbents typically utilized for CO2 capture applications, the alumina-supported amine adsorbents give better performance in terms of both capture capacity and amine efficiency, in particular, at ambient air conditions. In addn., the alumina-supported amines are stable over short multicycle temp. swing tests and, more importantly, appear to be more robust than the silica-based counterparts upon direct contact with steam. Thus, the resulting alumina-supported amines are suggested to be promising new materials for CO2 capture processes equipped with steam-stripping regeneration, esp. from ultradilute gas streams.
  11. 11
    Sakwa-Novak, M. A.; Jones, C. W. Steam Induced Structural Changes of a Poly(ethylenimine) Impregnated γ-Alumina Sorbent for CO2 Extraction from Ambient Air. ACS Appl. Mater. Interfaces 2014, 6, 9245– 9255,  DOI: 10.1021/am501500q
    Google Scholar
    11
    Steam Induced Structural Changes of a Poly(ethylenimine) Impregnated γ-Alumina Sorbent for CO2 Extraction from Ambient Air
    Sakwa-Novak, Miles A.; Jones, Christopher W.
    ACS Applied Materials & Interfaces (2014), 6 (12), 9245-9255CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Poly(ethylenimine) [PEI]-impregnated mesoporous γ-Al2O3 sorbents are used to adsorb CO2 from simulated dry and humid ambient air, and the sorbents are regenerated in a continuous exposure flow stream environment from 5 min to 24 h. Sorbents were compared based on equil. CO2 capacity from simulated air at 400 ppm CO2, 50% relative humidity, and 30°. Their physiochem. properties were detd. by x-ray diffraction; 27Al-NMR, IR, and Raman spectroscopies; N2 physisorption; and elemental anal. Sorbents retained >90% of the initial equil. capacity (∼1.7 mmol/g) at steam exposure times up to 12 h; however, PEI leaching reduced sorbent capacity to 0.66 mmol/g after 24 h continuous treatment. The γ-Al2O3 support partially hydrated to form a boehmite crystal phase at steam times ≥90 min; however this phase transition occurred predominately between 90 min and 12 h steam treatment, slowing at longer times (12 and 24 h treatment). Evidence is presented to suggest the presence of boehmite on the sorbent surface does not significantly alter the amine efficiency of impregnated PEI. Total results suggested γ-Al2O3/PEI composite materials are promising sorbents for CO2 capture from ambient air with flowing stream regeneration.
  12. 12
    Goeppert, A.; Zhang, H.; Czaun, M.; May, R. B.; Prakash, G. K. S.; Olah, G. A.; Narayanan, S. R. Easily Regenerable Solid Adsorbents Based on Polyamines for Carbon Dioxide Capture from the Air. ChemSusChem 2014, 7, 1386– 1397,  DOI: 10.1002/cssc.201301114
    Google Scholar
    12
    Easily Regenerable Solid Adsorbents Based on Polyamines for Carbon Dioxide Capture from the Air
    Goeppert, Alain; Zhang, Hang; Czaun, Miklos; May, Robert B.; Prakash, G. K. Surya; Olah, George A.; Narayanan, S. R.
    ChemSusChem (2014), 7 (5), 1386-1397CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Adsorbents prepd. easily by impregnation of fumed silica with polyethylenimine (PEI) are promising candidates for the capture of CO2 directly from the air. These inexpensive adsorbents have high CO2 adsorption capacity at ambient temp. and can be regenerated in repeated cycles under mild conditions. Despite the very low CO2 concn., they are able to scrub efficiently all CO2 out of the air in the initial hours of the expts. The influence of parameters such as PEI loading, adsorption and desorption temp., particle size, and PEI mol. wt. on the adsorption behavior were investigated. The mild regeneration temps. required could allow the use of waste heat available in many industrial processes as well as solar heat. CO2 adsorption from the air has a no. of applications. Removal of CO2 from a closed environment, such as a submarine or space vehicles, is essential for life support. The supply of CO2-free air is also crit. for alk. fuel cells and batteries. Direct air capture of CO2 could also help mitigate the rising concerns about atm. CO2 concn. and assocd. climatic changes, while, at the same time, provide the first step for an anthropogenic carbon cycle.
  13. 13
    Zhang, H.; Goeppert, A.; Prakash, G. K. S.; Olah, G. Applicability of linear polyethylenimine supported on nano-silica for the adsorption of CO2 from various sources including dry air. RSC Adv. 2015, 5, 52550– 52562,  DOI: 10.1039/C5RA05428A
    Google Scholar
    13
    Applicability of linear polyethylenimine supported on nano-silica for the adsorption of CO2 from various sources including dry air
    Zhang, Hang; Goeppert, Alain; Prakash, G. K. Surya; Olah, George
    RSC Advances (2015), 5 (65), 52550-52562CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    Adsorbents based on linear polyethylenimines (LPEIs) supported on fumed silica were prepd. and studied for the reversible adsorption of CO2 under mild conditions from various gas mixts., including dry air with a CO2 concn. of only 400 ppm. While the adsorption kinetics were similar between linear and branched PEI impregnated on fumed silica, the desorption rate was noticeably faster on linear PEI, which is advantageous for fast adsorption/desorption cycling. The enthalpy of CO2 adsorption was also lower on LPEI based adsorbents (-43 to -53 kJ mol-1 CO2). Desorption of the adsorbed CO2 occurred rapidly at relatively low temps. (50 to 100 °C). The adsorption/desorption process can be repeated for more than one hundred cycles with no noticeable decrease in adsorption capacity even under humid conditions. The stability of the adsorbents under CO2, air, and N2 was also investigated.
  14. 14
    Sakwa-Novak, M. A.; Yoo, C.-J.; Tan, S.; Rashidi, F.; Jones, C. W. Poly(ethylenimine)-Functionalized Monolithic Alumina Honeycomb Adsorbents for CO2 Capture from Air. ChemSusChem 2016, 9, 1859– 1868,  DOI: 10.1002/cssc.201600404
    Google Scholar
    14
    Poly(ethylenimine)-Functionalized Monolithic Alumina Honeycomb Adsorbents for CO2 Capture from Air
    Sakwa-Novak, Miles A.; Yoo, Chun-Jae; Tan, Shuai; Rashidi, Fereshteh; Jones, Christopher W.
    ChemSusChem (2016), 9 (14), 1859-1868CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Development of practical, effective gas/solid contactors is an important area for CO2 capture technologies. Target CO2 capture applications, e.g,. post-combustion C capture and sequestration from power generation flue gas or CO2 directly extd. from ambient air, require high gas flow rates and low cost processing. Extruded monolithic honeycomb structures, e.g., those used in automotive catalytic converters, have excellent potential as structured contactors for CO2 adsorption applications due to the low pressure drop imposed on fluids moving through the straight channels of such structures. This work reports the impregnation of poly(ethylenimine) (PEI), an effective amino-polymer commonly reported for CO2 sepn., into extruded monolithic Al2O3 form structured CO2 sorbents. These structured sorbents were prepd. on a small scale, thoroughly characterized, and compared with powd. sorbents with similar compn. Despite consistent differences obsd. in mesopore filling with PEI between monolithic and powd. sorbents, their CO2 adsorption performance wa similar across a range of PEI contents. A larger monolithic cylinder (1 in. diam. x 4 in. length) was evaluated under conditions closer to those which may be used in large-scale applications, and showed a similar performance to the smaller monoliths and powders initially tested. This larger structure, evaluated over 5 CO2 adsorption/steam desorption cycles, demonstrated a volumetric capacity of 350 mol CO2/m3 monolith and an equilibration time of 350 min at a 0.4 m/s linear flow velocity through monolith channels with 400 ppm CO2 in N2 as adsorption gas at 30°. This volumetric capacity surpassed that of a similar, previously considered technol. which suggested CO2 could be removed from air at an operating cost as low as $100/ton.
  15. 15
    Sayari, A.; Liu, Q.; Mishra, P. Enhanced Adsorption Efficiency through Materials Design for Direct Air Capture over Supported Polyethylenimine. ChemSusChem 2016, 9, 2796– 2803,  DOI: 10.1002/cssc.201600834
    Google Scholar
    15
    Enhanced Adsorption Efficiency through Materials Design for Direct Air Capture over Supported Polyethylenimine
    Sayari, Abdelhamid; Liu, Qing; Mishra, Prashant
    ChemSusChem (2016), 9 (19), 2796-2803CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Until recently, carbon capture and sequestration (CCS) was regarded as the most promising technol. to address the alarming increase in the concn. of anthropogenic CO2 in the atm. There is now an increasing interest in carbon capture and utilization (CCU). In this context, the capture of CO2 from air is an ideal soln. to supply pure CO2 wherever it is needed. Here, we describe innovative materials for direct air capture (DAC) with unprecedented efficiency. Polyethylenimine (PEI) was supported on PME, which is an extra-large-pore silica (pore-expanded MCM-41) with its internal surfaces fully covered by a uniform layer of readily accessible C16 chains from cetyltrimethylammonium (CTMA+) cations. The CTMA+ layer plays a key role in enhancing the amine efficiency toward dry or humid ultradilute CO2 (400 ppm CO2/N2) to unprecedented levels. At the same PEI content, the amine efficiency of PEI/PME was two to four times higher than that of the corresponding calcined mesoporous silica loaded with PEI or with different combinations of C16 chains and PEI. Under humid conditions, the amine efficiency of 40 wt % PEI/PME reached 7.31 mmolCO2/gPEI, the highest ever reported for any supported PEI in the presence of 400 ppm CO2. Thus, amine accessibility, which reflects both the state of PEI dispersion and the adsorption efficiency, is intimately assocd. with the mol. design of the adsorbent.
  16. 16
    Kwon, H. T.; Sakwa-Novak, M. A.; Pang, S. H.; Sujan, A. R.; Ping, E. W.; Jones, C. W. Aminopolymer-Impregnated Hierarchical Silica Structures: Unexpected Equivalent CO2 Uptake under Simulated Air Capture and Flue Gas Capture Conditions. Chem. Mater. 2019, 31, 5229– 5237,  DOI: 10.1021/acs.chemmater.9b01474
    Google Scholar
    16
    Aminopolymer-Impregnated Hierarchical Silica Structures: Unexpected Equivalent CO2 Uptake under Simulated Air Capture and Flue Gas Capture Conditions
    Kwon, Hyuk Taek; Sakwa-Novak, Miles A.; Pang, Simon H.; Sujan, Achintya R.; Ping, Eric W.; Jones, Christopher W.
    Chemistry of Materials (2019), 31 (14), 5229-5237CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Poly(ethyleneimine)-impregnated sorbents are prepd. using a hierarchical SiO2 support with bimodal meso-/macroporosity. The sorbents behave unexpectedly during CO2 adsorption from simulated air and flue gases (400 ppm and 10% CO2) at a fixed temp., as compared to systems built on commonly studied mesoporous materials. The results demonstrate that (1) impregnation methods influence the efficacy of sorption performance and (2) the sorbents show almost similar uptake capacities under 400 ppm and 10% dry CO2 at 30°, exhibiting step-like CO2 adsorption isotherms. These unusual observations are rationalized via control expts. and a hypothesized sorption mechanism. While the sorption performance near room temp. is unexpectedly identical under 400 ppm and 10% CO2 conditions, there is an optimal temp. at each gas concn. where the uptake is maximized. The max. sorption capacities are 2.6 and 4.1 mmol CO2/g sorbent at the optimized sorption temps. using 400 ppm and 10% dry CO2, resp. The presence of H2O vapor under 400 ppm CO2 conditions further improves the sorption capacity to 3.4 mmol/g sorbent, which is the highest capacity under direct air capture conditions among known amine sorbents impregnated with a similar polymer, to the best of the knowledge.
  17. 17
    Sujan, A. R.; Pang, S. H.; Zhu, G.; Jones, C. W.; Lively, R. P. Direct CO2 Capture from Air using Poly(ethylenimine)-Loaded Polymer/Silica Fiber Sorbents. ACS Sustainable Chem. Eng. 2019, 7, 5264– 5273,  DOI: 10.1021/acssuschemeng.8b06203
    Google Scholar
    17
    Direct CO2 Capture from Air using Poly(ethylenimine)-Loaded Polymer/Silica Fiber Sorbents
    Sujan, Achintya R.; Pang, Simon H.; Zhu, Guanghui; Jones, Christopher W.; Lively, Ryan P.
    ACS Sustainable Chemistry & Engineering (2019), 7 (5), 5264-5273CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
    Direct CO2 capture from atm. air is gaining increased attention as 1 of the most scalable neg. C approaches available to tackle climate change if coupled with the sequestration of CO2 geol. Also, it can also provide CO2 for further use from a globally uniform source, which is esp. advantageous for economies without natural sources of C-based feedstocks. Solid-supported amine-based materials are effective for direct air capture (DAC) due to their high CO2 uptakes and acceptable sorption kinetics at ambient temp. We describe the application of polymer/SiO2 fiber sorbents functionalized with a primary amine-rich polymer, poly(ethylenimine) (PEI), for DAC. Monolithic fiber sorbents composed of cellulose acetate and SiO2 are synthesized via the dry-jet, wet quench spinning technique. These fibers are then functionalized with PEI (Mw 800 Da) in a simple and scalable post-spinning infusion step and tested for CO2 capture under pseudoequil. conditions as well as under breakthrough conditions. A study to study the effect of feed flow rate, adsorption temp., and presence of moisture in the feed on the CO2 breakthrough performance of a densely packed fiber sorbent module is conducted to highlight the potential application of this class of structured contactors in direct air capture. The pressure drop of these contactors at high gas velocities is also evaluated. Finally, a vacuum-assisted desorption step is demonstrated for prodn. of high-purity CO2 from both dry and humid ambient air mixts.
  18. 18
    Lively, R. P.; Realff, M. J. On thermodynamic separation efficiency: Adsorption processes. AIChE J. 2016, 62, 3699– 3705,  DOI: 10.1002/aic.15269
    Google Scholar
    18
    On thermodynamic separation efficiency: Adsorption processes
    Lively, Ryan P.; Realff, Matthew J.
    AIChE Journal (2016), 62 (10), 3699-3705CODEN: AICEAC; ISSN:0001-1541. (John Wiley & Sons, Inc.)
    A simplified thermodn. anal. of adsorption processes in temp. swing adsorption (TSA) and pressure swing adsorption (PSA) modes as a function of adsorbate concn. and the adsorbent-adsorbate interaction strength is presented in this article. The thermodn. sepn. efficiency of a TSA process is optimal at dil. feed conditions, and becomes more thermodynamically efficient with increasing adsorbate affinity even though the energy of sepn. increases. The adsorption process is spontaneous, and for a strong isotherm, the energy required to reverse the adsorption is nearly independent of the adsorbate concn. as adsorbate loading in nearly-satd. materials is essentially const. with feed concn. PSA units are efficient thermodynamically and the efficiency increases with the concn. of the desired adsorbate. This thermodn. treatment has implications for sepn. processes that address carbon emissions. TSA systems operate more efficiently (thermodynamically) in the "air capture" case because they apply work to the concd. product rather than the dil. feed.
  19. 19
    Robeson, L. M.; Liu, Q.; Freeman, B. D.; Paul, D. R. Comparison of transport properties of rubbery and glassy polymers and the relevance to the upper bound relationship. J. Membr. Sci. 2015, 476, 421– 431,  DOI: 10.1016/j.memsci.2014.11.058
    Google Scholar
    19
    Comparison of transport properties of rubbery and glassy polymers and the relevance to the upper bound relationship
    Robeson, Lloyd M.; Liu, Qiang; Freeman, Benny D.; Paul, Donald R.
    Journal of Membrane Science (2015), 476 (), 421-431CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)
    A database of permeability, diffusivity and soly. for He, H2, O2, N2, CO2 and CH4 was compiled from the literature for rubbery polymers. These data were compared with results for a similar study conducted for glassy polymers published in 2013. Based on this comparison, glassy polymers have higher soly. coeffs. than rubbery polymers due to the excess vol. (or free vol.) stemming from the non-equil. nature of polymers below the glass transition temp., Tg, which is well described by the dual-mode sorption model. When compared at equal permeability, rubbery polymers have higher diffusion coeffs. and lower soly. coeffs. Polymers having permselectivity values at or near the upper bound are virtually all glassy polymers. This phenomenon is widely ascribed to the better diffusivity selectivity of glassy vs. rubbery polymers. Comparison of the upper-bound plot of log Pi/Pj vs. log Pi (where Pi represents the permeability of the more permeable gas) shows that glassy polymers dominate the upper bounds for all 15 gas pairs possible. However, when log Pi/Pj is plotted vs. log Di, many of the gas pairs have overlapping data for glassy and rubbery polymers. Thus, glassy polymers dominate the upper bound due, in part, to their higher soly. coeffs.
  20. 20
    Sakwa-Novak, M. A.; Tan, S.; Jones, C. W. Role of Additives in Composite PEI/Oxide CO2 Adsorbents: Enhancement in the Amine Efficiency of Supported PEI by PEG in CO2 Capture from Simulated Ambient Air. ACS Appl. Mater. Interfaces 2015, 7, 24748– 24759,  DOI: 10.1021/acsami.5b07545
    Google Scholar
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    Role of Additives in Composite PEI/Oxide CO2 Adsorbents: Enhancement in the Amine Efficiency of Supported PEI by PEG in CO2 Capture from Simulated Ambient Air
    Sakwa-Novak, Miles A.; Tan, Shuai; Jones, Christopher W.
    ACS Applied Materials & Interfaces (2015), 7 (44), 24748-24759CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Supported amines are promising candidate adsorbents for the removal of CO2 from flue gases and directly from ambient air. The incorporation of additives into polymeric amines such as poly(ethylenimine) (PEI) supported on mesoporous oxides is an effective strategy to improve the performance of the materials. Here, several practical aspects of this strategy are addressed with regards to direct air capture. The influence of three additives (CTAB, PEG200, PEG1000) was systematically explored under dry simulated air capture conditions (400 ppm of CO2, 30 °C). With SBA-15 as a model support for poly(ethylenimine) (PEI), the nature of the additive induced heterogeneities in the deposition of org. on the interior and exterior of the particles, an important consideration for future scale up to practical systems. The PEG200 additive increased the obsd. thermodn. performance (∼60% increase in amine efficiency) of the adsorbents regardless of the PEI content, while the other mols. had less pos. effects. A threshold PEG200/PEI value was identified at which the diffusional limitations of CO2 within the materials were nearly eliminated. The threshold PEG/PEI ratio may have phys. origin in the interactions between PEI and PEG, as the optimal ratio corresponded to nearly equimolar OH/reactive (1°, 2°) amine ratios. The strategy is shown to be robust to the characteristics of the host support, as PEG200 improved the amine efficiency of PEI when supported on two varieties of mesoporous γ-alumina with PEI.
  21. 21
    Ellison, C. J.; Torkelson, J. M. The distribution of glass-transition temperatures in nanoscopically confined glass formers. Nat. Mater. 2003, 2, 695– 700,  DOI: 10.1038/nmat980
    Google Scholar
    21
    The distribution of glass-transition temperatures in nanoscopically confined glass formers
    Ellison, Christopher J.; Torkelson, John M.
    Nature Materials (2003), 2 (10), 695-700CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    Despite the decade-long study of the effect of nanoconfinement on the glass-transition temp. (Tg) of amorphous materials, the quest to probe the distribution of Tgs in nanoconfined glass formers has remained unfulfilled. Here the distribution of Tgs across polystyrene films has been obtained by a fluorescence/multilayer method, revealing that the enhancement of dynamics at a surface affects Tg several tens of nanometers into the film. The extent to which dynamics smoothly transition from enhanced to bulk states depends strongly on nanoconfinement. When polymer films are sufficiently thin that a redn. in thickness leads to a redn. in overall Tg, the surface-layer Tg actually increases with a redn. in overall thickness, whereas the substrate-layer Tg decreases. These results indicate that the gradient in Tg dynamics is not abrupt, and that the size of a cooperatively rearranging region is much smaller than the distance over which interfacial effects propagate.
  22. 22
    Elmahdy, M. M.; Chrissopoulou, K.; Afratis, A.; Floudas, G.; Anastasiadis, S. H. Effect of Confinement on Polymer Segmental Motion and Ion Mobility in PEO/Layered Silicate Nanocomposites. Macromolecules 2006, 39, 5170– 5173,  DOI: 10.1021/ma0608368
    Google Scholar
    22
    Effect of Confinement on Polymer Segmental Motion and Ion Mobility in PEO/Layered Silicate Nanocomposites
    Elmahdy, M. M.; Chrissopoulou, K.; Afratis, A.; Floudas, G.; Anastasiadis, S. H.
    Macromolecules (2006), 39 (16), 5170-5173CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    In this paper, a dielec. spectroscopy investigation is presented, aiming to probe the role of nanoconfinement on both the polymer and the cation dynamics utilizing intercalated polymer/layered silicate nanocomposites with ~1 nm PEO films residing within the galleries of hydrophilic Na+MMT. Confinement results in a speedup of the PEO segmental relaxation dynamics, which display an Arrhenius temp. dependence and persist for temps. much lower than the bulk Tg. Moreover, the ionic mobility is found to be enhanced in the nanocomposites.
  23. 23
    Rittigstein, P.; Priestley, R. D.; Broadbelt, L. J.; Torkelson, J. M. Model polymer nanocomposites provide an understanding of confinement effects in real nanocomposites. Nat. Mater. 2007, 6, 278– 282,  DOI: 10.1038/nmat1870
    Google Scholar
    23
    Model polymer nanocomposites provide an understanding of confinement effects in real nanocomposites
    Rittigstein, Perla; Priestley, Rodney D.; Broadbelt, Linda J.; Torkelson, John M.
    Nature Materials (2007), 6 (4), 278-282CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    Owing to the improvement of properties including cond., toughness and permeability, polymer nanocomposites are slated for applications ranging from membranes to fuel cells. The enhancement of polymer properties by the addn. of inorg. nanoparticles is a complex function of interfacial interactions, interfacial area and the distribution of inter-nano-filler distances. The latter two factors depend on nano-filler dispersion, making it difficult to develop a fundamental understanding of their effects on nanocomposite properties. Here, we design model poly(Me methacrylate)-silica and poly(2-vinyl pyridine)-silica nanocomposites consisting of polymer films confined between silica slides. We compare the dependence of the glass-transition temp. (Tg) and phys. aging on the interlayer distance in model nanocomposites with the dependence of silica nanoparticle content in real nanocomposites. We show that model nanocomposites provide a simple way to gain insight into the effect of interparticle spacing on Tg and to predict the approx. aging response of real nanocomposites.
  24. 24
    Uemura, T.; Yanai, N.; Watanabe, S.; Tanaka, H.; Numaguchi, R.; Miyahara, M. T.; Ohta, Y.; Nagaoka, M.; Kitagawa, S. Unveiling thermal transitions of polymers in subnanometre pores. Nat. Commun. 2010, 1, 83  DOI: 10.1038/ncomms1091
    Google Scholar
    24
    Unveiling thermal transitions of polymers in subnanometre pores
    Uemura Takashi; Yanai Nobuhiro; Watanabe Satoshi; Tanaka Hideki; Numaguchi Ryohei; Miyahara Minoru T; Ohta Yusuke; Nagaoka Masataka; Kitagawa Susumu
    Nature communications (2010), 1 (), 83 ISSN:.
    The thermal transitions of confined polymers are important for the application of polymers in molecular scale devices and advanced nanotechnology. However, thermal transitions of ultrathin polymer assemblies confined in subnanometre spaces are poorly understood. In this study, we show that incorporation of polyethylene glycol (PEG) into nanochannels of porous coordination polymers (PCPs) enabled observation of thermal transitions of the chain assemblies by differential scanning calorimetry. The pore size and surface functionality of PCPs can be tailored to study the transition behaviour of confined polymers. The transition temperature of PEG in PCPs was determined by manipulating the pore size and the pore-polymer interactions. It is also striking that the transition temperature of the confined PEG decreased as the molecular weight of PEG increased.
  25. 25
    Stafford, C. M.; Harrison, C.; Beers, K. L.; Karim, A.; Amis, E. J.; VanLandingham, M. R.; Kim, H.-C.; Volksen, W.; Miller, R. D.; Simonyi, E. E. A buckling-based metrology for measuring the elastic moduli of polymeric thin films. Nat. Mater. 2004, 3, 545– 550,  DOI: 10.1038/nmat1175
    Google Scholar
    25
    A buckling-based metrology for measuring the elastic moduli of polymeric thin films
    Stafford, Christopher M.; Harrison, Christopher; Beers, Kathryn L.; Karim, Alamgir; Amis, Eric J.; VanLandingham, Mark R.; Kim, Ho-Cheol; Volksen, Willi; Miller, Robert D.; Simonyi, Eva E.
    Nature Materials (2004), 3 (8), 545-550CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    As technol. continues towards smaller, thinner and lighter devices, more stringent demands are placed on thin polymer films as diffusion barriers, dielec. coatings, electronic packaging and so on. Therefore, there is a growing need for testing platforms to rapidly det. the mech. properties of thin polymer films and coatings. We introduce here an elegant, efficient measurement method that yields the elastic moduli of nanoscale polymer films in a rapid and quant. manner without the need for expensive equipment or material-specific modeling. The technique exploits a buckling instability that occurs in bilayers consisting of a stiff, thin film coated onto a relatively soft, thick substrate. Using the spacing of these highly periodic wrinkles, we calc. the film's elastic modulus by applying well-established buckling mechanics. We successfully apply this new measurement platform to several systems displaying a wide range of thicknessess (nanometer to micrometre) and moduli (MPa to GPa).
  26. 26
    Stafford, C. M.; Vogt, B. D.; Harrison, C.; Julthongpiput, D.; Huang, R. Elastic Moduli of Ultrathin Amorphous Polymer Films. Macromolecules 2006, 39, 5095– 5099,  DOI: 10.1021/ma060790i
    Google Scholar
    26
    Elastic Moduli of Ultrathin Amorphous Polymer Films
    Stafford, Christopher M.; Vogt, Bryan D.; Harrison, Christopher; Julthongpiput, Duangrut; Huang, Rui
    Macromolecules (2006), 39 (15), 5095-5099CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The elastic moduli of ultrathin poly(styrene) (PS) and poly(methylmethacrylate) (PMMA) films of thickness ranging from 200 nm to 5 nm were investigated using a buckling-based metrol. Below 40 nm, the apparent modulus of the PS and PMMA films decreases dramatically, with an order of magnitude decrease compared to bulk values for the thinnest films measured. We can account for the obsd. decrease in apparent modulus by applying a composite model based on the film having a surface layer with a reduced modulus and of finite thickness. The obsd. decrease in the apparent modulus highlights issues in mech. stability and robustness of sub-40 nm polymer films and features.
  27. 27
    O’Connell, P. A.; McKenna, G. B. The stiffening of ultrathin polymer films in the rubbery regime: The relative contributions of membrane stress and surface tension. J. Polym. Sci., Part B: Polym. Phys. 2009, 47, 2441– 2448,  DOI: 10.1002/polb.21876
    Google Scholar
    27
    The stiffening of ultrathin polymer films in the rubbery regime: The relative contributions of membrane stress and surface tension
    O'Connell, Paul A.; McKenna, Gregory B.
    Journal of Polymer Science, Part B: Polymer Physics (2009), 47 (24), 2441-2448CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
    We have previously reported on a new nanobubble inflation technique we have developed to measure the abs. creep compliance of polymer films at thicknesses down to ∼10 nm (1-5). One of the more surprising results to come out of these studies was the observation that as the film thickness decreased the rubbery plateau compliance was seen to decrease dramatically. At the thinnest film thickness (∼10 nm) the compliance decreased (or conversely the stiffness increased) by some 3 orders of magnitude from the bulk value. It is known that, at the nanometer scale, surface tension effects can become significant. We examine here the contribution of surface tension to the obsd. stiffening and show that, while the contribution is important, it does not account for the degree of stiffening obsd. This suggests that mol. or confinement induced stiffening is the major factor. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2441-2448, 2009.
  28. 28
    Li, X.; McKenna, G. B. Ultrathin Polymer Films: Rubbery Stiffening, Fragility, and Tg Reduction. Macromolecules 2015, 48, 6329– 6336,  DOI: 10.1021/acs.macromol.5b01263
    Google Scholar
    28
    Ultrathin Polymer Films: Rubbery Stiffening, Fragility, and Tg Reduction
    Li, Xiguang; McKenna, Gregory B.
    Macromolecules (Washington, DC, United States) (2015), 48 (17), 6329-6336CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The mech. and viscoelastic responses of poly(Et methacrylate) (PEMA) ultrathin films over thicknesses ranging from 21 to 112 nm have been studied using a nanobubble inflation method. The stress-strain response of the PEMA thin films shows a rubbery stiffening as the film thickness decreases, and the present results are combined with prior measurements of the rubbery stiffening index S for multiple polymers. We find that S is linearly correlated with the dynamic fragility index m. The results are also consistent with expectation from Ngai et al.'s [ J. Polym. Sci., Part B: Polym. Phys. 2013, 51 (3)] recent proposition based on his coupling model but do not seem to correlate with the mol. composite concept proposed by Page et al. [ Nano Lett. 2014, 14 (5)] as a means to explain the dependence of the rubbery stiffening on chem. structure of the polymer. In addn., we observe a redn. in glass transition temp. of as much as 15.7 K for PEMA films of 21 nm thickness.
  29. 29
    Mapesa, E. U.; Cantillo, N. M.; Hamilton, S. T.; Harris, M. A.; Zawodzinski, T. A.; Park, A.-H.; Sangoro, J. Localized and Collective Dynamics in Liquid-like Polyethylenimine-Based Nanoparticle Organic Hybrid Materials. Macromolecules 2021, 54, 2296– 2305,  DOI: 10.1021/acs.macromol.0c02370
    Google Scholar
    29
    Localized and Collective Dynamics in Liquid-like Polyethylenimine-Based Nanoparticle Organic Hybrid Materials
    Mapesa, Emmanuel Urandu; Cantillo, Nelly M.; Hamilton, Sara T.; Harris, Matthew A.; Zawodzinski Jr., Thomas A.; Alissa Park, Ah-Hyung; Sangoro, Joshua
    Macromolecules (Washington, DC, United States) (2021), 54 (5), 2296-2305CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Broadband dielec. spectroscopy, rheol., and NMR spectroscopy are employed to study mol. dynamics in a nanoparticle org. hybrid material (NOHMs) system comprising 20 wt. % silica nanoparticles ionically bonded to a polyethylenimine canopy. By comparing the neat polymer (used as a canopy) to the deriv. NOHMs, we find that timescales characterizing segmental dynamics in the NOHM are identical to those for the neat polymer. Detailed anal. of the carbon-spin lattice relaxation times yields mechanistic insights into localized and collective dynamics, in quant. agreement with dielec. results. Interestingly, the NOHMs retain liq.-like characteristics unlike conventional polymer nanocomposites but exhibit higher viscosity due to addnl. contributions from tethered polymer chains and mesoscopic structuring. These findings demonstrate the potential of achieving unique and desired material properties via NOHMs by an informed choice of the canopy material.
