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Applications of Polymer, Composite, and Coating Materials
Nano-Confinement Effects on Structural Development and Organic Solvent-Induced Swelling of Ultrathin Carbon Molecular Sieve FilmsClick to copy article linkArticle link copied!
- Wojciech OgiegloWojciech OgiegloFunctional Polymer Membranes Group, Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, 23955 Thuwal, Saudi ArabiaMore by Wojciech Ogieglo
- Kepeng SongKepeng SongNanostructured Functional Materials, Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, 23955 Thuwal, Saudi ArabiaMore by Kepeng Song
- Cailing ChenCailing ChenNanostructured Functional Materials, Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, 23955 Thuwal, Saudi ArabiaMore by Cailing Chen
- Qiong LeiQiong LeiNanostructured Functional Materials, Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, 23955 Thuwal, Saudi ArabiaMore by Qiong Lei
- Yu HanYu HanNanostructured Functional Materials, Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, 23955 Thuwal, Saudi ArabiaMore by Yu Han
- Ingo Pinnau*Ingo Pinnau*Email: [email protected]Functional Polymer Membranes Group, Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, 23955 Thuwal, Saudi ArabiaMore by Ingo Pinnau
ACS Applied Materials & Interfaces
Cite this: ACS Appl. Mater. Interfaces 2021, 13, 18, 21765–21774
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Abstract
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Successful implementation of carbon molecular sieve (CMS) membranes in large scale chemical processes inevitably relies on fabrication of high performance integrally skinned asymmetric or thin-film composite membranes. In principle, to maximize separation efficiency the selective CMS layer should be as thin as possible which requires its lateral confinement to a supporting structure. In this work, we studied pyrolysis-induced structural development as well as ethanol vapor-induced swelling of ultrathin CMS films made from a highly aromatic polyimide of an intrinsic microporosity (PIM–PI) precursor. Utilization of a light polarization-sensitive technique, spectroscopic ellipsometry, allowed for the identification of an internal orientation within the turbostratic amorphous CMS structure driven by the laterally constraining support. Our results indicated a significant thickness dependence both in the extent of pyrolytic collapse and response to organic vapor penetrant. Thinner, substrate-confined films (∼30 nm) collapsed more extensively leading to a reduction of microporosity in comparison to their thicker (∼300 nm) as well as self-supported (∼70 μm) counterparts. The reduced microporosity in the thinner films induced changes in the balance between penetrant-induced dilation (swelling) and filling of micropores. In comparison to thicker films, the initial lower microporosity of the thinner films was accompanied by slightly enhanced organic vapor-induced swelling. The presented results are anticipated to generate the fundamental knowledge necessary to design optimized ultrathin CMS membranes. In particular, our results reinforce previous findings that excessive reduction of the selective layer thickness in amorphous microporous materials (such as PIMs or CMS) beyond several hundred nanometers may not be optimal for maximizing their fluid transport performance.
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Copyright © 2021 The Authors. Published by American Chemical Society
1. Introduction
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Carbon molecular sieve (CMS) membranes represent a special class of inorganic amorphous membrane materials with a significant potential in technologically important molecular separations such as hydrogen purification, natural gas processing, air separations, or carbon capture. (1−5) Recently, CMS membranes have been demonstrated to be very effective in challenging organic solvent (6) and olefin/paraffin (7−9) separations. Consequently, CMS membranes are perceived as potential future contributors in the necessary transition of our society toward more energy efficient industrial separations. The widespread use of this technology, however, relies on transformation of the CMS materials into high-performance thin-film membranes with highly selective and simultaneously highly efficient (high permeance) molecular transport. The most common strategy to achieve high permeances relies on a reduction of the selective layer thickness, typically to submicron range, to minimize transport resistance.
The significant potential of CMS thin-film composite membranes originates from their microporous nature. CMS materials possess a turbostratic structure, which can be approximated by considering graphene-like nanosheets randomly arranged in an amorphous network. The microporosity of the CMS materials is thought to have a bimodal character with smaller ultramicropores (<0.7 nm) and larger micropores (<2 nm) present simultaneously. (4) This bimodal pore size distribution is responsible for outstanding molecular separation properties where ultramicropores provide high selectivities by a molecular sieving mechanism whereas the larger micropores are responsible for lowering overall transport resistance leading to high gas permeance. Similar to CMS materials, polymers of intrinsic microporosity (PIMs) typically contain a bimodal pore size distribution where highly contorted backbones trap large amounts of excess free volume in the solid state. (10) The presence of micropores results in both PIMs and CMS outperforming the state-of-the-art polymeric membrane materials, sometimes by a very large margin. (11) In addition, CMS membranes are highly chemically and thermally stable even in long-term field operation. (12,13) However, similarly to other high free volume amorphous membrane materials, CMS membranes suffer from a progressive structural densification (physical aging) leading to significant reductions of permeance. (14,15) Moreover, physical aging, and to some degree dilation (or swelling) induced by condensable gases like CO2 or organic vapors, are well-known to amplify in thinner films, particularly in the submicron region. (16−19)
In glassy polymers, including PIMs, the combination of nanoconfinement in the form of ultrathin films and the presence of penetrants is known to have significant consequences to their molecular separation performance. (19−23) In particular, swelling resulting from interaction with organics which may be present in the feed mixtures (24) has been shown to depend on film thickness. This effect originates from a growing influence of the interfaces on the overall behavior of thin films. (20,25) While the topic of swelling in ultrathin organic polymer films has been addressed in the past 20 years, hardly any data exist on swelling of thin and ultrathin CMS films. Understanding of the solvent-induced swelling is indispensable to advance the important emerging applications of the CMS membranes, such as organic solvent reverse osmosis (OSRO) or organic solvent forward osmosis (OSFO). (1,26−28)
In this work, we investigated organic-vapor-induced swelling of supported CMS thin films produced by pyrolyzing a polyimide of intrinsic microporosity (PIM–PI) precursor in two thickness ranges: ∼300 and ∼30 nm. Combination of ex situ and in situ interference-enhanced spectroscopic ellipsometry allowed the swelling and refractive index changes to be resolved independently and provided strong evidence for a much larger relative pyrolysis-induced collapse in thinner ∼30 nm films as compared with thicker ∼300 nm films. The utilization of uniaxial anisotropic optical modeling indicated a large degree of structural orientation within the CMS films in the plane of the substrate driven by the laterally constraining substrate. Ethanol-induced swelling has been shown to strongly reduce with increasing pyrolysis temperature. At the same time, the balance between the fraction of microporosity accessible to the penetrant and the penetrant-induced swelling showed a subtle thickness dependence.
2. Experimental Section
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2.1. Sample Preparation and Characterization
The CMS precursor, a polyimide of intrinsic microporosity, SBFDA-DMN (Figure 1), was synthesized by a polymerization reaction of spirobifluorene-based dianhydride with 3,3′-dimethylnaphthidine, as described previously. (29) The polymer was characterized by a molecular weight Mn = 6.5 × 104 g mol–1 with a polydispersity of 1.92 and an internal surface area of SBET = 686 m2 g–1 measured at 77 K using N2. The thermal decomposition onset was determined by TGA at ∼520 °C (Supporting Information, Figure S1). The polymer combined a PIM character (high internal surface area and a rigid backbone) with a very high aromatic carbon content (84 wt %) which in our earlier work was proven to result in high-performance carbon molecular sieve membranes following pyrolysis. (15)
Figure 1
Figure 1. SBFDA-DMN polyimide with intrinsic microporosity (PIM–PI) used as carbon molecular sieve precursor in this study.
Thin SBFDA-DMN precursor films in two thicknesses, ∼300 and ∼30 nm, were spin-coated on top of 500 nm thermal silicon oxide wafer pieces (Si-Mat, Germany) from a chloroform solution of an adjusted concentration (between 0.5 and 3 wt %) at 2000 rpm. All silicon wafer pieces were separately characterized prior to film deposition to determine the exact silicon oxide thickness, which varied between about 493 and 498 nm. After spin-coating all samples were annealed at 50 °C for 16 h in air to remove the solvent. The pyrolysis process was conducted in a horizontal quartz tube furnace (Carbolite) under 1000 (STP) cm3 min–1 nitrogen flow at a ramp rate of 3 °C min–1 and 60 min dwell time at each temperature set point. Subsequently, the oven was left to passively cool within about 7–9 h. The pyrolysis set points were 500, 600, 700, and 800 °C, respectively. The oxygen concentration was monitored at the outlet of the furnace and was always below 5 ppm.
Transmission electron microscopy was performed with a low-base Titan electron microscope without Cs-corrector. The Cs was 1.2 mm, and the images were taken at high voltage (300 kV). The samples were cut with focused ion beam at low voltage. Raman spectra were recorded using 633 nm HeNe laser as excitation source on a Horiba Aramis device.
2.2. Ellipsometry Measurements and Data Analysis
A spectroscopic ellipsometer (M-2000 DI, J. A. Woollam, Co.) operating in a wavelength range of 193–1690 nm together with accompanying optical modeling software CompleteEASE v. 6.51 was employed throughout this study to conduct both ex situ and in situ (ethanol swelling) sample characterization. Ex situ analysis for both the thicker ∼300 and thinner ∼30 nm films was performed in a wavelength range of 600–1690 nm at a minimum of three angles of incidence (65, 70, and 75°), whereas 75° was used for in situ ethanol vapor experiments. Even though CMS are considered amorphous materials, structural orientation may develop upon confinement to substrates. (30) To study the development of structural orientation within the CMS films as a result of pyrolysis and confinement to the substrate, we have chosen to employ anisotropic optical modeling. To preserve consistency, all samples were modeled using exactly the same, anisotropic (uniaxial), model. For the weakly light-absorbing samples (pristine precursor, 500 and 600 °C) a Cauchy-type model with fitted extinction coefficient was used. For the strongly light-absorbing samples (700 and 800 °C) a Kramers–Kronig consistent B-Spline model (31) with a node resolution of 0.3 eV (for both xy and z components) was employed, Figure 2. To simplify the model by reducing the number of fit parameters only a difference in the zeroth order of the anisotropic nxy and nz component (“A” parameter) was fit. This procedure kept the real parts of the optical dispersion parallel, while the light absorption was fitted individually for each sample but was assumed the same in both x/y and z directions. The refractive index components were reported at 1000 nm, instead of at 632.8 nm as typically done, to avoid being too close to the edge of the modeling range (600–1690 nm). The presence of the ∼500 nm thick silicon oxide underneath each polymer/carbon film amplified the accuracy of the analysis versus the more broadly used native oxide wafers, as thoroughly investigated before. (15,32,33) An example of the optical model is presented in the Supporting Information (Figure S2). Error bars were estimated based on the fit parameter uniqueness analysis assuming as threshold a 25% reduction of the mean squared error (MSE).
Figure 2
Figure 2. Scheme of the anisotropic, uniaxial optical model used for the sample analysis throughout this study.
2.3. In Situ Ethanol Swelling
The in situ ethanol vapor swelling experiments were performed on freshly made CMS films in a commercially available (J. A. Woollam, Co.) flow cell at 21 ± 0.5 °C using a fully automated vapor generation system on freshly pyrolyzed samples (within 1 day from pyrolysis) by following exactly the same protocol for thick (∼300 nm) and thin (∼30 nm) samples. The desired ethanol vapor concentration was adjusted by two computer-controlled mass flow controllers (Alicat), one for the control of the pure carrier gas (nitrogen) and one for the control of ethanol-saturated stream (at 21 ± 0.5 °C). Both mass flow controllers always operated at a combined flow of 50 cm3 (STP) min–1. The protocol involved stabilization of the sample under pure carrier gas flow for 90 min and a subsequent stepwise exposure to increasing ethanol p/psat up to 0.8. Each step lasted 90 min. In situ ellipsometry data were continuously recorded every 5 s. An example of the in situ data is shown in the Supporting Information, Figure S3.
2.4. Approximate Calculation of Ethanol Concentration within the Pristine PIM–PI and Carbon Films
Ellipsometry-derived changes in thickness and refractive index can be used to approximately calculate the concentration of ethanol sorbed into the thin PIM–PI precursor and carbon films. In this work, the Clausius-Mossotti (34) approach was used where the refractive index of the component i, ni, is related with the molar refraction, Rj, molecular weight, Mi, and density, ρi, by
The ratio Ri/Mi is constant for a given substance and is denoted as qi. In a mixture of two components i and j, the refractive index nmix carries contributions from all components. These contributions are additive and lead to the following expression containing concentrations expressed in units of density (g cm–3):
In swollen films, the concentration of polymer (or carbon) reduces with swelling and can be calculated using the swollen and dry thicknesses as
Polymer and carbon densities were assumed to be the same as in self-standing thick films, as determined by Hazazi et al. (11) and ranged from 1.13 for the pristine PIM–PI to 1.18 g cm–3 for the CMS prepared at 800 °C. In this study, the extremely high glass transition temperature of the precursor and carbon films as well as moderate ethanol-induced swelling assured that the Clausius-Mossotti-derived concentrations remained relatively accurate, (35) in particular for films pyrolyzed above 500 °C.
(1)
(2)
(3)
3. Results and Discussion
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The pyrolysis-induced thickness reduction of the CMS precursor films in both thick (∼300 nm) and thin (∼30 nm) films, is depicted in Figure 3a. The relative refractive index values were derived from the anisotropic model using an average refractive index calculated as n = (2nxy + nz)/3 to reflect the relative changes in the overall film optical density (30) and compare between the thick and thin films. We note here that in spectroscopic ellipsometry modeling thickness and refractive index data are to a large extent independent from each other and thus represent independent pieces of information about the properties of the pyrolyzed films. From Figure 3a it is clear that progressively more volumetric collapse occurred going from the self-supported, ∼70 μm (15) to ∼300 nm and ∼30 nm films. At 700 °C, the ∼30 nm confined films collapsed approximately two times more (∼43%) as compared with the ∼300 nm films (∼22%). This large difference is also reflected by the much larger relative refractive indices for the ∼30 nm films. In addition, ∼30 nm films seem to have reached the maximum extent of volumetric collapse already at 700 °C as opposed to both ∼300 nm and ∼70 μm films. Figure 3a indicates a smooth trend of increasingly collapsed microporosity going from thick to thinner confined films such as those employed as selective layer of composite CMS membranes. A very similar trend has been reported in our recent work for PIM-1 and PTMSP ultrathin films, (36) which may suggest that this behavior could be a general trend for amorphous microporous films. This thickness-dependent pyrolysis-induced densification may proceed in a fashion similar to physical aging which is known to accelerate in thinner films of other amorphous materials (17,23,37,38) and has pronounced consequences for molecular fluid transport. (15,17,19,39,40)
Figure 3
Figure 3. (a) Relative thickness and relative refractive index as a function of the pyrolysis temperature for both thick (∼300 nm) and thin (∼30 nm) polymer precursor films; ∼70 μm data is for a self-supported “bulk” film (15) reprinted with permission from ref (15). Copyright 2019 American Chemical Society. (b) Cross-sectional transmission electron microscopy images showing the microstructure of the thick CMS films; (c) normalized Raman spectra (633 nm excitation wavelength) showing the typical “D” and “G” peaks observed in CMS materials for both ∼300 and ∼30 nm films.
TEM cross-sectional images for the ∼300 nm films pyrolyzed at the highest temperatures (700 and 800 °C), Figure 3b, seem to suggest that a slightly more heterogeneous CMS structure formed at 800 °C which may indicate some differences in the microporosity between the two samples. We note, however, that such an image analysis has an approximate character and it is difficult to draw conclusions about the changes in the total volume fraction of the micropores. Because of the fragility of pyrolyzed ∼30 nm films and reduced image contrast, TEM analysis in this case was very challenging and could only serve to confirm the approximate thickness range which was in agreement with ellipsometry (pristine film of 22 nm developed into 13.5 nm CMS film at 700 °C), Supporting Information, Figure S7.
Normalized Raman spectra for both film thickness ranges recorded for samples pyrolyzed at 700 and 800 °C are shown in Figure 3c. The spectra show “D” (for disordered) and “G” (for graphitic) peaks at ∼1320 and ∼1587 cm–1, respectively. Such peaks are typical for microcrystalline or amorphous carbonaceous materials. Consistent with ellipsometry, Figure 3a, the ∼300 nm films showed a significant change in the D/G ratio going from 700 to 800 °C. In amorphous carbons the development of a stronger “D” peak usually indicates increased ordering whereas the opposite is true for graphene. (41,42) This suggests a more developed ordered structure for the ∼300 nm film at the higher pyrolysis temperature of 800 °C. On the other hand, the “G” peaks for both ∼30 nm films almost exactly overlap suggesting little difference in the CMS structure in the ultrathin films for the two highest pyrolysis temperatures. This finding is again consistent with ellipsometry data from Figure 3a indicating that these two thinner samples possessed nearly identical average refractive indices. The lower “G” peaks for the ∼30 nm CMS films as compared to ∼300 nm films indicate that the thinner samples possessed a more developed (ordered) CMS structure. This is supported by the peak area analysis shown in Table S1 in the Supporting Information. However, some degree of caution needs to be taken while interpreting D/G ratios because the exact trends will depend on many factors which are difficult to determine experimentally such as the crystallite size, stress, dopants, etc. (41) As-recorded Raman spectra for samples pyrolyzed at 600 °C, shown in the Supporting Information, Figure S8, indicate that at 600 °C slightly more progression toward development of the CMS structure is again observed for the ∼30 nm films in comparison to the ∼300 nm films where only very weak “D” and “G” peaks are seen. Therefore, 600 °C clearly represents a transition regime where the precursor material has already lost its functional groups due to thermal decomposition (15) but the turbostratic CMS structure only starts to develop. As demonstrated earlier, (11,15) these transition CMS films possess particularly attractive gas separation properties often much above the gas permeability/selectivity trade-off lines representing state-of-the-art materials.
To learn more about the morphology of the films during the pyrolytic collapse Figure 4 presents results of the uniaxial anisotropic modeling for both thick (a) and thin (b) films. In Figure 4a,b the in-plane (nxy) and out-of-plane (nz) components are presented which correspond to the refractive indices parallel and perpendicular to the silicon wafer substrate. We note here, that because of the confinement to the wafer substrate the lateral x-y dimensions of the films did not change during pyrolysis. Thickness change was thus identical to volume change, as opposed to free-standing CMS films which are known to shrink in all dimensions following pyrolysis. In the case of the thick films, both refractive index components seem to quickly separate above the pyrolysis temperature of 500 °C and the nz component remains significantly lower than the nxy. This is in excellent agreement with our previous study (15) as well as the behavior of much thicker supported films (10–70 μm) (30) and suggests development of a pronounced preferential microscopic orientation of the forming graphene-like plates in the direction parallel to the substrate. This microscopic orientation is specific to supported film geometry and does not develop nearly as much in isotropic thick CMS films. (30) The lower value of the nz component in the thick films indicates that the oriented plates are to some extent separated horizontally by regions of lower density, and thus the thick films have higher interplane microporosity, Figure 4c. On the other hand, ∼30 nm films, Figure 4b, show much less separation between the nxy and nz components whereas the nxy still remains slightly larger than nz. This remarkable development of thickness-dependent anisotropy corroborates a much more compacted structure of the thinner films, Figure 4c, which possess much less microporosity.
Figure 4
Figure 4. Results of the uniaxially anisotropic modeling of the pyrolytic collapse in (a) a thick (∼300 nm) and (b) thin (∼30 nm) films together with (c) a proposed scheme of the morphological transformations. Because of the lateral confinement to the substrate, the whole volume change as a result of pyrolysis is accommodated only by the change in film thickness.
In addition, the presented results suggest that the lateral confinement to the substrate followed by the pyrolysis-induced volume (thickness) shrinkage are the primary drivers behind the structural orientations that develop within the thin CMS films. Similarly to our films produced by spin-coating, anisotropy (or birefringence) within pyrolysis-derived thin, (15) as well as thick supported films, (30) were observed for drop cast and slowly evaporated samples, respectively. Moreover, the lack of significant optical anisotropy in the pristine, nonpyrolyzed films further indicated that the structural orientation developed as a result of pyrolysis and was probably not triggered by the fabrication method of the precursor films.
Further suggestion for the existence of the internal orientation of in the supported CMS films is provided by the 2D Fourier transforms (2D FT) of the TEM images, Figure 5. While for a fully isotropic amorphous CMS structure (Figure 5, left) and in the absence of significant astigmatism the 2D FT pattern is expected to be perfectly circular, our ∼300 nm films show a slightly elongated ellipse (Figure 5, right). To account for the possible astigmatism of the imaging electron optics the 2D FT of the CMS film were evaluated in reference to the supporting Si wafer visible in the same image (identical imaging conditions) which could be assumed isotropic. The ellipticity of the CMS film pattern in the direction perpendicular to the supporting Si wafer was ∼7% greater than for the support (Supporting Information, Figure S9). This effect may suggest the slight preferential orientation within the TEM micrograph in parallel to the substrate which is in excellent agreement with the optical anisotropy detected by ellipsometry, Figure 4. However, we note that a more detailed study with appropriate isotropic control samples and careful correction for the possible imaging artifacts would have to be conducted to conclusively support TEM-based detection of preferential orientation within cross sections of the CMS thin films.
