Time-Resolved Small-Angle X-ray Scattering Studies during Aqueous Emulsion Polymerization
- Adam Czajka*Adam Czajka*[email protected]Department of Chemistry, University of Sheffield, Dainton Building, Brook Hill, Sheffield S3 7HF, United KingdomMore by Adam Czajka
- and
- Steven P. Armes*Steven P. Armes*[email protected]Department of Chemistry, University of Sheffield, Dainton Building, Brook Hill, Sheffield S3 7HF, United KingdomMore by Steven P. Armes
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Abstract
The persulfate-initiated aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) is studied by time-resolved small-angle X-ray scattering (SAXS) at 60 °C using a stirrable reaction cell. TFEMA was preferred to styrene because it offers much greater X-ray scattering contrast relative to water, which is essential for sufficient temporal resolution. The evolution in particle size is monitored by both in situ SAXS and ex situ DLS in the absence or presence of an anionic surfactant (sodium dodecyl sulfate, SDS). Post-mortem SAXS studies confirmed the formation of well-defined spherical latexes, with volume-average diameters of 353 ± 9 nm and 68 ± 4 nm being obtained for the surfactant-free and SDS formulations, respectively. 1H NMR spectroscopy studies of the equivalent laboratory-scale formulations indicated TFEMA conversions of 99% within 80 min and 93% within 60 min for the surfactant-free and SDS formulations, respectively. Comparable polymerization kinetics are observed for the in situ SAXS experiments and the laboratory-scale syntheses, with nucleation occurring after approximately 6 min in each case. After nucleation, scattering patterns are fitted using a hard sphere scattering model to determine the evolution in particle growth for both formulations. Moreover, in situ SAXS enables identification of the three main intervals (I, II, and III) that are observed during aqueous emulsion polymerization in the presence of surfactant. These intervals are consistent with those indicated by solution conductivity and optical microscopy studies. Significant differences between the surfactant-free and SDS formulations are observed, providing useful insights into the mechanism of emulsion polymerization.
Introduction
ARTICLE SECTIONS
Aqueous emulsion polymerization is an environmentally friendly process that is widely used on an industrial scale to polymerize many water-immiscible vinyl monomers, including styrene, methacrylates, acrylates, vinyl acetate, vinyl chloride, etc. (1,2) Such heterophase polymerizations account for approximately 25% of synthetic polymers produced globally, (3) with tens of millions of tons of copolymer latexes being prepared each year. (3,4) Importantly, microcompartmentalization enables the efficient production of high molecular weight polymer chains in convenient low-viscosity form while offering good control over heat dissipation. (2,5−9) The resulting latex particles are used for many applications, including architectural paints, anticorrosion coatings, adhesives, varnishes, cement and concrete additives, rheology modifiers; they can also serve as the mobile phase for immunodiagnostic assays. (10)
Aqueous emulsion polymerizations are inherently heterogeneous in nature. Thus, such formulations usually require vigorous stirring to generate micrometer-sized monomer droplets. Such droplets act as reservoirs and provide a sufficiently high interfacial area to ensure efficient mass transport of the water-immiscible monomer to the growing particles during polymerization. Various in situ techniques have been utilized to monitor the kinetics of aqueous emulsion polymerization, including 1H NMR spectroscopy combined with a flow cell, (11) Raman spectroscopy, (12) and near-IR spectroscopy. (13,14) However, such studies do not enable the evolution in particle morphology to be assessed, hence they can provide only rather limited insights regarding the complex mechanism of emulsion polymerization. (2,15,16)
The kinetics of emulsion polymerization has been extensively studied. (6,17−19) The generally accepted mechanism comprises three distinct regions, which are denoted as Intervals I, II, and III (see Figure 1). (1,6−9,16,20−22) A typical batch emulsion polymerization formulation comprises a vinyl monomer of relatively low water solubility (e.g., styrene), water, surfactant, and a water-soluble initiator. Prior to polymerization, the hydrophobic monomer mainly resides in the monomer droplets, with a relatively small fraction solubilized within surfactant micelles and a further (minor) fraction dissolved within the aqueous continuous phase. Free radicals derived from the water-soluble initiator polymerize monomer dissolved in the aqueous phase to form oligomeric radicals. At some critical chain length, these oligomeric radicals become sufficiently hydrophobic to enter the monomer-swollen micelles, which vastly exceeds the monomer droplets in terms of both number density and overall interfacial area. (6,7) Further monomer then diffuses from the monomer droplets into these nascent particles and new polymer chains are initiated within the monomer-swollen particles, which continue to grow in size. To maintain colloidal stability, the remaining surfactant micelles undergo dissociation to supply additional surfactant and hence ensure monolayer coverage of the surface of the growing polymer particles. Furthermore, the surfactant molecules that act as an emulsifier desorb from the (shrinking) monomer droplets to coat these particles. Once there are no remaining surfactant micelles, particle nucleation (i.e., Interval I) is complete, see Figure 1a. Thereafter, the number of latex particles remains relatively constant. Polymerization continues primarily within monomer-swollen particles with monomer droplets serving as reservoirs to supply the growing particles with further monomer (and surfactant). This particle growth stage (Interval II, Figure 1b) is complete when there are no remaining monomer droplets. This leads to so-called “monomer-starved” conditions and the polymerization proceeds at a slower rate until all the monomer is consumed (Interval III, Figure 1c).
Figure 1
Figure 1. Representation of the three main intervals (I, II, and III) that occur during the aqueous emulsion polymerization of a water-immiscible monomer (e.g., styrene) in the presence of a surfactant above its critical micelle concentration. (2,9,16)
However, aqueous emulsion polymerization can also occur under surfactant-free conditions. (23−29) In this case, thermal decomposition of an ionic initiator (e.g., persulfate) generates charged water-soluble radicals that react with dissolved monomer within the aqueous phase. This generates a growing polymer radical with a terminal anionic sulfate group that becomes insoluble at some critical chain length to form a primary particle. These primary particles are colloidally unstable and thus undergo aggregation. The ensuing increase in surface charge density produces colloidally stable mature particle nuclei into which monomer can diffuse from the droplet reservoirs and/or the aqueous phase. Latexes prepared under surfactant-free conditions tend to be significantly larger than those prepared in the presence of surfactant, which has been attributed to a coagulative nucleation mechanism. (30)
Small-angle X-ray scattering (SAXS) is ideally suited for characterizing systems exhibiting multiple colloidal length scales. (31) Furthermore, using a synchrotron X-ray source ensures superb temporal resolution for in situ studies, thus providing unique insights into various phenomena, including particle formation and growth, (32) kinetics (33) and self-assembly. (34,35) Recently, we have demonstrated that time-resolved SAXS is a powerful technique for studying the evolution in block copolymer morphology that occurs during polymerization-induced self-assembly (PISA). (36−38) Herein we utilize our recently reported stirrable reaction cell (36) to conduct in situ SAXS studies during the free persulfate-initiated aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) at 60 °C. More specifically, we examined two formulations: one was conducted in the presence of an anionic surfactant (sodium dodecyl sulfate, SDS) while the other was performed under surfactant-free conditions, (23) (see Figure 2).
Figure 2
Figure 2. (a) Representation of the synthesis of PTFEMA latex particles formed via aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) using an anionic free radical initiator (potassium persulfate, KPS) at 60 °C either in the presence of an anionic surfactant (SDS) or under surfactant-free conditions targeting 5.0% w/w solids. (b) Schematic cross-section of the stirrable reaction cell used for time-resolved small-angle X-ray scattering (SAXS) studies of such formulations. The volume of the reaction solution within this cell is approximately 2.0 mL, which is sufficient to enable post-mortem analysis using 1H NMR spectroscopy, TEM, and dynamic light scattering.
Results and Discussion
ARTICLE SECTIONS
Preliminary Experiments
From an academic perspective, the most widely studied aqueous emulsion polymerization formulation involves the homopolymerization of styrene. (39−42) Although the glass transition temperature of polystyrene is too high for paints and coatings applications, polystyrene latexes are widely used as calibration standards for particle size analysis (43) and for visual agglutination immunodiagnostic assays. (44) Given these considerations, our original aim was to conduct in situ SAXS studies of the aqueous emulsion polymerization of styrene. Unfortunately, this prototypical formulation offers very poor X-ray contrast between the polystyrene particles and the aqueous continuous phase owing to the remarkably similar scattering length densities (SLD, or ξ) of water (ξwater = 9.42 × 1010 cm–2) and polystyrene (ξPolystyrene = 9.41 × 1010 cm–2). (45) Indeed, there is almost no difference between the scattering curve recorded at 40% styrene conversion during the surfactant-free aqueous emulsion polymerization of styrene and that for pure water (see Figure S1 in the Supporting Information, SI). With the benefit of hindsight, these observations are not surprising: X-ray contrast correlates quite closely with density, and the solid-state density of polystyrene (1.05 g cm–3) is simply too close to that of water (1.00 g cm–3). In view of this problem, we sought an alternative vinyl polymer with a significantly higher density (and hence SLD) than that of water. Previously, we had prepared sterically stabilized diblock copolymer nanoparticles via RAFT aqueous emulsion polymerization of TFEMA. (46) This monomer has a density of 1.18 g cm–3 and the corresponding PTFEMA homopolymer has a solid-state density of 1.47 g cm–3. Therefore, we elected to use TFEMA monomer instead of styrene because it provides much stronger contrast relative to water during in situ SAXS studies (ξPTFEMA = 12.76 × 1010 cm–2). TFEMA has an aqueous solubility of approximately 2.9 g dm–3 at 25 °C, which is approximately an order of magnitude higher than that of styrene (0.31 g dm–3 at 25 °C). Nevertheless, the aqueous solubility of TFEMA is sufficiently low to ensure a genuine aqueous emulsion polymerization formulation. Furthermore, given that the Tg of PTFEMA homopolymer is around 55 °C, the nanoparticles retain their original morphology during TEM analysis.
In principle, particle growth during emulsion polymerization can be monitored by analyzing aliquots periodically extracted from the reaction mixture using techniques such as DLS. However, for formulations involving an ionic surfactant such as SDS, significant changes in solution conductivity also occur during polymerization. This is because the solution conductivity depends mainly on the concentration of free surfactant dissolved in the aqueous continuous phase (Figure 1). Initially, most of this surfactant is either present in the form of micelles or is adsorbed at the surface of the monomer droplets. At the end of the polymerization, the majority of the surfactant is adsorbed at the surface of the final latex particles. At intermediate monomer conversions, the solution conductivity—which can be readily monitored in situ—depends on the relative populations of monomer droplets, micelles, free (dissolved) surfactant, and growing latex particles. Thus, the evolution in solution conductivity during aqueous emulsion polymerization can provide valuable information on the polymerization kinetics, (47) particle nucleation, (5) and the underlying mechanism of emulsion polymerization. (48,49)Figure 3 shows in situ solution conductivity data recorded during the laboratory-scale synthesis of PTFEMA latex particles in the presence of SDS surfactant under the conditions shown in Figure 2. Once particle nucleation has occurred, free surfactant molecules adsorb onto the growing nascent particles to confer anionic surface charge and hence colloidal stability. This depletion of free surfactant leads to a gradual reduction in conductivity and the period between 0 and 11 min corresponds to Interval I (Figure 1a). (49) At the end of Interval I, there is no more molecularly dissolved surfactant in the aqueous continuous phase. Thereafter, there is an increase in conductivity, which indicates the onset of Interval II (Figure 1b). (49) This occurs because, as the polymerization proceeds and monomer is consumed, surfactant molecules desorb from the surface of the shrinking monomer droplets, which leads to higher solution conductivities for the aqueous continuous phase. A local maximum in conductivity is observed after approximately 28 min. This period corresponds to the onset of Interval III. At this point, essentially all the monomer droplets have been consumed, so the remaining monomer is mainly located within the growing PTFEMA latex particles (because TFEMA monomer is a good solvent for PTFEMA homopolymer). Any free surfactant molecules remaining within the aqueous phase adsorb onto the latex particles during the latter stages of their growth, which accounts for the gradual reduction in solution conductivity observed over the following 32 min. After 60 min, the conductivity remains constant, suggesting that the TFEMA polymerization is complete.
Figure 3
Figure 3. Solution conductivity measurements recorded in situ during the aqueous emulsion polymerization of TFEMA in the presence of SDS surfactant at 60 °C targeting 5.0% w/w solids. The highlighted three time intervals (I, II, and III) are known to occur when such polymerizations are performed in the presence of a surfactant above its CMC (Figure 1).
The kinetics of TFEMA polymerization and the corresponding evolution in particle size were simultaneously monitored during a laboratory-scale synthesis (conducted under the conditions shown in Figure 2) by periodically withdrawing aliquots from the heterogeneous reaction mixture for analysis. The polymerization was quenched by immediately immersing each aliquot into an ice bath with concomitant exposure of the reaction mixture to air. Instantaneous TFEMA conversions were determined via 1H NMR spectroscopy by diluting 80 μL of each extracted aliquot in 500 μL CDCl3, with anhydrous MgSO4 being used to remove residual water. The evolution in particle size was monitored by dynamic light scattering (DLS) studies of 0.20% w/w aqueous dispersions obtained by diluting 40 μL of each extracted aliquot using deionized water (960 μL). Volume-average size distributions were calculated from the intensity-average size distributions obtained by DLS using the Mie theory that is embedded within the instrument manufacturer’s software, see SI for further details. Accordingly, Figure 4 shows the conversion vs time curves and the evolution in volume-average particle diameter over time during the aqueous emulsion polymerization of TFEMA obtained either under surfactant-free conditions or in the presence of SDS surfactant. Furthermore, the time intervals corresponding to those determined by in situ conductivity measurements for the SDS formulation (Figure 3) are also included in Figure 4b. For the surfactant-free formulation, no further increase in TFEMA conversion is observed after 80 min (Figure 4a). At this time point, 1H NMR spectroscopy indicated a final monomer conversion of 98%, while DLS studies reported a volume-average particle diameter of 485 nm (DLS polydispersity = 0.02). TEM studies confirm the formation of relatively uniform spherical latex particles with a number-average diameter of 464 nm, see Figure 5c. A slightly faster rate of polymerization occurs in the presence of SDS, with no further increase in conversion being observed after 60 min (see Figure 4b). This agrees rather well with the overall time scale required for this polymerization indicated by the solution conductivity measurements (Figure 3). Furthermore, this is consistent with DLS studies, which indicates that the volume- average particle diameter remained constant at 91 nm (DLS polydispersity = 0.01) on the same time scale. TEM studies confirm the formation of well-defined spherical latex particles (see Figure 5d), with a number-average diameter of approximately 89 nm. The DLS data for both formulations shown in Figure 4 is also included in Table S1. For free radical-initiated aqueous emulsion polymerization formulations reported in the literature, smaller latex particles and faster rates of polymerization are typically observed in the presence of surfactant. (26,42) Under surfactant-free conditions, latex surface charge is solely conferred by sulfate groups (derived from the persulfate initiator) located on the polymer chain-ends. (50−52) In contrast, the PTFEMA particles produced in the presence of surfactant acquire anionic surface charge from both these sulfate end-groups and also the adsorption of SDS at the latex surface. (1,2,9) This accounts for the substantial difference in particle size for these two formulations indicated by TEM and DLS studies. Furthermore, microcompartmentalization of the growing polymer radicals within surfactant micelles suppresses their termination, which leads to a faster overall rate of polymerization and a significantly higher molecular weight than the equivalent solution polymerization. (1) This is supported by the molecular weight distributions obtained for each formulation using gel permeation chromatography (see Figure S2).