  30. 30
    Holewinski, A.; Sakwa-Novak, M. A.; Jones, C. W. Linking CO2 Sorption Performance to Polymer Morphology in Aminopolymer/Silica Composites through Neutron Scattering. J. Am. Chem. Soc. 2015, 137, 11749– 11759,  DOI: 10.1021/jacs.5b06823
    Google Scholar
    30
    Linking CO2 Sorption Performance to Polymer Morphology in Aminopolymer/Silica Composites through Neutron Scattering
    Holewinski, Adam; Sakwa-Novak, Miles A.; Jones, Christopher W.
    Journal of the American Chemical Society (2015), 137 (36), 11749-11759CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Composites of poly(ethylenimine) (PEI) and mesoporous silica are effective, reversible adsorbents for CO2, both from flue gas and in direct air-capture applications. The morphol. of the PEI within the silica can strongly impact the overall carbon capture efficiency and rate of satn. Here, we directly probe the spatial distribution of the supported polymer through small-angle neutron scattering (SANS). Combined with textural characterization from physisorption anal., the data indicate that PEI first forms a thin conformal coating on the pore walls, but all addnl. polymer aggregates into plug(s) that grow along the pore axis. This model is consistent with obsd. trends in amine-efficiency (CO2/N binding ratio) and pore size distributions, and points to a trade-off between achieving high chem. accessibility of the amine binding sites, which are inaccessible when they strongly interact with the silica, and high accessibility for mass transport, which can be hampered by diffusion through PEI plugs. We illustrate this design principle by demonstrating higher CO2 capacity and uptake rate for PEI supported in a hydrophobically modified silica, which exhibits repulsive interactions with the PEI, freeing up binding sites.
  31. 31
    Holewinski, A.; Sakwa-Novak, M. A.; Carrillo, J. Y.; Potter, M. E.; Ellebracht, N.; Rother, G.; Sumpter, B. G.; Jones, C. W. Aminopolymer Mobility and Support Interactions in Silica-PEI Composites for CO2 Capture Applications: A Quasielastic Neutron Scattering Study. J. Phys. Chem. B 2017, 121, 6721– 6731,  DOI: 10.1021/acs.jpcb.7b04106
    Google Scholar
    31
    Aminopolymer Mobility and Support Interactions in Silica-PEI Composites for CO2 Capture Applications: A Quasielastic Neutron Scattering Study
    Holewinski, Adam; Sakwa-Novak, Miles A.; Carrillo, Jan-Michael Y.; Potter, Matthew E.; Ellebracht, Nathan; Rother, Gernot; Sumpter, Bobby G.; Jones, Christopher W.
    Journal of Physical Chemistry B (2017), 121 (27), 6721-6731CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
    Composite gas sorbents, with an active polymer phase and a porous support, are promising materials to sep. acid gases from a variety of gas streams. Significant changes in sorption performance (capacity, rate, stability) can be achieved by tuning the polymer properties and the nature of interactions between polymer and support. This work used quasi-elastic neutron scattering (QENS) and coarse-grained mol. dynamics (MD) simulations to characterize the dynamic behavior of the most commonly reported polymer in such materials, poly(ethylenimine) (PEI), in bulk form and when supported in a mesoporous SiO2 framework. Polymer chain dynamics (rotational and translational diffusion) were characterized using two neutron back-scattering spectrometers which had overlapping time scales, ranging from pico-seconds to several nanoseconds. Two motion modes were detected for the PEI mol. in QENS. At low energy transfer, a slow process (∼200 ps) was obsd. and attributed to jump-mediated, center-of-mass diffusion. A second, fast process at ∼20 ps was obsd. and is attributed to locally confined, jump-diffusion. Characteristic data (time scale, spectral wt.) of these processes were compared to those characterized by MD; reasonable agreement was achieved. For nanopore-confined PEI, a significant redn. in polymer motion time scale was obsd. vs. bulk. The effect of SiO2 surface functionalization and polymer fill fraction in SiO2 pores (controlling the portion of polymer mols. in contact with pore walls), were examd. in detail. Hydrophobic functionalization of SiO2 led to an increased PEI mobility, above that of native silanol-terminated SiO2; however, the dynamics were still slower than those in bulk PEI. Sorbents with faster PEI dynamics were also more efficient for CO2 capture, possibly because sorption sites were more accessible than those in systems with slower PEI dynamics. Results supported the existence of a link between the support affinity for PEI and the accessibility of active sorbent functional groups.
  32. 32
    Zhang, R.; Wang, X.; Liu, S.; He, L.; Song, C.; Jiang, X.; Blach, T. P. Discovering Inherent Characteristics of Polyethylenimine-Functionalized Porous Materials for CO2 Capture. ACS Appl. Mater. Interfaces 2019, 11, 36515– 36524,  DOI: 10.1021/acsami.9b08496
    Google Scholar
    32
    Discovering Inherent Characteristics of Polyethylenimine-Functionalized Porous Materials for CO2 Capture
    Zhang, Rui; Wang, Xiaoxing; Liu, Shimin; He, Lilin; Song, Chunshan; Jiang, Xiao; Blach, Tomasz P.
    ACS Applied Materials & Interfaces (2019), 11 (40), 36515-36524CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    CO2 capture is vital for addressing greenhouse gas (GHG)-based environmental issues worldwide. Amine-polymer/silica sorbents have been extensively studied for CO2 capture, but the fundamental understandings of polyethylenimine (PEI) loading effect, thermal effect, and CO2 sorption behavior are still lacking. Small-angle neutron scattering (SANS) offers promising opportunities for characterizing CO2 sorption behavior of PEI-functionalized SBA-15. Herein, in situ SANS has been used to investigate not only PEI loading distribution but also PEI thermal swelling and temp.-dependent CO2 sorption behavior of PEI-functionalized SBA-15. The results indicate that PEI could disperse on the mesopore surface for the sample with low PEI loading, while for the sample with high PEI loading, PEI could not only disperse on the mesopore surface but also partially fill in the mesopore as plugs. The sample with high PEI loading shows a two-stage swelling of PEI with increasing temp. from 25 to 120 °C in vacuum, in which the size of the intramol. voids between PEI chains has no change from 25 to 75 °C but expands from 75 to 120 °C, whereas only a subtle swelling is obsd. up to 120 °C for the sample with low PEI loading. Besides the fact that in situ SANS successfully detects physisorbed CO2 on the mesopore surface and chemisorbed CO2 by the amine groups simultaneously: (1) the amt. of physisorbed CO2 increases with increasing pressure but decreases with increasing temp., and (2) the amt. of chemisorbed CO2 has a trend of VCO2 (75 °C) > VCO2 (120 °C) > VCO2 (25 °C). The thermal swelling of PEI causes dilation of intramol. voids and thus increases the accessibility of chemisorption sites, resulting in higher CO2 sorption capacity. Therefore, temp. and PEI swelling are essential factors for kinetic and thermodn. controls of CO2 capture in amine-functionalized porous adsorbents.
  33. 33
    Burroughs, M. J.; Christie, D.; Gray, L. A. G.; Chowdhury, M.; Priestley, R. D. 21st Century Advances in Fluorescence Techniques to Characterize Glass-Forming Polymers at the Nanoscale. Macromol. Chem. Phys. 2018, 219, 1700368  DOI: 10.1002/macp.201700368
    Google Scholar
    There is no corresponding record for this reference.
  34. 34
    Hooker, J. C.; Torkelson, J. M. Coupling of Probe Reorientation Dynamics and Rotor Motions to Polymer Relaxation As Sensed by Second Harmonic Generation and Fluorescence. Macromolecules 1995, 28, 7683– 7692,  DOI: 10.1021/ma00127a014
    Google Scholar
    34
    Coupling of Probe Reorientation Dynamics and Rotor Motions to Polymer Relaxation As Sensed by Second Harmonic Generation and Fluorescence
    Hooker, Jacob C.; Torkelson, John M.
    Macromolecules (1995), 28 (23), 7683-92CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The coupling of various rotational motions of the rotor probes 4-(tricyanovinyl)-N-(2-hydroxyethyl)-N-ethylaniline (TCl) and julolidenemalononitrile (JMN) to the relaxation dynamics of poly(Et methacrylate), poly(iso-Bu methacrylate), and an iso-Bu methacrylate-TC1 labeled methacrylate copolymer has been investigated by second harmonic generation (SHG) and steady-state fluorescence in both the glassy and rubbery states. In the rubbery state, the temp. dependence of the av. rotational reorientation relaxation times, 〈τ〉, of TC1, both doped and labeled, detd. from SHG measurements can be fitted well to the WLF equation with reasonable C1 and C2 parameters, indicating coupling to the α-relaxation in these polymer systems. The value of 〈τ〉 at the glass transition temp. and the weaker temp. dependence of 〈τ〉 in the glassy state also support the conclusion of coupling to the α-relaxation. However, from fluorescence measurements a much weaker temp. dependence is obsd. for the smaller scale motions involving internal rotations and/or isomerizations of the acceptor and/or donor moieties on TC1 and JMN, indicating significant decoupling from the α-relaxation. The decoupling of these internal probe motions from the α-relaxation mechanism is discussed in terms of x, a probe-dependent parameter introduced by Loutfy, and ξ, a parameter described by Ehrlich and Sillescu as indicating the degree of coupling to the α-relaxation. A consideration of the time scales and activation energies assocd. with the smaller scale, internal rotation of these various moieties suggests at least some coupling to sub-β-relaxations. We also note the importance of carefully considering the results of a WLF fit in order to interpret appropriately the nature of the probe coupling to the polymer relaxation.
  35. 35
    Bao, S.; Wu, Q.; Qin, W.; Yu, Q.; Wang, J.; Liang, G.; Tang, B. Z. Sensitive and reliable detection of glass transition of polymers by fluorescent probes based on AIE luminogens. Polym. Chem. 2015, 6, 3537– 3542,  DOI: 10.1039/C5PY00308C
    Google Scholar
    35
    Sensitive and reliable detection of glass transition of polymers by fluorescent probes based on AIE luminogens
    Bao, Suping; Wu, Qihua; Qin, Wei; Yu, Qiuling; Wang, Jing; Liang, Guodong; Tang, Ben Zhong
    Polymer Chemistry (2015), 6 (18), 3537-3542CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    The glass transition of polymers is an immensely-used yet less-understood phenomenon concerning the dynamics of polymer chains in bulk or in confined surroundings, which dictates directly their performances in engineering sectors. Monitoring of the glass transitions or dynamics of polymers is hampered by the lack of facile yet robust methodologies. Herein, we developed a sensitive, reliable and straightforward approach for the detection of glass transitions of polymers using fluorescent probes based on aggregation induced emission (AIE) luminogens. Fluorescence emission of polymers doped with AIE luminogens, including tetraphenylethene (TPE) or its derivs., showed a sensitive response to the glass transitions of polymers. The sensitivity of fluorescence to glass transition could be optimized by increasing TPE loading. Fluorescence intensity of TPE-doped polymers dropped as much as 25 fold with increasing temp. in the investigated range. The temp. dependence of the fluorescence intensity gave rise to the straightforward detn. of the glass transitions of the polymers. Moreover, it is worth mentioning that simply mixing AIE luminogens with polymers, rather than covalently labeling, is possible due to the AIE characteristics of the probes. This significantly facilitated measurements. Given the significant advantages of AIE luminogens as probes, including high and tunable sensitivity, immunity to aggregation, facile operation and simple data processing, fluorescence techniques based on AIE luminogens offer new access for the investigation of the glass dynamics of polymer chains in confined spaces.
  36. 36
    Paeng, K.; Swallen, S. F.; Ediger, M. D. Direct Measurement of Molecular Motion in Freestanding Polystyrene Thin Films. J. Am. Chem. Soc. 2011, 133, 8444– 8447,  DOI: 10.1021/ja2022834
    Google Scholar
    36
    Direct Measurement of Molecular Motion in Freestanding Polystyrene Thin Films
    Paeng, Keewook; Swallen, Stephen F.; Ediger, M. D.
    Journal of the American Chemical Society (2011), 133 (22), 8444-8447CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    An optical photobleaching technique has been used to measure the reorientation of dil. probes in freestanding polystyrene films as thin as 14 nm. Temp.-ramping and isothermal anisotropy measurements reveal the existence of two subsets of probe mols. with different dynamics. While the slow subset shows bulk-like dynamics, the more mobile subset reorients within a few hundred seconds even at Tg,DSC - 25 K (Tg,DSC is the glass transition temp. of bulk polystyrene). At Tg,DSC - 5 K, the mobility of these two subsets differs by 4 orders of magnitude. These data are interpreted as indicating the presence of a high-mobility layer at the film surface whose thickness is independent of polymer mol. wt. and total film thickness. The thickness of the mobile surface layer increases with temp. and equals 7 nm at Tg,DSC.
  37. 37
    Paeng, K.; Richert, R.; Ediger, M. D. Molecular mobility in supported thin films of polystyrene, poly(methyl methacrylate), and poly(2-vinyl pyridine) probed by dye reorientation. Soft Matter 2012, 8, 819– 826,  DOI: 10.1039/C1SM06501G
    Google Scholar
    37
    Molecular mobility in supported thin films of polystyrene, poly(methyl methacrylate), and poly(2-vinyl pyridine) probed by dye reorientation
    Paeng, Keewook; Richert, Ranko; Ediger, M. D.
    Soft Matter (2012), 8 (3), 819-826CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
    Temp.-ramping anisotropy measurements were used to probe the mol. mobility of fluorescent probes in polystyrene, poly(Me methacrylate), and poly(2-vinyl pyridine) films supported upon silicon wafers with native oxide coatings. All polymer films showed evidence of high mobility at the free surface. The fraction of a film with high mobility was characterized as a mobile surface layer thickness, which increased with temp. The mobile surface layer thickness for supported films of polystyrene and poly(Me methacrylate) reasonably matched that previously deduced from freestanding films of these polymers; for poly(Me methacrylate), enhanced mobility extends about 4 nm into the film from the free surface at Tg. For supported polystyrene and poly(Me methacrylate) films, the results are consistent with no decrease in mobility near the solid substrate but do not eliminate this possibility. On the other hand, the mobility of supported poly(2-vinyl pyridine) thin films provides some evidence for slower-than-bulk relaxation near the solid substrate.
  38. 38
    Ellison, C. J.; Kim, S. D.; Hall, D. B.; Torkelson, J. M. Confinement and processing effects on glass transition temperature and physical aging in ultrathin polymer films: Novel fluorescence measurements. Eur. Phys. J. E 2002, 8, 155– 166,  DOI: 10.1140/epje/i2001-10057-y
    Google Scholar
    38
    Confinement and processing effects on glass transition temperature and physical aging in ultrathin polymer films: Novel fluorescence measurements
    Ellison, C. J.; Kim, S. D.; Hall, D. B.; Torkelson, J. M.
    European Physical Journal E: Soft Matter (2002), 8 (2), 155-166CODEN: EPJSFH; ISSN:1292-8941. (EDP Sciences)
    Fluorescence intensity measurements of chromophore-doped or -labeled polymers were used for the first time to det. the effects of decreasing film thickness on glass transition temp., Tg, the relative strength of the glass transition, and the relative rate of phys. aging below Tg in supported, ultrathin polymer films. The temp. dependence of fluorescence intensity measured in the glassy state of thin and ultrathin films of pyrene-doped polystyrene (PS), poly(iso-Bu methacrylate) (PiBMA), and poly(2-vinylpyridine) (P2VP) differs from that in the rubbery state with a transition at Tg. Pos. deviations from bulk Tg are obsd. in ultrathin PiBMA and P2VP films on silica substrates while substantial neg. deviations from bulk Tg are obsd. in ultrathin PS films on silica substrates. The relative difference in the temp. dependences of fluorescence intensity in the rubbery and glassy states is usually reduced with decreasing film thickness, indicating that the strength of the glass transition is reduced in thinner films. The temp. dependence of fluorescence intensity also provides useful information on effects of processing history as well as on the degree of polymer-substrate interaction. In addn., when used as a polymer label, a mobility-sensitive rotor chromophore is demonstrated to be useful in measuring relative rates of phys. aging in films as thin as 10 nm.
  39. 39
    Priestley, R. D.; Ellison, C. J.; Broadbelt, L. J.; Torkelson, J. M. Structural Relaxation of Polymer Glasses at Surfaces, Interfaces, and In Between. Science 2005, 309, 456– 459,  DOI: 10.1126/science.1112217
    Google Scholar
    39
    Structural Relaxation of Polymer Glasses at Surfaces, Interfaces, and In Between
    Priestley, Rodney D.; Ellison, Christopher J.; Broadbelt, Linda J.; Torkelson, John M.
    Science (Washington, DC, United States) (2005), 309 (5733), 456-459CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    We analyzed the glassy-state structural relaxation of polymers near surfaces and interfaces by monitoring fluorescence in multilayer films. Relative to that of bulk, the rate of structural relaxation of poly(Me methacrylate) is reduced by a factor of 2 at a free surface and by a factor of 15 at a silica substrate interface; the latter exhibits a nearly complete arresting of relaxation. The distribution in relaxation rates extends more than 100 nm into the film interior, a distance greater than that over which surfaces and interfaces affect the glass transition temp.
  40. 40
    Askar, S.; Evans, C. M.; Torkelson, J. M. Residual stress relaxation and stiffness in spin-coated polymer films: Characterization by ellipsometry and fluorescence. Polymer 2015, 76, 113– 122,  DOI: 10.1016/j.polymer.2015.08.036
    Google Scholar
    40
    Residual stress relaxation and stiffness in spin-coated polymer films: Characterization by ellipsometry and fluorescence
    Askar, Shadid; Evans, Christopher M.; Torkelson, John M.
    Polymer (2015), 76 (), 113-122CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    Ellipsometry and fluorescence are used via measurements of film thickness and pyrenyl dye emission spectral shape, resp., to characterize residual stress relaxation in polystyrene (PS) films. In particular, fluorescence of pyrene-labeled PS (MPy-PS) films, with ∼1 mol% pyrene label, provides sensitivity to film stress relaxation and stiffness by the dependence of the ratio of the first to third vibronic peak intensities (I1/I3) of the pyrenyl dye to nanosecond-time-scale mol. caging. Both techniques show that residual stress relaxation occurs over a period of hours despite the PS films being 15-40 °C above the film glass transition temp. (Tg). Both techniques also show that film Tg is unaffected by stress relaxation, even when stress relaxation is accompanied by measurable changes in thickness. Fluorescence shows that stress relaxation time follows an Arrhenius temp. dependence with an activation energy of ∼110 kJ/mol, which is consistent with stress relaxation occurring by β-relaxation. Using a bilayer/fluorescence technique with bulk bilayer films, it was obsd. by I1/I3 measurements that a 30-nm-thick MPy-PS layer located at a glass substrate interface is stiffer than a 30-nm-thick MPy-PS layer located at a free surface. Over a 20-400 nm thickness range, fluorescence of MPy-PS films show a significant effect of substrate on mol. caging and hence stiffness, with stiffness increasing in the following order: free-standing films (no substrate) < films supported on a polydimethylsiloxane (soft) substrate < films supported on a glass (hard) substrate.
  41. 41
    Askar, S.; Torkelson, J. M. Stiffness of thin, supported polystyrene films: Free-surface, substrate, and confinement effects characterized via self-referencing fluorescence. Polymer 2016, 99, 417– 426,  DOI: 10.1016/j.polymer.2016.07.042
    Google Scholar
    41
    Stiffness of thin, supported polystyrene films: Free-surface, substrate, and confinement effects characterized via self-referencing fluorescence
    Askar, Shadid; Torkelson, John M.
    Polymer (2016), 99 (), 417-426CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    Stiffness-confinement effects are characterized via a non-contact, self-referencing fluorescence approach in polystyrene (PS) films labeled with trace levels of 1-pyrenylmethyl methacrylate. The pyrene fluorescence measurable I1/I3 is sensitive to mol. caging, which increases with stiffness. At 140 °C, mol. caging and hence stiffness in single-layer PS films supported on silica is independent of thickness down to 240 nm and increases with decreasing thickness at 165 nm and below. In contrast, near Tg at 100 °C and in the glassy state at 60 °C, mol. caging and hence stiffness in single-layer films is independent of thickness down to 63 nm and increases with decreasing thickness at 36 nm and below. In bulk bilayer films, perturbations originating at the substrate interface (free-surface interface) cause major increases (decreases) in caging and hence stiffness in 20-nm-thick substrate-adjacent (free-surface-adjacent) layers. In contrast, in 40-nm-thick bilayer films, the 20-nm-thick substrate-adjacent and free-surface-adjacent layers exhibit little difference in caging and stiffness. Thus, the gradient in stiffness from a film interface depends significantly on confinement, which we hypothesize begins to occur when thickness becomes comparable to the combined length scales over which free-surface and substrate perturbations propagate inside the film. Bulk bilayer films were used to investigate the length scales assocd. with interfacial perturbations. At 100 °C and 60 °C, stiffness-gradient length scales extend ∼45-85 nm from the substrate and ∼35-85 nm from the free surface. At 140 °C, the stiffness-gradient length scales extend ∼85-200 nm from the substrate and .ltorsim. 20 nm from the free surface.
  42. 42
    Kim, S.; Torkelson, J. M. Distribution of Glass Transition Temperatures in Free-Standing, Nanoconfined Polystyrene Films: A Test of de Gennes’ Sliding Motion Mechanism. Macromolecules 2011, 44, 4546– 4553,  DOI: 10.1021/ma200617j
    Google Scholar
    42
    Distribution of Glass Transition Temperatures in Free-Standing, Nanoconfined Polystyrene Films: A Test of de Gennes' Sliding Motion Mechanism
    Kim, Soyoung; Torkelson, John M.
    Macromolecules (Washington, DC, United States) (2011), 44 (11), 4546-4553CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Effects of nanoscale confinement on the distribution of glass transition temps. (Tgs) in free-standing polystyrene (PS) films are detd. via a multilayer/self-referencing fluorescence method employing a pyrene dye label. Av. film Tgs yield a Tg-confinement effect in agreement with the mol. wt. (MW) dependence reported by Forrest, Dalnoki-Veress, and Dutcher. Multilayer films, with one pyrene-labeled layer, reveal that a 14 nm thick free-surface layer in sufficiently thick films (≥∼56 nm) exhibits Tg = Tg,bulk - ∼34 K, independent of film thickness and indicative of a strong Tg gradient near a surface. In sufficiently thin films (≤∼56 nm), a 14 nm thick free-surface layer reports Tg that decreases with decreasing film thickness and is equal to the Tg of a 14 nm thick middle layer and the av. film Tg. Thus, the strongly perturbed Tg at the two surfaces affects Tg several tens of nanometers into and across the film, resulting in greater Tg redns. than obsd. in supported films. This study also tests de Gennes' "sliding motion mechanism", devised to explain the MW dependence of the Tg-confinement effect in free-standing films. No midlayer chain in a multilayer film forms loops or bridges reaching a surface. The de Gennes' mechanism indicates that Tg redns. occur only at locations where segments are present from chains forming loops or bridges at a surface. Major Tg redns. (as large as ∼54 K below Tg,bulk) are obsd. in midlayers of nanoconfined free-standing PS films, disproving a key premise of the mechanism.
  43. 43
    Baglay, R. R.; Roth, C. B. Communication: Experimentally determined profile of local glass transition temperature across a glassy-rubbery polymer interface with a Tg difference of 80 K. J. Chem. Phys. 2015, 143, 111101  DOI: 10.1063/1.4931403
    Google Scholar
    43
    Communication: Experimentally determined profile of local glass transition temperature across a glassy-rubbery polymer interface with a Tg difference of 80 K
    Baglay, Roman R.; Roth, Connie B.
    Journal of Chemical Physics (2015), 143 (11), 111101/1-111101/5CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    Studying the local glass transition temp. Tg across a boundary, we investigate the characteristic length scales of cooperative dynamics. High mol. wt. polymers have a large sepn. in time scales between cooperative segmental motion (α-relaxation) and chain diffusion allowing us to measure the local Tg(z) profile across a glassy-rubbery interface of polystyrene/poly(Bu methacrylate) using fluorescence. We find this profile in cooperative dynamics does not correlate with the 7-nm wide sym. compn. profile of the interface, but instead is very broad, spanning 350-400 nm from one bulk Tg value to another, and highly asym., extending further into the glassy side. (c) 2015 American Institute of Physics.
  44. 44
    Baglay, R. R.; Roth, C. B. Local glass transition temperature Tg(z) of polystyrene next to different polymers: Hard vs. soft confinement. J. Chem. Phys. 2017, 146, 203307  DOI: 10.1063/1.4975168
    Google Scholar
    44
    Local glass transition temperature Tg(z) of polystyrene next to different polymers: Hard vs. soft confinement
    Baglay, Roman R.; Roth, Connie B.
    Journal of Chemical Physics (2017), 146 (20), 203307/1-203307/13CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    The depth to which the local glass transition temp. Tg and alpha-relaxations are perturbed near a boundary is believed to be related to the characteristic length scales assocd. with cooperative dynamics in dynamically heterogeneous glasses. Following our recent work [R. R. Baglay and C. R. Roth, J. Chem. Phys. 143, 111101 (2015)] that measured a very broad 350-400 nm local Tg(z) profile across a glassy-rubbery interface of polystyrene (PS)/poly(Bu methacrylate) (PnBMA), we compare here how the Tg(z) profile in PS varies when changing the neighboring polymer from a lower Tg material to a higher Tg material. Here we report local Tg(z) profiles for PS when in contact with polysulfone (PSF), poly(Me methacrylate) (PMMA), and poly(iso-Bu methacrylate) (PiBMA). We find that the distance from the interface before bulk Tg of PS (Tgbulk = 101 °C) is recovered depends on whether PS forms the high-Tg glassy component experiencing so-called soft confinement, z ≈ 225-250 nm for PS next to PiBMA (Tgbulk = 62 °C) and PnBMA (Tgbulk = 21 °C), or PS forms the low-Tg rubbery component experiencing hard confinement, z ≈ 100-125 nm for PS next to PSF (Tgbulk = 186 °C) and PMMA (Tgbulk = 120 °C). The depth to which these Tg(z) perturbations persist and the magnitude of the local Tg perturbation at the interface are independent of the difference in Tgbulk between the two polymers, the interaction parameter, and the chem. structure. We demonstrate that these broad, extended Tg(z) length scales appear to be universal across these different systems but show that the strong dynamical coupling across the dissimilar polymer-polymer interface only occurs when this interface has been annealed to equil. We consider why dissimilar polymer-polymer interfaces exhibit continuous local dynamics across the interface in contrast to polymer-free surface, polymer-substrate, or polymer-liq. interfaces that show discontinuous local dynamics. (c) 2017 American Institute of Physics.
  45. 45
    Mundra, M. K.; Ellison, C. J.; Rittigstein, P.; Torkelson, J. M. Fluorescence studies of confinement in polymer films and nanocomposites: Glass transition temperature, plasticizer effects, and sensitivity to stress relaxation and local polarity. Eur. Phys. J. Spec. Top. 2007, 141, 143,  DOI: 10.1140/epjst/e2007-00032-0
    Google Scholar
    There is no corresponding record for this reference.
  46. 46
    Lu, W.; Xiao, P.; Gu, J.; Zhang, J.; Huang, Y.; Huang, Q.; Chen, T. Aggregation-induced emission of tetraphenylethylene-modified polyethyleneimine for highly selective CO2 detection. Sens. Actuators, B 2016, 228, 551– 556,  DOI: 10.1016/j.snb.2016.01.096
    Google Scholar
    46
    Aggregation-induced emission of tetraphenylethylene-modified polyethyleneimine for highly selective CO2 detection
    Lu, Wei; Xiao, Peng; Gu, Jincui; Zhang, Jiawei; Huang, Youju; Huang, Qing; Chen, Tao
    Sensors and Actuators, B: Chemical (2016), 228 (), 551-556CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
    A polymer-based visible and quant. fluorometric assay for CO2 gas is constructed using branched polyethyleneimine (PEI) covalently modified with tetraphenylethylene (TPE). The sensing mechanism relies on the reaction of CO2 with alkylamines of PEI to induce the "soln.-to-pptn." phase transition of the sensory polymer (TPE-PEI), thus resulting in strong aggregation-induced fluorescent emission of TPE-PEI. It works in a relatively environmental benign ethanol medium and avoids the use of toxic amine compds. with unpleasant odor. More importantly, this system is proved to be highly tolerant to possibly coexisting water, carbon monoxide, acid SO2 and H2S gases as well as many common volatile org. compds. These characteristics make the presently developed fluorescent chemosensor hold great potential for many real-world applications.
  47. 47
    Wang, C.; Li, Q.; Wang, B.; Li, D.; Yu, J. Fluorescent sensors based on AIEgen-functionalised mesoporous silica nanoparticles for the detection of explosives and antibiotics. Inorg. Chem. Front. 2018, 5, 2183– 2188,  DOI: 10.1039/C8QI00622A
    Google Scholar
    47
    Fluorescent sensors based on AIEgen-functionalised mesoporous silica nanoparticles for the detection of explosives and antibiotics
    Wang, Chen; Li, Qinglan; Wang, Bolun; Li, Dongdong; Yu, Jihong
    Inorganic Chemistry Frontiers (2018), 5 (9), 2183-2188CODEN: ICFNAW; ISSN:2052-1553. (Royal Society of Chemistry)
    Aggregation-induced emission luminogen (AIEgen)-functionalised mesoporous silica nanoparticles were synthesized by post-grafting two types of tetraphenylethene derivs. on mesoporous materials. The fluorescent chem. sensors, denoted as FMSN-1 and FMSN-2, emitted strong blue fluorescence under UV irradn. Both of them exhibited quick and sensitive responses to 2,4,6-trinitrophenol (PA) and 2,4-dinitrophenol (2,4-DNP) via a fluorescence quenching process. In particular, the obtained materials also showed remarkable sensing ability for the antibiotics furazolidone (FZD) and nitrofurazone (NF) with low detection limits. The highly efficient sensing abilities of FMSNs for PA, 2,4-DNP, FZD, and NF can be attributed to fluorescence resonance energy transfer (FRET) from AIEgens to analytes. These results demonstrate the potential value of AIEgen-functionalised mesoporous materials in environmental protection.