Figure 5
Figure 5. 2D Fourier transforms for an isotropic amorphous CMS structure (left, adapted with permission from ref (43). Copyright 2013 Stefano Casciardi et al. under Creative Commons Attribution License.) and ∼300 nm Si-wafer supported PIM–PI derived CMS films from this study (right); dashed lines indicate perfect circles for reference.
The thickness-dependence in the developing microstructure may have significant consequences on the molecular fluid transport performance of the resulting CMS materials. This is because the larger micropore fractions generally lead to lower transport resistances and thus potentially more permeable membranes for gas separations. Gas sorption experiments (e.g., BET analysis) are a convenient way to elucidate the internal surface areas and porosities of polymeric and carbonaceous materials. However, such analyses remain very challenging in thin films (<several μm) because of the lack of necessary sensitivity. For the thin films in this study, we have used the particular advantage of in situ spectroscopic ellipsometry to independently study both the swelling and refractive index changes in pristine and carbon films as thin as ∼30 nm or less. (25)Figure 6 summarizes the obtained results by depicting the swelling factors (hswollen/hdry) and relative refractive indices (nsw/ndry) for both thick and thin films. The relative refractive indices were calculated from the average values of the nxy and nz, as described earlier, and given at a wavelength of 1000 nm. For clarity of presentation and further discussion, we have included the numerical values at ethanol p/psat = 0.8 on each of the graphs in Figure 6.
Figure 6
Figure 6. Swelling factors (a and b) and relative refractive indices (c and d) for the thick (∼300 nm) and thin (∼30 nm) pristine PIM–PI and carbon films upon exposure to ethanol vapors. Error bars are omitted for the sake of clarity; in each ease the errors are estimated at <5%.
The swelling data for freshly made CMS films using ethanol vapors as a model organic solvent (Figure 6a,b) reveal a very strong influence of the pyrolysis-induced physical and chemical transformations (e.g., loss of functional groups, π–π stacking, etc.) on the swelling behavior of the thin films with the maximum swelling factor rapidly decreasing with increasing pyrolysis temperature. The films pyrolyzed at the highest temperature of 800 °C hardly dilated in ethanol vapor atmosphere at all. The trends are very similar for the thick and thin films; however, the thin films dilated slightly more at each of the corresponding pyrolysis temperatures. This consistent difference between the thick and thin films will manifest itself later for the calculation of the penetrant concentration. The swelling isotherms were almost linear for the pristine PIM–PI precursor which was also observed in our earlier study on PIMs swelling in compressed CO2. (32) In Figure 6c,d, a dashed line represents a relative refractive index of 1 to divide the two different regimes of the film density response to the sorbing penetrant. Whenever the relative refractive index rose above 1, the micropores of the material were filled with the penetrant. On the other hand, if the value reduced below 1, the swelling (molecular scale mixing and resulting volume dilation) dominated as the (optical) density of the film reduced below its initial value. This second effect occurred because the refractive index of liquid ethanol is much lower than the pristine or carbon films (nethanol = 1.36 vs npristine = 1.64) and thus a polymer (or carbon) with sorbed ethanol has a lower refractive index. (35) In this view, the refractive index data (Figure 6c,d) provide corroboration of the results presented in Figure 4. While the differences in the relative refractive index behavior of the thick and thin films of the pristine materials were small, the pyrolyzed films (500–800 °C) showed a significant thickness dependence. In particular, at 500 °C the relative refractive index immediately reduced below 1, whereas for the thick film it increased, going through a maximum and reduced at higher ethanol vapor pressures. This effect indicated that, while both thick and thin films were still largely polymeric at the beginning of the pyrolytic decomposition (degradation temperature onset for bulk film is ∼520 °C), the microporosity in the thinner film was already very significantly reduced. Ethanol was forced to swell the matrix resulting in a progressively decreasing relative refractive index and increased swelling. This effect amplified at 600 °C where the increase of the relative refractive index in the thinner film was only about a third of that for the thicker film and, correspondingly, the maximum swelling was much larger (1.042 versus 1.025). The samples pyrolyzed at 700 °C continued the same trend while at the same time showing a much smaller response of the relative refractive index which is consistent with the reduced microporosity accessible to ethanol as a result of further progressing pyrolytic collapse. The thick film pyrolyzed at 800 °C showed very little swelling (swelling factor = 1.014) but displayed a microporosity filling effect as evidenced by the similar relative refractive index to that of the 700 °C film. In the thinner film pyrolyzed at 800 °C virtually no response was observed either in swelling or in the refractive index. For this sample, apparently the structure compacted so significantly that ethanol was not able either to enter the micropores or sorb within the matrix causing swelling.
The information about film swelling and refractive index can be converted into estimated penetrant concentrations using the well-known Clausius-Mossotti approach which has been previously utilized in similar ellipsometry studies. (32,44,45) The results for all studied samples are shown in Figure 7 and clearly indicate that, in general, pyrolysis leads to a reduction of the penetrant sorption with higher pyrolysis temperatures reducing sorption even further. This behavior further indicates that the pyrolysis-induced collapse dominates over microporosity creation accompanying the chemical transformations. For the pristine PIM–PI precursor, the larger swelling of the thinner film dominated and produced slightly larger estimated ethanol concentrations. We suggest this may be related with an increased effect of the more swellable free surface at the polymer/vapor interface. (20,25) For the samples pyrolyzed in the transitional temperature range of 500 and 600 °C, despite significant differences between the thick and thin films, as shown in Figure 6, the estimated concentrations did not significantly differ. Apparently, the loss of microporosity related with reducing film thickness from 300 to 30 nm was compensated by the significantly larger swelling of the thinner films in each pair which, as a result, produced similar ethanol concentration. At 700 °C the swelling of the thinner film, which was almost two times larger than for the thicker film, seems to dominate and resulted in slightly larger concentrations. At 800 °C, as discussed earlier, some accessible microporosity of the thicker film allowed ethanol to sorb into the structure, which was not the case in the already almost completely impenetrable thinner film pyrolyzed at the same temperature.
Figure 7
Figure 7. Concentration of ethanol estimated via the Clausius-Mossotti calculations for (a) thick (∼300 nm) and (b) thin (∼30 nm) pristine PIM–PI and carbon films (500, 600, 700, and 800 °C). Error bars are omitted for the sake of clarity; in each ease the errors are estimated at <5%.
This work may serve to provide more direct evidence for some of the anomalies in transport behavior of membranes based on thin amorphous selective CMS and PIM–PI films. In particular, slower than expected fluid transport by a simple extrapolation from the bulk properties of thick films (15,39,46) may have its origin in the significantly compacted microporous structure in thinner layers. To avoid those hurdles excessive reduction of the selective layer thickness beyond several hundred nanometers needs to be avoided unless the collapse of the internal microporosity could be avoided by other means.
4. Conclusions
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Pyrolytic collapse and ethanol-induced swelling in a thin polyimide of intrinsic microporosity (PIM–PI) precursor and derived carbon molecular sieve (CMS) films in two thickness ranges, ∼300 nm and ∼30 nm, were investigated using interference-enhanced spectroscopic ellipsometry, transmission electron microscopy and Raman spectroscopy. We discovered that pyrolysis of thin precursor films led to significant orientation of the CMS structure in the direction parallel to the substrate guided by the lateral constraint. A strong thickness dependence of the degree of volumetric collapse was found: ultrathin films collapsed to a much larger extent and became significantly denser than their thicker counterparts. Raman spectroscopy suggested that the ultrathin films in the range of ∼30 nm developed the CMS structure earlier (i.e., at lower pyrolysis temperatures) than the thicker ∼300 nm films. In both thicker and thinner films, the degree of ethanol-induced swelling strongly decreased with increasing pyrolysis temperature. For the thinner ∼30 nm films, in the transition carbon region (500–600 °C), lower extent of pore filling by the sorbing ethanol vapor was found as a result of the reduced microporosity. This effect was offset by a slightly larger swelling leading ultimately to similar calculated ethanol concentration for the thicker and thinner films. At higher pyrolysis temperatures, the differences between the thicker and thinner films amplified and at 800 °C the thinner film became virtually impenetrable to the ethanol vapor, in contrast to the thicker film pyrolyzed at the same temperature.
The results presented in this work are anticipated to improve the understanding of the thickness-dependent structural development in thin-film CMS membranes, as well as their interaction with technologically important separations with feeds involving condensable penetrants such as CO2, organic solvents, or olefins and paraffins. Our results reinforce previous findings that excessive reduction of the selective layer thickness in amorphous microporous materials (such as PIMs or CMS) beyond several hundred nanometers may lead to extremely compact structures which in turn may not be optimal for molecular transport and separation.
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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.1c03392.
Thermogravimetric, volumetric, and density data for bulk powder and ∼70 μm films of the CMS precursor PIM-polyimide SBFDA-DMN (in comparison to another non-PIM polyimide); optical model fitting; kinetic data for an in situ ethanol swelling experiment; relative refractive index plotted as a function of swelling factor of thick and thin films; swelling factor plotted versus ethanol concentration; atomic force microscopy images; optical images; cross-sectional transmission electron microscopy images; and Raman spectra for both thick and thin films (PDF)
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Author Information
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- Ingo Pinnau - Functional Polymer Membranes Group, Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, 23955 Thuwal, Saudi Arabia;
http://orcid.org/0000-0003-3040-9088;
- Wojciech Ogieglo - Functional Polymer Membranes Group, Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, 23955 Thuwal, Saudi Arabia;http://orcid.org/0000-0002-5335-9725
- Cailing Chen - Nanostructured Functional Materials, Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, 23955 Thuwal, Saudi Arabia;http://orcid.org/0000-0003-2598-1354
- Qiong Lei - Nanostructured Functional Materials, Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, 23955 Thuwal, Saudi Arabia;http://orcid.org/0000-0002-7285-9901
- Yu Han - Nanostructured Functional Materials, Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, 23955 Thuwal, Saudi Arabia;http://orcid.org/0000-0003-1462-1118
Acknowledgments
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I.P. acknowledges financial support for this research from KAUST (Baseline funding BAS/1/1323-01-01). W.O. is grateful for the extensive use of the KAUST Solar Center facilities.
References
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This article references 46 other publications.
- 1Atkinson, S. Carbon Molecular Sieve Membranes Aim to Cut Energy Use in Hydrocarbon Separations. Membr. Technol. 2017, 2017 (1), 9– 10, DOI: 10.1016/S0958-2118(17)30017-4Google ScholarThere is no corresponding record for this reference.
- 2Sholl, D. S.; Lively, R. P. Seven Chemical Separations to Change the World. Nature 2016, 532 (7600), 435– 437, DOI: 10.1038/532435aGoogle Scholar2Seven chemical separations to change the worldSholl David S; Lively Ryan PNature (2016), 532 (7600), 435-7 ISSN:.There is no expanded citation for this reference.
- 3Zhang, C.; Koros, W. J. Ultraselective Carbon Molecular Sieve Membranes with Tailored Synergistic Sorption Selective Properties. Adv. Mater. 2017, 29 (33), 1– 6Google ScholarThere is no corresponding record for this reference.
- 4Sanyal, O.; Zhang, C.; Wenz, G. B.; Fu, S.; Bhuwania, N.; Xu, L.; Rungta, M.; Koros, W. J. Next Generation Membranes —Using Tailored Carbon. Carbon 2018, 127, 688– 698, DOI: 10.1016/j.carbon.2017.11.031Google Scholar4Next generation membranes-using tailored carbonSanyal, Oishi; Zhang, Chen; Wenz, Graham B.; Fu, Shilu; Bhuwania, Nitesh; Xu, Liren; Rungta, Meha; Koros, William J.Carbon (2018), 127 (), 688-698CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)A review. Carbon mol. sieve (CMS) membranes are a special class of nanoporous membranes with angstrom-level mol. discrimination properties, which make them appealing for sepg. a wide spectrum of gas-pairs. The mechanism of pyrolysis by which a polymer coil is transformed into these rigid sieves is complex; however, we present a framework that can explain this transformation. Representative polymer precursors and pyrolysis conditions are discussed that yield attractive CMS membrane sepn. performance for extremely challenging gas pairs. Control of penetrant motions in the diffusion activated state, reflected in the entropy of activation of subtly different penetrants, enables the attractive diffusion selectivity of such membranes. This control, virtually absent even in rigid state-of-the-art polymeric membranes, makes CMS materials extraordinarily attractive. Moreover, unlike other rigid sieving materials, CMS membranes have the added advantage of being processable into highly productive, flexible hollow fibers with good mech. properties and long-term stability under const. gas feeds. We also identify some key areas of CMS which would greatly benefit from expertise from other fields like computation or materials characterization that can potentially complement transport-based studies.
- 5Galizia, M.; Chi, W. S.; Smith, Z. P.; Merkel, T. C.; Baker, R. W.; Freeman, B. D. 50th Anniversary Perspective: Polymers and Mixed Matrix Membranes for Gas and Vapor Separation: A Review and Prospective Opportunities. Macromolecules 2017, 50 (20), 7809– 7843, DOI: 10.1021/acs.macromol.7b01718Google Scholar550Th Anniversary Perspective: Polymers and Mixed Matrix Membranes for Gas and Vapor Separation: A Review and Prospective OpportunitiesGalizia, Michele; Chi, Won Seok; Smith, Zachary P.; Merkel, Timothy C.; Baker, Richard W.; Freeman, Benny D.Macromolecules (Washington, DC, United States) (2017), 50 (20), 7809-7843CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)A review. Membrane gas sepn. is a mature and expanding technol. However, the availability of better membrane materials would promote faster growth. In this Perspective we analyze the state of the art of membrane materials, including polymers and hybrid materials, as well as the current issues and barriers, and finally, we outline future research directions in membrane science. Development of new membrane materials for large scale sepns. will rely on a multidisciplinary approach that embraces the broad fields of chem. and materials engineering, polymer science, and materials chem.
- 6Koh, D. Y.; McCool, B. A.; Deckman, H. W.; Lively, R. P. Reverse Osmosis Molecular Differentiation of Organic Liquids Using Carbon Molecular Sieve Membranes. Science 2016, 353 (6301), 804– 807, DOI: 10.1126/science.aaf1343Google Scholar6Reverse osmosis molecular differentiation of organic liquids using carbon molecular sieve membranesKoh, Dong-Yeun; McCool, Benjamin A.; Deckman, Harry W.; Lively, Ryan P.Science (Washington, DC, United States) (2016), 353 (6301), 804-807CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Liq.-phase sepns. of similarly sized org. mols. using membranes is a major challenge for energy-intensive industrial sepn. processes. We created free-standing carbon mol. sieve membranes that translate the advantages of reverse osmosis for aq. sepns. to the sepn. of org. liqs. Polymer precursors were cross-linked with a one-pot technique that protected the porous morphol. of the membranes from thermally induced structural rearrangement during carbonization. Permeation studies using benzene derivs. whose kinetic diams. differ by less than an angstrom show kinetically selective org. liq. reverse osmosis. Ratios of single-component fluxes for para- and ortho-xylene exceeding 25 were obsd. and para- and ortho- liq. mixts. were efficiently sepd., with an equimolar feed enriched to 81 mol % para-xylene, without phase change and at ambient temp.
- 7Salinas, O.; Ma, X.; Litwiller, E.; Pinnau, I. High-Performance Carbon Molecular Sieve Membranes for Ethylene/Ethane Separation Derived from an Intrinsically Microporous Polyimide. J. Membr. Sci. 2016, 500, 115– 123, DOI: 10.1016/j.memsci.2015.11.013Google Scholar7High-performance carbon molecular sieve membranes for ethylene/ethane separation derived from an intrinsically microporous polyimideSalinas, Octavio; Ma, Xiaohua; Litwiller, Eric; Pinnau, IngoJournal of Membrane Science (2016), 500 (), 115-123CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)An intrinsically microporous polymer with hydroxyl functionalities, PIM-6FDA-OH, was used as a precursor for various types of carbon mol. sieve (CMS) membranes for ethylene/ethane sepn. The pristine polyimide films were heated under controlled N2 atmosphere at different stages from 500 to 800 °C. All CMS samples carbonized above 600 °C surpassed the polymeric ethylene/ethane upper bound. Pure-gas selectivity reached 17.5 for the CMS carbonized at 800 °C with an ethylene permeability of about 10 Barrer at 2 bar and 35 °C, becoming the most selective CMS for ethylene/ethane sepn. reported to date. As expected, gravimetric sorption expts. showed that all CMS membranes had ethylene/ethane soly. selectivities close to one. The permselectivity increased with increasing pyrolysis temp. due to densification of the micropores in the CMS membranes, leading to enhanced diffusivity selectivity. Mixed-gas tests with a binary 50:50 vol./vol. ethylene/ethane feed showed a decrease in selectivity from 14 to 8.3 as the total feed pressure was increased from 4 to 20 bar. The selectivity drop under mixed-gas conditions was attributed to non-ideal effects: (i) competitive sorption that reduced the permeability of ethylene and (ii) dilation of the CMS that resulted in an increase in the ethane permeability.
- 8Salinas, O.; Ma, X.; Litwiller, E.; Pinnau, I. Ethylene/Ethane Permeation, Diffusion and Gas Sorption Properties of Carbon Molecular Sieve Membranes Derived from the Prototype Ladder Polymer of Intrinsic Microporosity (PIM-1). J. Membr. Sci. 2016, 504, 133– 140, DOI: 10.1016/j.memsci.2015.12.052Google Scholar8Ethylene/ethane permeation, diffusion and gas sorption properties of carbon molecular sieve membranes derived from the prototype ladder polymer of intrinsic microporosity (PIM-1)Salinas, Octavio; Ma, Xiaohua; Litwiller, Eric; Pinnau, IngoJournal of Membrane Science (2016), 504 (), 133-140CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)Fine-tuning the microporosity of PIM-1 by heat treatment was applied to develop a suitable carbon mol. sieve membrane for ethylene/ethane sepn. Pristine PIM-1 films were heated from 400 to 800 °C under inert N2 atmosphere (<2 ppm O2). At 400 °C, PIM-1 self-crosslinked and developed polar carbonyl and hydroxyl groups due to partial dioxane splitting in the polymer backbone. Significant degrdn. occurred at 600 °C due to carbonization of PIM-1 and resulted in 30% increase in cumulative surface area compared to its crosslinked predecessor. In addn., PIM-1-based CMS developed smaller ultramicropores with increasing pyrolysis temp., which enhanced their mol. sieving capability by restricted diffusion of ethylene and ethane through the matrix due to microstructural carbon densification. Consequently, the pure-gas ethylene permeability (measured at 35 °C and 2 bar) decreased from 1600 Barrer for the pristine PIM-1 to 1.3 Barrer for the amorphous carbon generated at 800°, whereas the ethylene/ethane pure-gas selectivity increased significantly from 1.8 to 13.
- 9Salinas, O.; Ma, X.; Wang, Y.; Han, Y.; Pinnau, I. Carbon Molecular Sieve Membrane from a Microporous Spirobisindane-Based Polyimide Precursor with Enhanced Ethylene/Ethane Mixed-Gas Selectivity. RSC Adv. 2017, 7 (6), 3265– 3272, DOI: 10.1039/C6RA24699KGoogle Scholar9Carbon molecular sieve membrane from a microporous spirobisindane-based polyimide precursor with enhanced ethylene/ethane mixed-gas selectivitySalinas, Octavio; Ma, Xiaohua; Wang, Yingge; Han, Yu; Pinnau, IngoRSC Advances (2017), 7 (6), 3265-3272CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)Ethylene is typically produced by steam cracking of various hydrocarbon feedstocks. The gaseous products are then sepd. in a demethanizer followed by a deethanizer unit and finally sent to a C2 splitter for the final purifn. step. Cryogenic distn. of ethylene from ethane is the most energy-intensive unit operation process in the chem. industry. Therefore, the development of more energy-efficient processes for ethylene purifn. is highly desirable. Membrane-based sepn. has been proposed as an alternative option for replacement or debottlenecking of C2 splitters but current polymer membrane materials exhibit insufficient mixed-gas C2H4/C2H6 selectivity (<7) to be tech. and economically attractive. In this work, a highly selective carbon mol. sieve (CMS) membrane derived from a novel spirobisindane-based polyimide of intrinsic microporosity (PIM-6FDA) was developed and characterized. PIM-6FDA showed a single-stage degrdn. process under an inert nitrogen atm. which commenced at ~ 480°C. The CMS formed by pyrolysis at 800°C had a diffusion/size-sieving-controlled morphol. with a mixed-gas (50% C2H4/50% C2H6) ethylene/ethane selectivity of 15.6 at 20 bar feed pressure at 35°C. The mixed-gas ethylene/ethane selectivity is the highest reported value for CMS-type membranes to date.