Figure 4
Figure 4. (a) Conversion vs time curve obtained by 1H NMR spectroscopy and evolution in volume-average particle diameter and polydispersity determined by DLS for the laboratory-scale surfactant-free aqueous emulsion polymerization of TFEMA at 60 °C targeting 5.0% w/w solids. (b) Equivalent data for the laboratory-scale aqueous emulsion polymerization of TFEMA at 60 °C targeting 5.0% w/w solids in the presence of SDS surfactant (2.0 mol % based on TFEMA), where the three regions corresponding to Intervals I, II, and III indicated by solution conductivity measurements (Figure 3) are also shown.
Figure 5
Figure 5. TEM images recorded for PTFEMA latex particles prepared during the aqueous emulsion polymerization of TFEMA at 60 °C in the absence or presence of SDS surfactant. Images a–d correspond to PTFEMA nanoparticles formed during the laboratory-scale synthesis. Images e and f correspond to post-mortem analysis of PTFEMA nanoparticles formed during the in situ SAXS synthesis using the stirrable reaction cell.
The three distinct time intervals observed during emulsion polymerization (see Figure 1) and identified by solution conductivity measurements (see Figure 3) are consistent with the NMR-derived kinetic data obtained for the SDS formulation shown in Figure 4b. According to Figure 3, Interval I lies between 0 and 11 min. During this time period, 1H NMR analysis indicates a discernible increase in the rate of polymerization, suggesting that particle nucleation occurs within this time frame. Furthermore, Interval I typically exists up to 10–20% monomer conversion (2) and, according to the data presented in Figure 4b, the end of Interval I corresponds to approximately 20% TFEMA conversion. Inspecting Figure 3, Interval II is complete after around 28 min, which is consistent with the period of rapid polymerization observed by 1H NMR spectroscopy over this time period. According to the literature, the typical monomer conversion at the end of Interval II is around 60%. (2) However, for the specific formulation studied herein, the TFEMA conversion at the end of Interval II is approximately 84%. After this time point, 1H NMR indicates a reduction in the rate of reaction until the TFEMA polymerization is more or less complete after 60 min. This matches the concomitant reduction in solution conductivity—and hence the beginning of Interval III—observed in Figure 3. Furthermore, DLS studies indicate a significant reduction in the rate of particle growth over the second half of the polymerization.
In situ SAXS Studies during TFEMA Polymerization
In the literature, in situ experiments have been conducted during aqueous emulsion polymerization using Raman (12) or FT–IR spectroscopy. (13,14) However, such techniques can only monitor the instantaneous monomer concentration; they provide no particle size information. SAXS is a well-established structural characterization technique in colloid science. (31,53−56) It has been used to characterize the particle size distributions of various polymer latexes prepared via free radical-initiated aqueous emulsion polymerization. (57−61) However, as far as we are aware, there have been no in situ studies for such heterogeneous formulations. One likely reason for this surprising omission is the requirement for efficient stirring during aqueous emulsion polymerization, which is simply not feasible using the capillary cells that are normally used for SAXS measurements. However, we have recently reported in situ SAXS studies during the reversible addition–fragmentation chain transfer (RAFT) aqueous emulsion polymerization of 2-methoxyethyl methacrylate using a stirrable reaction cell (Figure 2b). (36) In essence, this cell comprises a capillary positioned above a 2.0 mL chamber (equipped with a magnetic flea), which is encased within an aluminum block that enables efficient heat transfer via a circulating water jacket. The reaction mixture can be stirred sufficiently vigorously to create the micrometer-sized monomer droplets that are required for aqueous emulsion polymerization to proceed. One important feature of this stirrable reaction cell is that its sample volume is sufficient to enable post-mortem characterization of the final latex particles using multiple techniques. Herein, we use this new experimental setup to perform time-resolved SAXS studies during the aqueous emulsion polymerization of TFEMA. The in situ polymerization formulations were conducted on a smaller scale than the equivalent laboratory-scale reactions reported in Figures 3 and 4. A synchrotron source is essential for such in situ SAXS experiments: it ensures sufficient temporal resolution to monitor the relatively fast kinetics of the TFEMA polymerization (Figure 4). This enables many high-quality scattering patterns to be recorded on a relatively short time scale, thus providing information regarding both nucleation and subsequent particle growth.
Particle Nucleation
Figure 6 shows the X-ray scattering intensity, I(q), plotted against the scattering vector, q, for selected SAXS patterns recorded in situ during the aqueous emulsion polymerization of TFEMA at 60 °C in the presence or absence of surfactant, with 5.0% w/w solids being targeted in each case. This relatively low monomer concentration was chosen to minimize interparticle interactions, which nevertheless still required the introduction of a structure factor (see later). Figure 6 also includes selected scattering patterns (and representative data fits) recorded at specific time points for both formulations. For scattering patterns that are not scaled by an arbitrary factor and also residual fits to final scattering patterns, see Figures S8 and S9 in the SI. In the low q regime, I(q) is proportional to the volume of a scattering object; this relationship can be used to identify the onset of particle nucleation. Thus, I(q) was plotted against time during the early stages of the polymerization at arbitrary q values of 0.02 nm–1 and 0.1 nm–1 for the surfactant-free and SDS formulations respectively, see Figure 7. [N.B. It was necessary to select a suitably low q value for the surfactant-free formulation to avoid the multiple fringes within the associated scattering patterns.] The pronounced upturns in I(q) highlighted by the blue arrows in Figure 7 indicate the point at which particle nucleation occurs (with the corresponding scattering pattern also highlighted in Figure 6). Nucleation is observed after approximately 8 and 6 min for the surfactant-free and SDS formulations, respectively. Identifying the onset of nucleation for either formulation during the equivalent laboratory-scale syntheses (see Figure 4) is somewhat problematic owing to the difficulty in sampling such heterogeneous reaction mixtures during the early stages of polymerization. However, DLS studies revealed a pronounced upturn in the scattered light intensity (derived count rate) after 6 min for the SDS formulation and 10 min for the surfactant-free formulation respectively, see Figure 7. In principle, this should correspond to nucleation. These approximate nucleation times agree well with those observed by measuring I(q) during the equivalent in situ SAXS syntheses. Nucleation appears to occur on a shorter time scale for the surfactant-free formulation during the in situ SAXS experiments. In principle, this could constitute evidence for an X-ray beam-induced rate enhancement. Indeed, our prior in situ SAXS studies conducted during PISA syntheses in mineral oil revealed a significant rate enhancement that was attributed to an additional radical flux generated by the high-energy X-ray beam. (36,38) However, TEM analysis conducted on aliquots extracted from the laboratory-scale syntheses confirmed the formation of nascent nuclei within the short time scales indicated by the in situ SAXS experiments, see Figure 5a,b. Therefore, nucleation seems to occur on similar time scales in both cases. The spherical nuclei observed by TEM after 6 min (SDS formulation) and 8 min (surfactant-free formulation) have number-average particle diameters of 39 and 62 nm, respectively. DLS studies of the same aliquots indicated volume-average particle diameters of 41 and 88 nm for the corresponding SDS and surfactant-free formulations, respectively. As expected, DLS studies of aliquots extracted prior to nucleation exhibited significantly low scattered light intensity after serial dilution, suggesting no particle formation.
Figure 6
Figure 6. SAXS patterns recorded in situ during the aqueous emulsion polymerization of TFEMA at 60 °C targeting 5% w/w solids (a) under surfactant-free conditions and (b) in the presence of SDS surfactant. The onset of particle nucleation is indicated by the arrow. (c) Representative fits for scattering patterns recorded at specific time points for both formulations with data fits represented by either yellow (surfactant-free formulation) or green (SDS formulation) lines, respectively. All scattering patterns are scaled by an arbitrary factor to avoid overlap and improve clarity.
Figure 7
Figure 7. Evolution in I(q) recorded at arbitrary q values during the in situ synthesis and light scattering count rate determined by DLS studies of the equivalent laboratory-based aqueous emulsion polymerization of TFEMA at 60 °C when targeting 5% w/w solids for (a) a surfactant-free formulation and (b) in the presence of SDS surfactant. The onset of particle nucleation is indicated in each case.
The aqueous emulsion polymerization of TFEMA was judged to be complete when no discernible difference was observed between consecutive scattering patterns. This occurred after reaction times of 80 and 60 min for the surfactant-free and SDS formulations, respectively (see Figure S3). These time scales are equivalent to those observed for the equivalent laboratory-scale syntheses (see Figure 4). It is also noteworthy that the surfactant-free formulation produced SAXS patterns with multiple fringes (see Figure 6a), whereas the SDS formulation led to relatively featureless scattering patterns (see Figure 6b). This indicates that the surfactant-free formulation produces PTFEMA particles with a significantly narrower size distribution. (62) Post-mortem 1H NMR analysis of quenched reaction mixtures retrieved from the stirrable reaction cell indicated final TFEMA conversions of 99% and 93% for the surfactant-free and SDS formulations, respectively. The corresponding intensity-average particle diameters indicated by DLS studies were 444 nm (DLS polydispersity = 0.114) and 113 nm (DLS polydispersity = 0.076). These data are consistent with the equivalent laboratory-scale syntheses. Post-mortem TEM analysis confirmed the formation of PTFEMA latex particles with a well-defined spherical morphology in each case, with final number-average particle diameters of 328 and 75 nm being estimated for the surfactant-free and SDS formulations respectively, see Figure 5e,f.
Particle Growth
The surface character of the two PTFEMA latexes was assessed by aqueous electrophoresis. In both cases, highly negative zeta potentials were obtained over the entire pH range investigated, see Figure S4. Given the strongly anionic character of the latex particles, the scattering patterns obtained after particle nucleation were fitted using a well-known scattering model for spheres (63) by incorporating a hard-sphere structure factor (solved with the Percus–Yevick closure relation (64)) to account for interparticle interactions.
Figure 8 shows the evolution in volume-average diameter for the growing latex particles during the TFEMA polymerization as determined by in situ SAXS studies using the stirrable reaction cell. For the surfactant-free formulation, two distinct regimes are observed after nucleation (see Figure 8a). First, there is a period of linear growth up to 27 min. Thereafter, there is a brief increase in the rate of particle growth, which then slows down until the TFEMA polymerization is more or less complete, producing colloidally stable latex particles with a volume-average particle diameter of 353 ± 9 nm after 80 min. Bearing in mind the effect of polydispersity, this final particle size is reasonably consistent with the volume-average particle diameter of 444 nm determined by post-mortem DLS analysis. Furthermore, the evolution in particle diameter determined by in situ SAXS (Figure 8a) is similar to that indicated by DLS studies of the equivalent laboratory-scale synthesis (Figure 4a). For example, mean diameters of the nascent particles observed after 8 min are 88 and 94 nm for the SAXS and DLS data, respectively. The rate of particle growth begins to slow down after approximately 40 min for both the SAXS and equivalent laboratory-scale syntheses. At this time point, the mean particle diameters are 312 and 413 nm, respectively. During the early stages of the TFEMA polymerization (8–27 min), the rate of particle growth is constant. Both in situ SAXS and DLS studies suggest a brief increase in the rate of growth after approximately 27 min. In principle, this feature should correspond to the end of Interval II (Figure 1b). Since there are no remaining monomer droplets, polymerization proceeds under monomer-starved conditions, which explains the slower rate of particle growth observed after 30 min. The solution conductivity was also monitored in situ during the aqueous emulsion polymerization of TFEMA using the surfactant-free formulation, see Figure S5. In this case, there is no measurable solution conductivity for the first 28 min of the TFEMA polymerization, at which point the instantaneous monomer conversion is approximately 60%, see Figure 4a. Subsequently, there is a dramatic increase in solution conductivity in the 29–31 min interval. Interestingly, this time point corresponds to a discernible inflection point during the evolution in particle size indicated by DLS studies during the equivalent laboratory-scale synthesis, see Figure 4a. Moreover, optical microscopy studies confirm essentially full consumption of the monomer droplets after approximately 30 min, see Figure S7. Thus, it seems likely that this time point corresponds to the Interval II/Interval III boundary as shown in Figure 8a. Thereafter, the rate of increase in solution conductivity is reduced, with a maximum solution conductivity of 640 μS cm–1 being observed after 55 min followed by a gradual reduction in conductivity to a limiting value of 590 μS cm–1 after 75 min. According to the NMR kinetic data in Figure 4a, this latter time point corresponds to the end of the polymerization. In summary, solution conductivity measurements undertaken during the surfactant-free aqueous emulsion polymerization of TFEMA may provide some useful information during the latter stages of the reaction, but it appears that this technique cannot be used to pinpoint the Interval I/Interval II boundary for such formulations.
Figure 8
Figure 8. Evolution of the PTFEMA latex particle diameter determined by in situ SAXS studies conducted during the aqueous emulsion polymerization of TFEMA at 60 °C targeting 5.0% w/w solids for (a) a surfactant-free formulation and (b) an SDS formulation. The three characteristic time intervals (I, II, and III) identified by solution conductivity measurements for the SDS formulation (Figure 3) are shown for comparison. The Interval II/III boundary for the surfactant-free formulation is also shown.