  48. 48
    Potter, M. E.; Pang, S. H.; Jones, C. W. Adsorption Microcalorimetry of CO2 in Confined Aminopolymers. Langmuir 2017, 33, 117– 124,  DOI: 10.1021/acs.langmuir.6b03793
    Google Scholar
    48
    Adsorption Microcalorimetry of CO2 in Confined Aminopolymers
    Potter, Matthew E.; Pang, Simon H.; Jones, Christopher W.
    Langmuir (2017), 33 (1), 117-124CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Aminopolymers confined within mesoporous supports showed promise as materials for direct capture of CO2 from ambient air. In spite of this, relatively little is known about the energetics of CO2 binding in these materials, and the limited calorimetric studies published to date have focused on materials made using mol. aminosilanes, rather than amine polymers. In this work poly(ethyleneimine) (PEI) is impregnated within mesoporous SBA-15, and the heats of CO2 adsorption at 30° were studied using a Tian-Calvet calorimeter with emphasis on the role of PEI loading, and CO2 pressure in the compositional region relevant to direct capture of CO2 from ambient air. In parallel, CO2 uptakes of these materials are measured using multiple complimentary approaches, including both volumetric and gravimetric methods, and distinct changes in uptake as a function of CO2 pressure and amine loading are obsd. The CO2 sorption behavior is directly linked to textural data describing the porosity and PEI distribution in the materials.
  49. 49
    Mei, J.; Leung, N. L. C.; Kwok, R. T. K.; Lam, J. W. Y.; Tang, B. Z. Aggregation-Induced Emission: Together We Shine, United We Soar!. Chem. Rev. 2015, 115, 11718– 11940,  DOI: 10.1021/acs.chemrev.5b00263
    Google Scholar
    49
    Aggregation-Induced Emission: Together We Shine, United We Soar!
    Mei, Ju; Leung, Nelson L. C.; Kwok, Ryan T. K.; Lam, Jacky W. Y.; Tang, Ben Zhong
    Chemical Reviews (Washington, DC, United States) (2015), 115 (21), 11718-11940CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    The United Nations has proclaimed 2015 the International Year of Light and Light-based Technologies to acknowledge the great roles of light in scientific discoveries and technol. innovations. Aggregation-induced emission, (AIE), just as its name implies, refers to a photophys. effect that light emission of a luminogen is activated by aggregate formation. The luminogens with AIE effects are called AIEgens. This article is a review of the fundamentals of the AIE phenomenon.
  50. 50
    La, D. D.; Bhosale, S. V.; Jones, L. A.; Bhosale, S. V. Tetraphenylethylene-Based AIE-Active Probes for Sensing Applications. ACS Appl. Mater. Interfaces 2018, 10, 12189– 12216,  DOI: 10.1021/acsami.7b12320
    Google Scholar
    50
    Tetraphenylethylene-Based AIE-Active Probes for Sensing Applications
    La, Duong Duc; Bhosale, Sidhanath V.; Jones, Lathe A.; Bhosale, Sheshanath V.
    ACS Applied Materials & Interfaces (2018), 10 (15), 12189-12216CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    A review. This Review provides a comprehensive anal. of recent development in the field of aggregation-induced emission (AIE)-active tetraphenylethylene (TPE) luminophores and their applications in biomol. science. It begins with a discussion of the diverse range of structural motifs that have found particular applications in sensing and demonstrates that TPE structures and their derivs. have been used for a diverse range of analytes such as such as H+, anions, cations, heavy metals, org. volatiles, and toxic gases. Advances are discussed in depth where TPE was used as a mechanoluminescent material in bioinspired receptor units with specificity for analytes for such as glucose or RNA. The rapid advances in sensor research make this summary of recent developments in AIE-active TPE luminophores timely, to disseminate the advantages of these materials for sensing of analytes in soln., as well as the importance of solid and aggregated states in controlling sensing behavior.
  51. 51
    Sharath Kumar, K. S.; Girish, Y. R.; Ashrafizadeh, M.; Mirzaei, S.; Rakesh, K. P.; Hossein Gholami, M.; Zabolian, A.; Hushmandi, K.; Orive, G.; Kadumudi, F. B.; Dolatshahi-Pirouz, A.; Thakur, V. K.; Zarrabi, A.; Makvandi, P.; Rangappa, K. S. AIE-featured tetraphenylethylene nanoarchitectures in biomedical application: Bioimaging, drug delivery and disease treatment. Coord. Chem. Rev. 2021, 447, 214135  DOI: 10.1016/j.ccr.2021.214135
    Google Scholar
    51
    AIE-featured tetraphenylethylene nanoarchitectures in biomedical application: Bioimaging, drug delivery and disease treatment
    Sharath Kumar, Kothanahally S.; Girish, Yarabahally R.; Ashrafizadeh, Milad; Mirzaei, Sepideh; Rakesh, Kadalipura P.; Hossein Gholami, Mohammad; Zabolian, Amirhossein; Hushmandi, Kiavash; Orive, Gorka; Kadumudi, Firoz Babu; Dolatshahi-Pirouz, Alireza; Thakur, Vijay Kumar; Zarrabi, Ali; Makvandi, Pooyan; Rangappa, Kanchugarakoppal S.
    Coordination Chemistry Reviews (2021), 447 (), 214135CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
    A review. The development of aggregation-induced emission (AIE) has received extreme considerations from basic and clin. researches. To date, various luminogens with AIE property (AIEgens) have been broadly utilized in optoelectronic devices, fluorescent bio-probes, drug delivery, anticancer and chemosensors and many more. Scientists have likewise dedicated to investigating the possibilities of AIEgens in the biomedical field. Among the various AIE luminophores studied, tetraphenylethylene (TPE) derivs. have demonstrated as most promising AIEgen, owing to their capacity in self-organization and conjugation with aggregation-caused quenching (ACQ) fluorophores to form larger multi-component assemblies. It likewise generally utilized in different fields, like org. and therapeutic science, supramol. chem., org. electronics, cancer therapy, apoptosis and inflammation, microorganism imaging therapy, etc. This review encompasses the recent advances of TPE based AIE-active luminophores and their potential applications in biomol. science.
  52. 52
    Yang, Z.; Chi, Z.; Mao, Z.; Zhang, Y.; Liu, S.; Zhao, J.; Aldred, M. P.; Chi, Z. Recent advances in mechano-responsive luminescence of tetraphenylethylene derivatives with aggregation-induced emission properties. Mater. Chem. Front. 2018, 2, 861– 890,  DOI: 10.1039/C8QM00062J
    Google Scholar
    52
    Recent advances in mechano-responsive luminescence of tetraphenylethylene derivatives with aggregation-induced emission properties
    Yang, Zhiyong; Chi, Zhihe; Mao, Zhu; Zhang, Yi; Liu, Siwei; Zhao, Juan; Aldred, Matthew P.; Chi, Zhenguo
    Materials Chemistry Frontiers (2018), 2 (5), 861-890CODEN: MCFAC5; ISSN:2052-1537. (Royal Society of Chemistry)
    A review. Since the realization in 2011 that most aggregation-induced emission (AIE) mols. exhibit mechano-responsive luminescence (MRL), research regarding the MRL of AIE mols. has drawn much attention, and this area has been expanding tremendously. As one of the most extensively studied AIE cores, tetraphenylethylene (TPE) has been widely used to construct MRL mols. This review will focus on recent advances in MRL of TPE derivs. with AIE properties, including a brief history of mechano-responsive AIE-active materials, mechanistic studies on MRL, mechano-responsive luminogens based on TPE, mechano-responsive luminogens contg. multiple AIE-active units, mechano-memory chromism and mechanoluminescence of TPE derivs. Moreover, this review will give a perspective on the possible opportunities and future challenges that exist in this research area.
  53. 53
    Iasilli, G.; Battisti, A.; Tantussi, F.; Fuso, F.; Allegrini, M.; Ruggeri, G.; Pucci, A. Aggregation-Induced Emission of Tetraphenylethylene in Styrene-Based Polymers. Macromol. Chem. Phys. 2014, 215, 499– 506,  DOI: 10.1002/macp.201300698
    Google Scholar
    53
    Aggregation-Induced Emission of Tetraphenylethylene in Styrene-Based Polymers
    Iasilli, Giuseppe; Battisti, Antonella; Tantussi, Francesco; Fuso, Francesco; Allegrini, Maria; Ruggeri, Giacomo; Pucci, Andrea
    Macromolecular Chemistry and Physics (2014), 215 (6), 499-506CODEN: MCHPES; ISSN:1022-1352. (Wiley-VCH Verlag GmbH & Co. KGaA)
    In the present work, the prepn. of different styrene-based polymer films contg. small amts. of TPE and the evaluation of their photoluminescent behavior is reported. When TPE is dispersed in a poor solvent or in a glassy PS matrix, the arrested intramol. rotations of its aryls favor the strong emission of light centered at about 455-460 nm. Conversely, TPE fluorescence significantly weakens to a faint signal when good solvents or viscous but not glassy polymer matrixes are used. Near-field optical microscopy correlates the fluorescence behavior with the different matrix morphologies. These results should be able to be used for developing a new tool for polymer traceability.
  54. 54
    Barbara, P. F.; Rand, S. D.; Rentzepis, P. M. Direct measurements of tetraphenylethylene torsional motion by picosecond spectroscopy. J. Am. Chem. Soc. 1981, 103, 2156– 2162,  DOI: 10.1021/ja00399a003
    Google Scholar
    54
    Direct measurements of tetraphenylethylene torsional motion by picosecond spectroscopy
    Barbara, P. F.; Rand, S. D.; Rentzepis, P. M.
    Journal of the American Chemical Society (1981), 103 (9), 2156-62CODEN: JACSAT; ISSN:0002-7863.
    The time- and wavelength-resolved fluorescence of C2Ph4 (I), induced by 355-nm ps excitation in several solvents over a range of temps. and viscosities, was investigated. Several distinct fluorescence kinetic processes were identified, which are manifested by (i) time-dependent fluorescence-spectral shifts, (ii) time-dependent fluorescent spectral-shape changes, and (iii) nonexponential fluorescence-decay kinetics. The relaxation rates of these processes depend strongly on temp. and solvent viscosity. The obsd. fluorescence dynamics of I are complex, and suggest that several channels are available for excited-state relaxation. The relaxation pathways are assigned to radiative and radiationless electronic decay, vibrational relaxation, and 2 forms of excited-state conformational relaxation. A unified model is proposed for the photochem. dynamics of I.
  55. 55
    Demchenko, A. P. The concept of λ-ratiometry in fluorescence sensing and imaging. J. Fluoresc. 2010, 20, 1099– 1128,  DOI: 10.1007/s10895-010-0644-y
    Google Scholar
    55
    The concept of λ-ratiometry in fluorescence sensing and imaging
    Demchenko Alexander P
    Journal of fluorescence (2010), 20 (5), 1099-128 ISSN:.
    Very limited number of parameters is available for fluorescence sensing and imaging. The changes of intensity are of low analytical value due to the absence of internal reference. Anisotropy and lifetime sensing have their own limitations. In this respect the λ-ratiometric (based on intensity ratios at two or more wavelengths) recording of spectral changes becomes more popular. Because the spectral changes are connected directly with the variations of interaction energies this approach is seen as the most universal method to study intermolecular interactions. It is applicable for different sensor formats and for obtaining analytical information from cell images. Here we critically analyze different approaches in λ-ratiometric sensing that use single and double fluorescence emitters and are based on different mechanisms producing spectroscopic change. Very promising is the exploration of mechanisms that allow obtaining ratiometric response from a single dye.
  56. 56
    Jimbo, T.; Tsuji, M.; Taniguchi, R.; Sada, K.; Kokado, K. Control of Aggregation-Induced Emission from a Tetraphenylethene Derivative through the Components in the Co-crystal. Cryst. Growth Des. 2018, 18, 3863– 3869,  DOI: 10.1021/acs.cgd.8b00141
    Google Scholar
    56
    Control of Aggregation-Induced Emission from a Tetraphenylethene Derivative through the Components in the Co-crystal
    Jimbo, Takahiro; Tsuji, Mikako; Taniguchi, Ryosuke; Sada, Kazuki; Kokado, Kenta
    Crystal Growth & Design (2018), 18 (7), 3863-3869CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
    We aim to control the photoluminescence property of co-crystals derived from an aggregation-induced emission luminogen (AIEgen) through other components in the co-crystal. For this purpose, we prepd. co-crystals of a typical AIEgen, tetraphenylethene having four hydroxy groups (THPE), and hydrogen-bond acceptors (HBAs) contg. nitrogen atoms. The crystallog. study showed that the hydrogen-bonding pattern and inclusion of crystn. solvents are significantly influenced by the employed HBA, depending on the size, position of nitrogen atoms, and basicity of the HBA, thanks to the moderate hydrogen-bonding ability of THPE. The photoluminescence properties of the co-crystals are governed by the employed HBA, and thus, co-crystals derived from imidazole derivs. or 1,4-diazabicyclo[2.2.2]octane exhibit intense photoluminescence, while those from pyridine derivs. and an electron-deficient imidazole deriv. do not show any photoluminescence. The involvement of photoinduced electron transfer causes quenching of the co-crystals derived from pyridine derivs., which is confirmed by theor. computations. These observations imply that the photoluminescence properties of co-crystals derived from AIEgens can be tuned through other components in the co-crystal.
  57. 57
    Román, F.; Colomer, P.; Calventus, Y.; Hutchinson, J. M. Study of Hyperbranched Poly(ethyleneimine) Polymers of Different Molecular Weight and Their Interaction with Epoxy Resin. Materials 2018, 11, 410  DOI: 10.3390/ma11030410
    Google Scholar
    57
    Study of hyperbranched poly(ethyleneimine) polymers of different molecular weight and their interaction with epoxy resin
    Roman, Frida; Colomer, Pere; Calventus, Yolanda; Hutchinson, John M.
    Materials (2018), 11 (3), 410/1-410/26CODEN: MATEG9; ISSN:1996-1944. (MDPI AG)
    Two different com. hyperbranched poly(ethyleneimine)s (HBPEI), with mol. wts. (MW) of 800 and 25,000 g/mol, and denoted as PEI800 and PEI25000, resp., as well as the mixts. with a Diglycidyl Ether of Bisphenol-A (DGEBA) epoxy resin, have been studied using thermal anal. techniques (DSC, TGA), dielec. relaxation spectroscopy (DRS), and dynamic mech. anal. (DMA). Only a single glass transition is obsd. in these mixts. by DSC. DRS of the HBPEIs shows three dipolar relaxations: γ, β, and α. The av. activation energy for the γ-relaxation is similar for all HBPEIs and is assocd. with the motion of the terminal groups. The β-relaxation has the same av. activation energy for both PEI800 and PEI25000; this relaxation is attributed to the mobility of the branches. The α-relaxation peak for all the HBPEIs is an asym. peak with a shoulder on the high temp. side. This shoulder suggests the existence of ionic charge trapped in the PEI. For the mixts., the γ- and β-relaxations follow the behavior of the epoxy resin alone, indicating that the epoxy resin dominates the mol. mobility. The α-relaxation by DRS is obsd. only as a shoulder, as a consequence of an overlap with cond. effects, whereas by DMA, it is a clear peak.
  58. 58
    Hashida, T.; Tashiro, K. Structural Study on Water-induced Phase Transitions of Poly(ethylene imine) as Viewed from the Simultaneous Measurements of Wide-Angle X-ray Diffractions and DSC Thermograms. Macromol. Symp. 2006, 242, 262– 267,  DOI: 10.1002/masy.200651036
    Google Scholar
    58
    Structural study on water-induced phase transitions of poly(ethylene imine) as viewed from the simultaneous measurements of wide-angle X-ray diffractions and DSC thermograms
    Hashida, Tomoko; Tashiro, Kohji
    Macromolecular Symposia (2006), 242 (Polychar-14, World Forum on Advanced Materials, 2006), 262-267CODEN: MSYMEC; ISSN:1022-1360. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Thermal behavior of poly(ethylene imine) [PEI] was studied using simultaneous WAXD/DSC measurement system. PEI exhibits water-induced and thermally-induced phase transitions among four kinds of cryst. hydrates: anhydrate (EI/water = 1/0), hemihydrate (1/0.5), sesquihydrate (1/1.5), and dihydrate (1/2). The chain conformation changes from a double helix in the anhydrate to a planar zigzag form in the three hydrates. The anhydrate melts at 60 °C while the hydrates melt differently in the temp. region of 70-110 °C. By means of the simultaneous WAXD/DSC measurements, complex DSC thermograms of PEI hydrates were characterized on the basis of X-ray diffractions obtained concurrently.
  59. 59
    Aldred, M. P.; Li, C.; Zhu, M.-Q. Optical Properties and Photo-Oxidation of Tetraphenylethene-Based Fluorophores. Chem.─Eur. J. 2012, 18, 16037– 16045,  DOI: 10.1002/chem.201202715
    Google Scholar
    59
    Optical Properties and Photooxidation of Tetraphenylethene-Based Fluorophores
    Aldred, Matthew P.; Li, Chong; Zhu, Ming-Qiang
    Chemistry - A European Journal (2012), 18 (50), 16037-16045CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The authors report the optical properties of tetraphenylethene (TPE) and other TPE derivs. functionalized with an octyl group (TPE-OCT) and polyethylene glycol group (TPE-PEG) in the side chain. The authors compared TPE-OCT and TPE-PEG with TPE in both org. solvents and under aq. conditions. All materials exhibit aggregation-induced emission, however, uncommonly, TPE-PEG seems to aggregate in aq. soln. with enhanced photoluminescence quantum efficiency (PLQE) relative to that in org. solvents. All three materials can be photooxidized in soln. to their diphenylphenanthrene deriv. by irradn. with UV light (at both ≈1 and ≈5 mW cm-2), with a subsequent enhancement in PL efficiency. The electron-donating ether group increases the rate of oxidn. relative to bare TPE and also photooxidn. was shown to be solvent and concn. dependent. Finally, photooxidn. was also demonstrated in the aggregate state.
  60. 60
    Badrinarayanan, P.; Zheng, W.; Li, Q.; Simon, S. L. The glass transition temperature versus the fictive temperature. J. Non-Cryst. Solids 2007, 353, 2603– 2612,  DOI: 10.1016/j.jnoncrysol.2007.04.025
    Google Scholar
    60
    The glass transition temperature versus the fictive temperature
    Badrinarayanan, Prashanth; Zheng, Wei; Li, Qingxiu; Simon, Sindee L.
    Journal of Non-Crystalline Solids (2007), 353 (26), 2603-2612CODEN: JNCSBJ; ISSN:0022-3093. (Elsevier B.V.)
    A comparison of the values of the glass transition temp. (T g) measured on cooling and the limiting fictive temp. ( T 'f ) measured on heating as a function of cooling rate is performed for a polystyrene sample using both capillary dilatometry and differential scanning calorimetry (DSC). The results from both techniques indicate that T 'f is systematically lower than T g presumably due to the breadth of the relaxation on cooling. The Tool-Narayanaswamy-Moynihan (TNM) model is used to fit the exptl. data from dilatometry and DSC to ascertain the origins of the higher value of T g compared to T 'f.
  61. 61
    Plazek, D. J.; Ngai, K. L. The Glass Temperature. In Physical Properties of Polymers Handbook, 2nd; Mark, J. E., Ed.; Springer Nature, 2007; pp 187– 215.
    Google Scholar
    There is no corresponding record for this reference.
  62. 62
    McKenna, G. B.; Simon, S. L. 50th Anniversary Perspective: Challenges in the Dynamics and Kinetics of Glass-Forming Polymers. Macromolecules 2017, 50, 6333– 6361,  DOI: 10.1021/acs.macromol.7b01014
    Google Scholar
    62
    50Th Anniversary Perspective: Challenges in the Dynamics and Kinetics of Glass-Forming Polymers
    McKenna, Gregory B.; Simon, Sindee L.
    Macromolecules (Washington, DC, United States) (2017), 50 (17), 6333-6361CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A review. The phenomenol. of the glass transition and the assocd. behavior in the near liq. and glassy states are detailed, including the cooling rate dependence of the glass transition, Kovacs' three signatures of structural recovery, and enthalpy overshoots. Dynamics in the liq. regime just above Tg and the assocd. temp. dependences are also covered since this behavior is important to understanding the glassy dynamics. The current models of the structural recovery and their shortcomings are presented. A no. of important unanswered questions are discussed, including how the relaxation time in the glassy state depends on structure, the relationship between the evolution of different properties, the resoln. of the Kauzmann paradox, and the behavior of the equil. relaxation time below Tg. New exptl. approaches are needed to make breakthroughs, such as two that are described: one involving 20 Ma amber to test whether the Vogel temp. dependence continues for the equil. state below Tg and another involving an ideal polymer/pentamer mixt. to obtain the entropy of the liq. far below TK in a test of the Kauzmann paradox. An unexplored regime of glassy behavior, characterized by ultrastability, high d., and low fictive temp., is identified, and expts. to understand the material behavior in this region are motivated.
  63. 63
    McKenna, G. B. Diverging views on glass transition. Nat. Phys. 2008, 4, 673,  DOI: 10.1038/nphys1063
    Google Scholar
    63
    Diverging views on glass transition
    McKenna, Gregory B.
    Nature Physics (2008), 4 (9), 673-674CODEN: NPAHAX; ISSN:1745-2473. (Nature Publishing Group)
    Anal. of the best available data on the behavior of a large no. of glass-forming org. liqs. suggests that the widespread belief that a glass ceases to flow below its transition temp. could be wrong.
  64. 64
    Plazek, D. J.; Frund, Z. N., Jr. Epoxy resins (DGEBA): The curing and physical aging process. J. Polym. Sci., Part B: Polym. Phys. 1990, 28, 431– 448,  DOI: 10.1002/polb.1990.090280401
    Google Scholar
    64
    Epoxy resins (DGEBA): the curing and physical aging process
    Plazek, D. J.; Frund, A. N., Jr.
    Journal of Polymer Science, Part B: Polymer Physics (1990), 28 (4), 431-48CODEN: JPBPEM; ISSN:0887-6266.
    DSC and IR spectroscopy were used to monitor the degree of cure of partially cured epoxy resin (Epon 828/methylenedianiline) samples. The extent of cure, as detd. by residual heat of reaction, concurred with that detd. by monitoring the IR radiation absorbance of the epoxide group near 916 cm-1. The fictive temp. Tf,g increased with the degree of cure, increasing rapidly during cure until reaching a value near the cure temp. Tc of 130° (∼80% cure) where the material vitrified. The greatly reduced reaction rate during the final 20% of cure was not only a consequence of vitrification but, as revealed by IR spectroscopy, the result of the depletion in the no. of reactive epoxide groups. The endothermic peak areas and peak temps. evident during the DSC scans were used as a measure of the extent of phys. aging which took place during the cure of this resin, and after, fully cured samples were aged 37° below their ultimate glass temp. (Tg) for various periods of time. The rate of phys. aging slowed as the temp. increment (Tf,g - Tc) increased. Although an endothermic peak was evident after only 1 h of cure (Tf,g = 138.3°C), such a peak did not appear until fully cured samples were aged for ≥16 h. Enthalpy data revealed that for partially cured material, the fictive temp. Tf,a, reflecting phys. aging, increased with curing time. In contrast, the Tf,a for fully cured samples decreased with sub-Tg aging time. The characteristic jump in the heat capacity which occurred at the Tf,g decreased as curing progressed. This decrease was dependent upon the rotational and vibrational degrees of freedom of the glass. Finally, a graphical method of detg. the fictive temp. Tf,a of partially and fully cured epoxy material from measured endothermic peak areas was developed.
  65. 65
    Kunal, K.; Robertson, C. G.; Pawlus, S.; Hahn, S. F.; Sokolov, A. P. Role of Chemical Structure in Fragility of Polymers: A Qualitative Picture. Macromolecules 2008, 41, 7232– 7238,  DOI: 10.1021/ma801155c
    Google Scholar
    65
    Role of Chemical Structure in Fragility of Polymers: A Qualitative Picture
    Kunal, Kumar; Robertson, Christopher G.; Pawlus, Sebastian; Hahn, Steven F.; Sokolov, Alexei P.
    Macromolecules (Washington, DC, United States) (2008), 41 (19), 7232-7238CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Understanding microscopic parameters that control steepness of the temp. variations of segmental relaxation (fragility) and the glass transition phenomenon remains a challenge. We present dielec. and mech. relaxation studies of segmental dynamics in various polymers with different side groups and backbone structures. The results have been analyzed in terms of flexibility of backbone and side groups of polymeric mols., as suggested by the recent theor. works by Dudowicz et al. A comparison of structures with identical backbones and varying side groups and identical side groups but different backbones reveals that the flexibility of side groups relative to the flexibility of the backbone is the most important factor controlling fragility in polymers, while the glass transition temp. Tg depends primarily on the backbone flexibility and the side group bulkiness (occupied vol.). Based on these results and anal. of literature data we formulated a modified approach to understand the role of chem. structure in segmental dynamics: (i) Polymers with stiff backbones always have high Tg and fragility, while (ii) polymers with flexible backbones and no side groups are the strongest; (iii) however, for the most common type of polymeric structure, C-C or Si-O backbone with side groups, fragility increases with increasing "relative" stiffness of side groups vs. the backbone. In this class of polymers, lowest fragility is expected when the side groups are of similar chem. structure (or flexibility) as the backbone, as in the case of polyisobutylene, one of the strongest polymers known.
  66. 66
    Fried, J. R. Sub Tg Transitions. In Physical Properties of Polymers Handbook, 2nd ed.; Mark, J. E., Ed.; Springer Nature, 2007; pp 217– 232.
    Google Scholar
    There is no corresponding record for this reference.
  67. 67
    Hill, A. J.; Tant, M. R. The Structure and Properties of Glassy Polymers. Structure and Properties of Glassy Polymers, American Chemical Society, 1999; pp 1– 20.
    Google Scholar
    There is no corresponding record for this reference.
  68. 68
    Toi, K.; Ito, T.; Ikemoto, I. Effect of aging and conditioning on the gas transport of poly(vinyl acetate). J. Polym. Sci., Polym. Lett. Ed. 1985, 23, 525– 529,  DOI: 10.1002/pol.1985.130231006
    Google Scholar
    68
    Effect of aging and conditioning on the gas transport of poly(vinyl acetate)
    Toi, K.; Ito, T.; Ikemoto, I.
    Journal of Polymer Science, Polymer Letters Edition (1985), 23 (10), 525-9CODEN: JPYBAN; ISSN:0360-6384.
    The temp. dependence curves of the apparent permeation coeff. at 10-50° for CO2 in poly(vinyl acetate) (I) [9003-20-7] did not show any clear break point but changed smoothly. The two curves did not fit in the case of cooling and heating and diverged most ∼30° (glass temp.). This indicated that the relaxation of polymer chains might contribute to transport of gas in I near the glass temp. region. Both the apparent permeation coeff. and the amt. of permeation in the apparent steady-state decreased with phys. aging.
  69. 69
    Chowdhury, M.; Priestley, R. D. Discrete mobility on the surface of glasses. Proc. Natl. Acad. Sci. U.S.A. 2017, 114, 4854– 4856,  DOI: 10.1073/pnas.1704886114
    Google Scholar
    69
    Discrete mobility on the surface of glasses
    Chowdhury, Mithun; Priestley, Rodney D.
    Proceedings of the National Academy of Sciences of the United States of America (2017), 114 (19), 4854-4856CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
    There is no expanded citation for this reference.
  70. 70
    Kim, H.; Cang, Y.; Kang, E.; Graczykowski, B.; Secchi, M.; Montagna, M.; Priestley, R. D.; Furst, E. M.; Fytas, G. Direct observation of polymer surface mobility via nanoparticle vibrations. Nat. Commun. 2018, 9, 2918  DOI: 10.1038/s41467-018-04854-w
    Google Scholar
    70
    Direct observation of polymer surface mobility via nanoparticle vibrations
    Kim Hojin; Furst Eric M; Cang Yu; Kang Eunsoo; Graczykowski Bartlomiej; Fytas George; Graczykowski Bartlomiej; Secchi Maria; Montagna Maurizio; Priestley Rodney D; Fytas George
    Nature communications (2018), 9 (1), 2918 ISSN:.
    Measuring polymer surface dynamics remains a formidable challenge of critical importance to applications ranging from pressure-sensitive adhesives to nanopatterning, where interfacial mobility is key to performance. Here, we introduce a methodology of Brillouin light spectroscopy to reveal polymer surface mobility via nanoparticle vibrations. By measuring the temperature-dependent vibrational modes of polystyrene nanoparticles, we identify the glass-transition temperature and calculate the elastic modulus of individual nanoparticles as a function of particle size and chemistry. Evidence of surface mobility is inferred from the first observation of a softening temperature, where the temperature dependence of the fundamental vibrational frequency of the nanoparticles reverses slope below the glass-transition temperature. Beyond the fundamental vibrational modes given by the shape and elasticity of the nanoparticles, another mode, termed the interaction-induced mode, was found to be related to the active particle-particle adhesion and dependent on the thermal behavior of nanoparticles.
  71. 71
    Zhang, W.; Douglas, J. F.; Starr, F. W. Why we need to look beyond the glass transition temperature to characterize the dynamics of thin supported polymer films. Proc. Nat. Acad. Sci. U.S.A. 2018, 115, 5641– 5646,  DOI: 10.1073/pnas.1722024115
    Google Scholar
    71
    Why we need to look beyond the glass transition temperature to characterize the dynamics of thin supported polymer films
    Zhang, Wengang; Douglas, Jack F.; Starr, Francis W.
    Proceedings of the National Academy of Sciences of the United States of America (2018), 115 (22), 5641-5646CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
    There is significant variation in the reported magnitude and even the sign of Tg shifts in thin polymer films with nominally the same chem., film thickness, and supporting substrate. The implicit assumption is that methods used to est. Tg in bulk materials are relevant for inferring dynamic changes in thin films. To test the validity of this assumption, we perform mol. simulations of a coarse-grained polymer melt supported on an attractive substrate. As obsd. in many expts., we find that Tg based on thermodn. criteria (temp. dependence of film height or enthalpy) decreases with decreasing film thickness, regardless of the polymer-substrate interaction strength ε. In contrast, we find that Tg based on a dynamic criterion (relaxation of the dynamic structure factor) also decreases with decreasing thickness when ε is relatively weak, but Tg increases when ε exceeds the polymer-polymer interaction strength. We show that these qual. different trends in Tg reflect differing sensitivities to the mobility gradient across the film. Apparently, the slowly relaxing polymer segments in the substrate region make the largest contribution to the shift of Tg in the dynamic measurement, but this part of the film contributes less to the thermodn. est. of Tg. Our results emphasize the limitations of using Tg to infer changes in the dynamics of polymer thin films. However, we show that the thermodn. and dynamic ests. of Tg can be combined to predict local changes in Tg near the substrate, providing a simple method to infer information about the mobility gradient.