- 10Wang, Y.; Ma, X.; Ghanem, B. S.; Alghunaimi, F.; Pinnau, I.; Han, Y. Polymers of Intrinsic Microporosity for Energy-Intensive Membrane-Based Gas Separations. Mater. Today Nano 2018, 3, 69– 95, DOI: 10.1016/j.mtnano.2018.11.003Google ScholarThere is no corresponding record for this reference.
- 11Hazazi, K.; Ma, X.; Wang, Y.; Ogieglo, W.; Alhazmi, A.; Han, Y.; Pinnau, I. Ultra-Selective Carbon Molecular Sieve Membranes for Natural Gas Separations Based on a Carbon-Rich Intrinsically Microporous Polyimide Precursor. J. Membr. Sci. 2019, 585, 1– 9, DOI: 10.1016/j.memsci.2019.05.020Google Scholar11Ultra-selective carbon molecular sieve membranes for natural gas separations based on a carbon-rich intrinsically microporous polyimide precursorHazazi, Khalid; Ma, Xiaohua; Wang, Yingge; Ogieglo, Wojciech; Alhazmi, Abdulrahman; Han, Yu; Pinnau, IngoJournal of Membrane Science (2019), 585 (), 1-9CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)A highly contorted, carbon-rich intrinsically microporous polyimide (PIM-PI) made from spirobifluorene dianhydride and 3,3-dimethylnaphthidine (SBFDA-DMN) was employed as a precursor for the formation of carbon mol. sieve (CMS) membranes at pyrolysis temps. from 550 to 1000 °C. The high carbon content of SBFDA-DMN (∼84%) resulted in only 28% total wt. loss during pyrolysis under a nitrogen atm. at 1000 °C. The development of the various microstructural textures was characterized by gas sorption anal., Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction, Raman spectroscopy, elec. cond., and gas transport properties. Heat treatment of a pristine SBFDA-DMN membrane at 550 °C resulted in reduced permeability for all gases (e.g.: PCO2 dropped from 4700 to 1500 barrer) as well as lower BET surface area from 621 to 545 m2 g-1. At 600 °C, new pores induced by pyrolysis increased the BET surface area to nearly that of the precursor and significantly improved gas sepn. performance. Above 600 °C, a progressive collapse of the micropores became evident with CMS membranes showing higher gas-pair selectivity but lower permeability. At 1000 °C, ultra-micropores comparable in size with the kinetic diam. of CH4 emerged and induced a prominent mol. sieving effect resulting in very high CH4 rejection. This strong size exclusion effect, further supported by gravimetric gas sorption measurements, resulted in unusually high N2/CH4 and CO2/CH4 selectivities of 35 and 1475, resp.
- 12Parsley, D.; Ciora, R. J.; Flowers, D. L.; Laukaitaus, J.; Chen, A.; Liu, P. K. T.; Yu, J.; Sahimi, M.; Bonsu, A.; Tsotsis, T. T. Field Evaluation of Carbon Molecular Sieve Membranes for the Separation and Purification of Hydrogen from Coal- and Biomass-Derived Syngas. J. Membr. Sci. 2014, 450, 81– 92, DOI: 10.1016/j.memsci.2013.08.008Google Scholar12Field evaluation of carbon molecular sieve membranes for the separation and purification of hydrogen from coal- and biomass-derived syngasParsley, Doug; Ciora, Richard J. Jr.; Flowers, Diane L.; Laukaitaus, John; Chen, Amy; Liu, Paul K. T.; Yu, Jiang; Sahimi, Muhammad; Bonsu, Alex; Tsotsis, Theodore T.Journal of Membrane Science (2014), 450 (), 81-92CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)High-temp. gas sepns. (GS) with inorg. membranes have attracted attention recently. In particular, the use of such membranes in membrane reactors (MR) has the potential to enhance process intensification and to increase energy savings and/or product yield. Though the potential benefits of high-temp. GS and/or MR processes are substantial, commercialization still remains elusive. A major tech. barrier is the lack of robust inorg. membranes and full-scale modules which are suitable for use at the high-temp. and high-pressure conditions required. C mol. sieve membranes (CMSM) were recently tested in the lab. by this team for the 1-box process. This technol. combines into a single MR unit contaminant removal and coal-derived and/or biomass-derived syngas conversion via the water gas shift reaction to produce high-purity H for power generation and/or chem. use. Towards technol. commercialization, 86-tube CMSM modules have been constructed and characterized comprehensively. Also, multiple field-tests, under non-reactive conditions, of these 86-tube CMSM modules were conducted at the US National C Capture Center coal gasification facility under conditions suitable for the 1-box process. This paper details the results of these tests which address key GS aspects of field implementation, including inorg. membrane/module scale-up, syngas contaminants removal, and membrane material and performance stability. During continuous use (more than 300 h) in raw coal-derived and/or biomass-derived syngas, the CMSM successfully rejected tar-like species present in the syngas without any evidence of fouling, as long as the operating temp. was maintained >250°. Also, the membrane permeation properties remained unchanged throughout this extended test. Simulations, based upon membrane GS properties measured during these field tests, demonstrate that the 1-box process, operating on a typical O-blown gasifier off-gas, can deliver >90% H recovery at >90% purity (dry-basis), and thus shows good promise for com. application. The successful prepn. and deployment by this team of the 86-tube CMSM module overcomes some of the tech. barriers which have, so far, hampered the com. implementation of inorg. membranes for high-temp. and high-pressure gas sepn. applications.
- 13Haider, S.; Lindbråthen, A.; Lie, J. A.; Hägg, M. B. Regenerated Cellulose Based Carbon Membranes for CO2 Separation: Durability and Aging under Miscellaneous Environments. J. Ind. Eng. Chem. 2019, 70, 363– 371, DOI: 10.1016/j.jiec.2018.10.037Google Scholar13Regenerated cellulose based carbon membranes for CO2 separation: Durability and aging under miscellaneous environmentsHaider, Shamim; Lindbraathen, Arne; Lie, Jon A.; Hagg, May-BrittJournal of Industrial and Engineering Chemistry (Amsterdam, Netherlands) (2019), 70 (), 363-371CODEN: JIECFI; ISSN:1226-086X. (Elsevier B.V.)Predictive models regarding the aging effect on membrane sepn. properties are required to est. the membrane life time with acceptable permeability and selectivity for the resp. application. The current article is reporting an insight into this topic regarding the aging of regenerated cellulose-based carbon hollow fibers (CHF) mounted in a membrane module when they were exposed to real biogas in three different fields. CHF were exposed to biogas for almost one year with H2S content extending from 0 to 2400 ppm, and gas permeation tests for single gases, N2, CO2, CH4, and O2 were analyzed periodically at the membrane prodn. facility. CHF storage methods under misc. dry environments like air, vacuum, CO2, etc. were studied. The air flow through bore side of the CHF under controlled conditions had a regenerative effect on the membrane permeability, and the membrane performance was quite steady until after 150 days under lab. environment.
- 14Xu, L.; Rungta, M.; Hessler, J.; Qiu, W.; Brayden, M.; Martinez, M.; Barbay, G.; Koros, W. J. Physical Aging in Carbon Molecular Sieve Membranes. Carbon 2014, 80 (1), 155– 166, DOI: 10.1016/j.carbon.2014.08.051Google Scholar14Physical aging in carbon molecular sieve membranesXu, Liren; Rungta, Meha; Hessler, John; Qiu, Wulin; Brayden, Mark; Martinez, Marcos; Barbay, Gregory; Koros, William J.Carbon (2014), 80 (), 155-166CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)This paper considers phys. aging in carbon mol. sieve (CMS) membranes. Moreover, the performance of stabilized membranes under practical operating conditions is discussed. Phys. aging has been studied extensively in glassy polymers, but aging in CMS membranes has previously focused primarily on adsorption: either chemisorption of oxygen, or phys. adsorption of water and orgs. in the pore structures. Exptl., in this study, for the samples considered, all of the above adsorption-induced aging mechanisms were excluded as significant factors through thoughtful exptl. design. Phys. aging appears to be the primary cause for rapid changes of transport properties in early stages after membrane fabrication for samples derived from high fractional free vol. precursors. The CMS pores are believed to age analogously to the "unrelaxed free vol." in glassy polymers. Over time, these pores tend to shrink to achieve thermodynamically more stable states. Results of sorption tests in CMS also support the above hypothesis. The significance of phys. aging phenomena on membrane testing protocols, structural tailoring, and performance evaluation are discussed. A long-term permeation test demonstrated excellent stability of stabilized CMS membranes under realistic conditions.
- 15Ogieglo, W.; Furchner, A.; Ma, X.; Hazazi, K.; Alhazmi, A. T.; Pinnau, I. Thin Composite Carbon Molecular Sieve Membranes from a Polymer of Intrinsic Microporosity Precursor. ACS Appl. Mater. Interfaces 2019, 11 (20), 18770– 18781, DOI: 10.1021/acsami.9b04602Google Scholar15Thin Composite Carbon Molecular Sieve Membranes from a Polymer of Intrinsic Microporosity PrecursorOgieglo, Wojciech; Furchner, Andreas; Ma, Xiaohua; Hazazi, Khalid; Alhazmi, Abdulrahman T.; Pinnau, IngoACS Applied Materials & Interfaces (2019), 11 (20), 18770-18781CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Ultra-thin composite carbon mol. sieve (CMS) membranes were fabricated on well-defined inorg. alumina substrates using a polymer of intrinsic microporosity (PIM) as a precursor. Details of the pyrolysis-related structural development were elucidated using focused-beam, interference-enhanced spectroscopic ellipsometry (both in the UV-vis and IR range), which allowed accurate detn. of the film thickness, optical properties as well as following the chem. transformations. The pyrolysis-induced collapse of thin and bulk PIM-derived CMS membranes was compared with CMS made from a well-known non-PIM precursor 6FDA-DABA. Significant differences between the PIM and non-PIM precursors were discovered and explained by a much larger possible vol. contraction in the PIM. In spite of the differences, surprisingly, the gas sepn. properties did not fundamentally differ. The high-temp. collapse of the initially amorphous and isotropic precursor structure was accompanied by a significant mol. orientation within the formed turbostratic carbon network guided by the laterally constraining presence of the substrate. This manifested itself in the development of uniaxial optical anisotropy, which was shown to correlate with increases in gas sepn. selectivity for multiple technol. important gas pairs. Redn. of CMS skin thickness significantly below ∼1 μm induced large losses in permeability coeffs. with only small to moderate effects on selectivity. Remarkably, skin thickness redn. and phys. aging seemed to superimpose onto the same trend, which explains and strengthens some of the earlier fundamental insights.
- 16Huang, Y.; Paul, D. R. Experimental Methods for Tracking Physical Aging of Thin Glassy Polymer Films by Gas Permeation. J. Membr. Sci. 2004, 244 (1–2), 167– 178, DOI: 10.1016/j.memsci.2004.06.058Google Scholar16Experimental methods for tracking physical aging of thin glassy polymer films by gas permeationHuang, Y.; Paul, D. R.Journal of Membrane Science (2004), 244 (1-2), 167-178CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)This paper describes methodologies that have been developed for studying the phys. aging of free-standing thin polymer films and its effect on gas permeability. Both soln. casting and spin coating methods were used to obtain thin polysulfone films having thicknesses in the range of 400-1000 nm. Ellipsometry has been employed to det. the thicknesses of these thin films. A thin wire frame was used to hold the thin free-standing films while heating above Tg to relax mol. orientation and to erase the ambiguous thermal history resulting from soln. casting. The film underwent a significant thickness change during heating above Tg as the polymer chains relaxed. By using the method of this study, the reproducibility of gas permeability change during phys. aging was demonstrated as well as the thermoreversibility of phys. aging. Comparison of the results obtained by using different methods to support the thin film during heating illustrated the preference for the free-standing scheme developed in this study.
- 17Huang, Y.; Paul, D. R. Physical Aging of Thin Glassy Polymer Films Monitored by Gas Permeability. Polymer 2004, 45 (25), 8377– 8393, DOI: 10.1016/j.polymer.2004.10.019Google Scholar17Physical aging of thin glassy polymer films monitored by gas permeabilityHuang, Y.; Paul, D. R.Polymer (2004), 45 (25), 8377-8393CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)The phys. aging at 35°C of three glassy polymers, polysulfone, a polyimide and poly(2,6-dimethyl-1,4-phenylene oxide), has been tracked by measurement of the permeation of three gases, O2, N2, and CH4, for over 200 days. Several techniques were used to accurately det. the thickness of films (∼400 nm-62 μm) in order to obtain abs. permeability coeffs. and to study the effects of film thickness on the rate of phys. aging. Each film was heated above the polymer Tg to set the aging clock to time zero; ellipsometry revealed that this procedure leads to isotropic films having initial characteristics independent of film thickness. A substantial pronounced aging response, attributed to a decrease in polymer free vol., was obsd. at temps. more than 150 °C below Tg for thin films of each polymer compared to what is obsd. for the bulk polymers. The films with thicknesses of approx. 400 nm of the three polymers exhibit an oxygen permeability decrease by as much as two-fold or more and about 14-15% increase in O2/N2 selectivity at an aging time of 1000 h. The results obtained in this study were compared with prior work on thickness dependent aging. The effects of crystallinity on phys. aging were examd. briefly.
- 18Xia, J.; Chung, T. S.; Li, P.; Horn, N. R.; Paul, D. R. Aging and Carbon Dioxide Plasticization of Thin Polyetherimide Films. Polymer 2012, 53 (10), 2099– 2108, DOI: 10.1016/j.polymer.2012.03.009Google Scholar18Aging and carbon dioxide plasticization of thin polyetherimide filmsXia, Jianzhong; Chung, Tai-Shung; Li, Pei; Horn, Norman R.; Paul, D. R.Polymer (2012), 53 (10), 2099-2108CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)Industrial gas sepn. membranes have selective dense layers with thicknesses around 100 nm. It has long been assumed that these thin layers have the same properties as thick (bulk) films. However, recent research has shown that thin films with such thickness experience accelerated phys. aging relative to bulk films and, thus, their permeation properties can differ significantly from the bulk. Thin films made from Extem XH 1015, a new com. polyetherimide, have been investigated by monitoring their gas permeability. The permeability of the thin films is originally greater than the thick films but eventually decreases well below the permeability of the thick film. The CO2 plasticization of Extem thin films is explored using a series of exposure protocols that indicate CO2 plasticization is a function of film thickness, aging time, exposure time, pressure and prior history.
- 19Horn, N. R.; Paul, D. R. Carbon Dioxide Sorption and Plasticization of Thin Glassy Polymer Films Tracked by Optical Methods. Macromolecules 2012, 45 (6), 2820– 2834, DOI: 10.1021/ma300177kGoogle Scholar19Carbon Dioxide Sorption and Plasticization of Thin Glassy Polymer Films Tracked by Optical MethodsHorn, Norman R.; Paul, D. R.Macromolecules (Washington, DC, United States) (2012), 45 (6), 2820-2834CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)Our previous publications have demonstrated that thin glassy polymer films respond to highly sorbing penetrants, such as CO2, quite differently than thick films. These studies focused on CO2 permeation behavior and revealed that, for thin films, CO2 permeability at const. CO2 pressure goes through a max. followed by a continual decrease in permeability owing to phys. aging. So far, thick and thin glassy polymer films have been compared in the context of permeability, but lack of substantial means of obtaining thin film sorption data has prevented adequate comparison of thick and thin films in the context of gas soly. In this paper, spectroscopic ellipsometry is used to obtain simultaneously the film thickness and CO2 sorption capacity for thin glassy polymer films. This allows a more comprehensive look at CO2 permeability, sorption, and diffusivity as a function of both CO2 pressure and exposure time. The evidence reported here suggests that thin film sorption behavior is substantially different than that of thick film counterparts. Partial molar volume is detd. from sorption-induced swelling data. Fractional free vol. and diffusivity are calcd. as a function of CO2 pressure. Dual sorption model parameters are presented for Matrimid thin films for different aging times. Dynamic ellipsometry expts. show that refractive index min., fractional free vol. maxima, and CO2 diffusivity maxima correlate well with obsd. CO2 permeability maxima obsd. for thin Matrimid films. The results support the claim that plasticization and phys. aging are competing processes but that aging dominates over long time scales. The CO2 diffusivity behavior over time is most affected by the competing effects of plasticization and aging, and the evolution of CO2 diffusivity is shown to be the main contributing factor to changes in CO2 permeability at const. pressure.
- 20Ogieglo, W.; Tempelman, K.; Napolitano, S.; Benes, N. E. Evidence of a Transition Layer between the Free Surface and the Bulk. J. Phys. Chem. Lett. 2018, 9 (6), 1195– 1199, DOI: 10.1021/acs.jpclett.8b00076Google Scholar20Evidence of transition layer between free surface and bulkOgieglo, Wojciech; Tempelman, Kristianne; Napolitano, Simone; Benes, Nieck E.Journal of Physical Chemistry Letters (2018), 9 (6), 1195-1199CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The free surface, a very thin layer at the interface between polymer and air, is considered the main source of the perturbations in the properties of ultrathin polymer films, i.e., nanoconfinement effects. The structural relaxation of such a layer is decoupled from the mol. dynamics of the bulk. The free surface is, in fact, able to stay liq. even below the temp. where the polymer resides in the glassy state. Importantly, this surface layer is expected to have a very sharp interface with the underlying bulk. Here, by analyzing the penetration of n-hexane into polystyrene films, we report on the existence of a transition region, not obsd. by previous investigations, extending for 12 nm below the free surface. The presence of such a layer permits reconciling the behavior of interfacial layers with current models and has profound implications on the performance of ultrathin membranes. We show that the expected increase in the flux of the permeating species is actually overruled by nanoconfinement.
- 21Ogieglo, W.; Wessling, M.; Benes, N. E. Polymer Relaxations in Thin Films in the Vicinity of a Penetrant- or Temperature-Induced Glass Transition. Macromolecules 2014, 47 (11), 3654– 3660, DOI: 10.1021/ma5002707Google Scholar21Polymer Relaxations in Thin Films in the Vicinity of a Penetrant- or Temperature-Induced Glass TransitionOgieglo, Wojciech; Wessling, Matthias; Benes, Nieck E.Macromolecules (Washington, DC, United States) (2014), 47 (11), 3654-3660CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)The transient properties of thin glassy polymer films in the vicinity of the glass transition are investigated. We compare the differences and similarities between sorption and temp.-induced glass transitions, referred to as Pg and Tg, resp. The exptl. technique used is in situ spectroscopic ellipsometry, which allows for a very precise dynamic measurement of the changes in the thickness and the refractive index of the thin films. It is shown that significant differences exist between the penetrant- and temp.-induced transitions. The Tg is relatively well-defined with a sharp change in polymer dynamics, causing a well-known curvature change, a kink, in the dilation curve. In contrast, the relaxations in the vicinity of Pg do not show a sharp change. In particular, the large degree of matrix deformation assocd. with the Pg may actuate addnl. relaxation processes that are not probed during transversing the glass transition via temp. scans. The interplay between various polymer relaxation modes can even lead to a slope change, a kink, in the dilation curve that cannot be interpreted as true glass transition. In fact, significant polymer relaxations are manifested upon slight desorption of penetrants from an excessively swollen system, which can be considered a quasi-equil. liq. The important practical implications of the findings are discussed.
- 22Lock, S. S. M.; Lau, K. K.; Shariff, A. M.; Yeong, Y. F.; Ahmad, F. Mathematical Modelling of Thickness and Temperature Dependent Physical Aging to O2/N2 Gas Separation in Polymeric Membranes. RSC Adv. 2018, 8 (53), 30265– 30279, DOI: 10.1039/C8RA05323EGoogle Scholar22Mathematical modelling of thickness and temperature dependent physical aging to O2/N2 gas separation in polymeric membranesLock, S. S. M.; Lau, K. K.; Shariff, A. M.; Yeong, Y. F.; Ahmad, FaizanRSC Advances (2018), 8 (53), 30265-30279CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)Polymeric membranes are glassy materials at non-equil. state and inherently undergo a spontaneous evolution towards equil. known as phys. aging. Vol. relaxation characteristic during the course of aging is governed by the surrounding temp. in which the polymeric material is aged. Although there are studies to understand how polymeric materials evolve over time towards equil. at different operating temps., the theories have been developed merely in response to exptl. observations and phenomenol. theory at bulk glassy state without the implementation of sample size effects. Limited work has been done to characterize the phys. aging process to thin polymeric films using reasonable phys. parameters and math. models with incorporation of thermodn. and film thickness consideration. The current work applies the Tait equation of states and thickness dependent glass transition temp., integrated within a simple linear correlation, to model the temp. and thickness dependent phys. aging. The math. model has been validated with exptl. aging data, whereby a small deviation is obsd. that has been explained by intuitive reasoning pertaining to the thermodn. parameters. The math. model has been further employed to study the gas transport properties of O2 and N2, which is anticipated to be applied in oxygen enriched combustion for generation of cleaner and higher efficiency fuel in future work.