Figure 8b shows the evolution in particle diameter during the in situ polymerization of TFEMA conducted in the presence of SDS surfactant. There are two regimes of linear particle growth during the first 25 min. Thereafter, there is a brief but discernible increase in the rate of particle growth, similar to that observed for the surfactant-free formulation. However, this feature is not observed by DLS for the equivalent laboratory-scale SDS synthesis (Figure 4a). Subsequently, the rate of particle growth remains constant until the TFEMA polymerization is essentially complete, producing spherical latex particles with a final volume-average particle diameter of 68 ± 4 nm. This final particle size is smaller than the volume-average particle diameter of 113 nm (polydispersity = 0.076) determined by post-mortem DLS analysis of the quenched reaction mixture. The points of inflection observed in Figure 8b occur at strikingly similar time scales to the Interval I/II and II/III boundaries indicated by in situ conductivity measurements (Figure 3). For example, the latter technique indicates that the II/III boundary occurs at around 28 min, whereas the in situ SAXS data suggests approximately 26 min. Furthermore, optical microscopy confirms that no monomer droplets are present after 30 min, see Figure S6. Such discrepancies are small and are most likely within experimental error, especially if the differing experimental set-ups (reaction volumes, heating rates etc.) are taken into account. Accordingly, the three main Intervals for the aqueous emulsion polymerization of TFEMA in the presence of SDS are assigned on Figure 8b and the likely Interval II/III boundary for the corresponding surfactant-free formulation is indicated in Figure 8a.
Conclusions
ARTICLE SECTIONS
The persulfate-initiated aqueous emulsion polymerization of TFEMA at 60 °C leads to the formation of well-defined spherical latex particles when performed either under surfactant-free conditions or in the presence of SDS surfactant. This semifluorinated vinyl monomer was preferred to styrene because it ensures much stronger X-ray contrast for the corresponding latex particles relative to water. Nucleation and subsequent particle growth has been monitored in situ for both formulations utilizing a stirrable reaction cell to perform time-resolved SAXS studies. This cell has a reaction solution volume of approximately 2.0 mL, which is sufficient to allow post-mortem analysis of the final latex particles by 1H NMR spectroscopy, DLS, and TEM.
For both formulations, the rate of polymerization appears to be unaffected when subjected to synchrotron X-ray irradiation. This is in marked contrast to our prior in situ SAXS study of the synthesis of diblock copolymer nanoparticles via RAFT dispersion polymerization in mineral oil, whereby the enhanced rate of polymerization was attributed to an additional radical flux generated by the high-energy X-ray beam. (36,38) Time-resolved SAXS measurements indicate that nucleation occurs after 8 min in the absence of surfactant and after 6 min in the presence of SDS surfactant, respectively. Following the nucleation event, nascent spherical nanoparticles are observed by TEM and are also detected by DLS. X-ray scattering patterns could be fitted using a simple sphere model, which enabled the evolution in particle diameter to be elucidated for both formulations. The PTFEMA latex particles prepared under surfactant-free conditions are significantly larger and also have a narrower particle size distribution, as judged by the multiple fringes observed for the corresponding patterns. Moreover, a faster rate of particle growth is observed for both formulations at intermediate monomer conversion, suggesting a transition during the polymerization. Similar behavior is also indicated by DLS analysis of the equivalent laboratory-scale synthesis of PTFEMA under surfactant-free conditions. The subsequent reduction in the rate of particle growth most likely corresponds to the disappearance of monomer droplets and hence the transition from Interval II to Interval III. Indeed, optical microscopy studies of laboratory-scale syntheses confirm that monomer droplet depletion occurs on this time scale. Furthermore, the boundaries between these three time intervals can be identified from in situ SAXS measurements for the SDS formulation and are comparable with those indicated by solution conductivity data. This observation may be important for formulations involving non-ionic surfactants, which are not amenable to solution conductivity measurements. SAXS analysis indicates final volume-average particle diameters of 353 ± 9 nm (TFEMA conversion = 99%) and 68 ± 4 nm (TFEMA conversion = 93%) for the surfactant-free and SDS formulations, respectively. These values are consistent with those obtained by 1H NMR and DLS analyses of the equivalent laboratory-scale syntheses, which confirms that the stirrable reaction cell provides sufficiently efficient stirring for representative experiments. In summary, this time-resolved SAXS study has enhanced our understanding of the mechanism of aqueous emulsion polymerization, which suggests that further studies with other vinyl monomers are warranted.
Supporting Information
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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.0c11183.
Full experimental details for PTFEMA particles; further characterization data including aqueous electrophoresis, additional SAXS patterns, optical microscopy images of monomer droplets recorded at various TFEMA conversions, and GPC analysis of PTFEMA chains; and details and examples of the supporting analysis, along with the hard sphere scattering model used to analyze the PTFEMA latexes (PDF)
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Author Information
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- Steven P. Armes - Department of Chemistry, University of Sheffield, Dainton Building, Brook Hill, Sheffield S3 7HF, United Kingdom;
http://orcid.org/0000-0002-8289-6351;
Acknowledgments
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S.P.A. acknowledges an EPSRC Established Career Particle Technology Fellowship grant (EP/R003009) and also postdoctoral support from The Leverhulme Trust (RPG-2016-330) for A.C. Diamond Light Source is acknowledged for granting synchrotron SAXS beam-time at I22 (proposal number SM21776). Finally, Prof. P. D. Topham (Aston, University, U.K.) is thanked for his design of the stirrable reaction cell used for these SAXS studies.
References
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- 1Gilbert, R. G. Emulsion Polymerization, a Mechanistic Approach.; Academic Press: London, 1996.Google ScholarThere is no corresponding record for this reference.
- 2Chern, C. S. Emulsion Polymerization Mechanisms and Kinetics. Prog. Polym. Sci. 2006, 31 (5), 443– 486, DOI: 10.1016/j.progpolymsci.2006.02.001[Crossref], [CAS], Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XkvFykt7s%253D&md5=146081cc2dbc90d88386a2b487c1509cEmulsion polymerization mechanisms and kineticsChern, C. S.Progress in Polymer Science (2006), 31 (5), 443-486CODEN: PRPSB8; ISSN:0079-6700. (Elsevier B.V.)A review. Emulsion polymn. involves the propagation reaction of free radicals with monomer mols. in a very large no. of discrete polymer particles (1016-1018 dm-3) dispersed in the continuous aq. phase. The nucleation and growth of latex particles control the colloidal and phys. properties of latex products. This review article focused on the polymn. mechanisms and kinetics involved in such a heterogeneous polymn. system over the preceding 10-yr period. First, an overview of the general features of emulsion polymn. was given, followed by the discussion of several techniques useful for studying the related polymn. mechanisms and kinetics. Emulsion polymns. using different stabilizers were studied extensively in the last few years and representative publications were reviewed. The performance properties of some specialty polymerizable, degradable or polymeric surfactants and surface-active initiators were also evaluated in emulsion polymn. At present, the particle nucleation process is still not well understood and deserves more research efforts. This article continued to discuss the origin of non-uniform latex particles from both the thermodn. and kinetic points of view. This was followed by the discussion of various reaction parameters that had significant effects on the development of particle morphol. Recent studies on the polymn. in non-uniform polymer particles were then reviewed. Finally, the polymn. mechanisms, kinetics and colloidal stability involved in the versatile semibatch emulsion polymn. were reviewed extensively.
- 3Distler, D. Wässrige Polymerdispersionen: Synthese, Eigenschaften, Anwendungen; Wiley-VCH: Weinheim, 1999.Google ScholarThere is no corresponding record for this reference.
- 4Asua, J. M. Miniemulsion Polymerization. Prog. Polym. Sci. 2002, 27 (7), 1283– 1346, DOI: 10.1016/S0079-6700(02)00010-2[Crossref], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XksFersLc%253D&md5=9efa5539a9ed9ee9e7e87d223245eb0eMiniemulsion polymerizationAsua, Jose M.Progress in Polymer Science (2002), 27 (7), 1283-1346CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Science Ltd.)A review on miniemulsion polymn., a method which has recently exploded in terms of publications and the development of a wide range of useful polymer materials only accessible through this polymn. technique. In the first part of this article, the fundamental aspects involved in the prepn. and polymn. of monomer miniemulsions are examd. The second part deals with the application of miniemulsion polymn. for the prodn. of specific products.
- 5Tauer, K.; Hernandez, H.; Kozempel, S.; Lazareva, O.; Nazaran, P. Towards a Consistent Mechanism of Emulsion Polymerization - New Experimental Details. Colloid Polym. Sci. 2008, 286 (5), 499– 515, DOI: 10.1007/s00396-007-1797-3[Crossref], [PubMed], [CAS], Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXkvVShsLY%253D&md5=8f1ba1abede03619b48af02d170f7829Towards a consistent mechanism of emulsion polymerization-new experimental detailsTauer, Klaus; Hernandez, Hugo; Kozempel, Steffen; Lazareva, Olga; Nazaran, PanteaColloid and Polymer Science (2008), 286 (5), 499-515CODEN: CPMSB6; ISSN:0303-402X. (Springer)The application of atypical exptl. methods such as cond. measurements, optical microscopy, and nonstirred polymns. to investigations of the classical' batch ab initio emulsion polymn. of styrene revealed astonishing facts. The most important result is the discovery of spontaneous emulsification leading to monomer droplets even in the quiescent styrene in water system. These monomer droplets with a size between a few and some hundreds of nanometers, which are formed by spontaneous emulsification as soon as styrene and water are brought into contact, have a strong influence on the particle nucleation, the particle morphol., and the swelling of the particles. Exptl. results confirm that micelles of low-mol.-wt. surfactants are not a major locus of particle nucleation. Brownian dynamics simulations show that the capture of matter by the particles strongly depends on the polymer vol. fraction and the size of the captured species (primary free radicals, oligomers, single monomer mols., or clusters).
- 6Smith, W. V.; Ewart, R. H. Kinetics of Emulsion Polymerization. J. Chem. Phys. 1948, 16 (6), 592– 599, DOI: 10.1063/1.1746951[Crossref], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaH1cXivFWrtg%253D%253D&md5=e939fd46132dd4c9c432294ed8b1f577Kinetics of emulsion polymerizationSmith, Wendell V.; Ewart, Roswell H.Journal of Chemical Physics (1948), 16 (), 592-9CODEN: JCPSA6; ISSN:0021-9606.As a basis for understanding emulsion polymerization, the kinetics of free-radical reactions in isolated loci is discussed subject to the condition that the free radicals are supplied to the loci from an external source. Three cases of interest are considered: (1) that in which the av. no. of free radicals per locus is small compared with unity, (2) that in which the no. approximates 1/2, and (3) that in which the no. is large. Of these 3 possibilities, the 2nd, in which the free radicals per locus approximate 1/2, is by far the most interesting, as it explains the characteristic features of styrene emulsion polymerization. For this case the av. rate of reaction per locus is independent of the size of the locus, since this rate is simply 1/2 the rate of polymerization of a single free radical. Thus the rate of emulsion polymerization, the concn. of monomer in the loci, and the no. of loci present provide the information needed for calcg. the chain propagation const. for the monomer. A simplified treatment is given for approximating the no. of reaction loci (polymer particles) produced in emulsion polymerization when the rate of polymerization per locus is const. (see case 2). The law obtained indicates that the no. of particles should increase with the soap concn. (3/5 power) and with the rate of formation of free radicals (2/5 power), but should decrease with increasing rate of growth of the free radicals (-2/5 power).
- 7Harkins, W. D. A. A General Theory of the Mechanism of Emulsion Polymerization. J. Am. Chem. Soc. 1947, 69 (6), 1428– 1444, DOI: 10.1021/ja01198a053[ACS Full Text
], [CAS], Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaH2sXivVOrsQ%253D%253D&md5=64d871f06a24c6fd81d160078eefa7dfTheory of the mechanism of emulsion polymerizationHarkins, Wm. D.Journal of the American Chemical Society (1947), 69 (), 1428-44CODEN: JACSAT; ISSN:0002-7863.cf. C.A. 40, 3325.3. A mechanism of emulsion polymerization is proposed in which the polymer growth is initiated in soap micelles. This locus ceases to be active at about 13 to 20% yield when 5% soap (based on monomers) is present initially. Further polymerization occurs in the polymer monomer particle. Evidence is presented that indicates that: (1) each double layer of soap is an independent micelle; (2) the micelle increases in size with soap concn.; (3) the crit. concn. for micelle formation is increased by a factor of 2 for each decrease by unity in the no. of C atoms in the soap mol. (4) the principal function of the monomer emulsion droplet is to serve as a storehouse from which the monomer particles diffuse into the aq. phase where they are trapped by soap micelles and polymer particles in both of which they polymerize. - 8Harkins, W. D. General Theory of Mechanism of Emulsion Polymerization. II. J. Polym. Sci. 1950, 5 (2), 217– 251, DOI: 10.1002/pol.1950.120050208[Crossref], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaG3cXjvFKmtQ%253D%253D&md5=188e533de88e687b7172cdc52b55f2c4General theory of mechanism of emulsion polymerization. IIHarkins, William D.Journal of Polymer Science (1950), 5 (), 217-51CODEN: JPSCAU; ISSN:0022-3832.cf. C.A. 41, 5779e. A general review and elaboration of the author's theory of polymerization which can be summarized as follows: monomer emulsion droplets serve merely as a storehouse of monomer molecules which diffuse into the water phase to soap micelles or polymer particles. With monomers having low H2O soly. (butadiene, styrene, isoprene), the polymer is formed primarily through the growth of free radicals in the monomer-polymer mixture. Almost every latex particle formed is a result of monomer solubilized inside a micelle. The no. of particles initiated within the micelle is a function of the soap concn. and the catalyst activity. Soap seems to stabilize the emulsion by forming a monolayer and giving a charge to the particles. Micelles solubilize a small core of monomer and provide a much larger target for contact with free radicals. Polymer-free radicals grow much larger than expected as a result of using monomer both from the micelle and the surrounding areas. In the mutual formula, 1018 micelles per cc. of H2O phase are present with K dodecanoate or K tetradecanoate.