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  • Abstract

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    Figure 1

    Figure 1. Chemical structures of tetrakis(4-hydroxyphenyl)ethylene (THPE) as well as linear and branched poly(ethylenimine) (PEI) are used in this work.

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    Figure 2

    Figure 2. (Top) Emission spectra of tetrahydrofuran doped with 0.02 wt % THPE as it is heated through its melting point at −109 °C. Excitation at 365 nm. (Middle) Normalized fluorescence intensity at 460 nm as a function of temperature for 0.02 wt % THPE solutions in tetrahydrofuran (red circles), naphthalene (black triangles), and 2,6-dimethylbenzonitrile (blue squares). (Bottom) Ratiometric fluorescence intensity (530/460 nm) for the same data set. Dashed vertical lines indicate literature mp values.

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    Figure 3

    Figure 3. Ratiometric fluorescence intensity (530/460 nm) for SBA15-OH with 50 wt % PEI doped with 1 wt % THPE. The sample was cycled 6 times between −80 and −20 °C, above and below the Tg of −65 °C.

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    Figure 4

    Figure 4. Temperature dependence of the ratiometric fluorescence intensity (530/460 nm) of bulk PEI 800 doped with 1 wt % TPHE upon heating at 1 °C/min. The cooling rate of one sample was controlled at 1 °C/min (purple), while the other sample (blue) was flash-cooled to −120 °C in 15 min.

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    Figure 5

    Figure 5. Temperature dependence of the ratiometric fluorescence intensity (530/460 nm) of branched PEI 800 (green), branched PEI 25,000 (blue), and linear PEI 2500 (black). Dashed lines illustrate Tg and onset of Tm estimated from DSC.

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    Figure 6

    Figure 6. Temperature dependence of the ratiometric fluorescence intensity (530/460 nm) of bulk PEI 800 as well as mesoporous silica composites with different PEI 800 loadings and surface functional groups (−OH vs −CH3).

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  • References

    This article references 71 other publications.