- 23Tiwari, R. R.; Jin, J.; Freeman, B. D.; Paul, D. R. Physical Aging, CO2 Sorption and Plasticization in Thin Films of Polymer with Intrinsic Microporosity (PIM-1). J. Membr. Sci. 2017, 537 (1), 362– 371, DOI: 10.1016/j.memsci.2017.04.069Google Scholar23Physical aging, CO2 sorption and plasticization in thin films of polymer with intrinsic microporosity (PIM-1)Tiwari, Rajkiran R.; Jin, Jianyong; Freeman, B. D.; Paul, D. R.Journal of Membrane Science (2017), 537 (), 362-371CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)Phys. aging of both thick and thin films of "high free-vol." glassy polymer, PIM-1 (polymer with intrinsic microporosity) was studied by monitoring changes in pure gas permeability of O2, N2 and CH4 at a fixed temp. of 35 °C. Permeability of PIM-1 is very sensitive to film thickness, post-treatment (methanol soak, water soak or dried) and casting solvent (chloroform and ortho-dichlorobenzene). Thin films of PIM-1 undergo accelerated aging, leading to initial permeability lower by an order of magnitude compared to thick films. The relative permeability for thin films of PIM-1 was decreased by 67% compared to 53% decrease for thick films at 1000 h of aging due to the higher aging rates in thin films. The effect of casting solvent (vapor pressure and b.p.) is more pronounced on aging and selectivity of thin films with initial permeability almost two times higher for the film casted from chloroform (CHCl3) compared to that prepd. from ortho-dichlorobenzene (o-DCB) solvent. The effect of casting solvent on the initial permeability is less prominent for thick films. The film thickness, casting solvent and CO2 exposure protocols also have significant effect on the abs. CO2 permeability and plasticization behavior of both thick and thin films. The thin films undergo significant increase in the relative permeability upon plasticization compared to thick films and permeability was found to increase even during CO2 depressurization. The long time, const. pressure CO2 exposure study revealed dominant aging effect in thin film where aging overcomes the CO2 plasticization effect just within 1.2 min of the CO2 exposure compared to 10 h for thick film. The ellipsometry measurements showed that the CO2 soly. in thin films decreases with increases in the aging time and temp., and with decrease in the mol. wt. A strong correlation was obsd. for the Langmuir sorption capacity, CH' and soly. at infinite diln., S0 with the aging time, temp. and mol. wt. of PIM-1.
- 24Kappert, E. J.; Raaijmakers, M. J. T.; Tempelman, K.; Cuperus, F. P.; Ogieglo, W.; Benes, N. E. Swelling of 9 Polymers Commonly Employed for Solvent-Resistant Nanofiltration Membranes: A Comprehensive Dataset. J. Membr. Sci. 2019, 569, 177– 199, DOI: 10.1016/j.memsci.2018.09.059Google Scholar24Swelling of 9 polymers commonly employed for solvent-resistant nanofiltration membranes: A comprehensive datasetKappert, Emiel J.; Raaijmakers, Michiel J. T.; Tempelman, Kristianne; Cuperus, F. Petrus; Ogieglo, Wojciech; Benes, Nieck E.Journal of Membrane Science (2019), 569 (), 177-199CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)The presence of a solvent in a dense polymeric nanofiltration membrane layer can affect the macromol. dynamics of the polymer material and the mobility of the solvent penetrant mols. In addn., even the affinity of the swollen material for the solvent mols. can be distinct from that of the pure polymer material. These effects can substantially affect the membrane's performance. This paper provides sorption and swelling data of 9 thin polymer films that are commonly used for org. solvent nanofiltration (P84, Matrimid, PEI, PAN, PES, PSf, PEBAX, PTMSP, PDMS) swollen by 10 common solvents (hexane, toluene, dichloromethane, Et acetate, Me Et ketone, acetone, isopropanol, ethanol, methanol, water). The paper describes the swelling dynamics during short-term solvent exposure (0-8 h), assesses the stability upon long-term solvent exposure (up to 2 mo), and provides quant. data on the solvent vol. fractions inside the swollen layers. Among the surprising findings are the glubbery behavior of PTMSP and the completely different response of PES and PSf to toluene exposure. The results of this work demonstrate three crucial findings relevant to org. solvent nanofiltration membranes and other applications:For many polymers, the swelling changes over long timescales of up to 2 mo and longer. Results obtained on short timescales do however not always allow for direct extrapolation to longer time scales. Structural similarity of polymers does not guarantee similar swelling behavior. Swelling behavior of solvents cannot be solely explained by classifying solvents into aprotic, polar aprotic and polar protic solvents. The results of this work can aid in constructing transport models and can help predicting polymer-solvent compatibility and membrane performance in OSN applications.
- 25Ogieglo, W.; Rahimi, K.; Rauer, S. B.; Ghanem, B.; Ma, X.; Pinnau, I.; Wessling, M. How Do Organic Vapors Swell Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1?. J. Phys. Chem. B 2017, 121 (29), 7210– 7220, DOI: 10.1021/acs.jpcb.7b03891Google Scholar25How Do Organic Vapors Swell Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1?Ogieglo, Wojciech; Rahimi, Khosorov; Rauer, Sebastian Bernhard; Ghanem, Bader; Ma, Xiaohua; Pinnau, Ingo; Wessling, MatthiasJournal of Physical Chemistry B (2017), 121 (29), 7210-7220CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)Dynamic sorption of ethanol and toluene vapor into ultra-thin supported PIM-1 films down to 6 nm are studied with a combination of in-situ spectroscopic ellipsometry and in-situ X-ray reflectivity. Both ethanol and toluene significantly swell the PIM-1 matrix and, at the same time, induce persistent structural relaxations of the frozen-in glassy PIM-1 morphol. For ethanol below 20 nm three effects were identified. First, the swelling magnitude at high vapor pressures is reduced by about 30% as compared to thicker films. Second, at low penetrant activities (below 0.3 p/p0) films below 20 nm are able to absorb slightly more penetrant as compared with thicker films despite similar swelling magnitude. Third, for the ultra-thin films the onset of the dynamic penetrant-induced glass transition Pg has been found to shift to higher values indicating higher resistance to plasticization. All of these effects are consistent with a view where immobilization of the super-glassy PIM-1 at the substrate surface leads to an arrested, even more rigid and plasticization-resistant, yet still very open, microporous structure. PIM-1 in contact with the larger and more condensable toluene shows very complex, heterogeneous swelling dynamics and two distinct penetrant-induced relaxation phenomena, probably assocd. with the film outer surface and the bulk, are detected. Following the direction of the penetrant's diffusion the surface seems to plasticize earlier than the bulk and the two relaxations remain well sepd. down to 6 nm film thickness, where they remarkably merge to form just a single relaxation.
- 26Lively, R. P.; Sholl, D. S. From Water to Organics in Membrane Separations: Membrane Materials Provide Economical Means to Achieve Various Separation Processes - And Their Capabilities for Processing Organic Fluids Look Set to Expand Significantly. Nat. Mater. 2017, 16 (3), 276– 279, DOI: 10.1038/nmat4860Google Scholar26From water to organics in membrane separationsLively, Ryan P.; Sholl, David S.Nature Materials (2017), 16 (3), 276-279CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Membrane materials provide economical means to achieve various sepn. processes - and their capabilities for processing org. fluids look set to expand significantly.
- 27Cui, Y.; Chung, T.-S. Pharmaceutical Concentration Using Organic Solvent Forward Osmosis for Solvent Recovery. Nat. Commun. 2018, 9 (1), 1– 9, DOI: 10.1038/s41467-018-03612-2Google Scholar27miRNA-mediated TUSC3 deficiency enhances UPR and ERAD to promote metastatic potential of NSCLCJeon, Young-Jun; Kim, Taewan; Park, Dongju; Nuovo, Gerard J.; Rhee, Siyeon; Joshi, Pooja; Lee, Bum-Kyu; Jeong, Johan; Suh, Sung-suk; Grotzke, Jeff E.; Kim, Sung-Hak; Song, Jieun; Sim, Hosung; Kim, Yonghwan; Peng, Yong; Jeong, Youngtae; Garofalo, Michela; Zanesi, Nicola; Kim, Jonghwan; Liang, Guang; Nakano, Ichiro; Cresswell, Peter; Nana-Sinkam, Patrick; Cui, Ri; Croce, Carlo M.Nature Communications (2018), 9 (1), 1-13CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)Non-small cell lung carcinoma (NSCLC) is leading cause of cancer-related deaths in the world. The Tumor Suppressor Candidate 3 (TUSC3) at chromosome 8p22 known to be frequently deleted in cancer is often found to be deleted in advanced stage of solid tumors. However, the role of TUSC3 still remains controversial in lung cancer and context-dependent in several cancers. Here we propose that miR-224/-520c-dependent TUSC3 deficiency enhances the metastatic potential of NSCLC through the alteration of three unfolded protein response pathways and HRD1-dependent ERAD. ATF6α-dependent UPR is enhanced whereas the affinity of HRD1 to its substrates, PERK, IRE1α and p53 is weakened. Consequently, the alteration of UPRs and the suppressed p53-NM23H1/2 pathway by TUSC3 deficiency is ultimately responsible for enhancing metastatic potential of lung cancer. These findings provide mechanistic insight of unrecognized roles of TUSC3 in cancer progression and the oncogenic role of HRD1-dependent ERAD in cancer metastasis.
- 28Li, B.; Japip, S.; Chung, T. S. Molecularly Tunable Thin-Film Nanocomposite Membranes with Enhanced Molecular Sieving for Organic Solvent Forward Osmosis. Nat. Commun. 2020, 11 (1), 1– 10Google ScholarThere is no corresponding record for this reference.
- 29Ma, X.; Ghanem, B.; Salines, O.; Litwiller, E.; Pinnau, I. Synthesis and Effect of Physical Aging on Gas Transport Properties of a Microporous Polyimide Derived from a Novel Spirobifluorene-Based Dianhydride. ACS Macro Lett. 2015, 4 (2), 231– 235, DOI: 10.1021/acsmacrolett.5b00009Google Scholar29Synthesis and Effect of Physical Aging on Gas Transport Properties of a Microporous Polyimide Derived from a Novel Spirobifluorene-Based DianhydrideMa, Xiaohua; Ghanem, Bader; Salines, Octavio; Litwiller, Eric; Pinnau, IngoACS Macro Letters (2015), 4 (2), 231-235CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)A novel generic method is reported for the synthesis of a spirobifluorene-based dianhydride (SBFDA). An intrinsically microporous polyimide was obtained by polycondensation reaction with 3,3'-dimethylnaphthidine (DMN). The corresponding polymer (SBFDA-DMN) exhibited good soly., excellent thermal stability, as well as significant microporosity with high BET surface area of 686 m2/g. The O2 permeability of a methanol-treated and air-dried membrane was 1193 Barrer with a moderate O2/N2 selectivity of 3.2. The post-treatment history and aging conditions had great effects on the membrane performance. A significant drop in permeability coupled with an increase in selectivity was obsd. after long-term aging. After storage of 200 days, the gas sepn. properties of SBFDA-DMN were located slightly above the latest Robeson upper bounds for several gas pairs such as O2/N2 and H2/N2.
- 30Hatori, H.; Yamada, Y.; Shiraishi, M. In-Plane Orientation and Graphitizability of Polyimide Films: II. Film Thickness Dependence. Carbon 1993, 31 (8), 1307– 1312, DOI: 10.1016/0008-6223(93)90090-WGoogle Scholar30In-plane orientation and graphitizability of polyimide films. II. Film thickness dependenceHatori, H.; Yamada, Y.; Shiraishi, M.Carbon (1993), 31 (8), 1307-12CODEN: CRBNAH; ISSN:0008-6223.The relation between the in-plane orientation of polyimide film and graphitizability was investigated. The degree of in-plane orientation was estd. by means of optical birefringence and ESR technique. The polyimide film had nonuniform orientation in the thickness direction because the thinner the film was, the greater the orientation. The inhomogeneity of orientation caused multiphase graphitization in a film with a composite profile of the X-ray diffraction peak.
- 31Johs, B.; Hale, J. S. Dielectric Function Representation by B-Splines. Phys. Status Solidi A 2008, 205 (4), 715– 719, DOI: 10.1002/pssa.200777754Google Scholar31Dielectric function representation by B-splinesJohs, Blaine; Hale, Jeffrey S.Physica Status Solidi A: Applications and Materials Science (2008), 205 (4), 715-719CODEN: PSSABA; ISSN:1862-6300. (Wiley-VCH Verlag GmbH & Co. KGaA)Accurate dielec. function values are essential for spectroscopic ellipsometry data anal. by traditional optical model-based anal. techniques. In this paper, we show that B-spline basis functions offer many advantages for parameterizing dielec. functions. A Kramers-Kronig consistent B-spline formulation, based on the std. B-spline recursion relation, is derived. B-spline representations of typical semiconductor and metal dielec. functions are also presented.
- 32Ogieglo, W.; Ghanem, B.; Ma, X.; Wessling, M.; Pinnau, I. High-Pressure CO2 Sorption in Polymers of Intrinsic Microporosity under Ultrathin Film Confinement. ACS Appl. Mater. Interfaces 2018, 10 (13), 11369– 11376, DOI: 10.1021/acsami.8b01402Google Scholar32High-Pressure CO2 Sorption in Polymers of Intrinsic Microporosity under Ultrathin Film ConfinementOgieglo, Wojciech; Ghanem, Bader; Ma, Xiaohua; Wessling, Matthias; Pinnau, IngoACS Applied Materials & Interfaces (2018), 10 (13), 11369-11376CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Ultrathin microporous polymer films are pertinent to the development and further spread of nanotechnol. with very promising potential applications in mol. sepns., sensors, catalysis, or batteries. Here, we report high-pressure CO2 sorption in ultrathin films of several chem. different polymers of intrinsic microporosity (PIMs), including the prototypical PIM-1. Films with thicknesses down to 7 nm were studied using interference-enhanced in situ spectroscopic ellipsometry. It was found that all PIMs swell much more than non-microporous polystyrene and other high-performance glassy polymers reported previously. Furthermore, chem. modifications of the parent PIM-1 strongly affected the swelling magnitude. By investigating the behavior of relative refractive index, nrel, it was possible to study the interplay between micropores filling and matrix expansion. Remarkably, all studied PIMs showed a max. in nrel at swelling of 2-2.5% indicating a threshold point above which the dissoln. in the dense matrix started to dominate over sorption in the micropores. At pressures above 25 bar, all PIMs significantly plasticized in compressed CO2 and for the ones with the highest affinity to the penetrant, a liquidlike mixing typical for rubbery polymers was obsd. Redn. of film thickness below 100 nm revealed pronounced nanoconfinement effects and resulted in a large swelling enhancement and a quick loss of the ultrarigid character. On the basis of the partial molar volumes of the dissolved CO2, the effective redn. of the Tg was estd. to be ∼200 °C going from 128 to 7 nm films.
- 33Ogieglo, W.; Furchner, A.; Ghanem, B.; Ma, X.; Pinnau, I.; Wessling, M. Mixed-Penetrant Sorption in Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1. J. Phys. Chem. B 2017, 121 (43), 10190– 10197, DOI: 10.1021/acs.jpcb.7b10061Google Scholar33Mixed-Penetrant Sorption in Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1Ogieglo, Wojciech; Furchner, Andreas; Ghanem, Bader; Ma, Xiaohua; Pinnau, Ingo; Wessling, MatthiasJournal of Physical Chemistry B (2017), 121 (43), 10190-10197CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)Mixed-penetrant sorption into ultrathin films of a superglassy polymer of intrinsic microporosity (PIM-1) was studied for the first time by using interference-enhanced in situ spectroscopic ellipsometry. PIM-1 swelling and the concurrent changes in its refractive index were detd. in ultrathin (12-14 nm) films exposed to pure and mixed penetrants. The penetrants included water, n-hexane, and ethanol and were chosen on the basis of their significantly different penetrant-penetrant and penetrant-polymer affinities. This allowed studying microporous polymer responses at diverse ternary compns. and revealed effects such as competition for the sorption sites (for water/n-hexane or ethanol/n-hexane) or enhancement in sorption of typically weakly sorbing water in the presence of more highly sorbing ethanol. The results reveal details of the mutual sorption effects which often complicate comprehension of glassy polymers' behavior in applications such as high-performance membranes, adsorbents, or catalysts. Mixed-penetrant effects are typically very challenging to study directly, and their understanding is necessary owing to a broadly recognized inadequacy of simple extrapolations from measurements in a pure component environment.
- 34Sirard, S. M.; Green, P. F.; Johnston, K. P. Spectroscopic Ellipsometry Investigation of the Swelling of Poly(Dimethylsiloxane) Thin Films with High Pressure Carbon Dioxide. J. Phys. Chem. B 2001, 105 (4), 766– 772, DOI: 10.1021/jp002592dGoogle Scholar34Spectroscopic Ellipsometry Investigation of the Swelling of Poly(Dimethylsiloxane) Thin Films with High Pressure Carbon DioxideSirard, S. M.; Green, P. F.; Johnston, K. P.Journal of Physical Chemistry B (2001), 105 (4), 766-772CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)The thickness and refractive index of poly(dimethylsiloxane) (PDMS) thin films on silicon, exposed to high-pressure carbon dioxide, have been measured in-situ by spectroscopic ellipsometry. The swelling of the film is detd. from the thickness and the sorption of CO2 from the refractive index. The sorption and swelling values for the thin films exceed those of the bulk films. These increases may be attributed to excess CO2 at the polymer thin film-CO2 and polymer-silica interfaces and the influence of the silica surface and CO2 on the orientation of the polymer. Pressure-induced birefringence of the fused-silica windows was addressed in the model calcns. and corrections were successful for a thermal oxide ref. wafer and the PDMS films. Large surface excesses of CO2 on the ref. wafer were obsd. in regions where CO2 is highly compressible due to crit. adsorption.
- 35Ogieglo, W.; Wormeester, H.; Wessling, M.; Benes, N. E. Effective Medium Approximations for Penetrant Sorption in Glassy Polymers Accounting for Excess Free Volume. Polymer 2014, 55 (7), 1737– 1744, DOI: 10.1016/j.polymer.2014.02.040Google Scholar35Effective medium approximations for penetrant sorption in glassy polymers accounting for excess free volumeOgieglo, Wojciech; Wormeester, Herbert; Wessling, Matthias; Benes, Nieck E.Polymer (2014), 55 (7), 1737-1744CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)An accurate detn. of a penetrant vol. fraction in a swollen polymer is of crucial importance in a range of different technologies. Using optical methods, such as in-situ spectroscopic ellipsometry, it is possible to ext. the thickness and refractive index of dry and swollen polymer films. The vol. fraction of the penetrant can then be calcd. from the change in thickness, or from the refractive index using effective medium approxns. For thermodynamically equilibrated and ideal swollen rubbery polymers, these calcns. yield accurate results. However, for glassy polymers the influence of the excess free vol. trapped within the polymer network during vitrification is rarely taken into account. In this work we investigate the effect of excess free vol. in the calcns. of penetrant vol. fraction in a model glassy polymer - penetrant system. The influence of the excess free vol. is included by extrapolating the properties of an equil. polymer matrix from above its glass transition temp. The error between the approaches that do, and do not, take account for the non-equil. of the glassy polymer is quantified and the implications for other systems are discussed. The errors are shown to be very significant, esp. when the dry polymer has a large excess free vol. Such materials are particularly relevant in membrane applications.
- 36Ogieglo, W.; Genduso, G.; Rubner, J.; Hofmann-Preveraud de Vaumas, J.; Wessling, M.; Pinnau, I. CO2/CH4 Pure- And Mixed-Gas Dilation and Sorption in Thin (∼500 nm) and Ultrathin (∼50 nm) Polymers of Intrinsic Microporosity. Macromolecules 2020, 53 (20), 8765– 8774, DOI: 10.1021/acs.macromol.0c01163Google Scholar36CO2/CH4 Pure- and Mixed-Gas Dilation and Sorption in Thin (∼ 500 nm) and Ultrathin (∼ 50 nm) Polymers of Intrinsic MicroporosityOgieglo, Wojciech; Genduso, Giuseppe; Rubner, Jens; Hofmann-Preveraud de Vaumas, Jacques; Wessling, Matthias; Pinnau, IngoMacromolecules (Washington, DC, United States) (2020), 53 (20), 8765-8774CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)In this work, we present (i) the dilation and refractive index variation assocd. with changes in film d. and (ii) gas uptake of pure CO2 and CH4, as well as their equimolar mixt. in thin films of two polymers of intrinsic microporosity (PIMs), i.e., PIM-1 and poly(trimethylsilyl)propyne (PTMSP). A conventional low-free-vol. glassy polymer, cellulose triacetate, was also investigated as the ref. material. All expts. were performed with ~ 50 and ~ 500 nm-thick films up to partial pressures of 25 bar using in situ interference-enhanced spectroscopic ellipsometry. In all cases, film thickness redn. promoted the collapse of the frozen-in free vol. Particularly for thin PIM-1 and PTMSP films, the CO2 and CH4 pure-gas uptakes were generally lower than in bulk samples. In the most extreme case of the ultrathin ~ 50 nm PTMSP film, we could detect a strikingly similar qual. behavior to the penetrant partial molar volume and dilation in rubbery polymers. Remarkably, in PIM-1, the collapse of the frozen-in free vol. seemed to be opposed by its ultra-micropores (<7 Å), which was not the case in PTMSP with larger micropores (>10 Å). In mixed-gas expts., the refractive index response of all investigated films closely followed the trend obsd. during CO2 pure-gas sorption. In both thickness ranges and throughout the entire pressure range, the samples dilated less in the multicomponent environment than under the corresponding ideal pure-gas conditions. We found this phenomenon consistent with the pure- and mixed-gas uptake behavior of PIM-1 and PTMSP bulk films reported in the literature.