- 9Thickett, S. C.; Gilbert, R. G. Emulsion Polymerization: State of the Art in Kinetics and Mechanisms. Polymer 2007, 48 (24), 6965– 6991, DOI: 10.1016/j.polymer.2007.09.031[Crossref], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXht12htrnE&md5=e7beca6d356e629ba63b093ff6c2b3e5Emulsion polymerization: State of the art in kinetics and mechanismsThickett, Stuart C.; Gilbert, Robert G.Polymer (2007), 48 (24), 6965-6991CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)A review. Over decades of carefully designed kinetic expts. and the development of complementary theory, a more or less complete picture of the mechanisms that govern emulsion polymn. systems was established. This required means of detg. the rate coeffs. for the individual processes as functions of controllable variables such as initiator concn. and particle size, means of interpreting the data with a min. of model-based assumptions, and the need to perform expts. that had the potential to actually refute a given mechanistic hypothesis. Significant advances were made within the area of understanding interfacial processes such as radical entry and exit into and out of an emulsion polymn. particle, for electrostatic, steric and electrosteric stabilizers (the latter two being poorly understood until recently). The mechanism for radical exit is chain transfer to monomer within the particle interior to form a monomeric radical which can either diffuse into the water phase or propagate to form a more hydrophobic species which cannot exit. Entry is through aq.-phase propagation of a radical derived directly from initiator, until a crit. d.p. z is reached; the value of z is such that the z-meric species is sufficiently surface active so that its only fate is to enter, whereas smaller aq.-phase radical species can either be terminated in the aq. phase or undergo further propagation. For both entry and exit, in the presence of (electro)steric stabilizers, two addnl. events are significant: transfer involving a labile hydrogen atom within the stabilizing layer to form a mid-chain radical which is slow to propagate and quick to terminate, and which may also undergo β-scission to form a water-sol. species. Proper consideration of the fates of the various aq.-phase radicals is essential for understanding the overall kinetic behavior. Intra-particle termination is explained in terms of diffusion-controlled chain-length-dependent events. A knowledge of the events controlling entry and exit, including the recent discoveries of the addnl. mechanisms operating with (electro)steric stabilizers, provides an extension to the micellar and homogeneous nucleation models which enables particle no. to be predicted with acceptable reliability, and also quantifies the amt. of secondary nucleation occurring during seeded growth. This knowledge provides tools to understand the kinetics of emulsion polymn., in both conventional and controlled/living polymn. systems, and to optimize reaction conditions to synthesize better polymer products.
- 10DeFusco, A. J.; Sehgal, K. C.; Bassett, D. R. Overview of Uses of Polymer Latexes. In Polymeric Dispersions: Principles and Applications; Springer: Netherlands, 1997; pp 379– 396.
- 11Vargas, M. A.; Cudaj, M.; Hailu, K.; Sachsenheimer, K.; Guthausen, G. Online Low-Field 1H NMR Spectroscopy: Monitoring of Emulsion Polymerization of Butyl Acrylate. Macromolecules 2010, 43 (13), 5561– 5568, DOI: 10.1021/ma1006599[ACS Full Text], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXmvF2rur0%253D&md5=01e02ca9f095c77330b6c3302a8af8d7Online Low-Field 1H NMR Spectroscopy: Monitoring of Emulsion Polymerization of Butyl AcrylateVargas, Maria A.; Cudaj, Markus; Hailu, Kidist; Sachsenheimer, Kerstin; Guthausen, GiselaMacromolecules (Washington, DC, United States) (2010), 43 (13), 5561-5568CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)The emulsion polymn. of Bu acrylate was monitored by online NMR spectroscopy at 20 MHz 1H frequency. The reaction progress could be followed, monitoring the conversion of the reactant time-resolved without any need of sample prepn. Exptl. data were analyzed with kinetic models for free-radical polymn. The data comprised the polymn. rate in seeded batch emulsion polymns. of Bu acrylate with doubly deionized water and D2O as solvent. The polymn. rate vs. conversion curve behaves compatible with the three rate intervals model, typically obsd. in emulsion polymns. Zero-one kinetics explains the exptl. results appropriately, leading to the detn. of entry and termination rate coeffs.
- 12Chen, X.; Laughlin, K.; Sparks, J. R.; Linder, L.; Farozic, V.; Masser, H.; Petr, M. In Situ Monitoring of Emulsion Polymerization by Raman Spectroscopy: A Robust and Versatile Chemometric Analysis Method. Org. Process Res. Dev. 2015, 19 (8), 995– 1003, DOI: 10.1021/acs.oprd.5b00045[ACS Full Text], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtFSjsLzI&md5=2a87af0b616ebb02275d9f01618d94e2In Situ Monitoring of Emulsion Polymerization by Raman Spectroscopy: A Robust and Versatile Chemometric Analysis MethodChen, Xiaoyun; Laughlin, Ken; Sparks, Justin R.; Linder, Linus; Farozic, Vince; Masser, Hanqing; Petr, MichaelOrganic Process Research & Development (2015), 19 (8), 995-1003CODEN: OPRDFK; ISSN:1083-6160. (American Chemical Society)Emulsion polymn. remains a challenging system for in situ Raman spectroscopic anal. despite extensive research on the necessary instrumentation and chemometric data anal. methods. In this study, we demonstrate a new and facile data anal. method, making in situ Raman spectroscopy a more versatile research tool for monitoring the concns. of monomers in reactions spanning a wide range of compns. The method improvement stems from the use of the homopolymer as an internal std. for the corresponding monomer. Classical least-squares or indirect hard modeling is used for the spectral anal. to det. the spectral responses of major monomers and polymers within the system. Once the relative response factor ratios for a no. of monomer-homopolymer pairs are detd. in the calibration, they can be used to calc. the concn. ratio for such pairs based on reaction spectra. This approach offers two important advantages in detg. the conversion of monomer to polymer. First, because the polymer internal std. will always be present for the corresponding monomer, it is straightforward to compensate for variable signal intensity due to changes in light scattering or instrumental fluctuations. Second, it is possible to calibrate based on a small set of monomer and homopolymer stds. The appropriate pairs can then be selected to establish a calibration method for any polymer product involving a combination of monomers from this set without the need for recalibration. To demonstrate this technique, we provide examples of in situ Raman monitoring for both batch and semibatch emulsion polymns.
- 13Reis, M. M.; Araújo, P. H. H.; Sayer, C.; Giudici, R. In Situ Near-Infrared Spectroscopy for Simultaneous Monitoring of Multiple Process Variables in Emulsion Copolymerization. Ind. Eng. Chem. Res. 2004, 43 (23), 7243– 7250, DOI: 10.1021/ie034277u[ACS Full Text], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXksVKiu70%253D&md5=78da04166ffc7b72fe6d956d19df1053In Situ Near-Infrared Spectroscopy for Simultaneous Monitoring of Multiple Process Variables in Emulsion CopolymerizationReis, Marlon M.; Araujo, Pedro H. H.; Sayer, Claudia; Giudici, ReinaldoIndustrial & Engineering Chemistry Research (2004), 43 (23), 7243-7250CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)In this work near-IR spectroscopy is used to monitor semicontinuous styrene-Bu acrylate emulsion copolymn. reactions. A set of nine reactions with slightly different formulations was carried out. The results of five reactions were used to fit a SIMPLS model, and the four remaining reactions were monitored in order to evaluate the model performance for estn. of important variables and latex properties such as individual monomer concns. and the av. polymer particle diam. These variables were used to calc. the online monomer conversion, copolymer compn., particle no., and av. no. of radicals per polymer particle.
- 14Silva, W. K.; Chicoma, D. L.; Giudici, R. In-Situ Real-Time Monitoring of Particle Size, Polymer, and Monomer Contents in Emulsion Polymerization of Methyl Methacrylate by near Infrared Spectroscopy. Polym. Eng. Sci. 2011, 51 (10), 2024– 2034, DOI: 10.1002/pen.22100[Crossref], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXpvVChs7c%253D&md5=be110ddabb31e64dfad69c5b4eed6ed1In-situ real-time monitoring of particle size, polymer, and monomer contents in emulsion polymerization of methyl methacrylate by near infrared spectroscopySilva, Wandeklebio K.; Chicoma, Dennis L.; Giudici, ReinaldoPolymer Engineering & Science (2011), 51 (10), 2024-2034CODEN: PYESAZ; ISSN:0032-3888. (John Wiley & Sons, Inc.)This work reports the results of in-situ real-time monitoring of the emulsion polymn. of Me methacrylate by near IR spectroscopy (NIRS) under different feed conditions. Besides the monitoring of the monomer and polymer content, the results show that reasonable ests. can be obtained from the spectra for the av. particle size of the growing polymer particles present in the reaction medium. This is possible because the presence of the particles affects the spectra (through scattering, diffraction, and other mechanisms). Thus, by using appropriate calibration, it is possible obtain reliable models for particle size, in addn. to monitoring the monomer and polymer concns. Exptl. results for emulsion polymns. conducted with various feed monomer conditions indicated that, in the spectral range studied, it is not only possible to monitor the evolution of the monomer and polymer contents, but also to follow the changes in the av. size of the polymer particle. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.
- 15Antonietti, M.; Tauer, K. 90 Years of Polymer Latexes and Heterophase Polymerization: More Vital than Ever. Macromol. Chem. Phys. 2003, 204 (2), 207– 219, DOI: 10.1002/macp.200290083[Crossref], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXitlOisLs%253D&md5=a958ec9506582eb237e913e179c7a4f690 Years of polymer latexes and heterophase polymerization: more vital than everAntonietti, Markus; Tauer, KlausMacromolecular Chemistry and Physics (2003), 204 (2), 207-219CODEN: MCHPES; ISSN:1022-1352. (Wiley-VCH Verlag GmbH & Co. KGaA)A review is given on the historical and possible future development of heterophase polymn. techniques in liq. continuous media to prep. polymer dispersions. The majority of heterophase polymns. is carried out in water as continuous phase and hence, they are belong to green chem. with increasing importance due to environmental reasons. The compartmentalization of the reaction vol. into domains of colloidal size (between a few nm3 and μm3) is the characteristic feature and relates both to the problems and the potential promises of this class of polymers. Special emphasis is placed with regard to the development of new heterophase polymn. techniques, the adoption of new polymn. mechanism to the particular conditions of heterophase polymn., the synthesis of block copolymers and nanoparticulate hybrid structures, the development of new stabilizers and polymn. aids, and the usage of specialty latexes as model systems to learn more about complex matter.
- 16Lovell, P. A.; Schork, F. J. Fundamentals of Emulsion Polymerization. Biomacromolecules 2020, 21 (11), 4396– 4441, DOI: 10.1021/acs.biomac.0c00769[ACS Full Text], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtFKjs7vF&md5=441a1c84f9d2e1771b027bccbd84618bFundamentals of Emulsion PolymerizationLovell, Peter A.; Schork, F. JosephBiomacromolecules (2020), 21 (11), 4396-4441CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)A review. A comprehensive overview of the fundamentals of emulsion polymn. and related processes is presented with the object of providing theor. and practical understanding to researchers considering use of these methods for synthesis of polymer colloids across a wide range of applications. Hence, the overview has been written for a general scientific audience with no prior knowledge assumed. Succinct introductions are given to key topics of background science to assist the reader. Importance is placed on ensuring mechanistic understanding of these complex polymns. and how the processes can be used to create polymer colloids that have particles with well-defined properties and morphol. Math. equations and assocd. theory are given where they enhance understanding and learning and where they are particularly useful for practical application. Practical guidance also is given for new researchers so that they can begin using the various processes effectively and in ways that avoid common mistakes.
- 17O’toole, J. T. Kinetics of Emulsion Polymerization. J. Appl. Polym. Sci. 1965, 9 (4), 1291– 1297, DOI: 10.1002/app.1965.070090410[Crossref], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF2MXptFemtA%253D%253D&md5=e556af63ea1443143afcab995392a596Kinetics of emulsion polymerizationO'Toole, J. T.Journal of Applied Polymer Science (1965), 9 (4), 1291-7CODEN: JAPNAB; ISSN:0021-8995.The quant. theory of free-radical mechanisms in emulsion polymerizations was reexamd. The proposed modifications resulted in a closer resemblance to homogeneous systems. Explicit expressions for the distribution of radicals are also given. The importance of interphase transfer is emphasized.
- 18Ballard, M. J.; Napper, D. H.; Gilbert, R. G. Kinetics of Emulsion Polymerization of Methyl Methacrylate. J. Polym. Sci., Polym. Chem. Ed. 1984, 22 (11), 3225– 3253, DOI: 10.1002/pol.1984.170221141[Crossref], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXisFWjtg%253D%253D&md5=f364d3b67c843aea4999ba49be2c9d8fKinetics of emulsion polymerization of methyl methacrylateBallard, Mathew J.; Napper, Donald H.; Gilbert, Robert G.Journal of Polymer Science, Polymer Chemistry Edition (1984), 22 (11, Pt. 2), 3225-53CODEN: JPLCAT; ISSN:0360-6376.The kinetics of emulsion polymn. of Me methacrylate (I) [80-62-6] at 50° were studied in seeded systems using both chem. initiation and γ-radiolysis initiation. Both steady-state rates and (for γ-radiolysis) the relaxation from the steady state were obsd. The av. no. of free radicals per particle was quite high (e.g., ∼0.7 for 10-3 mol dm-3 S2O62 initiator). The data are quant. interpreted using a generalized Smith-Ewart-Harkins model, allowing for free radical entry, exit, bimol. termination within the latex particles, and aq. phase hetero-termination and re-entry. From this treatment, there results (1) the dependence of the termination rate coeffs. (kt) on the wt. fraction of polymer (wp), (2) lower bounds for the dependence of the entry rate coeff. on initiator concn., and (3) the conclusion that most exited free radicals undergo subsequent reentry into particles rather than hetero-termination. The results for k1(wp) are consistent with diffusion control at temps. below the glass transition point. Comparisons are presented of the behavior of I, Bu methacrylate, and styrene in emulsion polymn. systems.
- 19Heuts, J. P. A.; Gilbert, R. G.; Radom, L. A Priori Prediction of Propagation Rate Coefficients in Free-Radical Polymerizations: Propagation of Ethylene. Macromolecules 1995, 28 (26), 8771– 8781, DOI: 10.1021/ma00130a009[ACS Full Text], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXpsFWqu7w%253D&md5=3c2352025cf1f9d07da38c830b209932A Priori Prediction of Propagation Rate Coefficients in Free-Radical Polymerizations: Propagation of EthyleneHeuts, Johan P. A.; Gilbert, Robert G.; Radom, LeoMacromolecules (1995), 28 (26), 8771-81CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)A method is derived for calcg. Arrhenius parameters for propagation reactions in free-radical polymns. from first principles. Ab initio MO calcns. are carried out initially to det. the geometries, vibrational frequencies, and energies of the reactants and the transition state. Transition state theory then yields the Arrhenius parameters. The lowest frequencies are replaced by appropriate (hindered or unhindered) internal rotors, to better model these modes in the calcn. of frequency factors. It is found that a high level of MO theory (e.g., QCISD(T)/6-311G**) is required to produce reasonable activation energies, whereas satisfactory frequency factors can be obtained at a relatively simple level of theory (e.g., HF/3-21G), because the frequency factor is largely detd. by mol. geometries which can be reliably predicted at such a level. Obtaining reliable frequency factors for quite large systems is thus possible. The overall procedure is illustrated by calcns. on the propagation of ethylene, and the results are in accord with literature exptl. data. Means are also derived for extending the results from propagation of monomeric radicals to propagation of polymeric radicals, without addnl. computational requirements. The method is expected to be generally applicable to those propagation reactions that are not significantly influenced by the presence of solvent (i.e., relatively nonpolar monomers in nonpolar solvents). The calcns. show that the magnitude of the frequency factor is largely governed by the degree to which the internal rotations of the transition state are hindered. They also suggest that there can be a significant penultimate unit effect in free-radical copolymn. Furthermore, the calcns. explain the rate-enhancing effect found upon deuteration of the monomers and explain why the rate coeff. for the first propagation step is larger than that for the long-chain propagation step.