    1. 1
      National Academies of Sciences, Engineering, and Medicine. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda; The National Academies Press, 2019.
      There is no corresponding record for this reference.
    2. 2
      Baker, S. E.; Stolaroff, J. K.; Peridas, G.; Pang, S. H.; Goldstein, H. M.; Lucci, F. R.; Li, W.; Slessarev, E. W.; Pett-Ridge, J.; Ryerson, F. J. Getting to Neutral: Options for Negative Carbon Emissions in California, LLNL-TR-796100; Lawrence Livermore National Laboratory: Livermore, CA, 2020.
      There is no corresponding record for this reference.
    3. 3
      Sanz-Pérez, E. S.; Murdock, C. R.; Didas, S. A.; Jones, C. W. Direct Capture of CO2 from Ambient Air. Chem. Rev. 2016, 116, 11840– 11876,  DOI: 10.1021/acs.chemrev.6b00173
      3
      Direct Capture of CO2 from Ambient Air
      Sanz-Perez, Eloy S.; Murdock, Christopher R.; Didas, Stephanie A.; Jones, Christopher W.
      Chemical Reviews (Washington, DC, United States) (2016), 116 (19), 11840-11876CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review providing a historical overview of direct air capture (DAC; direct removal of CO2 from air), including an exhaustive description of the use of chem. sorbents targeted for this application, is given. Topics discussed include: introduction (CO2 emissions and related problems, processes to reduct CO2 emissions [pre-combustion, capture during combustion, post-combustion], reducing CO2 emissions vs. neg. C technologies); capturing CO2 from air (rationale and role in atm. CO2 redn., C utilization, DAC via sorbent-based processes); aq. hydroxide solvents (causticization with alkali and alkali-earth hydroxides, alternative causticization processes); solid alkali carbonates (bulk and supported alkali carbonates); org./inorg. hybrid sorbents (amines phys. adsorbed to oxide supports [temp. and moisture effects], amines covalently tethered to oxide supports [moisture effect], amines supported by solid org. material, using metal-org. frameworks (MOF) and their high degree of tunability [amines tethered to MOF]); alternative DAC approaches; feasibility, economics, and design considerations for DAC processes (thermodn. anal. of feasibility, DAC design considerations and cost ests. [aq. alk. and solid sorbent systems]); and conclusions.
    4. 4
      Beuttler, C.; Charles, L.; Wurzbacher, J. The Role of Direct Air Capture in Mitigation of Anthropogenic Greenhouse Gas Emissions. Front. Clim. 2019, 1, 10  DOI: 10.3389/fclim.2019.00010
      There is no corresponding record for this reference.
    5. 5
      Shi, X.; Xiao, H.; Azarabadi, H.; Song, J.; Wu, X.; Chen, X.; Lackner, K. S. Sorbents for the Direct Capture of CO2 from Ambient Air. Angew. Chem., Int. Ed. 2020, 59, 6984– 7006,  DOI: 10.1002/anie.201906756
      5
      Sorbents for the Direct Capture of CO2 from Ambient Air
      Shi, Xiaoyang; Xiao, Hang; Azarabadi, Habib; Song, Juzheng; Wu, Xiaolong; Chen, Xi; Lackner, Klaus S.
      Angewandte Chemie, International Edition (2020), 59 (18), 6984-7006CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. The urgency to address global climate change induced by greenhouse gas emissions is increasing. In particular, the rise in atm. CO2 levels is generating alarm. Technologies to remove CO2 from ambient air, or "direct air capture" (DAC), have recently demonstrated that they can contribute to "neg. carbon emission." Recent advances in surface chem. and material synthesis have resulted in new generations of CO2 sorbents, which may drive the future of DAC and its large-scale deployment. This Review describes major types of sorbents designed to capture CO2 from ambient air and they are categorized by the sorption mechanism: physisorption, chemisorption, and moisture-swing sorption.
    6. 6
      McQueen, N.; Gomes, K. V.; McCormick, C.; Blumanthal, K.; Pisciotta, M.; Wilcox, J. A review of direct air capture (DAC): scaling up commercial technologies and innovating for the future. Prog. Energy 2021, 3, 032001  DOI: 10.1088/2516-1083/abf1ce
      There is no corresponding record for this reference.
    7. 7
      Xu, X.; Song, C.; Andresen, J. M.; Miller, B. G.; Scaroni, A. W. Novel Polyethylenimine-Modified Mesoporous Molecular Sieve of MCM-41 Type as High-Capacity Adsorbent for CO2 Capture. Energy Fuels 2002, 16, 1463– 1469,  DOI: 10.1021/ef020058u
      7
      Novel Polyethylenimine-Modified Mesoporous Molecular Sieve of MCM-41 Type as High-Capacity Adsorbent for CO2 Capture
      Xu, Xiaochun; Song, Chunshan; Andresen, John M.; Miller, Bruce G.; Scaroni, Alan W.
      Energy & Fuels (2002), 16 (6), 1463-1469CODEN: ENFUEM; ISSN:0887-0624. (American Chemical Society)
      A nanoporous solid adsorbent suitable for "mol. basket-type" adsorption of CO2 in the condensed form was prepd. by impregnation of polyethylenimine (PEI) onto MCM-41 mesoporous mol. sieve. The phys. properties of the adsorbents were characterized by x-ray powder diffraction, N2 adsorption/desorption, and thermogravimetric anal. The structure of the MCM-41 was preserved after loading the PEI, and the PEI was uniformly dispersed into the channels of the mol. sieve. The CO2 adsorption/desorption performance was tested in a flow system using a microbalance to track the wt. change. The mesoporous mol. sieve had a synergetic effect on the adsorption of CO2 by PEI. A CO2 adsorption capacity as high as 215 mg-CO2/g-PEI was obtained with MCM-41-PEI-50 at 75°, which is 24 times higher than that of the MCM-41 and is even 2 times that of the pure PEI. With an increase in the CO2 concn. in the CO2/N2 gas mixt., the CO2 adsorption capacity increased. The cyclic adsorption/desorption operation indicated that the performance of the adsorbent was stable. The adsorbent has interest in the sequestration and storage of CO2 from combustion processes.
    8. 8
      Son, W.-J.; Choi, J.-S.; Ahn, W.-S. Adsorptive removal of carbon dioxide using polyethyleneimine-loaded mesoporous silica materials. Microporous Mesoporous Mater. 2008, 113, 31– 40,  DOI: 10.1016/j.micromeso.2007.10.049
      8
      Adsorptive removal of carbon dioxide using polyethyleneimine-loaded mesoporous silica materials
      Son, Won-Jin; Choi, Jung-Sik; Ahn, Wha-Seung
      Microporous and Mesoporous Materials (2008), 113 (1-3), 31-40CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier)
      Mesoporous silica materials, MCM-41, MCM-48, SBA-15, SBA-16, and KIT-6, were synthesized and impregnated with 50% polyethyleneimine (PEI) in methanol to evaluate the performances of the materials in terms of CO2 adsorption (adsorption-desorption in 150 min cycle each at 75°). These PEI-loaded mesoporous silica materials were characterized by XRD, N2 adsorption isotherm, TGA, and TEM/SEM to monitor their textural properties before and after PEI-impregnation. All the PEI-loaded mesoporous silica samples exhibited reversible CO2 adsorption-desorption behaviors with >99% recovery. The CO2 adsorption capacities of the materials were substantially higher than that of pure PEI (79 mg CO2/g-adsorbent), and varied in the order of KIT-6 > SBA-16 ≈ SBA-15 > MCM-48 > MCM-41. The PEI-loaded mesoporous silica samples also showed faster adsorption kinetics than pure-PEI, and the performance of these materials as a CO2 adsorbent was influenced primarily by their pore size. KIT-6 with the largest pores in 3-dimensional arrangement was impregnated with 50% PEI, and showed the highest CO2 adsorption capacity (135 mg/g-adsorbent) in the fastest response time. It also exhibited stable adsorption-desorption behavior in three consecutive test cycles in 900 min.
    9. 9
      Goeppert, A.; Czaun, M.; May, R. B.; Prakash, G. K. S.; Olah, G. A.; Narayanan, S. R. Carbon Dioxide Capture from the Air Using a Polyamine Based Regenerable Solid Adsorbent. J. Am. Chem. Soc. 2011, 133, 20164– 20167,  DOI: 10.1021/ja2100005
      9
      Carbon Dioxide Capture from the Air Using a Polyamine Based Regenerable Solid Adsorbent
      Goeppert, Alain; Czaun, Miklos; May, Robert B.; Prakash, G. K. Surya; Olah, George A.; Narayanan, S. R.
      Journal of the American Chemical Society (2011), 133 (50), 20164-20167CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Easy-to-prep. solid materials based on polyethylenimine-impregnated fumed SiO2 were superior adsorbents for direct CO2 capture from air. During the initial hours of expts., these adsorbents effectively scrubbed all CO2 from air despite its occurrence at very low concns. The effect of moisture on adsorption characteristics and capacity was examd. at room temp. Regenerative ability was also detd. in a short series of adsorption/desorption cycles.
    10. 10
      Chaikittisilp, W.; Kim, H.-J.; Jones, C. W. Mesoporous Alumina-Supported Amines as Potential Steam-Stable Adsorbents for Capturing CO2 from Simulated Flue Gas and Ambient Air. Energy Fuels 2011, 25, 5528– 5537,  DOI: 10.1021/ef201224v
      10
      Mesoporous Alumina-Supported Amines as Potential Steam-Stable Adsorbents for Capturing CO2 from Simulated Flue Gas and Ambient Air
      Chaikittisilp, Watcharop; Kim, Hyung-Ju; Jones, Christopher W.
      Energy & Fuels (2011), 25 (11), 5528-5537CODEN: ENFUEM; ISSN:0887-0624. (American Chemical Society)
      Carbon management by a means of CO2 capture from large stationary sources such as coal-fired power plants or from ambient air is a significant global issue. In the context of steam-stripping as a regeneration process for solid CO2 adsorbents, new adsorbent materials robust enough for direct contact with low temp. steam are needed. Here, mesoporous γ-alumina-supported poly(ethyleneimine) composite materials are prepd. and evaluated as effective CO2 adsorbents, using dil. CO2 streams such as simulated flue gas (10% CO2) and ultradilute streams such as simulated ambient air (400 ppm CO2). In comparison to the silica-supported amine adsorbents typically utilized for CO2 capture applications, the alumina-supported amine adsorbents give better performance in terms of both capture capacity and amine efficiency, in particular, at ambient air conditions. In addn., the alumina-supported amines are stable over short multicycle temp. swing tests and, more importantly, appear to be more robust than the silica-based counterparts upon direct contact with steam. Thus, the resulting alumina-supported amines are suggested to be promising new materials for CO2 capture processes equipped with steam-stripping regeneration, esp. from ultradilute gas streams.
    11. 11
      Sakwa-Novak, M. A.; Jones, C. W. Steam Induced Structural Changes of a Poly(ethylenimine) Impregnated γ-Alumina Sorbent for CO2 Extraction from Ambient Air. ACS Appl. Mater. Interfaces 2014, 6, 9245– 9255,  DOI: 10.1021/am501500q
      11
      Steam Induced Structural Changes of a Poly(ethylenimine) Impregnated γ-Alumina Sorbent for CO2 Extraction from Ambient Air
      Sakwa-Novak, Miles A.; Jones, Christopher W.
      ACS Applied Materials & Interfaces (2014), 6 (12), 9245-9255CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Poly(ethylenimine) [PEI]-impregnated mesoporous γ-Al2O3 sorbents are used to adsorb CO2 from simulated dry and humid ambient air, and the sorbents are regenerated in a continuous exposure flow stream environment from 5 min to 24 h. Sorbents were compared based on equil. CO2 capacity from simulated air at 400 ppm CO2, 50% relative humidity, and 30°. Their physiochem. properties were detd. by x-ray diffraction; 27Al-NMR, IR, and Raman spectroscopies; N2 physisorption; and elemental anal. Sorbents retained >90% of the initial equil. capacity (∼1.7 mmol/g) at steam exposure times up to 12 h; however, PEI leaching reduced sorbent capacity to 0.66 mmol/g after 24 h continuous treatment. The γ-Al2O3 support partially hydrated to form a boehmite crystal phase at steam times ≥90 min; however this phase transition occurred predominately between 90 min and 12 h steam treatment, slowing at longer times (12 and 24 h treatment). Evidence is presented to suggest the presence of boehmite on the sorbent surface does not significantly alter the amine efficiency of impregnated PEI. Total results suggested γ-Al2O3/PEI composite materials are promising sorbents for CO2 capture from ambient air with flowing stream regeneration.
    12. 12
      Goeppert, A.; Zhang, H.; Czaun, M.; May, R. B.; Prakash, G. K. S.; Olah, G. A.; Narayanan, S. R. Easily Regenerable Solid Adsorbents Based on Polyamines for Carbon Dioxide Capture from the Air. ChemSusChem 2014, 7, 1386– 1397,  DOI: 10.1002/cssc.201301114
      12
      Easily Regenerable Solid Adsorbents Based on Polyamines for Carbon Dioxide Capture from the Air
      Goeppert, Alain; Zhang, Hang; Czaun, Miklos; May, Robert B.; Prakash, G. K. Surya; Olah, George A.; Narayanan, S. R.
      ChemSusChem (2014), 7 (5), 1386-1397CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Adsorbents prepd. easily by impregnation of fumed silica with polyethylenimine (PEI) are promising candidates for the capture of CO2 directly from the air. These inexpensive adsorbents have high CO2 adsorption capacity at ambient temp. and can be regenerated in repeated cycles under mild conditions. Despite the very low CO2 concn., they are able to scrub efficiently all CO2 out of the air in the initial hours of the expts. The influence of parameters such as PEI loading, adsorption and desorption temp., particle size, and PEI mol. wt. on the adsorption behavior were investigated. The mild regeneration temps. required could allow the use of waste heat available in many industrial processes as well as solar heat. CO2 adsorption from the air has a no. of applications. Removal of CO2 from a closed environment, such as a submarine or space vehicles, is essential for life support. The supply of CO2-free air is also crit. for alk. fuel cells and batteries. Direct air capture of CO2 could also help mitigate the rising concerns about atm. CO2 concn. and assocd. climatic changes, while, at the same time, provide the first step for an anthropogenic carbon cycle.
    13. 13
      Zhang, H.; Goeppert, A.; Prakash, G. K. S.; Olah, G. Applicability of linear polyethylenimine supported on nano-silica for the adsorption of CO2 from various sources including dry air. RSC Adv. 2015, 5, 52550– 52562,  DOI: 10.1039/C5RA05428A
      13
      Applicability of linear polyethylenimine supported on nano-silica for the adsorption of CO2 from various sources including dry air
      Zhang, Hang; Goeppert, Alain; Prakash, G. K. Surya; Olah, George
      RSC Advances (2015), 5 (65), 52550-52562CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      Adsorbents based on linear polyethylenimines (LPEIs) supported on fumed silica were prepd. and studied for the reversible adsorption of CO2 under mild conditions from various gas mixts., including dry air with a CO2 concn. of only 400 ppm. While the adsorption kinetics were similar between linear and branched PEI impregnated on fumed silica, the desorption rate was noticeably faster on linear PEI, which is advantageous for fast adsorption/desorption cycling. The enthalpy of CO2 adsorption was also lower on LPEI based adsorbents (-43 to -53 kJ mol-1 CO2). Desorption of the adsorbed CO2 occurred rapidly at relatively low temps. (50 to 100 °C). The adsorption/desorption process can be repeated for more than one hundred cycles with no noticeable decrease in adsorption capacity even under humid conditions. The stability of the adsorbents under CO2, air, and N2 was also investigated.
    14. 14
      Sakwa-Novak, M. A.; Yoo, C.-J.; Tan, S.; Rashidi, F.; Jones, C. W. Poly(ethylenimine)-Functionalized Monolithic Alumina Honeycomb Adsorbents for CO2 Capture from Air. ChemSusChem 2016, 9, 1859– 1868,  DOI: 10.1002/cssc.201600404
      14
      Poly(ethylenimine)-Functionalized Monolithic Alumina Honeycomb Adsorbents for CO2 Capture from Air
      Sakwa-Novak, Miles A.; Yoo, Chun-Jae; Tan, Shuai; Rashidi, Fereshteh; Jones, Christopher W.
      ChemSusChem (2016), 9 (14), 1859-1868CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Development of practical, effective gas/solid contactors is an important area for CO2 capture technologies. Target CO2 capture applications, e.g,. post-combustion C capture and sequestration from power generation flue gas or CO2 directly extd. from ambient air, require high gas flow rates and low cost processing. Extruded monolithic honeycomb structures, e.g., those used in automotive catalytic converters, have excellent potential as structured contactors for CO2 adsorption applications due to the low pressure drop imposed on fluids moving through the straight channels of such structures. This work reports the impregnation of poly(ethylenimine) (PEI), an effective amino-polymer commonly reported for CO2 sepn., into extruded monolithic Al2O3 form structured CO2 sorbents. These structured sorbents were prepd. on a small scale, thoroughly characterized, and compared with powd. sorbents with similar compn. Despite consistent differences obsd. in mesopore filling with PEI between monolithic and powd. sorbents, their CO2 adsorption performance wa similar across a range of PEI contents. A larger monolithic cylinder (1 in. diam. x 4 in. length) was evaluated under conditions closer to those which may be used in large-scale applications, and showed a similar performance to the smaller monoliths and powders initially tested. This larger structure, evaluated over 5 CO2 adsorption/steam desorption cycles, demonstrated a volumetric capacity of 350 mol CO2/m3 monolith and an equilibration time of 350 min at a 0.4 m/s linear flow velocity through monolith channels with 400 ppm CO2 in N2 as adsorption gas at 30°. This volumetric capacity surpassed that of a similar, previously considered technol. which suggested CO2 could be removed from air at an operating cost as low as $100/ton.
    15. 15
      Sayari, A.; Liu, Q.; Mishra, P. Enhanced Adsorption Efficiency through Materials Design for Direct Air Capture over Supported Polyethylenimine. ChemSusChem 2016, 9, 2796– 2803,  DOI: 10.1002/cssc.201600834
      15
      Enhanced Adsorption Efficiency through Materials Design for Direct Air Capture over Supported Polyethylenimine
      Sayari, Abdelhamid; Liu, Qing; Mishra, Prashant
      ChemSusChem (2016), 9 (19), 2796-2803CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Until recently, carbon capture and sequestration (CCS) was regarded as the most promising technol. to address the alarming increase in the concn. of anthropogenic CO2 in the atm. There is now an increasing interest in carbon capture and utilization (CCU). In this context, the capture of CO2 from air is an ideal soln. to supply pure CO2 wherever it is needed. Here, we describe innovative materials for direct air capture (DAC) with unprecedented efficiency. Polyethylenimine (PEI) was supported on PME, which is an extra-large-pore silica (pore-expanded MCM-41) with its internal surfaces fully covered by a uniform layer of readily accessible C16 chains from cetyltrimethylammonium (CTMA+) cations. The CTMA+ layer plays a key role in enhancing the amine efficiency toward dry or humid ultradilute CO2 (400 ppm CO2/N2) to unprecedented levels. At the same PEI content, the amine efficiency of PEI/PME was two to four times higher than that of the corresponding calcined mesoporous silica loaded with PEI or with different combinations of C16 chains and PEI. Under humid conditions, the amine efficiency of 40 wt % PEI/PME reached 7.31 mmolCO2/gPEI, the highest ever reported for any supported PEI in the presence of 400 ppm CO2. Thus, amine accessibility, which reflects both the state of PEI dispersion and the adsorption efficiency, is intimately assocd. with the mol. design of the adsorbent.
    16. 16
      Kwon, H. T.; Sakwa-Novak, M. A.; Pang, S. H.; Sujan, A. R.; Ping, E. W.; Jones, C. W. Aminopolymer-Impregnated Hierarchical Silica Structures: Unexpected Equivalent CO2 Uptake under Simulated Air Capture and Flue Gas Capture Conditions. Chem. Mater. 2019, 31, 5229– 5237,  DOI: 10.1021/acs.chemmater.9b01474
      16
      Aminopolymer-Impregnated Hierarchical Silica Structures: Unexpected Equivalent CO2 Uptake under Simulated Air Capture and Flue Gas Capture Conditions
      Kwon, Hyuk Taek; Sakwa-Novak, Miles A.; Pang, Simon H.; Sujan, Achintya R.; Ping, Eric W.; Jones, Christopher W.
      Chemistry of Materials (2019), 31 (14), 5229-5237CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Poly(ethyleneimine)-impregnated sorbents are prepd. using a hierarchical SiO2 support with bimodal meso-/macroporosity. The sorbents behave unexpectedly during CO2 adsorption from simulated air and flue gases (400 ppm and 10% CO2) at a fixed temp., as compared to systems built on commonly studied mesoporous materials. The results demonstrate that (1) impregnation methods influence the efficacy of sorption performance and (2) the sorbents show almost similar uptake capacities under 400 ppm and 10% dry CO2 at 30°, exhibiting step-like CO2 adsorption isotherms. These unusual observations are rationalized via control expts. and a hypothesized sorption mechanism. While the sorption performance near room temp. is unexpectedly identical under 400 ppm and 10% CO2 conditions, there is an optimal temp. at each gas concn. where the uptake is maximized. The max. sorption capacities are 2.6 and 4.1 mmol CO2/g sorbent at the optimized sorption temps. using 400 ppm and 10% dry CO2, resp. The presence of H2O vapor under 400 ppm CO2 conditions further improves the sorption capacity to 3.4 mmol/g sorbent, which is the highest capacity under direct air capture conditions among known amine sorbents impregnated with a similar polymer, to the best of the knowledge.
    17. 17
      Sujan, A. R.; Pang, S. H.; Zhu, G.; Jones, C. W.; Lively, R. P. Direct CO2 Capture from Air using Poly(ethylenimine)-Loaded Polymer/Silica Fiber Sorbents. ACS Sustainable Chem. Eng. 2019, 7, 5264– 5273,  DOI: 10.1021/acssuschemeng.8b06203
      17
      Direct CO2 Capture from Air using Poly(ethylenimine)-Loaded Polymer/Silica Fiber Sorbents
      Sujan, Achintya R.; Pang, Simon H.; Zhu, Guanghui; Jones, Christopher W.; Lively, Ryan P.
      ACS Sustainable Chemistry & Engineering (2019), 7 (5), 5264-5273CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
      Direct CO2 capture from atm. air is gaining increased attention as 1 of the most scalable neg. C approaches available to tackle climate change if coupled with the sequestration of CO2 geol. Also, it can also provide CO2 for further use from a globally uniform source, which is esp. advantageous for economies without natural sources of C-based feedstocks. Solid-supported amine-based materials are effective for direct air capture (DAC) due to their high CO2 uptakes and acceptable sorption kinetics at ambient temp. We describe the application of polymer/SiO2 fiber sorbents functionalized with a primary amine-rich polymer, poly(ethylenimine) (PEI), for DAC. Monolithic fiber sorbents composed of cellulose acetate and SiO2 are synthesized via the dry-jet, wet quench spinning technique. These fibers are then functionalized with PEI (Mw 800 Da) in a simple and scalable post-spinning infusion step and tested for CO2 capture under pseudoequil. conditions as well as under breakthrough conditions. A study to study the effect of feed flow rate, adsorption temp., and presence of moisture in the feed on the CO2 breakthrough performance of a densely packed fiber sorbent module is conducted to highlight the potential application of this class of structured contactors in direct air capture. The pressure drop of these contactors at high gas velocities is also evaluated. Finally, a vacuum-assisted desorption step is demonstrated for prodn. of high-purity CO2 from both dry and humid ambient air mixts.
    18. 18
      Lively, R. P.; Realff, M. J. On thermodynamic separation efficiency: Adsorption processes. AIChE J. 2016, 62, 3699– 3705,  DOI: 10.1002/aic.15269
      18
      On thermodynamic separation efficiency: Adsorption processes
      Lively, Ryan P.; Realff, Matthew J.
      AIChE Journal (2016), 62 (10), 3699-3705CODEN: AICEAC; ISSN:0001-1541. (John Wiley & Sons, Inc.)
      A simplified thermodn. anal. of adsorption processes in temp. swing adsorption (TSA) and pressure swing adsorption (PSA) modes as a function of adsorbate concn. and the adsorbent-adsorbate interaction strength is presented in this article. The thermodn. sepn. efficiency of a TSA process is optimal at dil. feed conditions, and becomes more thermodynamically efficient with increasing adsorbate affinity even though the energy of sepn. increases. The adsorption process is spontaneous, and for a strong isotherm, the energy required to reverse the adsorption is nearly independent of the adsorbate concn. as adsorbate loading in nearly-satd. materials is essentially const. with feed concn. PSA units are efficient thermodynamically and the efficiency increases with the concn. of the desired adsorbate. This thermodn. treatment has implications for sepn. processes that address carbon emissions. TSA systems operate more efficiently (thermodynamically) in the "air capture" case because they apply work to the concd. product rather than the dil. feed.
    19. 19
      Robeson, L. M.; Liu, Q.; Freeman, B. D.; Paul, D. R. Comparison of transport properties of rubbery and glassy polymers and the relevance to the upper bound relationship. J. Membr. Sci. 2015, 476, 421– 431,  DOI: 10.1016/j.memsci.2014.11.058
      19
      Comparison of transport properties of rubbery and glassy polymers and the relevance to the upper bound relationship
      Robeson, Lloyd M.; Liu, Qiang; Freeman, Benny D.; Paul, Donald R.
      Journal of Membrane Science (2015), 476 (), 421-431CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)