- 37Zhou, C.; Chung, T. S.; Wang, R.; Liu, Y.; Goh, S. H. The Accelerated CO2 Plasticization of Ultra-Thin Polyimide Films and the Effect of Surface Chemical Cross-Linking on Plasticization and Physical Aging. J. Membr. Sci. 2003, 225 (1–2), 125– 134, DOI: 10.1016/j.memsci.2003.07.006Google Scholar37The accelerated CO2 plasticization of ultra-thin polyimide films and the effect of surface chemical cross-linking on plasticization and physical agingZhou, Chun; Chung, Tai-Shung; Wang, Rong; Liu, Ye; Goh, Suat HongJournal of Membrane Science (2003), 225 (1-2), 125-134CODEN: JMESDO; ISSN:0376-7388. (Elsevier Science B.V.)For the first time, the permeation expts. of CO2 are carried out on ultra-thin dense polyimide films (0.5-1.8 μm). The observation of accelerated CO2 plasticization indicates that the conventionally defined "plasticization pressure" as an inherent material properties measured from thick dense films is strongly thickness dependent. This accelerated plasticization phenomenon obsd. in ultra-thin dense films is probably attributed to two factors: (1) the swelling and softening effects of the sorbing CO2 mols. on the polymer chains; and (2) weak micro-mech. properties and less sorption capacity of ultra-thin films to accommodate the sorbed CO2 mols. Exptl. results suggest that chem. modified ultra-thin films show characteristics of retarded aging process and significantly suppressed plasticization.
- 38Huang, Y.; Paul, D. R. Effect of Temperature on Physical Aging of Thin Glassy Polymer Films. Macromolecules 2005, 38 (24), 10148– 10154, DOI: 10.1021/ma051284gGoogle Scholar38Effect of Temperature on Physical Aging of Thin Glassy Polymer FilmsHuang, Y.; Paul, D. R.Macromolecules (2005), 38 (24), 10148-10154CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)The effect of temp. on the kinetics of phys. aging of thin films formed from two amorphous glassy polymers, polysulfone based on bisphenol A and poly(2,6-dimethyl-1,4-phenylene oxide), was investigated by monitoring the changes in gas permeability and refractive index. Films with different thicknesses were subjected to isothermal aging at three temps., ranging from 35 to 55 °C, for a period of aging of more than 200 days. The rate of permeability loss and the rate of densification detd. from the refractive index change by using the Lorentz-Lorenz equation were found to increase with aging temp. Similar qual. trends of aging rate were noted by the two measurements. The combination of effects of aging temp. and film thickness on aging behavior were studied and compared with previous research.
- 39Ogieglo, W.; Puspasari, T.; Ma, X.; Pinnau, I. Sub-100 nm Carbon Molecular Sieve Membranes from a Polymer of Intrinsic Microporosity Precursor: Physical Aging and near-Equilibrium Gas Separation Properties. J. Membr. Sci. 2020, 597, 117752, DOI: 10.1016/j.memsci.2019.117752Google Scholar39Sub-100 nm carbon molecular sieve membranes from a polymer of intrinsic microporosity precursor: Physical aging and near-equilibrium gas separation propertiesOgieglo, Wojciech; Puspasari, Tiara; Ma, Xiaohua; Pinnau, IngoJournal of Membrane Science (2020), 597 (), 117752CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)Here, ultra-thin, sub-100 nm carbon mol. sieve (CMS) membranes based on a polymer of intrinsic microporosity precursor were fabricated and characterized with respect to their sepn. performance for six gases, He, H2, N2, O2, CO2 and CH4. The rarely reported in thin CMS membranes phys. aging was tracked until near-equil. was reached. The use of com. available, small pore size γ-alumina-coated α-alumina ceramic supports allowed for an easy membrane precursor fabrication by a simple soln. coating process. The subsequent application of a protective polydimethylsiloxane layer assured excellent defect control and produced CMS composite membranes with very high membrane permselectivities (e.g. CO2/CH4 = 84.5, H2/CH4 = 360). However, a surprisingly massive acceleration of the phys. aging in comparison to the bulk was detected in all sub-100 nm membranes including the precursor polymer. All CMS membranes reached near-equil. gas transport properties within 1-1.5 mo providing a rare opportunity to study aging-stabilized performance. For the aging-stabilized sub-100 nm membranes a decrease in gas permeabilities of up to 3 orders of magnitude was detected. Overall, our study provides an important observation that excessive redn. of the selective layer thickness, esp. in initially highly microporous materials, may not present the best strategy for the optimization of the long-term membrane performance.
- 40Rowe, B. W.; Freeman, B. D.; Paul, D. R. Physical Aging of Ultrathin Glassy Polymer Films Tracked by Gas Permeability. Polymer 2009, 50 (23), 5565– 5575, DOI: 10.1016/j.polymer.2009.09.037Google Scholar40Physical aging of ultrathin glassy polymer films tracked by gas permeabilityRowe, Brandon W.; Freeman, Benny D.; Paul, Donald R.Polymer (2009), 50 (23), 5565-5575CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)Membrane-based sepns. play a key role in energy conservation and reducing greenhouse gas emissions by providing low energy routes for a wide variety of industrially-important sepns. For reasons not completely understood, membrane permeability changes with time, due to phys. aging, and the rate of permeability change can become orders of magnitude faster in films thinner than one micron. The gas transport properties and phys. aging behavior of free-standing glassy polysulfone and Matrimid films as thin as 18 nm are presented. Phys. aging persists in glassy films approaching the length scale of individual polymer coils. The films studied ranged from 18-550 nm thick. They exhibited redns. in gas permeability, some more than 50%, after ∼1000 h of aging at 35 °C, and increases in selectivity. The properties of these ultrathin films deviate dramatically from bulk behavior, and the nature of these deviations is consistent with enhanced mobility and reduced T g in ultrathin films. The Struik phys. aging model was extended to account for the influence of film thickness on aging rate, and it was shown to adequately describe the aging data.
- 41Ferrari, A. C.; Basko, D. M. Raman Spectroscopy as a Versatile Tool for Studying the Properties of Graphene. Nat. Nanotechnol. 2013, 8 (4), 235– 246, DOI: 10.1038/nnano.2013.46Google Scholar41Raman spectroscopy as a versatile tool for studying the properties of grapheneFerrari, Andrea C.; Basko, Denis M.Nature Nanotechnology (2013), 8 (4), 235-246CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)A review. Raman spectroscopy is an integral part of graphene research. It is used to det. the no. and orientation of layers, the quality and types of edge, and the effects of perturbations, such as elec. and magnetic fields, strain, doping, disorder and functional groups. This, in turn, provides insight into all sp2-bonded carbon allotropes, because graphene is their fundamental building block. Here we review the state of the art, future directions and open questions in Raman spectroscopy of graphene. We describe essential phys. processes whose importance has only recently been recognized, such as the various types of resonance at play, and the role of quantum interference. We update all basic concepts and notations, and propose a terminol. that is able to describe any result in literature. We finally highlight the potential of Raman spectroscopy for layered materials other than graphene.
- 42Ferrari, A.; Robertson, J. Interpretation of Raman Spectra of Disordered and Amorphous Carbon. Phys. Rev. B: Condens. Matter Mater. Phys. 2000, 61 (20), 14095– 14107, DOI: 10.1103/PhysRevB.61.14095Google Scholar42Interpretation of Raman spectra of disordered and amorphous carbonFerrari, A. C.; Robertson, J.Physical Review B: Condensed Matter and Materials Physics (2000), 61 (20), 14095-14107CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)The model and theor. understanding of the Raman spectra in disordered and amorphous C are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of π states and the long-range polarizability of π bonding. Visible Raman data on disordered, amorphous, and diamondlike C are classified in a 3-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. The visible Raman spectra depend formally on the configuration of the sp2 sites in sp2-bonded clusters. In cases where the sp2 clustering is controlled by the sp3 fraction, such as in as-deposited tetrahedral amorphous C (ta-C) or hydrogenated amorphous C (a-C:H) films, the visible Raman parameters can be used to derive the sp3 fraction.
- 43Casciardi, S.; Sisto, R.; Diociaiuti, M. The Analytical Transmission Electron Microscopy: A Powerful Tool for the Investigation of Low-Dimensional Carbon Nanomaterials. J. Nanomater. 2013, 2013, 1, DOI: 10.1155/2013/506815Google ScholarThere is no corresponding record for this reference.
- 44Sirard, S. M.; Green, P. F.; Johnston, K. P. Spectroscopic Ellipsometry Investigation of the Swelling of Poly(dimethylsiloxane) Thin Films with High Pressure Carbon Dioxide. J. Phys. Chem. B 2001, 105 (4), 766– 772, DOI: 10.1021/jp002592dGoogle Scholar44Spectroscopic Ellipsometry Investigation of the Swelling of Poly(Dimethylsiloxane) Thin Films with High Pressure Carbon DioxideSirard, S. M.; Green, P. F.; Johnston, K. P.Journal of Physical Chemistry B (2001), 105 (4), 766-772CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)The thickness and refractive index of poly(dimethylsiloxane) (PDMS) thin films on silicon, exposed to high-pressure carbon dioxide, have been measured in-situ by spectroscopic ellipsometry. The swelling of the film is detd. from the thickness and the sorption of CO2 from the refractive index. The sorption and swelling values for the thin films exceed those of the bulk films. These increases may be attributed to excess CO2 at the polymer thin film-CO2 and polymer-silica interfaces and the influence of the silica surface and CO2 on the orientation of the polymer. Pressure-induced birefringence of the fused-silica windows was addressed in the model calcns. and corrections were successful for a thermal oxide ref. wafer and the PDMS films. Large surface excesses of CO2 on the ref. wafer were obsd. in regions where CO2 is highly compressible due to crit. adsorption.
- 45Simons, K.; Nijmeijer, K.; Sala, J. G.; van der Werf, H.; Benes, N. E.; Dingemans, T. J.; Wessling, M. CO2 Sorption and Transport Behavior of ODPA-Based Polyetherimide Polymer Films. Polymer 2010, 51 (17), 3907– 3917, DOI: 10.1016/j.polymer.2010.06.031Google Scholar45CO2 sorption and transport behavior of ODPA-based polyetherimide polymer filmsSimons, Katja; Nijmeijer, Kitty; Sala, Jordi Guilera; van der Werf, Hans; Benes, Nieck E.; Dingemans, Theo J.; Wessling, MatthiasPolymer (2010), 51 (17), 3907-3917CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)Plasticization phenomena can significantly reduce the performance of polymeric membranes in high-pressure applications. Polyetherimides (PEIs) are a promising group of membrane materials that combine relatively high CO2/CH4 selectivities with high chem. and thermal stability. In this work sorption, swelling, and mixed gas sepn. performance of 3,3',4,4'-oxydiphthalic dianhydride (ODPA)-based PEI polymers, with 1, 2 or 3 para-aryloxy substitutions in the diamine moiety, is investigated under conditions where com. membranes suffer from plasticization. Particular focus is on the influence of the amt. of para-aryloxy substitutions and the film thickness. Results are compared with those of com. available polymeric membrane materials (sulfonated PEEK, a segmented block-co-polymer PEBAX and the polyimide Matrimid). The glassy polymers display increasing CO2 sorption with increasing Tg. The larger extent of sorption results from a larger non-equil. excess free vol. Swelling of the polymers is induced by sorption of CO2 mols. in the non-equil. free vol. as well as from mols. dissolved in the matrix. Dilation of the polymer is similar for each mol. sorbed. Correspondingly, the partial molar volume of CO2 is similar for mols. present in both regions. Mixed gas sepn. expts. with a 50/50% CO2/CH4 feed gas mixt. showed high CO2/CH4 selectivities for the ODPA PEI films at elevated pressure. This shows that these materials could potentially be interesting for high-pressure gas sepn. applications, although addnl. gas permeation expts. using different feed gas compns. and thin films are required.
- 46Sanyal, O.; Hicks, S. T.; Bhuwania, N.; Hays, S.; Kamath, M. G.; Karwa, S.; Swaidan, R.; Koros, W. J. Cause and Effects of Hyperskin Features on Carbon Molecular Sieve (CMS) Membranes. J. Membr. Sci. 2018, 551, 113– 122, DOI: 10.1016/j.memsci.2018.01.021Google Scholar46Cause and effects of hyperskin features on carbon molecular sieve (CMS) membranesSanyal, Oishi; Hicks, Stephanie T.; Bhuwania, Nitesh; Hays, Samuel; Kamath, Manjeshwar G.; Karwa, Shweta; Swaidan, Raja; Koros, William J.Journal of Membrane Science (2018), 551 (), 113-122CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)This article considers a previously overlooked feature in carbon mol. sieve (CMS) membranes that we term a "hyperskin" present at the outermost region of dense CMS selective layers. Such a feature with much lower permeability, but similar selectivity compared to the bulk of the skin, reduces CMS hollow fiber permeance below that predicted from corresponding dense films. Effects of the hyperskin are considered for CMS hollow fibers with low skin thicknesses based on two polyimide precursors - Matrimid and 6FDA:BPDA-DAM. Although the fundamental formation mechanism for the hyperskin feature suggests its existence on virtually all CMS membranes, its impact on transport properties is shown to differ dramatically, depending on the detailed characteristic properties of the specific CMS membrane. Indeed, for hollow fibers with very low nominal resistance (i.e. ((SelectivelayerthicknessdeterminedbySEM)/(IntrinsicpermeabilityofthickdenseCMSfilms))), the obsd. permeance only reaches a small fraction of the predicted permeance. The selectivity between different gas penetrants, however, is not altered by the presence of this hyperskin. While identifying this issue is the major focus of this article, strategies to address this limitation, without compromising the mol. sieving properties of CMS membranes are briefly discussed.
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Abstract
Figure 1
Figure 1. SBFDA-DMN polyimide with intrinsic microporosity (PIM–PI) used as carbon molecular sieve precursor in this study.
Figure 2
Figure 2. Scheme of the anisotropic, uniaxial optical model used for the sample analysis throughout this study.
Figure 3
Figure 3. (a) Relative thickness and relative refractive index as a function of the pyrolysis temperature for both thick (∼300 nm) and thin (∼30 nm) polymer precursor films; ∼70 μm data is for a self-supported “bulk” film (15) reprinted with permission from ref (15). Copyright 2019 American Chemical Society. (b) Cross-sectional transmission electron microscopy images showing the microstructure of the thick CMS films; (c) normalized Raman spectra (633 nm excitation wavelength) showing the typical “D” and “G” peaks observed in CMS materials for both ∼300 and ∼30 nm films.
Figure 4
Figure 4. Results of the uniaxially anisotropic modeling of the pyrolytic collapse in (a) a thick (∼300 nm) and (b) thin (∼30 nm) films together with (c) a proposed scheme of the morphological transformations. Because of the lateral confinement to the substrate, the whole volume change as a result of pyrolysis is accommodated only by the change in film thickness.
Figure 5
Figure 5. 2D Fourier transforms for an isotropic amorphous CMS structure (left, adapted with permission from ref (43). Copyright 2013 Stefano Casciardi et al. under Creative Commons Attribution License.) and ∼300 nm Si-wafer supported PIM–PI derived CMS films from this study (right); dashed lines indicate perfect circles for reference.
Figure 6
Figure 6. Swelling factors (a and b) and relative refractive indices (c and d) for the thick (∼300 nm) and thin (∼30 nm) pristine PIM–PI and carbon films upon exposure to ethanol vapors. Error bars are omitted for the sake of clarity; in each ease the errors are estimated at <5%.
Figure 7
Figure 7. Concentration of ethanol estimated via the Clausius-Mossotti calculations for (a) thick (∼300 nm) and (b) thin (∼30 nm) pristine PIM–PI and carbon films (500, 600, 700, and 800 °C). Error bars are omitted for the sake of clarity; in each ease the errors are estimated at <5%.
References
This article references 46 other publications.
- 1Atkinson, S. Carbon Molecular Sieve Membranes Aim to Cut Energy Use in Hydrocarbon Separations. Membr. Technol. 2017, 2017 (1), 9– 10, DOI: 10.1016/S0958-2118(17)30017-4There is no corresponding record for this reference.
- 2Sholl, D. S.; Lively, R. P. Seven Chemical Separations to Change the World. Nature 2016, 532 (7600), 435– 437, DOI: 10.1038/532435a2Seven chemical separations to change the worldSholl David S; Lively Ryan PNature (2016), 532 (7600), 435-7 ISSN:.There is no expanded citation for this reference.
- 3Zhang, C.; Koros, W. J. Ultraselective Carbon Molecular Sieve Membranes with Tailored Synergistic Sorption Selective Properties. Adv. Mater. 2017, 29 (33), 1– 6There is no corresponding record for this reference.
- 4Sanyal, O.; Zhang, C.; Wenz, G. B.; Fu, S.; Bhuwania, N.; Xu, L.; Rungta, M.; Koros, W. J. Next Generation Membranes —Using Tailored Carbon. Carbon 2018, 127, 688– 698, DOI: 10.1016/j.carbon.2017.11.0314Next generation membranes-using tailored carbonSanyal, Oishi; Zhang, Chen; Wenz, Graham B.; Fu, Shilu; Bhuwania, Nitesh; Xu, Liren; Rungta, Meha; Koros, William J.Carbon (2018), 127 (), 688-698CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)A review. Carbon mol. sieve (CMS) membranes are a special class of nanoporous membranes with angstrom-level mol. discrimination properties, which make them appealing for sepg. a wide spectrum of gas-pairs. The mechanism of pyrolysis by which a polymer coil is transformed into these rigid sieves is complex; however, we present a framework that can explain this transformation. Representative polymer precursors and pyrolysis conditions are discussed that yield attractive CMS membrane sepn. performance for extremely challenging gas pairs. Control of penetrant motions in the diffusion activated state, reflected in the entropy of activation of subtly different penetrants, enables the attractive diffusion selectivity of such membranes. This control, virtually absent even in rigid state-of-the-art polymeric membranes, makes CMS materials extraordinarily attractive. Moreover, unlike other rigid sieving materials, CMS membranes have the added advantage of being processable into highly productive, flexible hollow fibers with good mech. properties and long-term stability under const. gas feeds. We also identify some key areas of CMS which would greatly benefit from expertise from other fields like computation or materials characterization that can potentially complement transport-based studies.
- 5Galizia, M.; Chi, W. S.; Smith, Z. P.; Merkel, T. C.; Baker, R. W.; Freeman, B. D. 50th Anniversary Perspective: Polymers and Mixed Matrix Membranes for Gas and Vapor Separation: A Review and Prospective Opportunities. Macromolecules 2017, 50 (20), 7809– 7843, DOI: 10.1021/acs.macromol.7b01718550Th Anniversary Perspective: Polymers and Mixed Matrix Membranes for Gas and Vapor Separation: A Review and Prospective OpportunitiesGalizia, Michele; Chi, Won Seok; Smith, Zachary P.; Merkel, Timothy C.; Baker, Richard W.; Freeman, Benny D.Macromolecules (Washington, DC, United States) (2017), 50 (20), 7809-7843CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)A review. Membrane gas sepn. is a mature and expanding technol. However, the availability of better membrane materials would promote faster growth. In this Perspective we analyze the state of the art of membrane materials, including polymers and hybrid materials, as well as the current issues and barriers, and finally, we outline future research directions in membrane science. Development of new membrane materials for large scale sepns. will rely on a multidisciplinary approach that embraces the broad fields of chem. and materials engineering, polymer science, and materials chem.