- 20Harkins, W. D. A General Theory of the Reaction Loci in Emulsion Polymerization. J. Chem. Phys. 1945, 13 (9), 381– 382, DOI: 10.1063/1.1724054[Crossref], [CAS], Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaH2MXjtl2qug%253D%253D&md5=44e408f037a237f872b42d24b18673c2A general theory of the reaction loci in emulsion polymerizationHarkins, William D.Journal of Chemical Physics (1945), 13 (), 381-2CODEN: JCPSA6; ISSN:0021-9606.There is no expanded citation for this reference.
- 21Gardon, J. L. Emulsion Polymerization. I. Recalculation and Extension of the Smith-Ewart Theory. J. Polym. Sci., Part A-1: Polym. Chem. 1968, 6 (3), 623– 641, DOI: 10.1002/pol.1968.150060318[Crossref], [CAS], Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF1cXhtFGms74%253D&md5=53c600178f7fdf1f5ce36753bb74f5deEmulsion polymerization. I. Recalculation and extension of the Smith-Ewart TheoryGardon, John L.Journal of Polymer Science, Part A-1: Polymer Chemistry (1968), 6 (3), 623-41CODEN: JPSPC3; ISSN:0449-296X.The most important assumptions underlying the Smith-Ewart theory are that the locus of chain propagation is the monomer-swollen latex particle, polymeric chains are initiated by radicals entering from the water phase into the particles, chain termination is an instantaneous reaction between two radicals within one particle, and particles are nucleated by radicals absorbed into monomer-swollen soap micelles. The proportionality const. between the particle no. and the appropriate powers of soap and initiator concns. is defined in terms of independent parameters. Abs. rate equations are presented for the intervals before and after the completion of particle nucleation. To calc. these rates, it is not necessary to have prior knowledge of the exptl. particle no. The conversion at which particle nucleation is complete is calcd. The mol. wt. is defined in terms of independent parameters. Predictions are made for the particle-size distribution. The validity of the theory is confined to specifiable intervals of conversion, to a certain range of monomer-water ratio, and to soap concns. whose upper and lower limits are given. 17 references.
- 22Soh, S. K.; Sundberg, D. C. Diffusion-Controlled Vinyl Polymerization. IV. Comparison of Theory and Experiment. J. Polym. Sci., Polym. Chem. Ed. 1982, 20 (5), 1345– 1371, DOI: 10.1002/pol.1982.170200516[Crossref], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL38XitFygsrk%253D&md5=7a5490842d692b8b742f181b50ff6f33Diffusion-controlled vinyl polymerization. IV. Comparison of theory and experimentSoh, S. K.; Sundberg, D. C.Journal of Polymer Science, Polymer Chemistry Edition (1982), 20 (5), 1345-71CODEN: JPLCAT; ISSN:0360-6376.Bulk polymn. data of methyl methacrylate [80-62-6], ethyl methacrylate [97-63-2], ethyl acrylate [140-88-5], propyl acrylate [925-60-0], vinyl acetate [108-05-4], and styrene [100-42-5] were compared with the predictions of a proposed theory. This theory of polymn. kinetics uses the concepts of free vol. and chain entanglements to describe the relation between chain mobility and chain length dependent termination reactions. Excellent agreement was found between the predictions of the theory and the polymn. rate and mol.wt. data of the 6 polymn. systems studied. Emphasis was placed on the ability to explain the development of higher order mol.wt. avs. (‾Mw, ‾M2, etc.) because they provide the most crucial tests for such a model. No changes were required in the model as it was applied to the different polymn. systems for a variety of reaction conditions. The theory offers a unified understanding of the diverse polymn. behavior displayed by such systems.
- 23Goodwin, J. W.; Hearn, J.; Ho, C. C.; Ottewill, R. H. Studies on the Preparation and Characterisation of Monodisperse Polystyrene Laticee - III. Preparation without Added Surface Active Agents. Colloid Polym. Sci. 1974, 252 (6), 464– 471, DOI: 10.1007/BF01554752[Crossref], [CAS], Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2MXktlyjuw%253D%253D&md5=01f188ed6ac95910dede33e401f1f182Preparation and characterization of monodisperse polystyrene latexes. III. Preparation without added surface active agentsGoodwin, J. W.; Hearn, J.; Ho, C. C.; Ottewill, R. H.Colloid and Polymer Science (1974), 252 (6), 464-71CODEN: CPMSB6; ISSN:0303-402X.By adjusting the ionic strength, initiator concn., and polymn. temp., monodisperse polystyrene [9003-53-6] latexes with particle sizes 0.1-1.0 μm were prepd. by single-stage polymns. in the absence of surfactants. In a typical polymn., 73 g styrene was added to 670 g H2O contg. NaCl under N with stirring at 60-95°, K2S2O8 initiator was added, and the dispersion was stirred for 24 hr. The total initial ionic strength largely detd. the particle size in the latexes.
- 24Kotera, A.; Furusawa, K.; Kudo, K. Colloid Chemical Studies of Polystyrene Latices Polymerized without Any Surface-Active Agents - II. Coagulation into Secondary Minimum. Colloid Polym. Sci. 1970, 240 (1–2), 837– 842, DOI: 10.1007/BF02160082
- 25Kühn, I.; Tauer, K. Nucleation in Emulsion Polymerization: A New Experimental Study. 1. Surfactant-Free Emulsion Polymerization of Styrene. Macromolecules 1995, 28 (24), 8122– 8128, DOI: 10.1021/ma00128a022[ACS Full Text], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXovFCntr4%253D&md5=4365e2676b666857f3c70c9d6439553eNucleation in Emulsion Polymerization: A New Experimental Study. 1. Surfactant-Free Emulsion Polymerization of StyreneKuehn, I.; Tauer, K.Macromolecules (1995), 28 (24), 8122-8CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)The very early stages of the emulsifier-free emulsion polymn. of styrene were investigated by online monitoring of the optical transmission and the cond. of the reaction mixt. Very careful degassing of the reaction mixt. is crucial to achieve high reproducibility. The higher the residual gas concn. the poorer the reproducibility no matter if the gas is air or N. The results lead to the conclusions that for particle nucleation the rate of initiation in the water phase is very important and that nucleation occurs via cluster formation of water-born oligomers. With the exptl. techniques employed, it was possible to investigate the conversion range from 0.47% to 1.8%. However, it was not possible to detect a particle no. max. Instead of a max., a decrease in the particle no. was obsd. followed by a leveling and another increase, indicating another nucleation step.
- 26Tauer, K.; Deckwer, R.; Kühn, I.; Schellenberg, C. A Comprehensive Experimental Study of Surfactant-Free Emulsion Polymerization of Styrene. Colloid Polym. Sci. 1999, 277, 607– 626, DOI: 10.1007/s003960050433[Crossref], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXksF2jurc%253D&md5=6af92fd7268def774ac44df106f1d115A comprehensive experimental study of surfactant-free emulsion polymerization of styreneTauer, K.; Deckwer, R.; Kuhn, I.; Schellenberg, C.Colloid and Polymer Science (1999), 277 (7), 607-626CODEN: CPMSB6; ISSN:0303-402X. (Springer-Verlag)Comprehensive exptl. results are presented for surfactant-free emulsion polymn. of styrene with water-sol., ionic initiators. Special emphasis is placed on the particle nucleation, the chem. structure of the nucleating species, the change of latex, particle and polymer properties as well as the development of particle morphol. with polymn. time. Under special conditions the appearance in transmission electron microscopy pictures of less electron dense anomalous particles is obsd. The formation of these structures is discussed and possible formation mechanisms presented. Dialysis of the latexes changed their properties drastically as they became unstable to coagulation. The original latexes did not change their properties over several months.
- 27Fitch, R. M. Homogeneous Nucleation of Polymer Colloids. Br. Polym. J. 1973, 5 (6), 467– 483, DOI: 10.1002/pi.4980050606[Crossref], [CAS], Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2cXktlOrsLs%253D&md5=cb8a8fbdaed88e91d569e1e562b8cef3Homogeneous nucleation of polymer colloidsFitch, Robert M.British Polymer Journal (1973), 5 (6), 467-83CODEN: BPOJAB; ISSN:0007-1641.Homogeneous nucleation of polymer colloids was reviewed with 35 refs., and a model for particle formation was based on free radical initiation in a continuous medium and self-nucleation or particle capture was proposed.
- 28Fitch, R. M.; Tsai, C. H. Homogeneous Nucleation of Polymer Colloids, IV: The Role of Soluble Oligomeric Radicals; Polymer Colloids; Plenum Press: New York, 1971; pp 103– 116.Google ScholarThere is no corresponding record for this reference.
- 29Priest, W. Particle Growth in Aqueous Polymerization of Vinyl Acetate. J. Phys. Chem. 1952, 56, 1077– 1083, DOI: 10.1021/j150501a010[ACS Full Text], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaG3sXitFaqtQ%253D%253D&md5=c66d8190bef42c31085c0753e6aaddebParticle growth in the aqueous polymerization of vinyl acetatePriest, W. J.Journal of Physical Chemistry (1952), 56 (), 1077-82CODEN: JPCHAX; ISSN:0022-3654.Electron-microscope observations of latexes produced by the polymerization of vinyl acetate in water showed that in nonmicellar systems (1) the max. no. of primary particles developed is equal to the no. of polymer chains long enough to give water insoly. formed throughout the course of the polymerization and (2) growth takes place by interparticle fusion. The no. of particles present at the completion of the polymerization is the total no. of primary particles less the reduction caused by coalescence during the course of the reaction. Coalescence can be controlled by the use of emulsion stabilizers, the most efficient of which are surfactants such as Na dodecylsulfonate. In the absence of surfactants the particles produced are large (0.1-1.0 μ in diam.), and their size distribution is narrow. Other factors affecting particle size and growth were investigated. Less detailed examn. of the latexes from other slightly water-sol. monomers indicate that the growth mechanism proposed for vinyl acetate is general.
- 30Feeney, P. J.; Napper, D. H.; Gilbert, R. G. Surfactant-Free Emulsion Polymerizations: Predictions of the Coagulative Nucleation Theory. Macromolecules 1987, 20 (11), 2922– 2930, DOI: 10.1021/ma00177a047[ACS Full Text], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXmtFyisL4%253D&md5=b02103930dffcef9f903316b5675eba3Surfactant-free emulsion polymerizations: predictions of the coagulative nucleation theoryFeeney, P. John; Napper, Donald H.; Gilbert, Robert G.Macromolecules (1987), 20 (11), 2922-30CODEN: MAMOBX; ISSN:0024-9297.Equations were given for the formation of latex particles in emulsion polymn. systems in the absence of added emulsifier. The model described the formation of colloidally unstable precursor particles through homogeneous nucleation, followed by their coagulation and propagational growth to form colloidally stable latex particles. Coagulation rates were obtained through DLVO theory and its modifications, with due allowance for the partial attraction that occurred in the coagulation between particles with different radii. Calcns. showed good agreement with the exptl. data of Ottewill et al. for the variation of particle no. d. with initiator concn. and ionic strength.
- 31Pedersen, J. S. Analysis of Small-Angle Scattering Data from Micelles and Microemulsions: Free-Form Approaches and Model Fitting. Curr. Opin. Colloid Interface Sci. 1999, 4 (3), 190– 196, DOI: 10.1016/S1359-0294(99)00033-3[Crossref], [CAS], Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXmslKisLo%253D&md5=e9fc133cbe6eee20dd6aa4d2f6983b10Analysis of small-angle scattering data from micelles and microemulsions: free-form approaches and model fittingPedersen, Jan SkovCurrent Opinion in Colloid & Interface Science (1999), 4 (3), 190-196CODEN: COCSFL; ISSN:1359-0294. (Elsevier Science Ltd.)A review with 51 refs. The free-form methods for analyzing small-angle scattering data have, during the last years, found more widespread use for micelles and microemulsions. Recent developments have made them applicable also to systems with size polydispersity and particle correlations, however, model fitting still constitutes a very important and partly complementary anal. tool.
- 32Pontoni, D.; Narayanan, T.; Rennie, A. R. Time-Resolved SAXS Study of Nucleation and Growth of Silica Colloids. Langmuir 2002, 18 (1), 56– 59, DOI: 10.1021/la015503c[ACS Full Text], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XivVKl&md5=b50de3d1bf12cb9621659ba774bf0904Time-Resolved SAXS Study of Nucleation and Growth of Silica ColloidsPontoni, D.; Narayanan, T.; Rennie, A. R.Langmuir (2002), 18 (1), 56-59CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)This paper reports a time-resolved small-angle x-ray scattering study of in situ Stober SiO2 synthesis. The hydrolysis reaction is initiated by rapidly mixing equal amts. of alc. solns. of NH3 and tetra-Et orthosilicate, using a stopped-flow device coupled to a flow-through capillary cell. Measurements covered the scattering wave vector (q) range of 0.02 ≤ q ≤ 6 nm-1 and time (t) range of 0.1 ≤ t ≤ 1000 s. The combination of high sensitivity, low background, and high dynamic range of the exptl. setup permitted observation of the primary particles of nucleation. During the entire growth process, the measured scattered intensity can be adequately described by a sphere scattering function weighted by a Schultz size distribution function. At the early stages of growth, the fitted radius increased linearly with time, subsequently crossing over to a smaller exponent of between 1/3 and 1/2. The obsd. behavior is consistent with an aggregation process involving primary particles of a few nanometers in size.