      A database of permeability, diffusivity and soly. for He, H2, O2, N2, CO2 and CH4 was compiled from the literature for rubbery polymers. These data were compared with results for a similar study conducted for glassy polymers published in 2013. Based on this comparison, glassy polymers have higher soly. coeffs. than rubbery polymers due to the excess vol. (or free vol.) stemming from the non-equil. nature of polymers below the glass transition temp., Tg, which is well described by the dual-mode sorption model. When compared at equal permeability, rubbery polymers have higher diffusion coeffs. and lower soly. coeffs. Polymers having permselectivity values at or near the upper bound are virtually all glassy polymers. This phenomenon is widely ascribed to the better diffusivity selectivity of glassy vs. rubbery polymers. Comparison of the upper-bound plot of log Pi/Pj vs. log Pi (where Pi represents the permeability of the more permeable gas) shows that glassy polymers dominate the upper bounds for all 15 gas pairs possible. However, when log Pi/Pj is plotted vs. log Di, many of the gas pairs have overlapping data for glassy and rubbery polymers. Thus, glassy polymers dominate the upper bound due, in part, to their higher soly. coeffs.
    20. 20
      Sakwa-Novak, M. A.; Tan, S.; Jones, C. W. Role of Additives in Composite PEI/Oxide CO2 Adsorbents: Enhancement in the Amine Efficiency of Supported PEI by PEG in CO2 Capture from Simulated Ambient Air. ACS Appl. Mater. Interfaces 2015, 7, 24748– 24759,  DOI: 10.1021/acsami.5b07545
      20
      Role of Additives in Composite PEI/Oxide CO2 Adsorbents: Enhancement in the Amine Efficiency of Supported PEI by PEG in CO2 Capture from Simulated Ambient Air
      Sakwa-Novak, Miles A.; Tan, Shuai; Jones, Christopher W.
      ACS Applied Materials & Interfaces (2015), 7 (44), 24748-24759CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Supported amines are promising candidate adsorbents for the removal of CO2 from flue gases and directly from ambient air. The incorporation of additives into polymeric amines such as poly(ethylenimine) (PEI) supported on mesoporous oxides is an effective strategy to improve the performance of the materials. Here, several practical aspects of this strategy are addressed with regards to direct air capture. The influence of three additives (CTAB, PEG200, PEG1000) was systematically explored under dry simulated air capture conditions (400 ppm of CO2, 30 °C). With SBA-15 as a model support for poly(ethylenimine) (PEI), the nature of the additive induced heterogeneities in the deposition of org. on the interior and exterior of the particles, an important consideration for future scale up to practical systems. The PEG200 additive increased the obsd. thermodn. performance (∼60% increase in amine efficiency) of the adsorbents regardless of the PEI content, while the other mols. had less pos. effects. A threshold PEG200/PEI value was identified at which the diffusional limitations of CO2 within the materials were nearly eliminated. The threshold PEG/PEI ratio may have phys. origin in the interactions between PEI and PEG, as the optimal ratio corresponded to nearly equimolar OH/reactive (1°, 2°) amine ratios. The strategy is shown to be robust to the characteristics of the host support, as PEG200 improved the amine efficiency of PEI when supported on two varieties of mesoporous γ-alumina with PEI.
    21. 21
      Ellison, C. J.; Torkelson, J. M. The distribution of glass-transition temperatures in nanoscopically confined glass formers. Nat. Mater. 2003, 2, 695– 700,  DOI: 10.1038/nmat980
      21
      The distribution of glass-transition temperatures in nanoscopically confined glass formers
      Ellison, Christopher J.; Torkelson, John M.
      Nature Materials (2003), 2 (10), 695-700CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      Despite the decade-long study of the effect of nanoconfinement on the glass-transition temp. (Tg) of amorphous materials, the quest to probe the distribution of Tgs in nanoconfined glass formers has remained unfulfilled. Here the distribution of Tgs across polystyrene films has been obtained by a fluorescence/multilayer method, revealing that the enhancement of dynamics at a surface affects Tg several tens of nanometers into the film. The extent to which dynamics smoothly transition from enhanced to bulk states depends strongly on nanoconfinement. When polymer films are sufficiently thin that a redn. in thickness leads to a redn. in overall Tg, the surface-layer Tg actually increases with a redn. in overall thickness, whereas the substrate-layer Tg decreases. These results indicate that the gradient in Tg dynamics is not abrupt, and that the size of a cooperatively rearranging region is much smaller than the distance over which interfacial effects propagate.
    22. 22
      Elmahdy, M. M.; Chrissopoulou, K.; Afratis, A.; Floudas, G.; Anastasiadis, S. H. Effect of Confinement on Polymer Segmental Motion and Ion Mobility in PEO/Layered Silicate Nanocomposites. Macromolecules 2006, 39, 5170– 5173,  DOI: 10.1021/ma0608368
      22
      Effect of Confinement on Polymer Segmental Motion and Ion Mobility in PEO/Layered Silicate Nanocomposites
      Elmahdy, M. M.; Chrissopoulou, K.; Afratis, A.; Floudas, G.; Anastasiadis, S. H.
      Macromolecules (2006), 39 (16), 5170-5173CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      In this paper, a dielec. spectroscopy investigation is presented, aiming to probe the role of nanoconfinement on both the polymer and the cation dynamics utilizing intercalated polymer/layered silicate nanocomposites with ~1 nm PEO films residing within the galleries of hydrophilic Na+MMT. Confinement results in a speedup of the PEO segmental relaxation dynamics, which display an Arrhenius temp. dependence and persist for temps. much lower than the bulk Tg. Moreover, the ionic mobility is found to be enhanced in the nanocomposites.
    23. 23
      Rittigstein, P.; Priestley, R. D.; Broadbelt, L. J.; Torkelson, J. M. Model polymer nanocomposites provide an understanding of confinement effects in real nanocomposites. Nat. Mater. 2007, 6, 278– 282,  DOI: 10.1038/nmat1870
      23
      Model polymer nanocomposites provide an understanding of confinement effects in real nanocomposites
      Rittigstein, Perla; Priestley, Rodney D.; Broadbelt, Linda J.; Torkelson, John M.
      Nature Materials (2007), 6 (4), 278-282CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      Owing to the improvement of properties including cond., toughness and permeability, polymer nanocomposites are slated for applications ranging from membranes to fuel cells. The enhancement of polymer properties by the addn. of inorg. nanoparticles is a complex function of interfacial interactions, interfacial area and the distribution of inter-nano-filler distances. The latter two factors depend on nano-filler dispersion, making it difficult to develop a fundamental understanding of their effects on nanocomposite properties. Here, we design model poly(Me methacrylate)-silica and poly(2-vinyl pyridine)-silica nanocomposites consisting of polymer films confined between silica slides. We compare the dependence of the glass-transition temp. (Tg) and phys. aging on the interlayer distance in model nanocomposites with the dependence of silica nanoparticle content in real nanocomposites. We show that model nanocomposites provide a simple way to gain insight into the effect of interparticle spacing on Tg and to predict the approx. aging response of real nanocomposites.
    24. 24
      Uemura, T.; Yanai, N.; Watanabe, S.; Tanaka, H.; Numaguchi, R.; Miyahara, M. T.; Ohta, Y.; Nagaoka, M.; Kitagawa, S. Unveiling thermal transitions of polymers in subnanometre pores. Nat. Commun. 2010, 1, 83  DOI: 10.1038/ncomms1091
      24
      Unveiling thermal transitions of polymers in subnanometre pores
      Uemura Takashi; Yanai Nobuhiro; Watanabe Satoshi; Tanaka Hideki; Numaguchi Ryohei; Miyahara Minoru T; Ohta Yusuke; Nagaoka Masataka; Kitagawa Susumu
      Nature communications (2010), 1 (), 83 ISSN:.
      The thermal transitions of confined polymers are important for the application of polymers in molecular scale devices and advanced nanotechnology. However, thermal transitions of ultrathin polymer assemblies confined in subnanometre spaces are poorly understood. In this study, we show that incorporation of polyethylene glycol (PEG) into nanochannels of porous coordination polymers (PCPs) enabled observation of thermal transitions of the chain assemblies by differential scanning calorimetry. The pore size and surface functionality of PCPs can be tailored to study the transition behaviour of confined polymers. The transition temperature of PEG in PCPs was determined by manipulating the pore size and the pore-polymer interactions. It is also striking that the transition temperature of the confined PEG decreased as the molecular weight of PEG increased.
    25. 25
      Stafford, C. M.; Harrison, C.; Beers, K. L.; Karim, A.; Amis, E. J.; VanLandingham, M. R.; Kim, H.-C.; Volksen, W.; Miller, R. D.; Simonyi, E. E. A buckling-based metrology for measuring the elastic moduli of polymeric thin films. Nat. Mater. 2004, 3, 545– 550,  DOI: 10.1038/nmat1175
      25
      A buckling-based metrology for measuring the elastic moduli of polymeric thin films
      Stafford, Christopher M.; Harrison, Christopher; Beers, Kathryn L.; Karim, Alamgir; Amis, Eric J.; VanLandingham, Mark R.; Kim, Ho-Cheol; Volksen, Willi; Miller, Robert D.; Simonyi, Eva E.
      Nature Materials (2004), 3 (8), 545-550CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      As technol. continues towards smaller, thinner and lighter devices, more stringent demands are placed on thin polymer films as diffusion barriers, dielec. coatings, electronic packaging and so on. Therefore, there is a growing need for testing platforms to rapidly det. the mech. properties of thin polymer films and coatings. We introduce here an elegant, efficient measurement method that yields the elastic moduli of nanoscale polymer films in a rapid and quant. manner without the need for expensive equipment or material-specific modeling. The technique exploits a buckling instability that occurs in bilayers consisting of a stiff, thin film coated onto a relatively soft, thick substrate. Using the spacing of these highly periodic wrinkles, we calc. the film's elastic modulus by applying well-established buckling mechanics. We successfully apply this new measurement platform to several systems displaying a wide range of thicknessess (nanometer to micrometre) and moduli (MPa to GPa).
    26. 26
      Stafford, C. M.; Vogt, B. D.; Harrison, C.; Julthongpiput, D.; Huang, R. Elastic Moduli of Ultrathin Amorphous Polymer Films. Macromolecules 2006, 39, 5095– 5099,  DOI: 10.1021/ma060790i
      26
      Elastic Moduli of Ultrathin Amorphous Polymer Films
      Stafford, Christopher M.; Vogt, Bryan D.; Harrison, Christopher; Julthongpiput, Duangrut; Huang, Rui
      Macromolecules (2006), 39 (15), 5095-5099CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The elastic moduli of ultrathin poly(styrene) (PS) and poly(methylmethacrylate) (PMMA) films of thickness ranging from 200 nm to 5 nm were investigated using a buckling-based metrol. Below 40 nm, the apparent modulus of the PS and PMMA films decreases dramatically, with an order of magnitude decrease compared to bulk values for the thinnest films measured. We can account for the obsd. decrease in apparent modulus by applying a composite model based on the film having a surface layer with a reduced modulus and of finite thickness. The obsd. decrease in the apparent modulus highlights issues in mech. stability and robustness of sub-40 nm polymer films and features.
    27. 27
      O’Connell, P. A.; McKenna, G. B. The stiffening of ultrathin polymer films in the rubbery regime: The relative contributions of membrane stress and surface tension. J. Polym. Sci., Part B: Polym. Phys. 2009, 47, 2441– 2448,  DOI: 10.1002/polb.21876
      27
      The stiffening of ultrathin polymer films in the rubbery regime: The relative contributions of membrane stress and surface tension
      O'Connell, Paul A.; McKenna, Gregory B.
      Journal of Polymer Science, Part B: Polymer Physics (2009), 47 (24), 2441-2448CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
      We have previously reported on a new nanobubble inflation technique we have developed to measure the abs. creep compliance of polymer films at thicknesses down to ∼10 nm (1-5). One of the more surprising results to come out of these studies was the observation that as the film thickness decreased the rubbery plateau compliance was seen to decrease dramatically. At the thinnest film thickness (∼10 nm) the compliance decreased (or conversely the stiffness increased) by some 3 orders of magnitude from the bulk value. It is known that, at the nanometer scale, surface tension effects can become significant. We examine here the contribution of surface tension to the obsd. stiffening and show that, while the contribution is important, it does not account for the degree of stiffening obsd. This suggests that mol. or confinement induced stiffening is the major factor. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2441-2448, 2009.
    28. 28
      Li, X.; McKenna, G. B. Ultrathin Polymer Films: Rubbery Stiffening, Fragility, and Tg Reduction. Macromolecules 2015, 48, 6329– 6336,  DOI: 10.1021/acs.macromol.5b01263
      28
      Ultrathin Polymer Films: Rubbery Stiffening, Fragility, and Tg Reduction
      Li, Xiguang; McKenna, Gregory B.
      Macromolecules (Washington, DC, United States) (2015), 48 (17), 6329-6336CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The mech. and viscoelastic responses of poly(Et methacrylate) (PEMA) ultrathin films over thicknesses ranging from 21 to 112 nm have been studied using a nanobubble inflation method. The stress-strain response of the PEMA thin films shows a rubbery stiffening as the film thickness decreases, and the present results are combined with prior measurements of the rubbery stiffening index S for multiple polymers. We find that S is linearly correlated with the dynamic fragility index m. The results are also consistent with expectation from Ngai et al.'s [ J. Polym. Sci., Part B: Polym. Phys. 2013, 51 (3)] recent proposition based on his coupling model but do not seem to correlate with the mol. composite concept proposed by Page et al. [ Nano Lett. 2014, 14 (5)] as a means to explain the dependence of the rubbery stiffening on chem. structure of the polymer. In addn., we observe a redn. in glass transition temp. of as much as 15.7 K for PEMA films of 21 nm thickness.
    29. 29
      Mapesa, E. U.; Cantillo, N. M.; Hamilton, S. T.; Harris, M. A.; Zawodzinski, T. A.; Park, A.-H.; Sangoro, J. Localized and Collective Dynamics in Liquid-like Polyethylenimine-Based Nanoparticle Organic Hybrid Materials. Macromolecules 2021, 54, 2296– 2305,  DOI: 10.1021/acs.macromol.0c02370
      29
      Localized and Collective Dynamics in Liquid-like Polyethylenimine-Based Nanoparticle Organic Hybrid Materials
      Mapesa, Emmanuel Urandu; Cantillo, Nelly M.; Hamilton, Sara T.; Harris, Matthew A.; Zawodzinski Jr., Thomas A.; Alissa Park, Ah-Hyung; Sangoro, Joshua
      Macromolecules (Washington, DC, United States) (2021), 54 (5), 2296-2305CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Broadband dielec. spectroscopy, rheol., and NMR spectroscopy are employed to study mol. dynamics in a nanoparticle org. hybrid material (NOHMs) system comprising 20 wt. % silica nanoparticles ionically bonded to a polyethylenimine canopy. By comparing the neat polymer (used as a canopy) to the deriv. NOHMs, we find that timescales characterizing segmental dynamics in the NOHM are identical to those for the neat polymer. Detailed anal. of the carbon-spin lattice relaxation times yields mechanistic insights into localized and collective dynamics, in quant. agreement with dielec. results. Interestingly, the NOHMs retain liq.-like characteristics unlike conventional polymer nanocomposites but exhibit higher viscosity due to addnl. contributions from tethered polymer chains and mesoscopic structuring. These findings demonstrate the potential of achieving unique and desired material properties via NOHMs by an informed choice of the canopy material.
    30. 30
      Holewinski, A.; Sakwa-Novak, M. A.; Jones, C. W. Linking CO2 Sorption Performance to Polymer Morphology in Aminopolymer/Silica Composites through Neutron Scattering. J. Am. Chem. Soc. 2015, 137, 11749– 11759,  DOI: 10.1021/jacs.5b06823
      30
      Linking CO2 Sorption Performance to Polymer Morphology in Aminopolymer/Silica Composites through Neutron Scattering
      Holewinski, Adam; Sakwa-Novak, Miles A.; Jones, Christopher W.
      Journal of the American Chemical Society (2015), 137 (36), 11749-11759CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Composites of poly(ethylenimine) (PEI) and mesoporous silica are effective, reversible adsorbents for CO2, both from flue gas and in direct air-capture applications. The morphol. of the PEI within the silica can strongly impact the overall carbon capture efficiency and rate of satn. Here, we directly probe the spatial distribution of the supported polymer through small-angle neutron scattering (SANS). Combined with textural characterization from physisorption anal., the data indicate that PEI first forms a thin conformal coating on the pore walls, but all addnl. polymer aggregates into plug(s) that grow along the pore axis. This model is consistent with obsd. trends in amine-efficiency (CO2/N binding ratio) and pore size distributions, and points to a trade-off between achieving high chem. accessibility of the amine binding sites, which are inaccessible when they strongly interact with the silica, and high accessibility for mass transport, which can be hampered by diffusion through PEI plugs. We illustrate this design principle by demonstrating higher CO2 capacity and uptake rate for PEI supported in a hydrophobically modified silica, which exhibits repulsive interactions with the PEI, freeing up binding sites.
    31. 31
      Holewinski, A.; Sakwa-Novak, M. A.; Carrillo, J. Y.; Potter, M. E.; Ellebracht, N.; Rother, G.; Sumpter, B. G.; Jones, C. W. Aminopolymer Mobility and Support Interactions in Silica-PEI Composites for CO2 Capture Applications: A Quasielastic Neutron Scattering Study. J. Phys. Chem. B 2017, 121, 6721– 6731,  DOI: 10.1021/acs.jpcb.7b04106
      31
      Aminopolymer Mobility and Support Interactions in Silica-PEI Composites for CO2 Capture Applications: A Quasielastic Neutron Scattering Study
      Holewinski, Adam; Sakwa-Novak, Miles A.; Carrillo, Jan-Michael Y.; Potter, Matthew E.; Ellebracht, Nathan; Rother, Gernot; Sumpter, Bobby G.; Jones, Christopher W.
      Journal of Physical Chemistry B (2017), 121 (27), 6721-6731CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
      Composite gas sorbents, with an active polymer phase and a porous support, are promising materials to sep. acid gases from a variety of gas streams. Significant changes in sorption performance (capacity, rate, stability) can be achieved by tuning the polymer properties and the nature of interactions between polymer and support. This work used quasi-elastic neutron scattering (QENS) and coarse-grained mol. dynamics (MD) simulations to characterize the dynamic behavior of the most commonly reported polymer in such materials, poly(ethylenimine) (PEI), in bulk form and when supported in a mesoporous SiO2 framework. Polymer chain dynamics (rotational and translational diffusion) were characterized using two neutron back-scattering spectrometers which had overlapping time scales, ranging from pico-seconds to several nanoseconds. Two motion modes were detected for the PEI mol. in QENS. At low energy transfer, a slow process (∼200 ps) was obsd. and attributed to jump-mediated, center-of-mass diffusion. A second, fast process at ∼20 ps was obsd. and is attributed to locally confined, jump-diffusion. Characteristic data (time scale, spectral wt.) of these processes were compared to those characterized by MD; reasonable agreement was achieved. For nanopore-confined PEI, a significant redn. in polymer motion time scale was obsd. vs. bulk. The effect of SiO2 surface functionalization and polymer fill fraction in SiO2 pores (controlling the portion of polymer mols. in contact with pore walls), were examd. in detail. Hydrophobic functionalization of SiO2 led to an increased PEI mobility, above that of native silanol-terminated SiO2; however, the dynamics were still slower than those in bulk PEI. Sorbents with faster PEI dynamics were also more efficient for CO2 capture, possibly because sorption sites were more accessible than those in systems with slower PEI dynamics. Results supported the existence of a link between the support affinity for PEI and the accessibility of active sorbent functional groups.
    32. 32
      Zhang, R.; Wang, X.; Liu, S.; He, L.; Song, C.; Jiang, X.; Blach, T. P. Discovering Inherent Characteristics of Polyethylenimine-Functionalized Porous Materials for CO2 Capture. ACS Appl. Mater. Interfaces 2019, 11, 36515– 36524,  DOI: 10.1021/acsami.9b08496
      32
      Discovering Inherent Characteristics of Polyethylenimine-Functionalized Porous Materials for CO2 Capture
      Zhang, Rui; Wang, Xiaoxing; Liu, Shimin; He, Lilin; Song, Chunshan; Jiang, Xiao; Blach, Tomasz P.
      ACS Applied Materials & Interfaces (2019), 11 (40), 36515-36524CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      CO2 capture is vital for addressing greenhouse gas (GHG)-based environmental issues worldwide. Amine-polymer/silica sorbents have been extensively studied for CO2 capture, but the fundamental understandings of polyethylenimine (PEI) loading effect, thermal effect, and CO2 sorption behavior are still lacking. Small-angle neutron scattering (SANS) offers promising opportunities for characterizing CO2 sorption behavior of PEI-functionalized SBA-15. Herein, in situ SANS has been used to investigate not only PEI loading distribution but also PEI thermal swelling and temp.-dependent CO2 sorption behavior of PEI-functionalized SBA-15. The results indicate that PEI could disperse on the mesopore surface for the sample with low PEI loading, while for the sample with high PEI loading, PEI could not only disperse on the mesopore surface but also partially fill in the mesopore as plugs. The sample with high PEI loading shows a two-stage swelling of PEI with increasing temp. from 25 to 120 °C in vacuum, in which the size of the intramol. voids between PEI chains has no change from 25 to 75 °C but expands from 75 to 120 °C, whereas only a subtle swelling is obsd. up to 120 °C for the sample with low PEI loading. Besides the fact that in situ SANS successfully detects physisorbed CO2 on the mesopore surface and chemisorbed CO2 by the amine groups simultaneously: (1) the amt. of physisorbed CO2 increases with increasing pressure but decreases with increasing temp., and (2) the amt. of chemisorbed CO2 has a trend of VCO2 (75 °C) > VCO2 (120 °C) > VCO2 (25 °C). The thermal swelling of PEI causes dilation of intramol. voids and thus increases the accessibility of chemisorption sites, resulting in higher CO2 sorption capacity. Therefore, temp. and PEI swelling are essential factors for kinetic and thermodn. controls of CO2 capture in amine-functionalized porous adsorbents.
    33. 33
      Burroughs, M. J.; Christie, D.; Gray, L. A. G.; Chowdhury, M.; Priestley, R. D. 21st Century Advances in Fluorescence Techniques to Characterize Glass-Forming Polymers at the Nanoscale. Macromol. Chem. Phys. 2018, 219, 1700368  DOI: 10.1002/macp.201700368
      There is no corresponding record for this reference.
    34. 34
      Hooker, J. C.; Torkelson, J. M. Coupling of Probe Reorientation Dynamics and Rotor Motions to Polymer Relaxation As Sensed by Second Harmonic Generation and Fluorescence. Macromolecules 1995, 28, 7683– 7692,  DOI: 10.1021/ma00127a014
      34
      Coupling of Probe Reorientation Dynamics and Rotor Motions to Polymer Relaxation As Sensed by Second Harmonic Generation and Fluorescence
      Hooker, Jacob C.; Torkelson, John M.
      Macromolecules (1995), 28 (23), 7683-92CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The coupling of various rotational motions of the rotor probes 4-(tricyanovinyl)-N-(2-hydroxyethyl)-N-ethylaniline (TCl) and julolidenemalononitrile (JMN) to the relaxation dynamics of poly(Et methacrylate), poly(iso-Bu methacrylate), and an iso-Bu methacrylate-TC1 labeled methacrylate copolymer has been investigated by second harmonic generation (SHG) and steady-state fluorescence in both the glassy and rubbery states. In the rubbery state, the temp. dependence of the av. rotational reorientation relaxation times, 〈τ〉, of TC1, both doped and labeled, detd. from SHG measurements can be fitted well to the WLF equation with reasonable C1 and C2 parameters, indicating coupling to the α-relaxation in these polymer systems. The value of 〈τ〉 at the glass transition temp. and the weaker temp. dependence of 〈τ〉 in the glassy state also support the conclusion of coupling to the α-relaxation. However, from fluorescence measurements a much weaker temp. dependence is obsd. for the smaller scale motions involving internal rotations and/or isomerizations of the acceptor and/or donor moieties on TC1 and JMN, indicating significant decoupling from the α-relaxation. The decoupling of these internal probe motions from the α-relaxation mechanism is discussed in terms of x, a probe-dependent parameter introduced by Loutfy, and ξ, a parameter described by Ehrlich and Sillescu as indicating the degree of coupling to the α-relaxation. A consideration of the time scales and activation energies assocd. with the smaller scale, internal rotation of these various moieties suggests at least some coupling to sub-β-relaxations. We also note the importance of carefully considering the results of a WLF fit in order to interpret appropriately the nature of the probe coupling to the polymer relaxation.
    35. 35
      Bao, S.; Wu, Q.; Qin, W.; Yu, Q.; Wang, J.; Liang, G.; Tang, B. Z. Sensitive and reliable detection of glass transition of polymers by fluorescent probes based on AIE luminogens. Polym. Chem. 2015, 6, 3537– 3542,  DOI: 10.1039/C5PY00308C
      35
      Sensitive and reliable detection of glass transition of polymers by fluorescent probes based on AIE luminogens
      Bao, Suping; Wu, Qihua; Qin, Wei; Yu, Qiuling; Wang, Jing; Liang, Guodong; Tang, Ben Zhong