- 6Koh, D. Y.; McCool, B. A.; Deckman, H. W.; Lively, R. P. Reverse Osmosis Molecular Differentiation of Organic Liquids Using Carbon Molecular Sieve Membranes. Science 2016, 353 (6301), 804– 807, DOI: 10.1126/science.aaf13436Reverse osmosis molecular differentiation of organic liquids using carbon molecular sieve membranesKoh, Dong-Yeun; McCool, Benjamin A.; Deckman, Harry W.; Lively, Ryan P.Science (Washington, DC, United States) (2016), 353 (6301), 804-807CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Liq.-phase sepns. of similarly sized org. mols. using membranes is a major challenge for energy-intensive industrial sepn. processes. We created free-standing carbon mol. sieve membranes that translate the advantages of reverse osmosis for aq. sepns. to the sepn. of org. liqs. Polymer precursors were cross-linked with a one-pot technique that protected the porous morphol. of the membranes from thermally induced structural rearrangement during carbonization. Permeation studies using benzene derivs. whose kinetic diams. differ by less than an angstrom show kinetically selective org. liq. reverse osmosis. Ratios of single-component fluxes for para- and ortho-xylene exceeding 25 were obsd. and para- and ortho- liq. mixts. were efficiently sepd., with an equimolar feed enriched to 81 mol % para-xylene, without phase change and at ambient temp.
- 7Salinas, O.; Ma, X.; Litwiller, E.; Pinnau, I. High-Performance Carbon Molecular Sieve Membranes for Ethylene/Ethane Separation Derived from an Intrinsically Microporous Polyimide. J. Membr. Sci. 2016, 500, 115– 123, DOI: 10.1016/j.memsci.2015.11.0137High-performance carbon molecular sieve membranes for ethylene/ethane separation derived from an intrinsically microporous polyimideSalinas, Octavio; Ma, Xiaohua; Litwiller, Eric; Pinnau, IngoJournal of Membrane Science (2016), 500 (), 115-123CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)An intrinsically microporous polymer with hydroxyl functionalities, PIM-6FDA-OH, was used as a precursor for various types of carbon mol. sieve (CMS) membranes for ethylene/ethane sepn. The pristine polyimide films were heated under controlled N2 atmosphere at different stages from 500 to 800 °C. All CMS samples carbonized above 600 °C surpassed the polymeric ethylene/ethane upper bound. Pure-gas selectivity reached 17.5 for the CMS carbonized at 800 °C with an ethylene permeability of about 10 Barrer at 2 bar and 35 °C, becoming the most selective CMS for ethylene/ethane sepn. reported to date. As expected, gravimetric sorption expts. showed that all CMS membranes had ethylene/ethane soly. selectivities close to one. The permselectivity increased with increasing pyrolysis temp. due to densification of the micropores in the CMS membranes, leading to enhanced diffusivity selectivity. Mixed-gas tests with a binary 50:50 vol./vol. ethylene/ethane feed showed a decrease in selectivity from 14 to 8.3 as the total feed pressure was increased from 4 to 20 bar. The selectivity drop under mixed-gas conditions was attributed to non-ideal effects: (i) competitive sorption that reduced the permeability of ethylene and (ii) dilation of the CMS that resulted in an increase in the ethane permeability.
- 8Salinas, O.; Ma, X.; Litwiller, E.; Pinnau, I. Ethylene/Ethane Permeation, Diffusion and Gas Sorption Properties of Carbon Molecular Sieve Membranes Derived from the Prototype Ladder Polymer of Intrinsic Microporosity (PIM-1). J. Membr. Sci. 2016, 504, 133– 140, DOI: 10.1016/j.memsci.2015.12.0528Ethylene/ethane permeation, diffusion and gas sorption properties of carbon molecular sieve membranes derived from the prototype ladder polymer of intrinsic microporosity (PIM-1)Salinas, Octavio; Ma, Xiaohua; Litwiller, Eric; Pinnau, IngoJournal of Membrane Science (2016), 504 (), 133-140CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)Fine-tuning the microporosity of PIM-1 by heat treatment was applied to develop a suitable carbon mol. sieve membrane for ethylene/ethane sepn. Pristine PIM-1 films were heated from 400 to 800 °C under inert N2 atmosphere (<2 ppm O2). At 400 °C, PIM-1 self-crosslinked and developed polar carbonyl and hydroxyl groups due to partial dioxane splitting in the polymer backbone. Significant degrdn. occurred at 600 °C due to carbonization of PIM-1 and resulted in 30% increase in cumulative surface area compared to its crosslinked predecessor. In addn., PIM-1-based CMS developed smaller ultramicropores with increasing pyrolysis temp., which enhanced their mol. sieving capability by restricted diffusion of ethylene and ethane through the matrix due to microstructural carbon densification. Consequently, the pure-gas ethylene permeability (measured at 35 °C and 2 bar) decreased from 1600 Barrer for the pristine PIM-1 to 1.3 Barrer for the amorphous carbon generated at 800°, whereas the ethylene/ethane pure-gas selectivity increased significantly from 1.8 to 13.
- 9Salinas, O.; Ma, X.; Wang, Y.; Han, Y.; Pinnau, I. Carbon Molecular Sieve Membrane from a Microporous Spirobisindane-Based Polyimide Precursor with Enhanced Ethylene/Ethane Mixed-Gas Selectivity. RSC Adv. 2017, 7 (6), 3265– 3272, DOI: 10.1039/C6RA24699K9Carbon molecular sieve membrane from a microporous spirobisindane-based polyimide precursor with enhanced ethylene/ethane mixed-gas selectivitySalinas, Octavio; Ma, Xiaohua; Wang, Yingge; Han, Yu; Pinnau, IngoRSC Advances (2017), 7 (6), 3265-3272CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)Ethylene is typically produced by steam cracking of various hydrocarbon feedstocks. The gaseous products are then sepd. in a demethanizer followed by a deethanizer unit and finally sent to a C2 splitter for the final purifn. step. Cryogenic distn. of ethylene from ethane is the most energy-intensive unit operation process in the chem. industry. Therefore, the development of more energy-efficient processes for ethylene purifn. is highly desirable. Membrane-based sepn. has been proposed as an alternative option for replacement or debottlenecking of C2 splitters but current polymer membrane materials exhibit insufficient mixed-gas C2H4/C2H6 selectivity (<7) to be tech. and economically attractive. In this work, a highly selective carbon mol. sieve (CMS) membrane derived from a novel spirobisindane-based polyimide of intrinsic microporosity (PIM-6FDA) was developed and characterized. PIM-6FDA showed a single-stage degrdn. process under an inert nitrogen atm. which commenced at ~ 480°C. The CMS formed by pyrolysis at 800°C had a diffusion/size-sieving-controlled morphol. with a mixed-gas (50% C2H4/50% C2H6) ethylene/ethane selectivity of 15.6 at 20 bar feed pressure at 35°C. The mixed-gas ethylene/ethane selectivity is the highest reported value for CMS-type membranes to date.
- 10Wang, Y.; Ma, X.; Ghanem, B. S.; Alghunaimi, F.; Pinnau, I.; Han, Y. Polymers of Intrinsic Microporosity for Energy-Intensive Membrane-Based Gas Separations. Mater. Today Nano 2018, 3, 69– 95, DOI: 10.1016/j.mtnano.2018.11.003There is no corresponding record for this reference.
- 11Hazazi, K.; Ma, X.; Wang, Y.; Ogieglo, W.; Alhazmi, A.; Han, Y.; Pinnau, I. Ultra-Selective Carbon Molecular Sieve Membranes for Natural Gas Separations Based on a Carbon-Rich Intrinsically Microporous Polyimide Precursor. J. Membr. Sci. 2019, 585, 1– 9, DOI: 10.1016/j.memsci.2019.05.02011Ultra-selective carbon molecular sieve membranes for natural gas separations based on a carbon-rich intrinsically microporous polyimide precursorHazazi, Khalid; Ma, Xiaohua; Wang, Yingge; Ogieglo, Wojciech; Alhazmi, Abdulrahman; Han, Yu; Pinnau, IngoJournal of Membrane Science (2019), 585 (), 1-9CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)A highly contorted, carbon-rich intrinsically microporous polyimide (PIM-PI) made from spirobifluorene dianhydride and 3,3-dimethylnaphthidine (SBFDA-DMN) was employed as a precursor for the formation of carbon mol. sieve (CMS) membranes at pyrolysis temps. from 550 to 1000 °C. The high carbon content of SBFDA-DMN (∼84%) resulted in only 28% total wt. loss during pyrolysis under a nitrogen atm. at 1000 °C. The development of the various microstructural textures was characterized by gas sorption anal., Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction, Raman spectroscopy, elec. cond., and gas transport properties. Heat treatment of a pristine SBFDA-DMN membrane at 550 °C resulted in reduced permeability for all gases (e.g.: PCO2 dropped from 4700 to 1500 barrer) as well as lower BET surface area from 621 to 545 m2 g-1. At 600 °C, new pores induced by pyrolysis increased the BET surface area to nearly that of the precursor and significantly improved gas sepn. performance. Above 600 °C, a progressive collapse of the micropores became evident with CMS membranes showing higher gas-pair selectivity but lower permeability. At 1000 °C, ultra-micropores comparable in size with the kinetic diam. of CH4 emerged and induced a prominent mol. sieving effect resulting in very high CH4 rejection. This strong size exclusion effect, further supported by gravimetric gas sorption measurements, resulted in unusually high N2/CH4 and CO2/CH4 selectivities of 35 and 1475, resp.
- 12Parsley, D.; Ciora, R. J.; Flowers, D. L.; Laukaitaus, J.; Chen, A.; Liu, P. K. T.; Yu, J.; Sahimi, M.; Bonsu, A.; Tsotsis, T. T. Field Evaluation of Carbon Molecular Sieve Membranes for the Separation and Purification of Hydrogen from Coal- and Biomass-Derived Syngas. J. Membr. Sci. 2014, 450, 81– 92, DOI: 10.1016/j.memsci.2013.08.00812Field evaluation of carbon molecular sieve membranes for the separation and purification of hydrogen from coal- and biomass-derived syngasParsley, Doug; Ciora, Richard J. Jr.; Flowers, Diane L.; Laukaitaus, John; Chen, Amy; Liu, Paul K. T.; Yu, Jiang; Sahimi, Muhammad; Bonsu, Alex; Tsotsis, Theodore T.Journal of Membrane Science (2014), 450 (), 81-92CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)High-temp. gas sepns. (GS) with inorg. membranes have attracted attention recently. In particular, the use of such membranes in membrane reactors (MR) has the potential to enhance process intensification and to increase energy savings and/or product yield. Though the potential benefits of high-temp. GS and/or MR processes are substantial, commercialization still remains elusive. A major tech. barrier is the lack of robust inorg. membranes and full-scale modules which are suitable for use at the high-temp. and high-pressure conditions required. C mol. sieve membranes (CMSM) were recently tested in the lab. by this team for the 1-box process. This technol. combines into a single MR unit contaminant removal and coal-derived and/or biomass-derived syngas conversion via the water gas shift reaction to produce high-purity H for power generation and/or chem. use. Towards technol. commercialization, 86-tube CMSM modules have been constructed and characterized comprehensively. Also, multiple field-tests, under non-reactive conditions, of these 86-tube CMSM modules were conducted at the US National C Capture Center coal gasification facility under conditions suitable for the 1-box process. This paper details the results of these tests which address key GS aspects of field implementation, including inorg. membrane/module scale-up, syngas contaminants removal, and membrane material and performance stability. During continuous use (more than 300 h) in raw coal-derived and/or biomass-derived syngas, the CMSM successfully rejected tar-like species present in the syngas without any evidence of fouling, as long as the operating temp. was maintained >250°. Also, the membrane permeation properties remained unchanged throughout this extended test. Simulations, based upon membrane GS properties measured during these field tests, demonstrate that the 1-box process, operating on a typical O-blown gasifier off-gas, can deliver >90% H recovery at >90% purity (dry-basis), and thus shows good promise for com. application. The successful prepn. and deployment by this team of the 86-tube CMSM module overcomes some of the tech. barriers which have, so far, hampered the com. implementation of inorg. membranes for high-temp. and high-pressure gas sepn. applications.
- 13Haider, S.; Lindbråthen, A.; Lie, J. A.; Hägg, M. B. Regenerated Cellulose Based Carbon Membranes for CO2 Separation: Durability and Aging under Miscellaneous Environments. J. Ind. Eng. Chem. 2019, 70, 363– 371, DOI: 10.1016/j.jiec.2018.10.03713Regenerated cellulose based carbon membranes for CO2 separation: Durability and aging under miscellaneous environmentsHaider, Shamim; Lindbraathen, Arne; Lie, Jon A.; Hagg, May-BrittJournal of Industrial and Engineering Chemistry (Amsterdam, Netherlands) (2019), 70 (), 363-371CODEN: JIECFI; ISSN:1226-086X. (Elsevier B.V.)Predictive models regarding the aging effect on membrane sepn. properties are required to est. the membrane life time with acceptable permeability and selectivity for the resp. application. The current article is reporting an insight into this topic regarding the aging of regenerated cellulose-based carbon hollow fibers (CHF) mounted in a membrane module when they were exposed to real biogas in three different fields. CHF were exposed to biogas for almost one year with H2S content extending from 0 to 2400 ppm, and gas permeation tests for single gases, N2, CO2, CH4, and O2 were analyzed periodically at the membrane prodn. facility. CHF storage methods under misc. dry environments like air, vacuum, CO2, etc. were studied. The air flow through bore side of the CHF under controlled conditions had a regenerative effect on the membrane permeability, and the membrane performance was quite steady until after 150 days under lab. environment.
- 14Xu, L.; Rungta, M.; Hessler, J.; Qiu, W.; Brayden, M.; Martinez, M.; Barbay, G.; Koros, W. J. Physical Aging in Carbon Molecular Sieve Membranes. Carbon 2014, 80 (1), 155– 166, DOI: 10.1016/j.carbon.2014.08.05114Physical aging in carbon molecular sieve membranesXu, Liren; Rungta, Meha; Hessler, John; Qiu, Wulin; Brayden, Mark; Martinez, Marcos; Barbay, Gregory; Koros, William J.Carbon (2014), 80 (), 155-166CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)This paper considers phys. aging in carbon mol. sieve (CMS) membranes. Moreover, the performance of stabilized membranes under practical operating conditions is discussed. Phys. aging has been studied extensively in glassy polymers, but aging in CMS membranes has previously focused primarily on adsorption: either chemisorption of oxygen, or phys. adsorption of water and orgs. in the pore structures. Exptl., in this study, for the samples considered, all of the above adsorption-induced aging mechanisms were excluded as significant factors through thoughtful exptl. design. Phys. aging appears to be the primary cause for rapid changes of transport properties in early stages after membrane fabrication for samples derived from high fractional free vol. precursors. The CMS pores are believed to age analogously to the "unrelaxed free vol." in glassy polymers. Over time, these pores tend to shrink to achieve thermodynamically more stable states. Results of sorption tests in CMS also support the above hypothesis. The significance of phys. aging phenomena on membrane testing protocols, structural tailoring, and performance evaluation are discussed. A long-term permeation test demonstrated excellent stability of stabilized CMS membranes under realistic conditions.
- 15Ogieglo, W.; Furchner, A.; Ma, X.; Hazazi, K.; Alhazmi, A. T.; Pinnau, I. Thin Composite Carbon Molecular Sieve Membranes from a Polymer of Intrinsic Microporosity Precursor. ACS Appl. Mater. Interfaces 2019, 11 (20), 18770– 18781, DOI: 10.1021/acsami.9b0460215Thin Composite Carbon Molecular Sieve Membranes from a Polymer of Intrinsic Microporosity PrecursorOgieglo, Wojciech; Furchner, Andreas; Ma, Xiaohua; Hazazi, Khalid; Alhazmi, Abdulrahman T.; Pinnau, IngoACS Applied Materials & Interfaces (2019), 11 (20), 18770-18781CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Ultra-thin composite carbon mol. sieve (CMS) membranes were fabricated on well-defined inorg. alumina substrates using a polymer of intrinsic microporosity (PIM) as a precursor. Details of the pyrolysis-related structural development were elucidated using focused-beam, interference-enhanced spectroscopic ellipsometry (both in the UV-vis and IR range), which allowed accurate detn. of the film thickness, optical properties as well as following the chem. transformations. The pyrolysis-induced collapse of thin and bulk PIM-derived CMS membranes was compared with CMS made from a well-known non-PIM precursor 6FDA-DABA. Significant differences between the PIM and non-PIM precursors were discovered and explained by a much larger possible vol. contraction in the PIM. In spite of the differences, surprisingly, the gas sepn. properties did not fundamentally differ. The high-temp. collapse of the initially amorphous and isotropic precursor structure was accompanied by a significant mol. orientation within the formed turbostratic carbon network guided by the laterally constraining presence of the substrate. This manifested itself in the development of uniaxial optical anisotropy, which was shown to correlate with increases in gas sepn. selectivity for multiple technol. important gas pairs. Redn. of CMS skin thickness significantly below ∼1 μm induced large losses in permeability coeffs. with only small to moderate effects on selectivity. Remarkably, skin thickness redn. and phys. aging seemed to superimpose onto the same trend, which explains and strengthens some of the earlier fundamental insights.
- 16Huang, Y.; Paul, D. R. Experimental Methods for Tracking Physical Aging of Thin Glassy Polymer Films by Gas Permeation. J. Membr. Sci. 2004, 244 (1–2), 167– 178, DOI: 10.1016/j.memsci.2004.06.05816Experimental methods for tracking physical aging of thin glassy polymer films by gas permeationHuang, Y.; Paul, D. R.Journal of Membrane Science (2004), 244 (1-2), 167-178CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)This paper describes methodologies that have been developed for studying the phys. aging of free-standing thin polymer films and its effect on gas permeability. Both soln. casting and spin coating methods were used to obtain thin polysulfone films having thicknesses in the range of 400-1000 nm. Ellipsometry has been employed to det. the thicknesses of these thin films. A thin wire frame was used to hold the thin free-standing films while heating above Tg to relax mol. orientation and to erase the ambiguous thermal history resulting from soln. casting. The film underwent a significant thickness change during heating above Tg as the polymer chains relaxed. By using the method of this study, the reproducibility of gas permeability change during phys. aging was demonstrated as well as the thermoreversibility of phys. aging. Comparison of the results obtained by using different methods to support the thin film during heating illustrated the preference for the free-standing scheme developed in this study.
- 17Huang, Y.; Paul, D. R. Physical Aging of Thin Glassy Polymer Films Monitored by Gas Permeability. Polymer 2004, 45 (25), 8377– 8393, DOI: 10.1016/j.polymer.2004.10.01917Physical aging of thin glassy polymer films monitored by gas permeabilityHuang, Y.; Paul, D. R.Polymer (2004), 45 (25), 8377-8393CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)The phys. aging at 35°C of three glassy polymers, polysulfone, a polyimide and poly(2,6-dimethyl-1,4-phenylene oxide), has been tracked by measurement of the permeation of three gases, O2, N2, and CH4, for over 200 days. Several techniques were used to accurately det. the thickness of films (∼400 nm-62 μm) in order to obtain abs. permeability coeffs. and to study the effects of film thickness on the rate of phys. aging. Each film was heated above the polymer Tg to set the aging clock to time zero; ellipsometry revealed that this procedure leads to isotropic films having initial characteristics independent of film thickness. A substantial pronounced aging response, attributed to a decrease in polymer free vol., was obsd. at temps. more than 150 °C below Tg for thin films of each polymer compared to what is obsd. for the bulk polymers. The films with thicknesses of approx. 400 nm of the three polymers exhibit an oxygen permeability decrease by as much as two-fold or more and about 14-15% increase in O2/N2 selectivity at an aging time of 1000 h. The results obtained in this study were compared with prior work on thickness dependent aging. The effects of crystallinity on phys. aging were examd. briefly.
- 18Xia, J.; Chung, T. S.; Li, P.; Horn, N. R.; Paul, D. R. Aging and Carbon Dioxide Plasticization of Thin Polyetherimide Films. Polymer 2012, 53 (10), 2099– 2108, DOI: 10.1016/j.polymer.2012.03.00918Aging and carbon dioxide plasticization of thin polyetherimide filmsXia, Jianzhong; Chung, Tai-Shung; Li, Pei; Horn, Norman R.; Paul, D. R.Polymer (2012), 53 (10), 2099-2108CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)Industrial gas sepn. membranes have selective dense layers with thicknesses around 100 nm. It has long been assumed that these thin layers have the same properties as thick (bulk) films. However, recent research has shown that thin films with such thickness experience accelerated phys. aging relative to bulk films and, thus, their permeation properties can differ significantly from the bulk. Thin films made from Extem XH 1015, a new com. polyetherimide, have been investigated by monitoring their gas permeability. The permeability of the thin films is originally greater than the thick films but eventually decreases well below the permeability of the thick film. The CO2 plasticization of Extem thin films is explored using a series of exposure protocols that indicate CO2 plasticization is a function of film thickness, aging time, exposure time, pressure and prior history.