- 33Tokumoto, M. S.; Pulcinelli, S. H.; Santilli, C. V.; Craievich, A. F. SAXS Study of the Kinetics of Formation of ZnO Colloidal Suspensions. J. Non-Cryst. Solids 1999, 247 (1–3), 176– 182, DOI: 10.1016/S0022-3093(99)00059-9[Crossref], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXjs1Ohu7g%253D&md5=c8bfd16bfcad19a6b5f6c2a8c7a3eaaaSAXS study of the kinetics of formation of ZnO colloidal suspensionsTokumoto, M. S.; Pulcinelli, S. H.; Santilli, C. V.; Craievich, A. F.Journal of Non-Crystalline Solids (1999), 247 (), 176-182CODEN: JNCSBJ; ISSN:0022-3093. (Elsevier Science B.V.)We have investigated, by in-situ small-angle X-ray scattering (SAXS), the kinetics of formation of zinc oxide colloidal suspensions obtained after refluxing alc. soln. of zinc acetate and catalyzed by lithium hydroxide. The exptl. results demonstrate that the suspensions are composed of colloidal spheroidal particles with a multimodal size distribution. The av. radius of the main mode, approx. 2 nm, is invariant but the no. of these basic particles continuously increases for increasing hydrolysis reaction time. The other two modes correspond to particles with av. radii close to 6 and 10 nm, resp. The larger particles are formed by coagulation of the smaller ones.
- 34Narayanan, S.; Wang, J.; Lin, X. M. Dynamical Self-Assembly of Nanocrystal Superlattices during Colloidal Droplet Evaporation by in Situ Small Angle x-Ray Scattering. Phys. Rev. Lett. 2004, 93 (13), 135503, DOI: 10.1103/PhysRevLett.93.135503[Crossref], [PubMed], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXnvFCitr8%253D&md5=b32afbbcdd0bbdae95190428c9831bddDynamical self-assembly of nanocrystal superlattices during colloidal droplet evaporation by in situ small angle x-ray scatteringNarayanan, Suresh; Wang, Jin; Lin, Xiao-MinPhysical Review Letters (2004), 93 (13), 135503/1-135503/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)The nucleation and growth kinetics of highly ordered gold nanocrystal superlattices during the evapn. of nanocrystal colloidal droplets was elucidated by in situ time-resolved small-angle x-ray scattering. The evapn. rate can affect the dimensionality of the superlattices. The formation of 2D nanocrystal superlattices at the liq.-air interface of the droplet has exponential growth kinetics that originates from interface crushing.
- 35Narayanan, T.; Gummel, J.; Gradzielski, M. Probing the Self-Assembly of Unilamellar Vesicles Using Time-Resolved SAXS. In Advances in Planar Lipid Bilayers and Liposomes; Elsevier B.V.: Amsterdam, 2014; Vol. 20, pp 171– 196.
- 36Brotherton, E. E.; Hatton, F. L.; Cockram, A. A.; Derry, M. J.; Czajka, A.; Cornel, E. J.; Topham, P. D.; Mykhaylyk, O. O.; Armes, S. P. In Situ Small-Angle X-Ray Scattering Studies during Reversible Addition-Fragmentation Chain Transfer Aqueous Emulsion Polymerization. J. Am. Chem. Soc. 2019, 141 (34), 13664– 13675, DOI: 10.1021/jacs.9b06788[ACS Full Text], [CAS], Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsVygtbrO&md5=6cf5c202cb326d41a0e15e84cd87547bIn Situ Small-Angle X-ray Scattering Studies During Reversible Addition-Fragmentation Chain Transfer Aqueous Emulsion PolymerizationBrotherton, Emma E.; Hatton, Fiona L.; Cockram, Amy A.; Derry, Matthew J.; Czajka, Adam; Cornel, Erik J.; Topham, Paul D.; Mykhaylyk, Oleksandr O.; Armes, Steven P.Journal of the American Chemical Society (2019), 141 (34), 13664-13675CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Polymn.-induced self-assembly (PISA) is a powerful platform technol. for the rational and efficient synthesis of a wide range of block copolymer nano-objects (e.g., spheres, worms or vesicles) in various media. In situ small-angle x-ray scattering (SAXS) studies of reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn. have previously provided detailed structural information during self-assembly (see M. J. Derry et al., Chem. Sci. 2016, 7, 5078-5090). However, conducting the analogous in situ SAXS studies during RAFT aq. emulsion polymns. poses a formidable tech. challenge because the inherently heterogeneous nature of such PISA formulations requires efficient stirring to generate sufficiently small monomer droplets. In the present study, the RAFT aq. emulsion polymn. of 2-methoxyethyl methacrylate (MOEMA) was explored for the first time. Chain extension of a relatively short non-ionic poly(glycerol monomethacrylate) (PGMA) precursor block leads to the formation of sterically-stabilized PGMA-PMOEMA spheres, worms or vesicles, depending on the precise reaction conditions. Construction of a suitable phase diagram enables each of these three morphologies to be reproducibly targeted at copolymer concns. ranging from 10 to 30% wt./wt. solids. High MOEMA conversions are achieved within 2 h at 70 °C, which makes this new PISA formulation well-suited for in situ SAXS studies using a new reaction cell. This bespoke cell enables efficient stirring and hence allows in situ monitoring during RAFT emulsion polymn. for the first time. For example, the onset of micellization and subsequent evolution in particle size can be studied when prepg. PGMA29-PMOEMA30 spheres at 10% wt./wt. solids. When targeting PGMA29-PMOEMA70 vesicles under the same conditions, both the micellar nucleation event and the subsequent evolution in the diblock copolymer morphol. from spheres to worms to vesicles are obsd. These new insights significantly enhance our understanding of the PISA mechanism during RAFT aq. emulsion polymn.
- 37Czajka, A.; Armes, S. P. In Situ SAXS Studies of a Prototypical RAFT Aqueous Dispersion Polymerization Formulation: Monitoring the Evolution in Copolymer Morphology during Polymerization-Induced Self-Assembly. Chem. Sci. 2020, 11 (42), 11443– 11454, DOI: 10.1039/D0SC03411H[Crossref], [PubMed], [CAS], Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhvVGgs7rJ&md5=067f3bfb363bace53ee7d9e288afb6ffIn situ SAXS studies of a prototypical RAFT aqueous dispersion polymerization formulation: monitoring the evolution in copolymer morphology during polymerization-induced self-assemblyCzajka, Adam; Armes, Steven P.Chemical Science (2020), 11 (42), 11443-11454CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)Small-angle X-ray scattering (SAXS) is used to characterize the in situ formation of diblock copolymer spheres, worms and vesicles during reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. of 2-hydroxypropyl methacrylate at 70°C using a poly(glycerol monomethacrylate) steric stabilizer. The 1H NMR spectroscopy indicates more than 99% HPMA conversion within 80 min, while transmission electron microscopy and dynamic light scattering studies are consistent with the final morphol. being pure vesicles. Anal. of time-resolved SAXS patterns for this prototypical polymn.-induced self-assembly (PISA) formulation enables the evolution in copolymer morphol., particle diam., mean aggregation no., solvent vol. fraction, surface d. of copolymer chains and their mean inter-chain sepn. distance at the nanoparticle surface to be monitored. Furthermore, the change in vesicle diam. and membrane thickness during the final stages of polymn. supports an 'inward growth' mechanism.
- 38Derry, M. J.; Fielding, L. A.; Warren, N. J.; Mable, C. J.; Smith, A. J.; Mykhaylyk, O. O.; Armes, S. P. In Situ Small-Angle X-Ray Scattering Studies of Sterically-Stabilized Diblock Copolymer Nanoparticles Formed during Polymerization-Induced Self-Assembly in Non-Polar Media. Chem. Sci. 2016, 7 (8), 5078– 5090, DOI: 10.1039/C6SC01243D[Crossref], [PubMed], [CAS], Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xms1Krs7o%253D&md5=2d1c2ec1a0a40ea201ff7892b346fa62In situ small-angle X-ray scattering studies of sterically-stabilized diblock copolymer nanoparticles formed during polymerization-induced self-assembly in non-polar mediaDerry, Matthew J.; Fielding, Lee A.; Warren, Nicholas J.; Mable, Charlotte J.; Smith, Andrew J.; Mykhaylyk, Oleksandr O.; Armes, Steven P.Chemical Science (2016), 7 (8), 5078-5090CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)Reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn. of benzyl methacrylate (BzMA) is utilized to prep. a series of poly(stearyl methacrylate)-poly(benzyl methacrylate) (PSMA-PBzMA) diblock copolymer nano-objects at 90°C directly in mineral oil. Polymn.-induced self-assembly (PISA) occurs under these conditions, with the resulting nanoparticles exhibiting spherical, worm-like or vesicular morphologies when using a relatively short PSMA13 macromol. chain transfer agent (macro-CTA), as confirmed by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies. Only kinetically-trapped spherical nanoparticles are obtained when using longer macro-CTAs (e.g. PSMA18 or PSMA31), with higher mean ds.p. (DPs) for the PBzMA core-forming block simply producing progressively larger spheres. SAXS is used for the first time to monitor the various morphol. transitions that occur in situ during the RAFT dispersion polymn. of BzMA when targeting either spheres or vesicles as the final copolymer morphol. This powerful characterization technique enables the evolution of particle diam., mean aggregation no., no. of copolymer chains per unit surface area (Sagg) and the distance between adjacent copolymer chains at the core-shell interface (ditt) to be monitored as a function of monomer conversion for kinetically-trapped spheres. Moreover, the gradual evolution of copolymer morphol. during PISA is confirmed unequivocally, with approx. 'lifetimes' assigned to the intermediate pure sphere and worm morphologies when targeting PSMA13-PBzMA150 vesicles. Within vesicle phase space, the membrane thickness (Tm) increases monotonically with PBzMA DP. Furthermore, a combination of dynamic light scattering (DLS), TEM and post mortem SAXS studies indicate that the lumen vol. is reduced while the overall vesicle dimensions remain essentially const. Thus the constrained vesicles grow inwards, as recently reported for an aq. PISA formulation. This suggests a universal vesicle growth mechanism for all PISA formulations.
- 39Goodall, A. R.; Wilkinson, M. C.; Hearn, J. Mechanism of Emulsion Polymerization of Styrene in Soap-Free Systems. J. Polym. Sci., Polym. Chem. Ed. 1977, 15 (9), 2193– 2218, DOI: 10.1002/pol.1977.170150912[Crossref], [CAS], Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2sXltlKntLs%253D&md5=be813787d96d6e9e512fa9b86a966d04Mechanism of emulsion polymerization of styrene in soap-free systemsGoodall, A. R.; Wilkinson, M. C.; Hearn, J.Journal of Polymer Science, Polymer Chemistry Edition (1977), 15 (9), 2193-218CODEN: JPLCAT; ISSN:0360-6376.The formation and growth of monodisperse polystyrene latex particles in the absence of added surfactant was studied by sampling polymn. reactions at different times and detg. the surface and bulk properties of the latex. A large no. of nuclei in excess of 5 x 1012/mL were generated during the first minute of reaction, but this decreased due to coagulation until a const. no. (1011-1012/mL) was reached. The rate of polymn. per particle was then proportional to the particle radius. Gel-permeation chromatog. showed that the initial particles consist mainly of material of mol. wt. 1000 with a small amt. of polymer up to mol. wt. 106, and the presence of this low mol. wt. polymer, which in many cases can still be detected after 100% conversion, is indicative of particle formation via a micellization-type mechanism involving short-chain (mol. wt. 500) free-radical oligomers. No.-av. mol. wt. values detd. for the latex particles throughout the reactions show that the mol. wt. increases to a max. of ∼105 as the particles grow. The presence of anomalous regions within the particles was confirmed by transmission electron microscopy, scanning electron microscopy, and gas adsorption studies. It was also possible to re-expose these regions within apparently homogeneous particles by stirring with styrene [100-42-5] monomer, indicating a mol. wt. heterogeneity within the latex particles. The presence of SO4, CO2H, and OH groups upon the latex particle surfaces was detd. by conductometric titrn.
- 40Hawkett, B. S.; Napper, D. H.; Gilbert, R. G. Seeded Emulsion Polymerization of Styrene. J. Chem. Soc., Faraday Trans. 1 1980, 76 (0), 1323– 1343, DOI: 10.1039/f19807601323[Crossref], [CAS], Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3cXksVOhtbY%253D&md5=c48293e078d0b68eea2de5cfdcd579f8Seeded emulsion polymerization of styreneHawkett, Brian S.; Napper, Donald H.; Gilbert, Robert G.Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases (1980), 76 (6), 1323-43CODEN: JCFTAR; ISSN:0300-9599.The kinetics of the seeded emulsion polymn. of styrene [100-42-5] with swollen seed of radii 44-79 nm were measured dilatometrically. Conversion vs. time curves showed an increase in the instantaneous polymn. rate followed by an apparent steady state domain. The kinetic parameters detg. both the entry of free radicals into the latex particles and 1st order loss of free radicals from the particles were detd. directly. The rate coeff. of the latter varied with the inverse square of the swollen particle radius, indicating diffusion control. The magnitude of the obsd. entry rate coeff. coupled with their dependence on initiator concn. indicated that free radical capture by the seed particles was relatively inefficient. The capture rate, however, increased significantly with decreasing initiator concn. for a const. no. of seed particles. The av. no. of radicals per particle can be <0.5 under suitable conditions and, thus, styrene can follow Smith-Ewart case 1 kinetics. A background initiation process requiring no initiator was obsd. and appeared to be the emulsion polymn. equiv. of thermal polymn. of bulk styrene.
- 41Capek, I.; Lin, S. Y.; Hsu, T. J.; Chern, C. S. Effect of Temperature on Styrene Emulsion Polymerization in the Presence of Sodium Dodecyl Sulfate. II. J. Polym. Sci., Part A: Polym. Chem. 2000, 38 (9), 1477– 1486, DOI: 10.1002/(SICI)1099-0518(20000501)38:9<1477::AID-POLA10>3.0.CO;2-Y[Crossref], [CAS], Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXisFOksr8%253D&md5=d811cf83e95ef8ba1fcfce3358f81fe3Effect of temperature on styrene emulsion polymerization in the presence of sodium dodecyl sulfate. IICapek, Ignac; Lin, Shi-Yow; Hsu, Tien-Jung; Chern, Chorng-ShyanJournal of Polymer Science, Part A: Polymer Chemistry (2000), 38 (9), 1477-1486CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)The batch emulsion polymn. kinetics of styrene initiated by a water-sol. peroxydisulfate, i.e., sodium peroxydisulfate, at different temps. in the presence of sodium dodecyl sulfate was investigated. The curves of the polymn. rate vs. conversion show two distinct nonstationary-rate intervals and a shoulder occurring at a high conversion, whereas the stationary-rate interval is very short. The nonstationary-state polymn. is discussed in terms of the long-term particle-nucleation period, the addnl. formation of radicals by thermal initiation, the depressed monomer-droplet degrdn., the elimination of charged radicals through aq.-phase termination, the relatively narrow particle-size distribution and const. polydispersity index throughout the reaction, and a mixed mode of continuous particle nucleation. The max. rate of polymn. (or the no. of polymer particles nucleated) is proportional to the rate of initiation to the 0.27 power, which indicates lower nucleation efficiency as compared to classical emulsion polymn. The low activation energy of polymn. is attributed to the small barrier for the entering radicals. The overall activation energy was controlled by the initiation and propagation steps. The high ratio of the absorption rate of radicals by latex particles to the formation rate of radicals in water can be attributed to the efficient entry of uncharged radicals and the addnl. formation of radicals by thermally induced initiation.