      Polymer Chemistry (2015), 6 (18), 3537-3542CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      The glass transition of polymers is an immensely-used yet less-understood phenomenon concerning the dynamics of polymer chains in bulk or in confined surroundings, which dictates directly their performances in engineering sectors. Monitoring of the glass transitions or dynamics of polymers is hampered by the lack of facile yet robust methodologies. Herein, we developed a sensitive, reliable and straightforward approach for the detection of glass transitions of polymers using fluorescent probes based on aggregation induced emission (AIE) luminogens. Fluorescence emission of polymers doped with AIE luminogens, including tetraphenylethene (TPE) or its derivs., showed a sensitive response to the glass transitions of polymers. The sensitivity of fluorescence to glass transition could be optimized by increasing TPE loading. Fluorescence intensity of TPE-doped polymers dropped as much as 25 fold with increasing temp. in the investigated range. The temp. dependence of the fluorescence intensity gave rise to the straightforward detn. of the glass transitions of the polymers. Moreover, it is worth mentioning that simply mixing AIE luminogens with polymers, rather than covalently labeling, is possible due to the AIE characteristics of the probes. This significantly facilitated measurements. Given the significant advantages of AIE luminogens as probes, including high and tunable sensitivity, immunity to aggregation, facile operation and simple data processing, fluorescence techniques based on AIE luminogens offer new access for the investigation of the glass dynamics of polymer chains in confined spaces.
    36. 36
      Paeng, K.; Swallen, S. F.; Ediger, M. D. Direct Measurement of Molecular Motion in Freestanding Polystyrene Thin Films. J. Am. Chem. Soc. 2011, 133, 8444– 8447,  DOI: 10.1021/ja2022834
      36
      Direct Measurement of Molecular Motion in Freestanding Polystyrene Thin Films
      Paeng, Keewook; Swallen, Stephen F.; Ediger, M. D.
      Journal of the American Chemical Society (2011), 133 (22), 8444-8447CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      An optical photobleaching technique has been used to measure the reorientation of dil. probes in freestanding polystyrene films as thin as 14 nm. Temp.-ramping and isothermal anisotropy measurements reveal the existence of two subsets of probe mols. with different dynamics. While the slow subset shows bulk-like dynamics, the more mobile subset reorients within a few hundred seconds even at Tg,DSC - 25 K (Tg,DSC is the glass transition temp. of bulk polystyrene). At Tg,DSC - 5 K, the mobility of these two subsets differs by 4 orders of magnitude. These data are interpreted as indicating the presence of a high-mobility layer at the film surface whose thickness is independent of polymer mol. wt. and total film thickness. The thickness of the mobile surface layer increases with temp. and equals 7 nm at Tg,DSC.
    37. 37
      Paeng, K.; Richert, R.; Ediger, M. D. Molecular mobility in supported thin films of polystyrene, poly(methyl methacrylate), and poly(2-vinyl pyridine) probed by dye reorientation. Soft Matter 2012, 8, 819– 826,  DOI: 10.1039/C1SM06501G
      37
      Molecular mobility in supported thin films of polystyrene, poly(methyl methacrylate), and poly(2-vinyl pyridine) probed by dye reorientation
      Paeng, Keewook; Richert, Ranko; Ediger, M. D.
      Soft Matter (2012), 8 (3), 819-826CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
      Temp.-ramping anisotropy measurements were used to probe the mol. mobility of fluorescent probes in polystyrene, poly(Me methacrylate), and poly(2-vinyl pyridine) films supported upon silicon wafers with native oxide coatings. All polymer films showed evidence of high mobility at the free surface. The fraction of a film with high mobility was characterized as a mobile surface layer thickness, which increased with temp. The mobile surface layer thickness for supported films of polystyrene and poly(Me methacrylate) reasonably matched that previously deduced from freestanding films of these polymers; for poly(Me methacrylate), enhanced mobility extends about 4 nm into the film from the free surface at Tg. For supported polystyrene and poly(Me methacrylate) films, the results are consistent with no decrease in mobility near the solid substrate but do not eliminate this possibility. On the other hand, the mobility of supported poly(2-vinyl pyridine) thin films provides some evidence for slower-than-bulk relaxation near the solid substrate.
    38. 38
      Ellison, C. J.; Kim, S. D.; Hall, D. B.; Torkelson, J. M. Confinement and processing effects on glass transition temperature and physical aging in ultrathin polymer films: Novel fluorescence measurements. Eur. Phys. J. E 2002, 8, 155– 166,  DOI: 10.1140/epje/i2001-10057-y
      38
      Confinement and processing effects on glass transition temperature and physical aging in ultrathin polymer films: Novel fluorescence measurements
      Ellison, C. J.; Kim, S. D.; Hall, D. B.; Torkelson, J. M.
      European Physical Journal E: Soft Matter (2002), 8 (2), 155-166CODEN: EPJSFH; ISSN:1292-8941. (EDP Sciences)
      Fluorescence intensity measurements of chromophore-doped or -labeled polymers were used for the first time to det. the effects of decreasing film thickness on glass transition temp., Tg, the relative strength of the glass transition, and the relative rate of phys. aging below Tg in supported, ultrathin polymer films. The temp. dependence of fluorescence intensity measured in the glassy state of thin and ultrathin films of pyrene-doped polystyrene (PS), poly(iso-Bu methacrylate) (PiBMA), and poly(2-vinylpyridine) (P2VP) differs from that in the rubbery state with a transition at Tg. Pos. deviations from bulk Tg are obsd. in ultrathin PiBMA and P2VP films on silica substrates while substantial neg. deviations from bulk Tg are obsd. in ultrathin PS films on silica substrates. The relative difference in the temp. dependences of fluorescence intensity in the rubbery and glassy states is usually reduced with decreasing film thickness, indicating that the strength of the glass transition is reduced in thinner films. The temp. dependence of fluorescence intensity also provides useful information on effects of processing history as well as on the degree of polymer-substrate interaction. In addn., when used as a polymer label, a mobility-sensitive rotor chromophore is demonstrated to be useful in measuring relative rates of phys. aging in films as thin as 10 nm.
    39. 39
      Priestley, R. D.; Ellison, C. J.; Broadbelt, L. J.; Torkelson, J. M. Structural Relaxation of Polymer Glasses at Surfaces, Interfaces, and In Between. Science 2005, 309, 456– 459,  DOI: 10.1126/science.1112217
      39
      Structural Relaxation of Polymer Glasses at Surfaces, Interfaces, and In Between
      Priestley, Rodney D.; Ellison, Christopher J.; Broadbelt, Linda J.; Torkelson, John M.
      Science (Washington, DC, United States) (2005), 309 (5733), 456-459CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      We analyzed the glassy-state structural relaxation of polymers near surfaces and interfaces by monitoring fluorescence in multilayer films. Relative to that of bulk, the rate of structural relaxation of poly(Me methacrylate) is reduced by a factor of 2 at a free surface and by a factor of 15 at a silica substrate interface; the latter exhibits a nearly complete arresting of relaxation. The distribution in relaxation rates extends more than 100 nm into the film interior, a distance greater than that over which surfaces and interfaces affect the glass transition temp.
    40. 40
      Askar, S.; Evans, C. M.; Torkelson, J. M. Residual stress relaxation and stiffness in spin-coated polymer films: Characterization by ellipsometry and fluorescence. Polymer 2015, 76, 113– 122,  DOI: 10.1016/j.polymer.2015.08.036
      40
      Residual stress relaxation and stiffness in spin-coated polymer films: Characterization by ellipsometry and fluorescence
      Askar, Shadid; Evans, Christopher M.; Torkelson, John M.
      Polymer (2015), 76 (), 113-122CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      Ellipsometry and fluorescence are used via measurements of film thickness and pyrenyl dye emission spectral shape, resp., to characterize residual stress relaxation in polystyrene (PS) films. In particular, fluorescence of pyrene-labeled PS (MPy-PS) films, with ∼1 mol% pyrene label, provides sensitivity to film stress relaxation and stiffness by the dependence of the ratio of the first to third vibronic peak intensities (I1/I3) of the pyrenyl dye to nanosecond-time-scale mol. caging. Both techniques show that residual stress relaxation occurs over a period of hours despite the PS films being 15-40 °C above the film glass transition temp. (Tg). Both techniques also show that film Tg is unaffected by stress relaxation, even when stress relaxation is accompanied by measurable changes in thickness. Fluorescence shows that stress relaxation time follows an Arrhenius temp. dependence with an activation energy of ∼110 kJ/mol, which is consistent with stress relaxation occurring by β-relaxation. Using a bilayer/fluorescence technique with bulk bilayer films, it was obsd. by I1/I3 measurements that a 30-nm-thick MPy-PS layer located at a glass substrate interface is stiffer than a 30-nm-thick MPy-PS layer located at a free surface. Over a 20-400 nm thickness range, fluorescence of MPy-PS films show a significant effect of substrate on mol. caging and hence stiffness, with stiffness increasing in the following order: free-standing films (no substrate) < films supported on a polydimethylsiloxane (soft) substrate < films supported on a glass (hard) substrate.
    41. 41
      Askar, S.; Torkelson, J. M. Stiffness of thin, supported polystyrene films: Free-surface, substrate, and confinement effects characterized via self-referencing fluorescence. Polymer 2016, 99, 417– 426,  DOI: 10.1016/j.polymer.2016.07.042
      41
      Stiffness of thin, supported polystyrene films: Free-surface, substrate, and confinement effects characterized via self-referencing fluorescence
      Askar, Shadid; Torkelson, John M.
      Polymer (2016), 99 (), 417-426CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      Stiffness-confinement effects are characterized via a non-contact, self-referencing fluorescence approach in polystyrene (PS) films labeled with trace levels of 1-pyrenylmethyl methacrylate. The pyrene fluorescence measurable I1/I3 is sensitive to mol. caging, which increases with stiffness. At 140 °C, mol. caging and hence stiffness in single-layer PS films supported on silica is independent of thickness down to 240 nm and increases with decreasing thickness at 165 nm and below. In contrast, near Tg at 100 °C and in the glassy state at 60 °C, mol. caging and hence stiffness in single-layer films is independent of thickness down to 63 nm and increases with decreasing thickness at 36 nm and below. In bulk bilayer films, perturbations originating at the substrate interface (free-surface interface) cause major increases (decreases) in caging and hence stiffness in 20-nm-thick substrate-adjacent (free-surface-adjacent) layers. In contrast, in 40-nm-thick bilayer films, the 20-nm-thick substrate-adjacent and free-surface-adjacent layers exhibit little difference in caging and stiffness. Thus, the gradient in stiffness from a film interface depends significantly on confinement, which we hypothesize begins to occur when thickness becomes comparable to the combined length scales over which free-surface and substrate perturbations propagate inside the film. Bulk bilayer films were used to investigate the length scales assocd. with interfacial perturbations. At 100 °C and 60 °C, stiffness-gradient length scales extend ∼45-85 nm from the substrate and ∼35-85 nm from the free surface. At 140 °C, the stiffness-gradient length scales extend ∼85-200 nm from the substrate and .ltorsim. 20 nm from the free surface.
    42. 42
      Kim, S.; Torkelson, J. M. Distribution of Glass Transition Temperatures in Free-Standing, Nanoconfined Polystyrene Films: A Test of de Gennes’ Sliding Motion Mechanism. Macromolecules 2011, 44, 4546– 4553,  DOI: 10.1021/ma200617j
      42
      Distribution of Glass Transition Temperatures in Free-Standing, Nanoconfined Polystyrene Films: A Test of de Gennes' Sliding Motion Mechanism
      Kim, Soyoung; Torkelson, John M.
      Macromolecules (Washington, DC, United States) (2011), 44 (11), 4546-4553CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Effects of nanoscale confinement on the distribution of glass transition temps. (Tgs) in free-standing polystyrene (PS) films are detd. via a multilayer/self-referencing fluorescence method employing a pyrene dye label. Av. film Tgs yield a Tg-confinement effect in agreement with the mol. wt. (MW) dependence reported by Forrest, Dalnoki-Veress, and Dutcher. Multilayer films, with one pyrene-labeled layer, reveal that a 14 nm thick free-surface layer in sufficiently thick films (≥∼56 nm) exhibits Tg = Tg,bulk - ∼34 K, independent of film thickness and indicative of a strong Tg gradient near a surface. In sufficiently thin films (≤∼56 nm), a 14 nm thick free-surface layer reports Tg that decreases with decreasing film thickness and is equal to the Tg of a 14 nm thick middle layer and the av. film Tg. Thus, the strongly perturbed Tg at the two surfaces affects Tg several tens of nanometers into and across the film, resulting in greater Tg redns. than obsd. in supported films. This study also tests de Gennes' "sliding motion mechanism", devised to explain the MW dependence of the Tg-confinement effect in free-standing films. No midlayer chain in a multilayer film forms loops or bridges reaching a surface. The de Gennes' mechanism indicates that Tg redns. occur only at locations where segments are present from chains forming loops or bridges at a surface. Major Tg redns. (as large as ∼54 K below Tg,bulk) are obsd. in midlayers of nanoconfined free-standing PS films, disproving a key premise of the mechanism.
    43. 43
      Baglay, R. R.; Roth, C. B. Communication: Experimentally determined profile of local glass transition temperature across a glassy-rubbery polymer interface with a Tg difference of 80 K. J. Chem. Phys. 2015, 143, 111101  DOI: 10.1063/1.4931403
      43
      Communication: Experimentally determined profile of local glass transition temperature across a glassy-rubbery polymer interface with a Tg difference of 80 K
      Baglay, Roman R.; Roth, Connie B.
      Journal of Chemical Physics (2015), 143 (11), 111101/1-111101/5CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      Studying the local glass transition temp. Tg across a boundary, we investigate the characteristic length scales of cooperative dynamics. High mol. wt. polymers have a large sepn. in time scales between cooperative segmental motion (α-relaxation) and chain diffusion allowing us to measure the local Tg(z) profile across a glassy-rubbery interface of polystyrene/poly(Bu methacrylate) using fluorescence. We find this profile in cooperative dynamics does not correlate with the 7-nm wide sym. compn. profile of the interface, but instead is very broad, spanning 350-400 nm from one bulk Tg value to another, and highly asym., extending further into the glassy side. (c) 2015 American Institute of Physics.
    44. 44
      Baglay, R. R.; Roth, C. B. Local glass transition temperature Tg(z) of polystyrene next to different polymers: Hard vs. soft confinement. J. Chem. Phys. 2017, 146, 203307  DOI: 10.1063/1.4975168
      44
      Local glass transition temperature Tg(z) of polystyrene next to different polymers: Hard vs. soft confinement
      Baglay, Roman R.; Roth, Connie B.
      Journal of Chemical Physics (2017), 146 (20), 203307/1-203307/13CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The depth to which the local glass transition temp. Tg and alpha-relaxations are perturbed near a boundary is believed to be related to the characteristic length scales assocd. with cooperative dynamics in dynamically heterogeneous glasses. Following our recent work [R. R. Baglay and C. R. Roth, J. Chem. Phys. 143, 111101 (2015)] that measured a very broad 350-400 nm local Tg(z) profile across a glassy-rubbery interface of polystyrene (PS)/poly(Bu methacrylate) (PnBMA), we compare here how the Tg(z) profile in PS varies when changing the neighboring polymer from a lower Tg material to a higher Tg material. Here we report local Tg(z) profiles for PS when in contact with polysulfone (PSF), poly(Me methacrylate) (PMMA), and poly(iso-Bu methacrylate) (PiBMA). We find that the distance from the interface before bulk Tg of PS (Tgbulk = 101 °C) is recovered depends on whether PS forms the high-Tg glassy component experiencing so-called soft confinement, z ≈ 225-250 nm for PS next to PiBMA (Tgbulk = 62 °C) and PnBMA (Tgbulk = 21 °C), or PS forms the low-Tg rubbery component experiencing hard confinement, z ≈ 100-125 nm for PS next to PSF (Tgbulk = 186 °C) and PMMA (Tgbulk = 120 °C). The depth to which these Tg(z) perturbations persist and the magnitude of the local Tg perturbation at the interface are independent of the difference in Tgbulk between the two polymers, the interaction parameter, and the chem. structure. We demonstrate that these broad, extended Tg(z) length scales appear to be universal across these different systems but show that the strong dynamical coupling across the dissimilar polymer-polymer interface only occurs when this interface has been annealed to equil. We consider why dissimilar polymer-polymer interfaces exhibit continuous local dynamics across the interface in contrast to polymer-free surface, polymer-substrate, or polymer-liq. interfaces that show discontinuous local dynamics. (c) 2017 American Institute of Physics.
    45. 45
      Mundra, M. K.; Ellison, C. J.; Rittigstein, P.; Torkelson, J. M. Fluorescence studies of confinement in polymer films and nanocomposites: Glass transition temperature, plasticizer effects, and sensitivity to stress relaxation and local polarity. Eur. Phys. J. Spec. Top. 2007, 141, 143,  DOI: 10.1140/epjst/e2007-00032-0
      There is no corresponding record for this reference.
    46. 46
      Lu, W.; Xiao, P.; Gu, J.; Zhang, J.; Huang, Y.; Huang, Q.; Chen, T. Aggregation-induced emission of tetraphenylethylene-modified polyethyleneimine for highly selective CO2 detection. Sens. Actuators, B 2016, 228, 551– 556,  DOI: 10.1016/j.snb.2016.01.096
      46
      Aggregation-induced emission of tetraphenylethylene-modified polyethyleneimine for highly selective CO2 detection
      Lu, Wei; Xiao, Peng; Gu, Jincui; Zhang, Jiawei; Huang, Youju; Huang, Qing; Chen, Tao
      Sensors and Actuators, B: Chemical (2016), 228 (), 551-556CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
      A polymer-based visible and quant. fluorometric assay for CO2 gas is constructed using branched polyethyleneimine (PEI) covalently modified with tetraphenylethylene (TPE). The sensing mechanism relies on the reaction of CO2 with alkylamines of PEI to induce the "soln.-to-pptn." phase transition of the sensory polymer (TPE-PEI), thus resulting in strong aggregation-induced fluorescent emission of TPE-PEI. It works in a relatively environmental benign ethanol medium and avoids the use of toxic amine compds. with unpleasant odor. More importantly, this system is proved to be highly tolerant to possibly coexisting water, carbon monoxide, acid SO2 and H2S gases as well as many common volatile org. compds. These characteristics make the presently developed fluorescent chemosensor hold great potential for many real-world applications.
    47. 47
      Wang, C.; Li, Q.; Wang, B.; Li, D.; Yu, J. Fluorescent sensors based on AIEgen-functionalised mesoporous silica nanoparticles for the detection of explosives and antibiotics. Inorg. Chem. Front. 2018, 5, 2183– 2188,  DOI: 10.1039/C8QI00622A
      47
      Fluorescent sensors based on AIEgen-functionalised mesoporous silica nanoparticles for the detection of explosives and antibiotics
      Wang, Chen; Li, Qinglan; Wang, Bolun; Li, Dongdong; Yu, Jihong
      Inorganic Chemistry Frontiers (2018), 5 (9), 2183-2188CODEN: ICFNAW; ISSN:2052-1553. (Royal Society of Chemistry)
      Aggregation-induced emission luminogen (AIEgen)-functionalised mesoporous silica nanoparticles were synthesized by post-grafting two types of tetraphenylethene derivs. on mesoporous materials. The fluorescent chem. sensors, denoted as FMSN-1 and FMSN-2, emitted strong blue fluorescence under UV irradn. Both of them exhibited quick and sensitive responses to 2,4,6-trinitrophenol (PA) and 2,4-dinitrophenol (2,4-DNP) via a fluorescence quenching process. In particular, the obtained materials also showed remarkable sensing ability for the antibiotics furazolidone (FZD) and nitrofurazone (NF) with low detection limits. The highly efficient sensing abilities of FMSNs for PA, 2,4-DNP, FZD, and NF can be attributed to fluorescence resonance energy transfer (FRET) from AIEgens to analytes. These results demonstrate the potential value of AIEgen-functionalised mesoporous materials in environmental protection.
    48. 48
      Potter, M. E.; Pang, S. H.; Jones, C. W. Adsorption Microcalorimetry of CO2 in Confined Aminopolymers. Langmuir 2017, 33, 117– 124,  DOI: 10.1021/acs.langmuir.6b03793
      48
      Adsorption Microcalorimetry of CO2 in Confined Aminopolymers
      Potter, Matthew E.; Pang, Simon H.; Jones, Christopher W.
      Langmuir (2017), 33 (1), 117-124CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Aminopolymers confined within mesoporous supports showed promise as materials for direct capture of CO2 from ambient air. In spite of this, relatively little is known about the energetics of CO2 binding in these materials, and the limited calorimetric studies published to date have focused on materials made using mol. aminosilanes, rather than amine polymers. In this work poly(ethyleneimine) (PEI) is impregnated within mesoporous SBA-15, and the heats of CO2 adsorption at 30° were studied using a Tian-Calvet calorimeter with emphasis on the role of PEI loading, and CO2 pressure in the compositional region relevant to direct capture of CO2 from ambient air. In parallel, CO2 uptakes of these materials are measured using multiple complimentary approaches, including both volumetric and gravimetric methods, and distinct changes in uptake as a function of CO2 pressure and amine loading are obsd. The CO2 sorption behavior is directly linked to textural data describing the porosity and PEI distribution in the materials.
    49. 49
      Mei, J.; Leung, N. L. C.; Kwok, R. T. K.; Lam, J. W. Y.; Tang, B. Z. Aggregation-Induced Emission: Together We Shine, United We Soar!. Chem. Rev. 2015, 115, 11718– 11940,  DOI: 10.1021/acs.chemrev.5b00263
      49
      Aggregation-Induced Emission: Together We Shine, United We Soar!
      Mei, Ju; Leung, Nelson L. C.; Kwok, Ryan T. K.; Lam, Jacky W. Y.; Tang, Ben Zhong
      Chemical Reviews (Washington, DC, United States) (2015), 115 (21), 11718-11940CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      The United Nations has proclaimed 2015 the International Year of Light and Light-based Technologies to acknowledge the great roles of light in scientific discoveries and technol. innovations. Aggregation-induced emission, (AIE), just as its name implies, refers to a photophys. effect that light emission of a luminogen is activated by aggregate formation. The luminogens with AIE effects are called AIEgens. This article is a review of the fundamentals of the AIE phenomenon.
    50. 50
      La, D. D.; Bhosale, S. V.; Jones, L. A.; Bhosale, S. V. Tetraphenylethylene-Based AIE-Active Probes for Sensing Applications. ACS Appl. Mater. Interfaces 2018, 10, 12189– 12216,  DOI: 10.1021/acsami.7b12320
      50
      Tetraphenylethylene-Based AIE-Active Probes for Sensing Applications
      La, Duong Duc; Bhosale, Sidhanath V.; Jones, Lathe A.; Bhosale, Sheshanath V.
      ACS Applied Materials & Interfaces (2018), 10 (15), 12189-12216CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      A review. This Review provides a comprehensive anal. of recent development in the field of aggregation-induced emission (AIE)-active tetraphenylethylene (TPE) luminophores and their applications in biomol. science. It begins with a discussion of the diverse range of structural motifs that have found particular applications in sensing and demonstrates that TPE structures and their derivs. have been used for a diverse range of analytes such as such as H+, anions, cations, heavy metals, org. volatiles, and toxic gases. Advances are discussed in depth where TPE was used as a mechanoluminescent material in bioinspired receptor units with specificity for analytes for such as glucose or RNA. The rapid advances in sensor research make this summary of recent developments in AIE-active TPE luminophores timely, to disseminate the advantages of these materials for sensing of analytes in soln., as well as the importance of solid and aggregated states in controlling sensing behavior.
    51. 51
      Sharath Kumar, K. S.; Girish, Y. R.; Ashrafizadeh, M.; Mirzaei, S.; Rakesh, K. P.; Hossein Gholami, M.; Zabolian, A.; Hushmandi, K.; Orive, G.; Kadumudi, F. B.; Dolatshahi-Pirouz, A.; Thakur, V. K.; Zarrabi, A.; Makvandi, P.; Rangappa, K. S. AIE-featured tetraphenylethylene nanoarchitectures in biomedical application: Bioimaging, drug delivery and disease treatment. Coord. Chem. Rev. 2021, 447, 214135  DOI: 10.1016/j.ccr.2021.214135
      51
      AIE-featured tetraphenylethylene nanoarchitectures in biomedical application: Bioimaging, drug delivery and disease treatment
      Sharath Kumar, Kothanahally S.; Girish, Yarabahally R.; Ashrafizadeh, Milad; Mirzaei, Sepideh; Rakesh, Kadalipura P.; Hossein Gholami, Mohammad; Zabolian, Amirhossein; Hushmandi, Kiavash; Orive, Gorka; Kadumudi, Firoz Babu; Dolatshahi-Pirouz, Alireza; Thakur, Vijay Kumar; Zarrabi, Ali; Makvandi, Pooyan; Rangappa, Kanchugarakoppal S.
      Coordination Chemistry Reviews (2021), 447 (), 214135CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