- 19Horn, N. R.; Paul, D. R. Carbon Dioxide Sorption and Plasticization of Thin Glassy Polymer Films Tracked by Optical Methods. Macromolecules 2012, 45 (6), 2820– 2834, DOI: 10.1021/ma300177k19Carbon Dioxide Sorption and Plasticization of Thin Glassy Polymer Films Tracked by Optical MethodsHorn, Norman R.; Paul, D. R.Macromolecules (Washington, DC, United States) (2012), 45 (6), 2820-2834CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)Our previous publications have demonstrated that thin glassy polymer films respond to highly sorbing penetrants, such as CO2, quite differently than thick films. These studies focused on CO2 permeation behavior and revealed that, for thin films, CO2 permeability at const. CO2 pressure goes through a max. followed by a continual decrease in permeability owing to phys. aging. So far, thick and thin glassy polymer films have been compared in the context of permeability, but lack of substantial means of obtaining thin film sorption data has prevented adequate comparison of thick and thin films in the context of gas soly. In this paper, spectroscopic ellipsometry is used to obtain simultaneously the film thickness and CO2 sorption capacity for thin glassy polymer films. This allows a more comprehensive look at CO2 permeability, sorption, and diffusivity as a function of both CO2 pressure and exposure time. The evidence reported here suggests that thin film sorption behavior is substantially different than that of thick film counterparts. Partial molar volume is detd. from sorption-induced swelling data. Fractional free vol. and diffusivity are calcd. as a function of CO2 pressure. Dual sorption model parameters are presented for Matrimid thin films for different aging times. Dynamic ellipsometry expts. show that refractive index min., fractional free vol. maxima, and CO2 diffusivity maxima correlate well with obsd. CO2 permeability maxima obsd. for thin Matrimid films. The results support the claim that plasticization and phys. aging are competing processes but that aging dominates over long time scales. The CO2 diffusivity behavior over time is most affected by the competing effects of plasticization and aging, and the evolution of CO2 diffusivity is shown to be the main contributing factor to changes in CO2 permeability at const. pressure.
- 20Ogieglo, W.; Tempelman, K.; Napolitano, S.; Benes, N. E. Evidence of a Transition Layer between the Free Surface and the Bulk. J. Phys. Chem. Lett. 2018, 9 (6), 1195– 1199, DOI: 10.1021/acs.jpclett.8b0007620Evidence of transition layer between free surface and bulkOgieglo, Wojciech; Tempelman, Kristianne; Napolitano, Simone; Benes, Nieck E.Journal of Physical Chemistry Letters (2018), 9 (6), 1195-1199CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The free surface, a very thin layer at the interface between polymer and air, is considered the main source of the perturbations in the properties of ultrathin polymer films, i.e., nanoconfinement effects. The structural relaxation of such a layer is decoupled from the mol. dynamics of the bulk. The free surface is, in fact, able to stay liq. even below the temp. where the polymer resides in the glassy state. Importantly, this surface layer is expected to have a very sharp interface with the underlying bulk. Here, by analyzing the penetration of n-hexane into polystyrene films, we report on the existence of a transition region, not obsd. by previous investigations, extending for 12 nm below the free surface. The presence of such a layer permits reconciling the behavior of interfacial layers with current models and has profound implications on the performance of ultrathin membranes. We show that the expected increase in the flux of the permeating species is actually overruled by nanoconfinement.
- 21Ogieglo, W.; Wessling, M.; Benes, N. E. Polymer Relaxations in Thin Films in the Vicinity of a Penetrant- or Temperature-Induced Glass Transition. Macromolecules 2014, 47 (11), 3654– 3660, DOI: 10.1021/ma500270721Polymer Relaxations in Thin Films in the Vicinity of a Penetrant- or Temperature-Induced Glass TransitionOgieglo, Wojciech; Wessling, Matthias; Benes, Nieck E.Macromolecules (Washington, DC, United States) (2014), 47 (11), 3654-3660CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)The transient properties of thin glassy polymer films in the vicinity of the glass transition are investigated. We compare the differences and similarities between sorption and temp.-induced glass transitions, referred to as Pg and Tg, resp. The exptl. technique used is in situ spectroscopic ellipsometry, which allows for a very precise dynamic measurement of the changes in the thickness and the refractive index of the thin films. It is shown that significant differences exist between the penetrant- and temp.-induced transitions. The Tg is relatively well-defined with a sharp change in polymer dynamics, causing a well-known curvature change, a kink, in the dilation curve. In contrast, the relaxations in the vicinity of Pg do not show a sharp change. In particular, the large degree of matrix deformation assocd. with the Pg may actuate addnl. relaxation processes that are not probed during transversing the glass transition via temp. scans. The interplay between various polymer relaxation modes can even lead to a slope change, a kink, in the dilation curve that cannot be interpreted as true glass transition. In fact, significant polymer relaxations are manifested upon slight desorption of penetrants from an excessively swollen system, which can be considered a quasi-equil. liq. The important practical implications of the findings are discussed.
- 22Lock, S. S. M.; Lau, K. K.; Shariff, A. M.; Yeong, Y. F.; Ahmad, F. Mathematical Modelling of Thickness and Temperature Dependent Physical Aging to O2/N2 Gas Separation in Polymeric Membranes. RSC Adv. 2018, 8 (53), 30265– 30279, DOI: 10.1039/C8RA05323E22Mathematical modelling of thickness and temperature dependent physical aging to O2/N2 gas separation in polymeric membranesLock, S. S. M.; Lau, K. K.; Shariff, A. M.; Yeong, Y. F.; Ahmad, FaizanRSC Advances (2018), 8 (53), 30265-30279CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)Polymeric membranes are glassy materials at non-equil. state and inherently undergo a spontaneous evolution towards equil. known as phys. aging. Vol. relaxation characteristic during the course of aging is governed by the surrounding temp. in which the polymeric material is aged. Although there are studies to understand how polymeric materials evolve over time towards equil. at different operating temps., the theories have been developed merely in response to exptl. observations and phenomenol. theory at bulk glassy state without the implementation of sample size effects. Limited work has been done to characterize the phys. aging process to thin polymeric films using reasonable phys. parameters and math. models with incorporation of thermodn. and film thickness consideration. The current work applies the Tait equation of states and thickness dependent glass transition temp., integrated within a simple linear correlation, to model the temp. and thickness dependent phys. aging. The math. model has been validated with exptl. aging data, whereby a small deviation is obsd. that has been explained by intuitive reasoning pertaining to the thermodn. parameters. The math. model has been further employed to study the gas transport properties of O2 and N2, which is anticipated to be applied in oxygen enriched combustion for generation of cleaner and higher efficiency fuel in future work.
- 23Tiwari, R. R.; Jin, J.; Freeman, B. D.; Paul, D. R. Physical Aging, CO2 Sorption and Plasticization in Thin Films of Polymer with Intrinsic Microporosity (PIM-1). J. Membr. Sci. 2017, 537 (1), 362– 371, DOI: 10.1016/j.memsci.2017.04.06923Physical aging, CO2 sorption and plasticization in thin films of polymer with intrinsic microporosity (PIM-1)Tiwari, Rajkiran R.; Jin, Jianyong; Freeman, B. D.; Paul, D. R.Journal of Membrane Science (2017), 537 (), 362-371CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)Phys. aging of both thick and thin films of "high free-vol." glassy polymer, PIM-1 (polymer with intrinsic microporosity) was studied by monitoring changes in pure gas permeability of O2, N2 and CH4 at a fixed temp. of 35 °C. Permeability of PIM-1 is very sensitive to film thickness, post-treatment (methanol soak, water soak or dried) and casting solvent (chloroform and ortho-dichlorobenzene). Thin films of PIM-1 undergo accelerated aging, leading to initial permeability lower by an order of magnitude compared to thick films. The relative permeability for thin films of PIM-1 was decreased by 67% compared to 53% decrease for thick films at 1000 h of aging due to the higher aging rates in thin films. The effect of casting solvent (vapor pressure and b.p.) is more pronounced on aging and selectivity of thin films with initial permeability almost two times higher for the film casted from chloroform (CHCl3) compared to that prepd. from ortho-dichlorobenzene (o-DCB) solvent. The effect of casting solvent on the initial permeability is less prominent for thick films. The film thickness, casting solvent and CO2 exposure protocols also have significant effect on the abs. CO2 permeability and plasticization behavior of both thick and thin films. The thin films undergo significant increase in the relative permeability upon plasticization compared to thick films and permeability was found to increase even during CO2 depressurization. The long time, const. pressure CO2 exposure study revealed dominant aging effect in thin film where aging overcomes the CO2 plasticization effect just within 1.2 min of the CO2 exposure compared to 10 h for thick film. The ellipsometry measurements showed that the CO2 soly. in thin films decreases with increases in the aging time and temp., and with decrease in the mol. wt. A strong correlation was obsd. for the Langmuir sorption capacity, CH' and soly. at infinite diln., S0 with the aging time, temp. and mol. wt. of PIM-1.
- 24Kappert, E. J.; Raaijmakers, M. J. T.; Tempelman, K.; Cuperus, F. P.; Ogieglo, W.; Benes, N. E. Swelling of 9 Polymers Commonly Employed for Solvent-Resistant Nanofiltration Membranes: A Comprehensive Dataset. J. Membr. Sci. 2019, 569, 177– 199, DOI: 10.1016/j.memsci.2018.09.05924Swelling of 9 polymers commonly employed for solvent-resistant nanofiltration membranes: A comprehensive datasetKappert, Emiel J.; Raaijmakers, Michiel J. T.; Tempelman, Kristianne; Cuperus, F. Petrus; Ogieglo, Wojciech; Benes, Nieck E.Journal of Membrane Science (2019), 569 (), 177-199CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)The presence of a solvent in a dense polymeric nanofiltration membrane layer can affect the macromol. dynamics of the polymer material and the mobility of the solvent penetrant mols. In addn., even the affinity of the swollen material for the solvent mols. can be distinct from that of the pure polymer material. These effects can substantially affect the membrane's performance. This paper provides sorption and swelling data of 9 thin polymer films that are commonly used for org. solvent nanofiltration (P84, Matrimid, PEI, PAN, PES, PSf, PEBAX, PTMSP, PDMS) swollen by 10 common solvents (hexane, toluene, dichloromethane, Et acetate, Me Et ketone, acetone, isopropanol, ethanol, methanol, water). The paper describes the swelling dynamics during short-term solvent exposure (0-8 h), assesses the stability upon long-term solvent exposure (up to 2 mo), and provides quant. data on the solvent vol. fractions inside the swollen layers. Among the surprising findings are the glubbery behavior of PTMSP and the completely different response of PES and PSf to toluene exposure. The results of this work demonstrate three crucial findings relevant to org. solvent nanofiltration membranes and other applications:For many polymers, the swelling changes over long timescales of up to 2 mo and longer. Results obtained on short timescales do however not always allow for direct extrapolation to longer time scales. Structural similarity of polymers does not guarantee similar swelling behavior. Swelling behavior of solvents cannot be solely explained by classifying solvents into aprotic, polar aprotic and polar protic solvents. The results of this work can aid in constructing transport models and can help predicting polymer-solvent compatibility and membrane performance in OSN applications.
- 25Ogieglo, W.; Rahimi, K.; Rauer, S. B.; Ghanem, B.; Ma, X.; Pinnau, I.; Wessling, M. How Do Organic Vapors Swell Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1?. J. Phys. Chem. B 2017, 121 (29), 7210– 7220, DOI: 10.1021/acs.jpcb.7b0389125How Do Organic Vapors Swell Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1?Ogieglo, Wojciech; Rahimi, Khosorov; Rauer, Sebastian Bernhard; Ghanem, Bader; Ma, Xiaohua; Pinnau, Ingo; Wessling, MatthiasJournal of Physical Chemistry B (2017), 121 (29), 7210-7220CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)Dynamic sorption of ethanol and toluene vapor into ultra-thin supported PIM-1 films down to 6 nm are studied with a combination of in-situ spectroscopic ellipsometry and in-situ X-ray reflectivity. Both ethanol and toluene significantly swell the PIM-1 matrix and, at the same time, induce persistent structural relaxations of the frozen-in glassy PIM-1 morphol. For ethanol below 20 nm three effects were identified. First, the swelling magnitude at high vapor pressures is reduced by about 30% as compared to thicker films. Second, at low penetrant activities (below 0.3 p/p0) films below 20 nm are able to absorb slightly more penetrant as compared with thicker films despite similar swelling magnitude. Third, for the ultra-thin films the onset of the dynamic penetrant-induced glass transition Pg has been found to shift to higher values indicating higher resistance to plasticization. All of these effects are consistent with a view where immobilization of the super-glassy PIM-1 at the substrate surface leads to an arrested, even more rigid and plasticization-resistant, yet still very open, microporous structure. PIM-1 in contact with the larger and more condensable toluene shows very complex, heterogeneous swelling dynamics and two distinct penetrant-induced relaxation phenomena, probably assocd. with the film outer surface and the bulk, are detected. Following the direction of the penetrant's diffusion the surface seems to plasticize earlier than the bulk and the two relaxations remain well sepd. down to 6 nm film thickness, where they remarkably merge to form just a single relaxation.
- 26Lively, R. P.; Sholl, D. S. From Water to Organics in Membrane Separations: Membrane Materials Provide Economical Means to Achieve Various Separation Processes - And Their Capabilities for Processing Organic Fluids Look Set to Expand Significantly. Nat. Mater. 2017, 16 (3), 276– 279, DOI: 10.1038/nmat486026From water to organics in membrane separationsLively, Ryan P.; Sholl, David S.Nature Materials (2017), 16 (3), 276-279CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Membrane materials provide economical means to achieve various sepn. processes - and their capabilities for processing org. fluids look set to expand significantly.
- 27Cui, Y.; Chung, T.-S. Pharmaceutical Concentration Using Organic Solvent Forward Osmosis for Solvent Recovery. Nat. Commun. 2018, 9 (1), 1– 9, DOI: 10.1038/s41467-018-03612-227miRNA-mediated TUSC3 deficiency enhances UPR and ERAD to promote metastatic potential of NSCLCJeon, Young-Jun; Kim, Taewan; Park, Dongju; Nuovo, Gerard J.; Rhee, Siyeon; Joshi, Pooja; Lee, Bum-Kyu; Jeong, Johan; Suh, Sung-suk; Grotzke, Jeff E.; Kim, Sung-Hak; Song, Jieun; Sim, Hosung; Kim, Yonghwan; Peng, Yong; Jeong, Youngtae; Garofalo, Michela; Zanesi, Nicola; Kim, Jonghwan; Liang, Guang; Nakano, Ichiro; Cresswell, Peter; Nana-Sinkam, Patrick; Cui, Ri; Croce, Carlo M.Nature Communications (2018), 9 (1), 1-13CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)Non-small cell lung carcinoma (NSCLC) is leading cause of cancer-related deaths in the world. The Tumor Suppressor Candidate 3 (TUSC3) at chromosome 8p22 known to be frequently deleted in cancer is often found to be deleted in advanced stage of solid tumors. However, the role of TUSC3 still remains controversial in lung cancer and context-dependent in several cancers. Here we propose that miR-224/-520c-dependent TUSC3 deficiency enhances the metastatic potential of NSCLC through the alteration of three unfolded protein response pathways and HRD1-dependent ERAD. ATF6α-dependent UPR is enhanced whereas the affinity of HRD1 to its substrates, PERK, IRE1α and p53 is weakened. Consequently, the alteration of UPRs and the suppressed p53-NM23H1/2 pathway by TUSC3 deficiency is ultimately responsible for enhancing metastatic potential of lung cancer. These findings provide mechanistic insight of unrecognized roles of TUSC3 in cancer progression and the oncogenic role of HRD1-dependent ERAD in cancer metastasis.
- 28Li, B.; Japip, S.; Chung, T. S. Molecularly Tunable Thin-Film Nanocomposite Membranes with Enhanced Molecular Sieving for Organic Solvent Forward Osmosis. Nat. Commun. 2020, 11 (1), 1– 10There is no corresponding record for this reference.
- 29Ma, X.; Ghanem, B.; Salines, O.; Litwiller, E.; Pinnau, I. Synthesis and Effect of Physical Aging on Gas Transport Properties of a Microporous Polyimide Derived from a Novel Spirobifluorene-Based Dianhydride. ACS Macro Lett. 2015, 4 (2), 231– 235, DOI: 10.1021/acsmacrolett.5b0000929Synthesis and Effect of Physical Aging on Gas Transport Properties of a Microporous Polyimide Derived from a Novel Spirobifluorene-Based DianhydrideMa, Xiaohua; Ghanem, Bader; Salines, Octavio; Litwiller, Eric; Pinnau, IngoACS Macro Letters (2015), 4 (2), 231-235CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)A novel generic method is reported for the synthesis of a spirobifluorene-based dianhydride (SBFDA). An intrinsically microporous polyimide was obtained by polycondensation reaction with 3,3'-dimethylnaphthidine (DMN). The corresponding polymer (SBFDA-DMN) exhibited good soly., excellent thermal stability, as well as significant microporosity with high BET surface area of 686 m2/g. The O2 permeability of a methanol-treated and air-dried membrane was 1193 Barrer with a moderate O2/N2 selectivity of 3.2. The post-treatment history and aging conditions had great effects on the membrane performance. A significant drop in permeability coupled with an increase in selectivity was obsd. after long-term aging. After storage of 200 days, the gas sepn. properties of SBFDA-DMN were located slightly above the latest Robeson upper bounds for several gas pairs such as O2/N2 and H2/N2.
- 30Hatori, H.; Yamada, Y.; Shiraishi, M. In-Plane Orientation and Graphitizability of Polyimide Films: II. Film Thickness Dependence. Carbon 1993, 31 (8), 1307– 1312, DOI: 10.1016/0008-6223(93)90090-W30In-plane orientation and graphitizability of polyimide films. II. Film thickness dependenceHatori, H.; Yamada, Y.; Shiraishi, M.Carbon (1993), 31 (8), 1307-12CODEN: CRBNAH; ISSN:0008-6223.The relation between the in-plane orientation of polyimide film and graphitizability was investigated. The degree of in-plane orientation was estd. by means of optical birefringence and ESR technique. The polyimide film had nonuniform orientation in the thickness direction because the thinner the film was, the greater the orientation. The inhomogeneity of orientation caused multiphase graphitization in a film with a composite profile of the X-ray diffraction peak.
- 31Johs, B.; Hale, J. S. Dielectric Function Representation by B-Splines. Phys. Status Solidi A 2008, 205 (4), 715– 719, DOI: 10.1002/pssa.20077775431Dielectric function representation by B-splinesJohs, Blaine; Hale, Jeffrey S.Physica Status Solidi A: Applications and Materials Science (2008), 205 (4), 715-719CODEN: PSSABA; ISSN:1862-6300. (Wiley-VCH Verlag GmbH & Co. KGaA)Accurate dielec. function values are essential for spectroscopic ellipsometry data anal. by traditional optical model-based anal. techniques. In this paper, we show that B-spline basis functions offer many advantages for parameterizing dielec. functions. A Kramers-Kronig consistent B-spline formulation, based on the std. B-spline recursion relation, is derived. B-spline representations of typical semiconductor and metal dielec. functions are also presented.
- 32Ogieglo, W.; Ghanem, B.; Ma, X.; Wessling, M.; Pinnau, I. High-Pressure CO2 Sorption in Polymers of Intrinsic Microporosity under Ultrathin Film Confinement. ACS Appl. Mater. Interfaces 2018, 10 (13), 11369– 11376, DOI: 10.1021/acsami.8b0140232High-Pressure CO2 Sorption in Polymers of Intrinsic Microporosity under Ultrathin Film ConfinementOgieglo, Wojciech; Ghanem, Bader; Ma, Xiaohua; Wessling, Matthias; Pinnau, IngoACS Applied Materials & Interfaces (2018), 10 (13), 11369-11376CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Ultrathin microporous polymer films are pertinent to the development and further spread of nanotechnol. with very promising potential applications in mol. sepns., sensors, catalysis, or batteries. Here, we report high-pressure CO2 sorption in ultrathin films of several chem. different polymers of intrinsic microporosity (PIMs), including the prototypical PIM-1. Films with thicknesses down to 7 nm were studied using interference-enhanced in situ spectroscopic ellipsometry. It was found that all PIMs swell much more than non-microporous polystyrene and other high-performance glassy polymers reported previously. Furthermore, chem. modifications of the parent PIM-1 strongly affected the swelling magnitude. By investigating the behavior of relative refractive index, nrel, it was possible to study the interplay between micropores filling and matrix expansion. Remarkably, all studied PIMs showed a max. in nrel at swelling of 2-2.5% indicating a threshold point above which the dissoln. in the dense matrix started to dominate over sorption in the micropores. At pressures above 25 bar, all PIMs significantly plasticized in compressed CO2 and for the ones with the highest affinity to the penetrant, a liquidlike mixing typical for rubbery polymers was obsd. Redn. of film thickness below 100 nm revealed pronounced nanoconfinement effects and resulted in a large swelling enhancement and a quick loss of the ultrarigid character. On the basis of the partial molar volumes of the dissolved CO2, the effective redn. of the Tg was estd. to be ∼200 °C going from 128 to 7 nm films.