- 42Wutzel, H.; Samhaber, W. M. Exploring the Limits of Emulsion Polymerization of Styrene for the Synthesis of Polymer Nanoparticles. Monatsh. Chem. 2007, 138 (4), 357– 361, DOI: 10.1007/s00706-007-0605-6[Crossref], [CAS], Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXktlOhurc%253D&md5=a42ee6c054fff2d88550d9a3a04b5b2aExploring the Limits of Emulsion Polymerization of Styrene for the Synthesis of Polymer NanoparticlesWutzel, Harald; Samhaber, Wolfgang M.Monatshefte fuer Chemie (2007), 138 (4), 357-361CODEN: MOCMB7; ISSN:0026-9247. (Springer Wien)Suspensions of polymer nanoparticles in water (latexes) with av. particle diams. between 20 and 80 nm were synthesized by batch emulsion polymn. of styrene using sodium dodecyl sulfate (SDS) as surfactant and potassium persulfate (KPS) as initiator. The influence of surfactant concn., initiator concn., monomer concn., and reaction temp. on the final av. particle diams. and size distributions of the latexes were studied. The no. of particles generated was proportional to the 0.56 power of the emulsifier concn. and to the 0.37 power of the initiator concn. in the whole concn. range which was obsd. Furthermore, the final no. of particles was dependent on the reaction temp. to the 2.06 power. With these correlations the av. particle no. and the av. particle size could be estd., and the results were in good agreement (±6%) with the exptl. values. A redn. of the monomer/water ratio from 1:5 to 1:20 yielded smaller particle diams., while leaving the particle no. unaffected. The lower particle size limits for monomer ratios of 1:10 and 1:15 were estd. with diams. of about 18 and 16 nm.
- 43Li, Y.; Lindsay, S. M. Polystyrene Latex Particles as a Size Calibration for the Atomic Force Microscope. Rev. Sci. Instrum. 1991, 62 (11), 2630– 2633, DOI: 10.1063/1.1142243[Crossref], [CAS], Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXms1ChtL0%253D&md5=d837da10ecaf98a456cd447f8903b24cPolystyrene latex particles as a size calibration for the atomic force microscopeLi, Y.; Lindsay, S. M.Review of Scientific Instruments (1991), 62 (11), 2630-3CODEN: RSINAK; ISSN:0034-6748.A simple method for spreading polystyrene-latex spheres onto mica substrates to form highly cryst. layers is described. These layers can be used as a simple calibration std. for the at. force microscope in the nanometer to micron size range. In particular, they provide simultaneous x, y, and z calibration. A concn. of particles of ∼0.01% is good for forming ordered structures. Two-dimensional polycryst. structures of polystyrene spheres with different packing orders (cubic and hexagonal close-pack) and some defects (vacancies, dislocations, and grain boundaries) were obsd.
- 44Molina-Bolívar, J. A.; Galisteo-González, F. Latex Immunoagglutination Assays. J. Macromol. Sci., Polym. Rev. 2005, 45 (1), 59– 98, DOI: 10.1081/MC-200045819[Crossref], [CAS], Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXit12ktb8%253D&md5=6f44930181bfad9ca02d8ff23d9a3f11Latex immunoagglutination assaysMolina-Bolivar, J. A.; Galisteo-Gonzalez, F.Journal of Macromolecular Science, Polymer Reviews (2005), C45 (1), 59-98CODEN: JMSPCG; ISSN:1532-1797. (Taylor & Francis, Inc.)Latex immunoagglutination assays continue to be widely used in biol. and medicine for the detection of small quantities of an antibody or antigen of interest in fluid test samples. Main characteristics of prepn. and use of these assays are examd. here. Phys. adsorption of proteins onto latex particles surface, with special relevance to Igs, is analyzed with major attention to those factors that influence adsorption: medium conditions such as pH and ionic strength, surface characteristics as type and amt. of charge, or hydrophobicity. Different functionalized latexes for covalent linking are also presented, as well as the corresponding chem. reactions. Techniques for the detection and quantification of the immunoreaction are briefly summarized, including visual observation, light scattering, turbidimetry, nephelometry, and angular anisotropy. Finally, some problems of colloidal stability of these latex assays are analyzed, as well as the different solns. applied by scientists to solve them.
- 45Seelenmeyer, S.; Ballauff, M. Analysis of Surfactants Adsorbed onto the Surface of Latex Particles by Small-Angle X-Ray Scattering. Langmuir 2000, 16 (9), 4094– 4099, DOI: 10.1021/la990998f[ACS Full Text], [CAS], Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXitFGhurY%253D&md5=6881a44ce50678888a1393154855556dAnalysis of Surfactants Adsorbed onto the Surface of Latex Particles by Small-Angle X-ray ScatteringSeelenmeyer, S.; Ballauff, M.Langmuir (2000), 16 (9), 4094-4099CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)A comprehensive study of the process of adsorption of a nonionic surfactant C18E112 onto poly(styrene) (PS) latex particles by small-angle X-ray scattering (SAXS) is presented. The PS latexes (particle radii 35 and 71 nm) employed in this investigation bear no chem. bound surface charges. The anal. of the process of adsorption by SAXS demonstrates that the point of satn. of the surface may be detd. directly from the scattering curves. Free micelles are formed beyond satn., and no second layer of the surfactant is built up at higher concns. of the surfactant. Any assocn. of the micelles with the covered latex particle can be ruled out as well. Moreover, an anal. of the radial structure of the surface layer in terms the zeroth and the second moment of the electron d. of the layers along the radial direction is given. Both moments can directly be obtained from the SAXS data. The zeroth moment of the excess electron d. corroborates the finding that the surfactant is firmly adsorbed onto the surface of the particles. The av. extension of the adsorbed layer (2-4 nm) as express through the second moment increases with the amt. of adsorbed surfactant. This points to a stretching of the chains due to their mutual interaction when the point of satn. of the surfaced is approached.
- 46Akpinar, B.; Fielding, L. A.; Cunningham, V. J.; Ning, Y.; Mykhaylyk, O. O.; Fowler, P. W.; Armes, S. P. Determining the Effective Density and Stabilizer Layer Thickness of Sterically Stabilized Nanoparticles. Macromolecules 2016, 49 (14), 5160– 5171, DOI: 10.1021/acs.macromol.6b00987[ACS Full Text], [CAS], Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFWgsL%252FI&md5=9fed176efbdb916c4bfb8fd962bf6f41Determining the Effective Density and Stabilizer Layer Thickness of Sterically Stabilized NanoparticlesAkpinar, Bernice; Fielding, Lee A.; Cunningham, Victoria J.; Ning, Yin; Mykhaylyk, Oleksandr O.; Fowler, Patrick W.; Armes, Steven P.Macromolecules (Washington, DC, United States) (2016), 49 (14), 5160-5171CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)A series of model sterically stabilized diblock copolymer nanoparticles has been designed to aid the development of anal. protocols in order to det. two key parameters: the effective particle d. and the steric stabilizer layer thickness. The former parameter is essential for high resoln. particle size anal. based on anal. (ultra)centrifugation techniques (e.g., disk centrifuge photosedimentometry, DCP), whereas the latter parameter is of fundamental importance in detg. the effectiveness of steric stabilization as a colloid stability mechanism. The diblock copolymer nanoparticles were prepd. via polymn.-induced self-assembly (PISA) using RAFT aq. emulsion polymn.: this approach affords relatively narrow particle size distributions and enables the mean particle diam. and the stabilizer layer thickness to be adjusted independently via systematic variation of the mean d.p. of the hydrophobic and hydrophilic blocks, resp. The hydrophobic core-forming block was poly(2,2,2-trifluoroethyl methacrylate) [PTFEMA], which was selected for its relatively high d. The hydrophilic stabilizer block was poly(glycerol monomethacrylate) [PGMA], which is a well-known non-ionic polymer that remains water-sol. over a wide range of temps. Four series of PGMAx-PTFEMAy nanoparticles were prepd. (x = 28, 43, 63, and 98, y = 100-1400) and characterized via transmission electron microscopy (TEM), dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS). It was found that the d.p. of both the PGMA stabilizer and core-forming PTFEMA had a strong influence on the mean particle diam., which ranged from 20 to 250 nm. Furthermore, SAXS was used to det. radii of gyration of 1.46 to 2.69 nm for the solvated PGMA stabilizer blocks. Thus, the mean effective d. of these sterically stabilized particles was calcd. and detd. to lie between 1.19 g cm-3 for the smaller particles and 1.41 g cm-3 for the larger particles; these values are significantly lower than the solid-state d. of PTFEMA (1.47 g cm-3). Since anal. centrifugation requires the d. difference between the particles and the aq. phase, detg. the effective particle d. is clearly vital for obtaining reliable particle size distributions. Furthermore, selected DCP data were recalcd. by taking into account the inherent d. distribution superimposed on the particle size distribution. Consequently, the true particle size distributions were found to be somewhat narrower than those calcd. using an erroneous single d. value, with smaller particles being particularly sensitive to this artifact.
- 47Fontenot, K.; Schork, F. J. Batch Polymerization of Methyl Methacrylate in Mini/Macroemulsions. J. Appl. Polym. Sci. 1993, 49 (4), 633– 655, DOI: 10.1002/app.1993.070490410[Crossref], [CAS], Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXltFOqs7o%253D&md5=5e7fba954a959d6858bfd552b10a55afBatch polymerization of methyl methacrylate in mini/macroemulsionsFontenot, K.; Schork, F. J.Journal of Applied Polymer Science (1993), 49 (4), 633-55CODEN: JAPNAB; ISSN:0021-8995.The kinetics of the isothermal batch macroemulsion and miniemulsion polymns. of Me methacrylate at 50° were studied. Hexadecane was used as the cosurfactant or swelling agent. The nucleation mechanisms were different between macroemulsions and miniemulsions. The effect of surfactant, cosurfactant, initiator, shear, and hold time on droplet nucleation was studied. The miniemulsion particles contained more radicals on av. than the macroemulsion particles using certain recipes. This resulted in higher polymn. rates for the miniemulsions at identical particle nos. The latex-particle-size distributions were similar even though the miniemulsion droplets start out with a high polydispersity of ∼1.5. Miniemulsion latexes were more stable under shear. Conductance of emulsions during polymn. was a valuable online tool for investigating particle nucleation and growth.
- 48Reimers, J. L.; Schork, F. J. Predominant Droplet Nucleation in Emulsion Polymerization. J. Appl. Polym. Sci. 1996, 60 (2), 251– 262, DOI: 10.1002/(SICI)1097-4628(19960411)60:2<251::AID-APP13>3.0.CO;2-8[Crossref], [CAS], Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xhs12lsLc%253D&md5=7661a6176082e19e1c739c8e4aac5a89Predominant droplet nucleation in emulsion polymerizationReimers, J. L.; Schork, F. J.Journal of Applied Polymer Science (1996), 60 (2), 251-62CODEN: JAPNAB; ISSN:0021-8995. (Wiley)Emulsions stabilized against diffusional degrdn. by incorporating a polymeric cosurfactant have been produced and polymd. The presence of large nos. of small droplets shifts the nucleation mechanism from micellar or homogeneous nucleation, to droplet nucleation. When an efficient cosurfactant is used, this process is referred to as miniemulsion polymn. The polymer, however, is a poor cosurfactant. Its advantage is that, unlike most cosurfactants, it is innocuous in the recipe. Results indicate that even a poor cosurfactant (polymer) is adequate to stabilize small droplets against diffusional degrdn. long enough to nucleate them into polymer particles. The dependence of the concn. and mol. wt. of the cosurfactant on the droplet size and distribution is investigated. Droplet diams. range from 19.5 to 141.2 nm with polydispersities of about 1.023. The polymeric cosurfactant affects the mechanism of nucleation. Online conductance measurements are used to successfully differentiate between nucleation mechanisms. The obsd. reaction rates are dependent on the amt. of polymeric cosurfactant present.
- 49Santos, A. F.; Lima, E. L.; Pinto, J. C.; Graillat, C.; McKenna, T. Online Monitoring of the Evolution of the Number of Particles in Emulsion Polymerization by Conductivity Measurements. I. Model Formulation. J. Appl. Polym. Sci. 2003, 90 (5), 1213– 1226, DOI: 10.1002/app.12657[Crossref], [CAS], Google Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXntFylur8%253D&md5=686e4b8bc29f1168f16f7f089a2854dbOnline monitoring of the evolution of the number of particles in emulsion polymerization by conductivity measurements. I. Model formulationSantos, A. F.; Lima, E. L.; Pinto, J. C.; Graillat, C.; McKenna, T.Journal of Applied Polymer Science (2003), 90 (5), 1213-1226CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)A cond. meter is an inexpensive instrument that can easily be installed in polymn. reactors. This instrument can be used to monitor ionic species without time-consuming calibrations. A probe is inserted into the media, providing in situ measurements of cond. in real time. For emulsion polymn. reactions, the cond. meter can respond to changes in the ionic surfactant concn., allowing the detn. of surfactant dynamics in the media. The surfactant concn. can then be related to the changes in the surface area of the polymer particle phase, which can be linked to nucleation or coagulation phenomena. In this study, a cond. meter was coupled to a calorimetric reactor to provide in situ and online measurements of cond. during the emulsion polymn. of styrene, with sodium dodecyl sulfate as an anionic surfactant and with potassium persulfate as a free-radical initiator. A semiempirical model was built to describe the cond. signal as a function of the latex compn. and the reactor temp. The model was inverted and combined with the available cond. signal, conversion, and temp. measurements and was able to accurately predict the no. of polymer particles in the latex and the surfactant concns. in the many phases, without online measurements of the particle size.