      A review. The development of aggregation-induced emission (AIE) has received extreme considerations from basic and clin. researches. To date, various luminogens with AIE property (AIEgens) have been broadly utilized in optoelectronic devices, fluorescent bio-probes, drug delivery, anticancer and chemosensors and many more. Scientists have likewise dedicated to investigating the possibilities of AIEgens in the biomedical field. Among the various AIE luminophores studied, tetraphenylethylene (TPE) derivs. have demonstrated as most promising AIEgen, owing to their capacity in self-organization and conjugation with aggregation-caused quenching (ACQ) fluorophores to form larger multi-component assemblies. It likewise generally utilized in different fields, like org. and therapeutic science, supramol. chem., org. electronics, cancer therapy, apoptosis and inflammation, microorganism imaging therapy, etc. This review encompasses the recent advances of TPE based AIE-active luminophores and their potential applications in biomol. science.
    52. 52
      Yang, Z.; Chi, Z.; Mao, Z.; Zhang, Y.; Liu, S.; Zhao, J.; Aldred, M. P.; Chi, Z. Recent advances in mechano-responsive luminescence of tetraphenylethylene derivatives with aggregation-induced emission properties. Mater. Chem. Front. 2018, 2, 861– 890,  DOI: 10.1039/C8QM00062J
      52
      Recent advances in mechano-responsive luminescence of tetraphenylethylene derivatives with aggregation-induced emission properties
      Yang, Zhiyong; Chi, Zhihe; Mao, Zhu; Zhang, Yi; Liu, Siwei; Zhao, Juan; Aldred, Matthew P.; Chi, Zhenguo
      Materials Chemistry Frontiers (2018), 2 (5), 861-890CODEN: MCFAC5; ISSN:2052-1537. (Royal Society of Chemistry)
      A review. Since the realization in 2011 that most aggregation-induced emission (AIE) mols. exhibit mechano-responsive luminescence (MRL), research regarding the MRL of AIE mols. has drawn much attention, and this area has been expanding tremendously. As one of the most extensively studied AIE cores, tetraphenylethylene (TPE) has been widely used to construct MRL mols. This review will focus on recent advances in MRL of TPE derivs. with AIE properties, including a brief history of mechano-responsive AIE-active materials, mechanistic studies on MRL, mechano-responsive luminogens based on TPE, mechano-responsive luminogens contg. multiple AIE-active units, mechano-memory chromism and mechanoluminescence of TPE derivs. Moreover, this review will give a perspective on the possible opportunities and future challenges that exist in this research area.
    53. 53
      Iasilli, G.; Battisti, A.; Tantussi, F.; Fuso, F.; Allegrini, M.; Ruggeri, G.; Pucci, A. Aggregation-Induced Emission of Tetraphenylethylene in Styrene-Based Polymers. Macromol. Chem. Phys. 2014, 215, 499– 506,  DOI: 10.1002/macp.201300698
      53
      Aggregation-Induced Emission of Tetraphenylethylene in Styrene-Based Polymers
      Iasilli, Giuseppe; Battisti, Antonella; Tantussi, Francesco; Fuso, Francesco; Allegrini, Maria; Ruggeri, Giacomo; Pucci, Andrea
      Macromolecular Chemistry and Physics (2014), 215 (6), 499-506CODEN: MCHPES; ISSN:1022-1352. (Wiley-VCH Verlag GmbH & Co. KGaA)
      In the present work, the prepn. of different styrene-based polymer films contg. small amts. of TPE and the evaluation of their photoluminescent behavior is reported. When TPE is dispersed in a poor solvent or in a glassy PS matrix, the arrested intramol. rotations of its aryls favor the strong emission of light centered at about 455-460 nm. Conversely, TPE fluorescence significantly weakens to a faint signal when good solvents or viscous but not glassy polymer matrixes are used. Near-field optical microscopy correlates the fluorescence behavior with the different matrix morphologies. These results should be able to be used for developing a new tool for polymer traceability.
    54. 54
      Barbara, P. F.; Rand, S. D.; Rentzepis, P. M. Direct measurements of tetraphenylethylene torsional motion by picosecond spectroscopy. J. Am. Chem. Soc. 1981, 103, 2156– 2162,  DOI: 10.1021/ja00399a003
      54
      Direct measurements of tetraphenylethylene torsional motion by picosecond spectroscopy
      Barbara, P. F.; Rand, S. D.; Rentzepis, P. M.
      Journal of the American Chemical Society (1981), 103 (9), 2156-62CODEN: JACSAT; ISSN:0002-7863.
      The time- and wavelength-resolved fluorescence of C2Ph4 (I), induced by 355-nm ps excitation in several solvents over a range of temps. and viscosities, was investigated. Several distinct fluorescence kinetic processes were identified, which are manifested by (i) time-dependent fluorescence-spectral shifts, (ii) time-dependent fluorescent spectral-shape changes, and (iii) nonexponential fluorescence-decay kinetics. The relaxation rates of these processes depend strongly on temp. and solvent viscosity. The obsd. fluorescence dynamics of I are complex, and suggest that several channels are available for excited-state relaxation. The relaxation pathways are assigned to radiative and radiationless electronic decay, vibrational relaxation, and 2 forms of excited-state conformational relaxation. A unified model is proposed for the photochem. dynamics of I.
    55. 55
      Demchenko, A. P. The concept of λ-ratiometry in fluorescence sensing and imaging. J. Fluoresc. 2010, 20, 1099– 1128,  DOI: 10.1007/s10895-010-0644-y
      55
      The concept of λ-ratiometry in fluorescence sensing and imaging
      Demchenko Alexander P
      Journal of fluorescence (2010), 20 (5), 1099-128 ISSN:.
      Very limited number of parameters is available for fluorescence sensing and imaging. The changes of intensity are of low analytical value due to the absence of internal reference. Anisotropy and lifetime sensing have their own limitations. In this respect the λ-ratiometric (based on intensity ratios at two or more wavelengths) recording of spectral changes becomes more popular. Because the spectral changes are connected directly with the variations of interaction energies this approach is seen as the most universal method to study intermolecular interactions. It is applicable for different sensor formats and for obtaining analytical information from cell images. Here we critically analyze different approaches in λ-ratiometric sensing that use single and double fluorescence emitters and are based on different mechanisms producing spectroscopic change. Very promising is the exploration of mechanisms that allow obtaining ratiometric response from a single dye.
    56. 56
      Jimbo, T.; Tsuji, M.; Taniguchi, R.; Sada, K.; Kokado, K. Control of Aggregation-Induced Emission from a Tetraphenylethene Derivative through the Components in the Co-crystal. Cryst. Growth Des. 2018, 18, 3863– 3869,  DOI: 10.1021/acs.cgd.8b00141
      56
      Control of Aggregation-Induced Emission from a Tetraphenylethene Derivative through the Components in the Co-crystal
      Jimbo, Takahiro; Tsuji, Mikako; Taniguchi, Ryosuke; Sada, Kazuki; Kokado, Kenta
      Crystal Growth & Design (2018), 18 (7), 3863-3869CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
      We aim to control the photoluminescence property of co-crystals derived from an aggregation-induced emission luminogen (AIEgen) through other components in the co-crystal. For this purpose, we prepd. co-crystals of a typical AIEgen, tetraphenylethene having four hydroxy groups (THPE), and hydrogen-bond acceptors (HBAs) contg. nitrogen atoms. The crystallog. study showed that the hydrogen-bonding pattern and inclusion of crystn. solvents are significantly influenced by the employed HBA, depending on the size, position of nitrogen atoms, and basicity of the HBA, thanks to the moderate hydrogen-bonding ability of THPE. The photoluminescence properties of the co-crystals are governed by the employed HBA, and thus, co-crystals derived from imidazole derivs. or 1,4-diazabicyclo[2.2.2]octane exhibit intense photoluminescence, while those from pyridine derivs. and an electron-deficient imidazole deriv. do not show any photoluminescence. The involvement of photoinduced electron transfer causes quenching of the co-crystals derived from pyridine derivs., which is confirmed by theor. computations. These observations imply that the photoluminescence properties of co-crystals derived from AIEgens can be tuned through other components in the co-crystal.
    57. 57
      Román, F.; Colomer, P.; Calventus, Y.; Hutchinson, J. M. Study of Hyperbranched Poly(ethyleneimine) Polymers of Different Molecular Weight and Their Interaction with Epoxy Resin. Materials 2018, 11, 410  DOI: 10.3390/ma11030410
      57
      Study of hyperbranched poly(ethyleneimine) polymers of different molecular weight and their interaction with epoxy resin
      Roman, Frida; Colomer, Pere; Calventus, Yolanda; Hutchinson, John M.
      Materials (2018), 11 (3), 410/1-410/26CODEN: MATEG9; ISSN:1996-1944. (MDPI AG)
      Two different com. hyperbranched poly(ethyleneimine)s (HBPEI), with mol. wts. (MW) of 800 and 25,000 g/mol, and denoted as PEI800 and PEI25000, resp., as well as the mixts. with a Diglycidyl Ether of Bisphenol-A (DGEBA) epoxy resin, have been studied using thermal anal. techniques (DSC, TGA), dielec. relaxation spectroscopy (DRS), and dynamic mech. anal. (DMA). Only a single glass transition is obsd. in these mixts. by DSC. DRS of the HBPEIs shows three dipolar relaxations: γ, β, and α. The av. activation energy for the γ-relaxation is similar for all HBPEIs and is assocd. with the motion of the terminal groups. The β-relaxation has the same av. activation energy for both PEI800 and PEI25000; this relaxation is attributed to the mobility of the branches. The α-relaxation peak for all the HBPEIs is an asym. peak with a shoulder on the high temp. side. This shoulder suggests the existence of ionic charge trapped in the PEI. For the mixts., the γ- and β-relaxations follow the behavior of the epoxy resin alone, indicating that the epoxy resin dominates the mol. mobility. The α-relaxation by DRS is obsd. only as a shoulder, as a consequence of an overlap with cond. effects, whereas by DMA, it is a clear peak.
    58. 58
      Hashida, T.; Tashiro, K. Structural Study on Water-induced Phase Transitions of Poly(ethylene imine) as Viewed from the Simultaneous Measurements of Wide-Angle X-ray Diffractions and DSC Thermograms. Macromol. Symp. 2006, 242, 262– 267,  DOI: 10.1002/masy.200651036
      58
      Structural study on water-induced phase transitions of poly(ethylene imine) as viewed from the simultaneous measurements of wide-angle X-ray diffractions and DSC thermograms
      Hashida, Tomoko; Tashiro, Kohji
      Macromolecular Symposia (2006), 242 (Polychar-14, World Forum on Advanced Materials, 2006), 262-267CODEN: MSYMEC; ISSN:1022-1360. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Thermal behavior of poly(ethylene imine) [PEI] was studied using simultaneous WAXD/DSC measurement system. PEI exhibits water-induced and thermally-induced phase transitions among four kinds of cryst. hydrates: anhydrate (EI/water = 1/0), hemihydrate (1/0.5), sesquihydrate (1/1.5), and dihydrate (1/2). The chain conformation changes from a double helix in the anhydrate to a planar zigzag form in the three hydrates. The anhydrate melts at 60 °C while the hydrates melt differently in the temp. region of 70-110 °C. By means of the simultaneous WAXD/DSC measurements, complex DSC thermograms of PEI hydrates were characterized on the basis of X-ray diffractions obtained concurrently.
    59. 59
      Aldred, M. P.; Li, C.; Zhu, M.-Q. Optical Properties and Photo-Oxidation of Tetraphenylethene-Based Fluorophores. Chem.─Eur. J. 2012, 18, 16037– 16045,  DOI: 10.1002/chem.201202715
      59
      Optical Properties and Photooxidation of Tetraphenylethene-Based Fluorophores
      Aldred, Matthew P.; Li, Chong; Zhu, Ming-Qiang
      Chemistry - A European Journal (2012), 18 (50), 16037-16045CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The authors report the optical properties of tetraphenylethene (TPE) and other TPE derivs. functionalized with an octyl group (TPE-OCT) and polyethylene glycol group (TPE-PEG) in the side chain. The authors compared TPE-OCT and TPE-PEG with TPE in both org. solvents and under aq. conditions. All materials exhibit aggregation-induced emission, however, uncommonly, TPE-PEG seems to aggregate in aq. soln. with enhanced photoluminescence quantum efficiency (PLQE) relative to that in org. solvents. All three materials can be photooxidized in soln. to their diphenylphenanthrene deriv. by irradn. with UV light (at both ≈1 and ≈5 mW cm-2), with a subsequent enhancement in PL efficiency. The electron-donating ether group increases the rate of oxidn. relative to bare TPE and also photooxidn. was shown to be solvent and concn. dependent. Finally, photooxidn. was also demonstrated in the aggregate state.
    60. 60
      Badrinarayanan, P.; Zheng, W.; Li, Q.; Simon, S. L. The glass transition temperature versus the fictive temperature. J. Non-Cryst. Solids 2007, 353, 2603– 2612,  DOI: 10.1016/j.jnoncrysol.2007.04.025
      60
      The glass transition temperature versus the fictive temperature
      Badrinarayanan, Prashanth; Zheng, Wei; Li, Qingxiu; Simon, Sindee L.
      Journal of Non-Crystalline Solids (2007), 353 (26), 2603-2612CODEN: JNCSBJ; ISSN:0022-3093. (Elsevier B.V.)
      A comparison of the values of the glass transition temp. (T g) measured on cooling and the limiting fictive temp. ( T 'f ) measured on heating as a function of cooling rate is performed for a polystyrene sample using both capillary dilatometry and differential scanning calorimetry (DSC). The results from both techniques indicate that T 'f is systematically lower than T g presumably due to the breadth of the relaxation on cooling. The Tool-Narayanaswamy-Moynihan (TNM) model is used to fit the exptl. data from dilatometry and DSC to ascertain the origins of the higher value of T g compared to T 'f.
    61. 61
      Plazek, D. J.; Ngai, K. L. The Glass Temperature. In Physical Properties of Polymers Handbook, 2nd; Mark, J. E., Ed.; Springer Nature, 2007; pp 187– 215.
      There is no corresponding record for this reference.
    62. 62
      McKenna, G. B.; Simon, S. L. 50th Anniversary Perspective: Challenges in the Dynamics and Kinetics of Glass-Forming Polymers. Macromolecules 2017, 50, 6333– 6361,  DOI: 10.1021/acs.macromol.7b01014
      62
      50Th Anniversary Perspective: Challenges in the Dynamics and Kinetics of Glass-Forming Polymers
      McKenna, Gregory B.; Simon, Sindee L.
      Macromolecules (Washington, DC, United States) (2017), 50 (17), 6333-6361CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A review. The phenomenol. of the glass transition and the assocd. behavior in the near liq. and glassy states are detailed, including the cooling rate dependence of the glass transition, Kovacs' three signatures of structural recovery, and enthalpy overshoots. Dynamics in the liq. regime just above Tg and the assocd. temp. dependences are also covered since this behavior is important to understanding the glassy dynamics. The current models of the structural recovery and their shortcomings are presented. A no. of important unanswered questions are discussed, including how the relaxation time in the glassy state depends on structure, the relationship between the evolution of different properties, the resoln. of the Kauzmann paradox, and the behavior of the equil. relaxation time below Tg. New exptl. approaches are needed to make breakthroughs, such as two that are described: one involving 20 Ma amber to test whether the Vogel temp. dependence continues for the equil. state below Tg and another involving an ideal polymer/pentamer mixt. to obtain the entropy of the liq. far below TK in a test of the Kauzmann paradox. An unexplored regime of glassy behavior, characterized by ultrastability, high d., and low fictive temp., is identified, and expts. to understand the material behavior in this region are motivated.
    63. 63
      McKenna, G. B. Diverging views on glass transition. Nat. Phys. 2008, 4, 673,  DOI: 10.1038/nphys1063
      63
      Diverging views on glass transition
      McKenna, Gregory B.
      Nature Physics (2008), 4 (9), 673-674CODEN: NPAHAX; ISSN:1745-2473. (Nature Publishing Group)
      Anal. of the best available data on the behavior of a large no. of glass-forming org. liqs. suggests that the widespread belief that a glass ceases to flow below its transition temp. could be wrong.
    64. 64
      Plazek, D. J.; Frund, Z. N., Jr. Epoxy resins (DGEBA): The curing and physical aging process. J. Polym. Sci., Part B: Polym. Phys. 1990, 28, 431– 448,  DOI: 10.1002/polb.1990.090280401
      64
      Epoxy resins (DGEBA): the curing and physical aging process
      Plazek, D. J.; Frund, A. N., Jr.
      Journal of Polymer Science, Part B: Polymer Physics (1990), 28 (4), 431-48CODEN: JPBPEM; ISSN:0887-6266.
      DSC and IR spectroscopy were used to monitor the degree of cure of partially cured epoxy resin (Epon 828/methylenedianiline) samples. The extent of cure, as detd. by residual heat of reaction, concurred with that detd. by monitoring the IR radiation absorbance of the epoxide group near 916 cm-1. The fictive temp. Tf,g increased with the degree of cure, increasing rapidly during cure until reaching a value near the cure temp. Tc of 130° (∼80% cure) where the material vitrified. The greatly reduced reaction rate during the final 20% of cure was not only a consequence of vitrification but, as revealed by IR spectroscopy, the result of the depletion in the no. of reactive epoxide groups. The endothermic peak areas and peak temps. evident during the DSC scans were used as a measure of the extent of phys. aging which took place during the cure of this resin, and after, fully cured samples were aged 37° below their ultimate glass temp. (Tg) for various periods of time. The rate of phys. aging slowed as the temp. increment (Tf,g - Tc) increased. Although an endothermic peak was evident after only 1 h of cure (Tf,g = 138.3°C), such a peak did not appear until fully cured samples were aged for ≥16 h. Enthalpy data revealed that for partially cured material, the fictive temp. Tf,a, reflecting phys. aging, increased with curing time. In contrast, the Tf,a for fully cured samples decreased with sub-Tg aging time. The characteristic jump in the heat capacity which occurred at the Tf,g decreased as curing progressed. This decrease was dependent upon the rotational and vibrational degrees of freedom of the glass. Finally, a graphical method of detg. the fictive temp. Tf,a of partially and fully cured epoxy material from measured endothermic peak areas was developed.
    65. 65
      Kunal, K.; Robertson, C. G.; Pawlus, S.; Hahn, S. F.; Sokolov, A. P. Role of Chemical Structure in Fragility of Polymers: A Qualitative Picture. Macromolecules 2008, 41, 7232– 7238,  DOI: 10.1021/ma801155c
      65
      Role of Chemical Structure in Fragility of Polymers: A Qualitative Picture
      Kunal, Kumar; Robertson, Christopher G.; Pawlus, Sebastian; Hahn, Steven F.; Sokolov, Alexei P.
      Macromolecules (Washington, DC, United States) (2008), 41 (19), 7232-7238CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Understanding microscopic parameters that control steepness of the temp. variations of segmental relaxation (fragility) and the glass transition phenomenon remains a challenge. We present dielec. and mech. relaxation studies of segmental dynamics in various polymers with different side groups and backbone structures. The results have been analyzed in terms of flexibility of backbone and side groups of polymeric mols., as suggested by the recent theor. works by Dudowicz et al. A comparison of structures with identical backbones and varying side groups and identical side groups but different backbones reveals that the flexibility of side groups relative to the flexibility of the backbone is the most important factor controlling fragility in polymers, while the glass transition temp. Tg depends primarily on the backbone flexibility and the side group bulkiness (occupied vol.). Based on these results and anal. of literature data we formulated a modified approach to understand the role of chem. structure in segmental dynamics: (i) Polymers with stiff backbones always have high Tg and fragility, while (ii) polymers with flexible backbones and no side groups are the strongest; (iii) however, for the most common type of polymeric structure, C-C or Si-O backbone with side groups, fragility increases with increasing "relative" stiffness of side groups vs. the backbone. In this class of polymers, lowest fragility is expected when the side groups are of similar chem. structure (or flexibility) as the backbone, as in the case of polyisobutylene, one of the strongest polymers known.
    66. 66
      Fried, J. R. Sub Tg Transitions. In Physical Properties of Polymers Handbook, 2nd ed.; Mark, J. E., Ed.; Springer Nature, 2007; pp 217– 232.
      There is no corresponding record for this reference.
    67. 67
      Hill, A. J.; Tant, M. R. The Structure and Properties of Glassy Polymers. Structure and Properties of Glassy Polymers, American Chemical Society, 1999; pp 1– 20.
      There is no corresponding record for this reference.
    68. 68
      Toi, K.; Ito, T.; Ikemoto, I. Effect of aging and conditioning on the gas transport of poly(vinyl acetate). J. Polym. Sci., Polym. Lett. Ed. 1985, 23, 525– 529,  DOI: 10.1002/pol.1985.130231006
      68
      Effect of aging and conditioning on the gas transport of poly(vinyl acetate)
      Toi, K.; Ito, T.; Ikemoto, I.
      Journal of Polymer Science, Polymer Letters Edition (1985), 23 (10), 525-9CODEN: JPYBAN; ISSN:0360-6384.
      The temp. dependence curves of the apparent permeation coeff. at 10-50° for CO2 in poly(vinyl acetate) (I) [9003-20-7] did not show any clear break point but changed smoothly. The two curves did not fit in the case of cooling and heating and diverged most ∼30° (glass temp.). This indicated that the relaxation of polymer chains might contribute to transport of gas in I near the glass temp. region. Both the apparent permeation coeff. and the amt. of permeation in the apparent steady-state decreased with phys. aging.
    69. 69
      Chowdhury, M.; Priestley, R. D. Discrete mobility on the surface of glasses. Proc. Natl. Acad. Sci. U.S.A. 2017, 114, 4854– 4856,  DOI: 10.1073/pnas.1704886114
      69
      Discrete mobility on the surface of glasses
      Chowdhury, Mithun; Priestley, Rodney D.
      Proceedings of the National Academy of Sciences of the United States of America (2017), 114 (19), 4854-4856CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      There is no expanded citation for this reference.
    70. 70
      Kim, H.; Cang, Y.; Kang, E.; Graczykowski, B.; Secchi, M.; Montagna, M.; Priestley, R. D.; Furst, E. M.; Fytas, G. Direct observation of polymer surface mobility via nanoparticle vibrations. Nat. Commun. 2018, 9, 2918  DOI: 10.1038/s41467-018-04854-w
      70
      Direct observation of polymer surface mobility via nanoparticle vibrations
      Kim Hojin; Furst Eric M; Cang Yu; Kang Eunsoo; Graczykowski Bartlomiej; Fytas George; Graczykowski Bartlomiej; Secchi Maria; Montagna Maurizio; Priestley Rodney D; Fytas George
      Nature communications (2018), 9 (1), 2918 ISSN:.
      Measuring polymer surface dynamics remains a formidable challenge of critical importance to applications ranging from pressure-sensitive adhesives to nanopatterning, where interfacial mobility is key to performance. Here, we introduce a methodology of Brillouin light spectroscopy to reveal polymer surface mobility via nanoparticle vibrations. By measuring the temperature-dependent vibrational modes of polystyrene nanoparticles, we identify the glass-transition temperature and calculate the elastic modulus of individual nanoparticles as a function of particle size and chemistry. Evidence of surface mobility is inferred from the first observation of a softening temperature, where the temperature dependence of the fundamental vibrational frequency of the nanoparticles reverses slope below the glass-transition temperature. Beyond the fundamental vibrational modes given by the shape and elasticity of the nanoparticles, another mode, termed the interaction-induced mode, was found to be related to the active particle-particle adhesion and dependent on the thermal behavior of nanoparticles.
    71. 71
      Zhang, W.; Douglas, J. F.; Starr, F. W. Why we need to look beyond the glass transition temperature to characterize the dynamics of thin supported polymer films. Proc. Nat. Acad. Sci. U.S.A. 2018, 115, 5641– 5646,  DOI: 10.1073/pnas.1722024115
      71
      Why we need to look beyond the glass transition temperature to characterize the dynamics of thin supported polymer films
      Zhang, Wengang; Douglas, Jack F.; Starr, Francis W.
      Proceedings of the National Academy of Sciences of the United States of America (2018), 115 (22), 5641-5646CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      There is significant variation in the reported magnitude and even the sign of Tg shifts in thin polymer films with nominally the same chem., film thickness, and supporting substrate. The implicit assumption is that methods used to est. Tg in bulk materials are relevant for inferring dynamic changes in thin films. To test the validity of this assumption, we perform mol. simulations of a coarse-grained polymer melt supported on an attractive substrate. As obsd. in many expts., we find that Tg based on thermodn. criteria (temp. dependence of film height or enthalpy) decreases with decreasing film thickness, regardless of the polymer-substrate interaction strength ε. In contrast, we find that Tg based on a dynamic criterion (relaxation of the dynamic structure factor) also decreases with decreasing thickness when ε is relatively weak, but Tg increases when ε exceeds the polymer-polymer interaction strength. We show that these qual. different trends in Tg reflect differing sensitivities to the mobility gradient across the film. Apparently, the slowly relaxing polymer segments in the substrate region make the largest contribution to the shift of Tg in the dynamic measurement, but this part of the film contributes less to the thermodn. est. of Tg. Our results emphasize the limitations of using Tg to infer changes in the dynamics of polymer thin films. However, we show that the thermodn. and dynamic ests. of Tg can be combined to predict local changes in Tg near the substrate, providing a simple method to infer information about the mobility gradient.

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