- 33Ogieglo, W.; Furchner, A.; Ghanem, B.; Ma, X.; Pinnau, I.; Wessling, M. Mixed-Penetrant Sorption in Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1. J. Phys. Chem. B 2017, 121 (43), 10190– 10197, DOI: 10.1021/acs.jpcb.7b1006133Mixed-Penetrant Sorption in Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1Ogieglo, Wojciech; Furchner, Andreas; Ghanem, Bader; Ma, Xiaohua; Pinnau, Ingo; Wessling, MatthiasJournal of Physical Chemistry B (2017), 121 (43), 10190-10197CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)Mixed-penetrant sorption into ultrathin films of a superglassy polymer of intrinsic microporosity (PIM-1) was studied for the first time by using interference-enhanced in situ spectroscopic ellipsometry. PIM-1 swelling and the concurrent changes in its refractive index were detd. in ultrathin (12-14 nm) films exposed to pure and mixed penetrants. The penetrants included water, n-hexane, and ethanol and were chosen on the basis of their significantly different penetrant-penetrant and penetrant-polymer affinities. This allowed studying microporous polymer responses at diverse ternary compns. and revealed effects such as competition for the sorption sites (for water/n-hexane or ethanol/n-hexane) or enhancement in sorption of typically weakly sorbing water in the presence of more highly sorbing ethanol. The results reveal details of the mutual sorption effects which often complicate comprehension of glassy polymers' behavior in applications such as high-performance membranes, adsorbents, or catalysts. Mixed-penetrant effects are typically very challenging to study directly, and their understanding is necessary owing to a broadly recognized inadequacy of simple extrapolations from measurements in a pure component environment.
- 34Sirard, S. M.; Green, P. F.; Johnston, K. P. Spectroscopic Ellipsometry Investigation of the Swelling of Poly(Dimethylsiloxane) Thin Films with High Pressure Carbon Dioxide. J. Phys. Chem. B 2001, 105 (4), 766– 772, DOI: 10.1021/jp002592d34Spectroscopic Ellipsometry Investigation of the Swelling of Poly(Dimethylsiloxane) Thin Films with High Pressure Carbon DioxideSirard, S. M.; Green, P. F.; Johnston, K. P.Journal of Physical Chemistry B (2001), 105 (4), 766-772CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)The thickness and refractive index of poly(dimethylsiloxane) (PDMS) thin films on silicon, exposed to high-pressure carbon dioxide, have been measured in-situ by spectroscopic ellipsometry. The swelling of the film is detd. from the thickness and the sorption of CO2 from the refractive index. The sorption and swelling values for the thin films exceed those of the bulk films. These increases may be attributed to excess CO2 at the polymer thin film-CO2 and polymer-silica interfaces and the influence of the silica surface and CO2 on the orientation of the polymer. Pressure-induced birefringence of the fused-silica windows was addressed in the model calcns. and corrections were successful for a thermal oxide ref. wafer and the PDMS films. Large surface excesses of CO2 on the ref. wafer were obsd. in regions where CO2 is highly compressible due to crit. adsorption.
- 35Ogieglo, W.; Wormeester, H.; Wessling, M.; Benes, N. E. Effective Medium Approximations for Penetrant Sorption in Glassy Polymers Accounting for Excess Free Volume. Polymer 2014, 55 (7), 1737– 1744, DOI: 10.1016/j.polymer.2014.02.04035Effective medium approximations for penetrant sorption in glassy polymers accounting for excess free volumeOgieglo, Wojciech; Wormeester, Herbert; Wessling, Matthias; Benes, Nieck E.Polymer (2014), 55 (7), 1737-1744CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)An accurate detn. of a penetrant vol. fraction in a swollen polymer is of crucial importance in a range of different technologies. Using optical methods, such as in-situ spectroscopic ellipsometry, it is possible to ext. the thickness and refractive index of dry and swollen polymer films. The vol. fraction of the penetrant can then be calcd. from the change in thickness, or from the refractive index using effective medium approxns. For thermodynamically equilibrated and ideal swollen rubbery polymers, these calcns. yield accurate results. However, for glassy polymers the influence of the excess free vol. trapped within the polymer network during vitrification is rarely taken into account. In this work we investigate the effect of excess free vol. in the calcns. of penetrant vol. fraction in a model glassy polymer - penetrant system. The influence of the excess free vol. is included by extrapolating the properties of an equil. polymer matrix from above its glass transition temp. The error between the approaches that do, and do not, take account for the non-equil. of the glassy polymer is quantified and the implications for other systems are discussed. The errors are shown to be very significant, esp. when the dry polymer has a large excess free vol. Such materials are particularly relevant in membrane applications.
- 36Ogieglo, W.; Genduso, G.; Rubner, J.; Hofmann-Preveraud de Vaumas, J.; Wessling, M.; Pinnau, I. CO2/CH4 Pure- And Mixed-Gas Dilation and Sorption in Thin (∼500 nm) and Ultrathin (∼50 nm) Polymers of Intrinsic Microporosity. Macromolecules 2020, 53 (20), 8765– 8774, DOI: 10.1021/acs.macromol.0c0116336CO2/CH4 Pure- and Mixed-Gas Dilation and Sorption in Thin (∼ 500 nm) and Ultrathin (∼ 50 nm) Polymers of Intrinsic MicroporosityOgieglo, Wojciech; Genduso, Giuseppe; Rubner, Jens; Hofmann-Preveraud de Vaumas, Jacques; Wessling, Matthias; Pinnau, IngoMacromolecules (Washington, DC, United States) (2020), 53 (20), 8765-8774CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)In this work, we present (i) the dilation and refractive index variation assocd. with changes in film d. and (ii) gas uptake of pure CO2 and CH4, as well as their equimolar mixt. in thin films of two polymers of intrinsic microporosity (PIMs), i.e., PIM-1 and poly(trimethylsilyl)propyne (PTMSP). A conventional low-free-vol. glassy polymer, cellulose triacetate, was also investigated as the ref. material. All expts. were performed with ~ 50 and ~ 500 nm-thick films up to partial pressures of 25 bar using in situ interference-enhanced spectroscopic ellipsometry. In all cases, film thickness redn. promoted the collapse of the frozen-in free vol. Particularly for thin PIM-1 and PTMSP films, the CO2 and CH4 pure-gas uptakes were generally lower than in bulk samples. In the most extreme case of the ultrathin ~ 50 nm PTMSP film, we could detect a strikingly similar qual. behavior to the penetrant partial molar volume and dilation in rubbery polymers. Remarkably, in PIM-1, the collapse of the frozen-in free vol. seemed to be opposed by its ultra-micropores (<7 Å), which was not the case in PTMSP with larger micropores (>10 Å). In mixed-gas expts., the refractive index response of all investigated films closely followed the trend obsd. during CO2 pure-gas sorption. In both thickness ranges and throughout the entire pressure range, the samples dilated less in the multicomponent environment than under the corresponding ideal pure-gas conditions. We found this phenomenon consistent with the pure- and mixed-gas uptake behavior of PIM-1 and PTMSP bulk films reported in the literature.
- 37Zhou, C.; Chung, T. S.; Wang, R.; Liu, Y.; Goh, S. H. The Accelerated CO2 Plasticization of Ultra-Thin Polyimide Films and the Effect of Surface Chemical Cross-Linking on Plasticization and Physical Aging. J. Membr. Sci. 2003, 225 (1–2), 125– 134, DOI: 10.1016/j.memsci.2003.07.00637The accelerated CO2 plasticization of ultra-thin polyimide films and the effect of surface chemical cross-linking on plasticization and physical agingZhou, Chun; Chung, Tai-Shung; Wang, Rong; Liu, Ye; Goh, Suat HongJournal of Membrane Science (2003), 225 (1-2), 125-134CODEN: JMESDO; ISSN:0376-7388. (Elsevier Science B.V.)For the first time, the permeation expts. of CO2 are carried out on ultra-thin dense polyimide films (0.5-1.8 μm). The observation of accelerated CO2 plasticization indicates that the conventionally defined "plasticization pressure" as an inherent material properties measured from thick dense films is strongly thickness dependent. This accelerated plasticization phenomenon obsd. in ultra-thin dense films is probably attributed to two factors: (1) the swelling and softening effects of the sorbing CO2 mols. on the polymer chains; and (2) weak micro-mech. properties and less sorption capacity of ultra-thin films to accommodate the sorbed CO2 mols. Exptl. results suggest that chem. modified ultra-thin films show characteristics of retarded aging process and significantly suppressed plasticization.
- 38Huang, Y.; Paul, D. R. Effect of Temperature on Physical Aging of Thin Glassy Polymer Films. Macromolecules 2005, 38 (24), 10148– 10154, DOI: 10.1021/ma051284g38Effect of Temperature on Physical Aging of Thin Glassy Polymer FilmsHuang, Y.; Paul, D. R.Macromolecules (2005), 38 (24), 10148-10154CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)The effect of temp. on the kinetics of phys. aging of thin films formed from two amorphous glassy polymers, polysulfone based on bisphenol A and poly(2,6-dimethyl-1,4-phenylene oxide), was investigated by monitoring the changes in gas permeability and refractive index. Films with different thicknesses were subjected to isothermal aging at three temps., ranging from 35 to 55 °C, for a period of aging of more than 200 days. The rate of permeability loss and the rate of densification detd. from the refractive index change by using the Lorentz-Lorenz equation were found to increase with aging temp. Similar qual. trends of aging rate were noted by the two measurements. The combination of effects of aging temp. and film thickness on aging behavior were studied and compared with previous research.
- 39Ogieglo, W.; Puspasari, T.; Ma, X.; Pinnau, I. Sub-100 nm Carbon Molecular Sieve Membranes from a Polymer of Intrinsic Microporosity Precursor: Physical Aging and near-Equilibrium Gas Separation Properties. J. Membr. Sci. 2020, 597, 117752, DOI: 10.1016/j.memsci.2019.11775239Sub-100 nm carbon molecular sieve membranes from a polymer of intrinsic microporosity precursor: Physical aging and near-equilibrium gas separation propertiesOgieglo, Wojciech; Puspasari, Tiara; Ma, Xiaohua; Pinnau, IngoJournal of Membrane Science (2020), 597 (), 117752CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)Here, ultra-thin, sub-100 nm carbon mol. sieve (CMS) membranes based on a polymer of intrinsic microporosity precursor were fabricated and characterized with respect to their sepn. performance for six gases, He, H2, N2, O2, CO2 and CH4. The rarely reported in thin CMS membranes phys. aging was tracked until near-equil. was reached. The use of com. available, small pore size γ-alumina-coated α-alumina ceramic supports allowed for an easy membrane precursor fabrication by a simple soln. coating process. The subsequent application of a protective polydimethylsiloxane layer assured excellent defect control and produced CMS composite membranes with very high membrane permselectivities (e.g. CO2/CH4 = 84.5, H2/CH4 = 360). However, a surprisingly massive acceleration of the phys. aging in comparison to the bulk was detected in all sub-100 nm membranes including the precursor polymer. All CMS membranes reached near-equil. gas transport properties within 1-1.5 mo providing a rare opportunity to study aging-stabilized performance. For the aging-stabilized sub-100 nm membranes a decrease in gas permeabilities of up to 3 orders of magnitude was detected. Overall, our study provides an important observation that excessive redn. of the selective layer thickness, esp. in initially highly microporous materials, may not present the best strategy for the optimization of the long-term membrane performance.
- 40Rowe, B. W.; Freeman, B. D.; Paul, D. R. Physical Aging of Ultrathin Glassy Polymer Films Tracked by Gas Permeability. Polymer 2009, 50 (23), 5565– 5575, DOI: 10.1016/j.polymer.2009.09.03740Physical aging of ultrathin glassy polymer films tracked by gas permeabilityRowe, Brandon W.; Freeman, Benny D.; Paul, Donald R.Polymer (2009), 50 (23), 5565-5575CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)Membrane-based sepns. play a key role in energy conservation and reducing greenhouse gas emissions by providing low energy routes for a wide variety of industrially-important sepns. For reasons not completely understood, membrane permeability changes with time, due to phys. aging, and the rate of permeability change can become orders of magnitude faster in films thinner than one micron. The gas transport properties and phys. aging behavior of free-standing glassy polysulfone and Matrimid films as thin as 18 nm are presented. Phys. aging persists in glassy films approaching the length scale of individual polymer coils. The films studied ranged from 18-550 nm thick. They exhibited redns. in gas permeability, some more than 50%, after ∼1000 h of aging at 35 °C, and increases in selectivity. The properties of these ultrathin films deviate dramatically from bulk behavior, and the nature of these deviations is consistent with enhanced mobility and reduced T g in ultrathin films. The Struik phys. aging model was extended to account for the influence of film thickness on aging rate, and it was shown to adequately describe the aging data.
- 41Ferrari, A. C.; Basko, D. M. Raman Spectroscopy as a Versatile Tool for Studying the Properties of Graphene. Nat. Nanotechnol. 2013, 8 (4), 235– 246, DOI: 10.1038/nnano.2013.4641Raman spectroscopy as a versatile tool for studying the properties of grapheneFerrari, Andrea C.; Basko, Denis M.Nature Nanotechnology (2013), 8 (4), 235-246CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)A review. Raman spectroscopy is an integral part of graphene research. It is used to det. the no. and orientation of layers, the quality and types of edge, and the effects of perturbations, such as elec. and magnetic fields, strain, doping, disorder and functional groups. This, in turn, provides insight into all sp2-bonded carbon allotropes, because graphene is their fundamental building block. Here we review the state of the art, future directions and open questions in Raman spectroscopy of graphene. We describe essential phys. processes whose importance has only recently been recognized, such as the various types of resonance at play, and the role of quantum interference. We update all basic concepts and notations, and propose a terminol. that is able to describe any result in literature. We finally highlight the potential of Raman spectroscopy for layered materials other than graphene.
- 42Ferrari, A.; Robertson, J. Interpretation of Raman Spectra of Disordered and Amorphous Carbon. Phys. Rev. B: Condens. Matter Mater. Phys. 2000, 61 (20), 14095– 14107, DOI: 10.1103/PhysRevB.61.1409542Interpretation of Raman spectra of disordered and amorphous carbonFerrari, A. C.; Robertson, J.Physical Review B: Condensed Matter and Materials Physics (2000), 61 (20), 14095-14107CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)The model and theor. understanding of the Raman spectra in disordered and amorphous C are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of π states and the long-range polarizability of π bonding. Visible Raman data on disordered, amorphous, and diamondlike C are classified in a 3-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. The visible Raman spectra depend formally on the configuration of the sp2 sites in sp2-bonded clusters. In cases where the sp2 clustering is controlled by the sp3 fraction, such as in as-deposited tetrahedral amorphous C (ta-C) or hydrogenated amorphous C (a-C:H) films, the visible Raman parameters can be used to derive the sp3 fraction.
- 43Casciardi, S.; Sisto, R.; Diociaiuti, M. The Analytical Transmission Electron Microscopy: A Powerful Tool for the Investigation of Low-Dimensional Carbon Nanomaterials. J. Nanomater. 2013, 2013, 1, DOI: 10.1155/2013/506815There is no corresponding record for this reference.
- 44Sirard, S. M.; Green, P. F.; Johnston, K. P. Spectroscopic Ellipsometry Investigation of the Swelling of Poly(dimethylsiloxane) Thin Films with High Pressure Carbon Dioxide. J. Phys. Chem. B 2001, 105 (4), 766– 772, DOI: 10.1021/jp002592d44Spectroscopic Ellipsometry Investigation of the Swelling of Poly(Dimethylsiloxane) Thin Films with High Pressure Carbon DioxideSirard, S. M.; Green, P. F.; Johnston, K. P.Journal of Physical Chemistry B (2001), 105 (4), 766-772CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)The thickness and refractive index of poly(dimethylsiloxane) (PDMS) thin films on silicon, exposed to high-pressure carbon dioxide, have been measured in-situ by spectroscopic ellipsometry. The swelling of the film is detd. from the thickness and the sorption of CO2 from the refractive index. The sorption and swelling values for the thin films exceed those of the bulk films. These increases may be attributed to excess CO2 at the polymer thin film-CO2 and polymer-silica interfaces and the influence of the silica surface and CO2 on the orientation of the polymer. Pressure-induced birefringence of the fused-silica windows was addressed in the model calcns. and corrections were successful for a thermal oxide ref. wafer and the PDMS films. Large surface excesses of CO2 on the ref. wafer were obsd. in regions where CO2 is highly compressible due to crit. adsorption.
- 45Simons, K.; Nijmeijer, K.; Sala, J. G.; van der Werf, H.; Benes, N. E.; Dingemans, T. J.; Wessling, M. CO2 Sorption and Transport Behavior of ODPA-Based Polyetherimide Polymer Films. Polymer 2010, 51 (17), 3907– 3917, DOI: 10.1016/j.polymer.2010.06.03145CO2 sorption and transport behavior of ODPA-based polyetherimide polymer filmsSimons, Katja; Nijmeijer, Kitty; Sala, Jordi Guilera; van der Werf, Hans; Benes, Nieck E.; Dingemans, Theo J.; Wessling, MatthiasPolymer (2010), 51 (17), 3907-3917CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)Plasticization phenomena can significantly reduce the performance of polymeric membranes in high-pressure applications. Polyetherimides (PEIs) are a promising group of membrane materials that combine relatively high CO2/CH4 selectivities with high chem. and thermal stability. In this work sorption, swelling, and mixed gas sepn. performance of 3,3',4,4'-oxydiphthalic dianhydride (ODPA)-based PEI polymers, with 1, 2 or 3 para-aryloxy substitutions in the diamine moiety, is investigated under conditions where com. membranes suffer from plasticization. Particular focus is on the influence of the amt. of para-aryloxy substitutions and the film thickness. Results are compared with those of com. available polymeric membrane materials (sulfonated PEEK, a segmented block-co-polymer PEBAX and the polyimide Matrimid). The glassy polymers display increasing CO2 sorption with increasing Tg. The larger extent of sorption results from a larger non-equil. excess free vol. Swelling of the polymers is induced by sorption of CO2 mols. in the non-equil. free vol. as well as from mols. dissolved in the matrix. Dilation of the polymer is similar for each mol. sorbed. Correspondingly, the partial molar volume of CO2 is similar for mols. present in both regions. Mixed gas sepn. expts. with a 50/50% CO2/CH4 feed gas mixt. showed high CO2/CH4 selectivities for the ODPA PEI films at elevated pressure. This shows that these materials could potentially be interesting for high-pressure gas sepn. applications, although addnl. gas permeation expts. using different feed gas compns. and thin films are required.
- 46Sanyal, O.; Hicks, S. T.; Bhuwania, N.; Hays, S.; Kamath, M. G.; Karwa, S.; Swaidan, R.; Koros, W. J. Cause and Effects of Hyperskin Features on Carbon Molecular Sieve (CMS) Membranes. J. Membr. Sci. 2018, 551, 113– 122, DOI: 10.1016/j.memsci.2018.01.02146Cause and effects of hyperskin features on carbon molecular sieve (CMS) membranesSanyal, Oishi; Hicks, Stephanie T.; Bhuwania, Nitesh; Hays, Samuel; Kamath, Manjeshwar G.; Karwa, Shweta; Swaidan, Raja; Koros, William J.Journal of Membrane Science (2018), 551 (), 113-122CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)This article considers a previously overlooked feature in carbon mol. sieve (CMS) membranes that we term a "hyperskin" present at the outermost region of dense CMS selective layers. Such a feature with much lower permeability, but similar selectivity compared to the bulk of the skin, reduces CMS hollow fiber permeance below that predicted from corresponding dense films. Effects of the hyperskin are considered for CMS hollow fibers with low skin thicknesses based on two polyimide precursors - Matrimid and 6FDA:BPDA-DAM. Although the fundamental formation mechanism for the hyperskin feature suggests its existence on virtually all CMS membranes, its impact on transport properties is shown to differ dramatically, depending on the detailed characteristic properties of the specific CMS membrane. Indeed, for hollow fibers with very low nominal resistance (i.e. ((SelectivelayerthicknessdeterminedbySEM)/(IntrinsicpermeabilityofthickdenseCMSfilms))), the obsd. permeance only reaches a small fraction of the predicted permeance. The selectivity between different gas penetrants, however, is not altered by the presence of this hyperskin. While identifying this issue is the major focus of this article, strategies to address this limitation, without compromising the mol. sieving properties of CMS membranes are briefly discussed.
Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.1c03392.
Thermogravimetric, volumetric, and density data for bulk powder and ∼70 μm films of the CMS precursor PIM-polyimide SBFDA-DMN (in comparison to another non-PIM polyimide); optical model fitting; kinetic data for an in situ ethanol swelling experiment; relative refractive index plotted as a function of swelling factor of thick and thin films; swelling factor plotted versus ethanol concentration; atomic force microscopy images; optical images; cross-sectional transmission electron microscopy images; and Raman spectra for both thick and thin films (PDF)
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