- 50Banthia, A. K.; Mandal, B. M.; Palit, S. R. Dye-Partition Method of Analysis of End Groups in Nonpolar Polymers Re-Examined: Sulfate End Groups in Persulfate-Initiated Polystyrene. J. Polym. Sci., Polym. Chem. Ed. 1977, 15 (4), 945– 957, DOI: 10.1002/pol.1977.170150416[Crossref], [CAS], Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2sXhsFKitbc%253D&md5=01c96e1c19f6c7c3269d2e4ff004b5c6Dye-partition method of analysis of end groups in nonpolar polymers re-examined: sulfate end groups in persulfate-initiated polystyreneBanthia, Ajit K.; Mandal, Broja M.; Palit, Santi R.Journal of Polymer Science, Polymer Chemistry Edition (1977), 15 (4), 945-57CODEN: JPLCAT; ISSN:0360-6376.Sulfate, sulfonate, and isothiouronium salt end groups in polystyrene (I) [9003-53-6] prepd. using K2S2O8, Na2SO3-Cu+2-O2, and FeCl3-thiourea initiators, resp., were estd. by the dye partition method. While the persulfate-initiated polymers contained very low amts. of sulfate end groups (0.05-0.3 per polymer mol.), the other 2 initiator systems yielded polymers with about 2 salt end groups per polymer mol. The low amt. of sulfate end group in persulfate-initiated I is in conformity with the initiation mechanism of A. Ledwith and P.J. Russell (1976) for persulfate-initiated emulsion polymn. of styrene, and supports earlier findings that polymer polarity does not affect the results of end-group anal. by the dye-partition technique.
- 51Ghosh, P.; Chadha, S. C.; Mukherjee, A. R.; Palit, S. R. Endgroup Studies in Persulfate-Initiated Vinyl Polymer by Dye Techniques. Part I. Initiation by Persulfate Alone. J. Polym. Sci., Part A: Gen. Pap. 1964, 2 (10), 4433– 4440, DOI: 10.1002/pol.1964.100021013
- 52Tauer, K.; Deckwer, R. Polymer End Groups in Persulfate-Initiated Styrene Emulsion Polymerization. Acta Polym. 1998, 49 (8), 411– 416, DOI: 10.1002/(SICI)1521-4044(199808)49:8<411::AID-APOL411>3.0.CO;2-D[Crossref], [CAS], Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXlslOjs7w%253D&md5=d21634e040f866d772d6ef48df835109Polymer and groups in persulfate-initiated styrene emulsion polymerizationTauer, K.; Deckwer, R.Acta Polymerica (1998), 49 (8), 411-416CODEN: ACPODY; ISSN:0323-7648. (Wiley-VCH Verlag GmbH)MALDI-TOF-MS investigations of the polymer inside the particles at the end of a persulfate-initiated emulsifier-free emulsion polymn. of styrene reveal, beside sulfate groups, a variety of different end groups of the polymer mols. almost independent of the buffer concn. employed during the polymn. The results support at least the existence of the following end group combinations: H-H, H-OH, K+-OO-OH, K+-OO-K+-OO, HO-OH, K+-OS3-H, K+-OSO3-OH, and K+-OSO3-K+-OSO3. These results lead to conclusions concerning particle nucleation and radical entry. As non-micellar particle nucleation is governed by the soly. of waterborne oligomers, chains started with radicals formed by side reactions in the aq. phase obviously play an important role in particle nucleation. Concerning radical entry, the results suggest that surface activity of the entering radicals is not a prerequisite.
- 53Pedersen, J. S.; Gerstenberg, M. C. Scattering Form Factor of Block Copolymer Micelles. Macromolecules 1996, 29 (4), 1363– 1365, DOI: 10.1021/ma9512115[ACS Full Text], [CAS], Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XltlWjsA%253D%253D&md5=e6f549fc773b455a50c0d6e157ca4981Scattering Form Factor of Block Copolymer MicellesPedersen, Jan Skov; Gerstenberg, Michael C.Macromolecules (1996), 29 (4), 1363-5CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)The form factor of a micelle model with a spherical core and Gaussian polymer chains attached to the surface was calcd. anal. and the results were compared to Monte Carlo simulations. Excluded vol. interactions between the core and the polymers were introduced in the simulations. The expansion of the coils due to this effect can be mimicked in the anal. calcns. by moving the center of mass of the chains away from the surface of the core. The anal. expression for the form factor has been used for analyzing small-angle scattering data.
- 54Li, T.; Senesi, A. J.; Lee, B. Small Angle X-Ray Scattering for Nanoparticle Research. Chem. Rev. 2016, 116 (18), 11128– 11180, DOI: 10.1021/acs.chemrev.5b00690[ACS Full Text], [CAS], Google Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlsF2qsrw%253D&md5=659565f88b80ce6994bb98c07f034eb2Small Angle X-ray Scattering for Nanoparticle ResearchLi, Tao; Senesi, Andrew J.; Lee, ByeongduChemical Reviews (Washington, DC, United States) (2016), 116 (18), 11128-11180CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)X-ray scattering is a structural characterization tool that has impacted diverse fields of study. It is unique in its ability to examine materials in real time and under realistic sample environments, enabling researchers to understand morphol. at nanometer and angstrom length scales using complementary small and wide angle X-ray scattering (SAXS, WAXS), resp. Herein, we focus on the use of SAXS to examine nanoscale particulate systems. We provide a theor. foundation for X-ray scattering, considering both form factor and structure factor, as well as the use of correlation functions, which may be used to det. a particle's size, size distribution, shape, and organization into hierarchical structures. The theory is expanded upon with contemporary use cases. Both transmission and reflection (grazing incidence) geometries are addressed, as well as the combination of SAXS with other X-ray and non-X-ray characterization tools. We conclude with an examn. of several key areas of research where X-ray scattering has played a pivotal role, including in situ nanoparticle synthesis, nanoparticle assembly, and operando studies of catalysts and energy storage materials. Throughout this review we highlight the unique capabilities of X-ray scattering for structural characterization of materials in their native environment.
- 55Narayanan, T.; Wacklin, H.; Konovalov, O.; Lund, R. Recent Applications of Synchrotron Radiation and Neutrons in the Study of Soft Matter. Crystallogr. Rev. 2017, 23 (3), 160– 226, DOI: 10.1080/0889311X.2016.1277212[Crossref], [CAS], Google Scholar55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXisVaks78%253D&md5=15e7445b1320185847e34352e9d3b5c8Recent applications of synchrotron radiation and neutrons in the study of soft matterNarayanan, Theyencheri; Wacklin, Hanna; Konovalov, Oleg; Lund, ReidarCrystallography Reviews (2017), 23 (3), 160-226CODEN: CRRVEN; ISSN:0889-311X. (Taylor & Francis Ltd.)The broad range of applications of synchrotron and neutron scattering in the investigation of soft condensed matter is reviewed. Appropriate combinations of these techniques allow probing the structure and dynamics of these complex systems from sub-nm to micron size scales and picoseconds to seconds and longer time ranges. Applications include a myriad of systems such as polymers, colloids, surfactants, phospholipids, biol. macromols. and functional materials both in bulk and at interfaces. Most studies are performed in situ under the real thermodn. state of the given system and large ensemble averaged information is readily obtained. The new generations of synchrotron and neutron sources open possibilities for investigating more complex soft matter systems in hitherto unexplored dynamical states.
- 56Takahashi, R.; Miwa, S.; Sobotta, F. H.; Lee, J. H.; Fujii, S.; Ohta, N.; Brendel, J. C.; Sakurai, K. Unraveling the Kinetics of the Structural Development during Polymerization-Induced Self-Assembly: Decoupling the Polymerization and the Micelle Structure. Polym. Chem. 2020, 11, 1514– 1524, DOI: 10.1039/C9PY01810G[Crossref], [CAS], Google Scholar56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtVektrk%253D&md5=85cb40c5284055c0b9b46c8bed6f5f50Unraveling the kinetics of the structural development during polymerization-induced self-assembly: decoupling the polymerization and the micelle structureTakahashi, Rintaro; Miwa, Shotaro; Sobotta, Fabian H.; Lee, Ji Ha; Fujii, Shota; Ohta, Noboru; Brendel, Johannes C.; Sakurai, KazuoPolymer Chemistry (2020), 11 (8), 1514-1524CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)Upon extending a hydrophobic polymer chain from the end of a preceding hydrophilic chain in aq. solns., the resultant block copolymers may eventually undergo self-assembly. Further chain propagation continues in the newly formed hydrophobic polymer rich domain. This process is often referred to as polymn.-induced self-assembly (PISA). Its kinetics are detd. by the polymn. and the micelle formation/growth, which may influence each other, possibly leading to a highly complex process of structural development. In this study, we examd. PISA in aq. soln. on the reversible addn. fragmentation chain transfer (RAFT) dispersion polymn. of poly(N-acryloylmorpholine)-b-poly(N-acryloylthiomorpholine). Using in situ small-angle X-ray scattering (SAXS) and NMR spectroscopy (NMR), the polymn. and micelle formation were obsd. In the anal., because the time scale of the micelle formation/growth is much shorter than that of the polymn., the polymn. and micelle formation/growth can be decoupled. Thus, these were sep. analyzed in depth, and a combination of the kinetics of RAFT polymn. and the simple scaling theory of the micellar structures can quant. describe the overall micellar structural development during PISA. This study provides an unprecedented insight into the processes underlying PISA and deepens our quant. understanding of it.
- 57Ballauff, M. SAXS and SANS Studies of Polymer Colloids. Curr. Opin. Colloid Interface Sci. 2001, 6 (2), 132– 139, DOI: 10.1016/S1359-0294(01)00072-3[Crossref], [CAS], Google Scholar57https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXktFWnsLY%253D&md5=9ce2496b9042232cbaf4d14400c977faSAXS and SANS studies of polymer colloidsBallauff, M.Current Opinion in Colloid & Interface Science (2001), 6 (2), 132-139CODEN: COCSFL; ISSN:1359-0294. (Elsevier Science Ltd.)The anal. of latex particles by small-angle scattering (small-angle X-ray scattering, SAXS; small-angle neutron scattering, SANS) is reviewed with 42 refs. Small-angle scattering techniques give information on the radial structure of the particles as well as on their spatial correlation. Recent progress in instrumentation allows to extend SANS and SAXS to the q-range of light scattering. Moreover, contrast variation employed in SANS and SAXS studies may lead to an unambiguous detn. of the radial scattering length d. of the particles in situ, i.e. in suspension. Hence, these techniques are highly valuable for a comprehensive anal. of polymer colloids as shown by the examples discussed herein.
- 58Wagner, J.; Härtl, W.; Hempelmann, R. Characterization of Monodisperse Colloidal Particles: Comparison between SAXS and DLS. Langmuir 2000, 16 (9), 4080– 4085, DOI: 10.1021/la991125o[ACS Full Text], [CAS], Google Scholar58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXhvFKms7w%253D&md5=0f379dc7d152f980e999a0a123e71077Characterization of monodisperse colloidal particles: comparison between SAXS and DLSWagner, Joachim; Haertl, Wolfram; Hempelmann, RolfLangmuir (2000), 16 (9), 4080-4085CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Fluoroalkyl (meth)acrylate polymer colloids with low refractive index are prepd. via emulsion polymn. The characterization is done using small-angle X-ray scattering and dynamic light scattering. The independently obtained particle size distributions are in remarkable mutual agreement and give evidence for the monodispersity of our particles. The small-angle scattering signal of such monodisperse samples is influenced by the resoln. of the exptl. setup. We discuss a method to take such instrumental contributions into consideration and show that the divergence of the primary beam is the most important factor using a pinhole camera with flat single-crystal monochromator.
- 59Bolze, J.; Ballauff, M.; Kijlstra, J.; Rudhardt, D. Application of Small-Angle X-Ray Scattering as a Tool for the Structural Analysis of Industrial Polymer Dispersions. Macromol. Mater. Eng. 2003, 288 (6), 495– 502, DOI: 10.1002/mame.200390046[Crossref], [CAS], Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXltlWitL0%253D&md5=177da42a2d945f20cf343318865d3a1cApplication of small-angle X-ray scattering as a tool for the structural analysis of industrial polymer dispersionsBolze, Joerg; Ballauff, Matthias; Kijlstra, Johan; Rudhardt, DanielMacromolecular Materials and Engineering (2003), 288 (6), 495-502CODEN: MMENFA; ISSN:1438-7492. (Wiley-VCH Verlag GmbH & Co. KGaA)Small-angle X-ray scattering (SAXS) was applied for the structural anal. of an industrial polymer dispersion in water (synthetic latex). For the prepn. of the spherical latex particles under investigation, butadiene, styrene, and acrylic acid were used as monomers in a seeded emulsion polymn. process. The product is widely used as a film-forming agent for coatings in the paper-making industry. It was demonstrated that by measuring the SAXS curves at different contrasts the overall particle size, mass d., polydispersity, and degree of heterogeneity can be estd. with a good accuracy, even without the necessity of a detailed fitting procedure. In particular, one obtains information about the spatial distribution of the various monomer units within the particles. Five isoscattering points could be obsd. in the contrast variation measurements and the scattering curves at all contrasts could be modeled with a fully consistent set of fit parameters. It is thus safe to conclude that the contrast agent sucrose does not affect the particle structure. A quant. fitting of the exptl. data set revealed that a significant amt. of the poly(acrylic acid) was preferentially located in a thin shell of ca. 2 nm thickness around the core of the particles, that was mainly formed by poly(styrene-co-butadiene). The obtained results were fully consistent with addnl. measurements of the particle mass d., of the hydrodynamic particle radius by dynamic light scattering, and of the particle surface charge by potentiometric titrn. It was concluded that SAXS is a highly useful tool for characterizing the structure of industrial latexes.
- 60Ballauff, M.; Bolze, J.; Dingenouts, N.; Hickl, P.; Pötschke, D. Small-Angle X-Ray Scattering on Latexes. Macromol. Chem. Phys. 1996, 197 (10), 3043– 3066, DOI: 10.1002/macp.1996.021971001[Crossref], [CAS], Google Scholar60https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xmt1WisLc%253D&md5=80f028fd6854b055abd25f84c1f2267fSmall-angle x-ray scattering on latexesBallauff, Matthias; Bolze, Joerg; Dingenouts, Nico; Hickl, Peter; Poetschke, DominicMacromolecular Chemistry and Physics (1996), 197 (10), 3043-3066CODEN: MCHPES; ISSN:1022-1352. (Huethig & Wepf)Recent small-angle x-ray scattering (SAXS) studies of polymer latexes are reviewed with 106 refs. to show that SAXS can be used to study the structure and interactions of polymer latexes with great accuracy.
- 61Balmer, J. A.; Mykhaylyk, O. O.; Schmid, A.; Armes, S. P.; Fairclough, J. P. A.; Ryan, A. J. Characterization of Polymer-Silica Nanocomposite Particles with Core-Shell Morphologies Using Monte Carlo Simulations and Small Angle X-Ray Scattering. Langmuir 2011, 27 (13), 8075– 8089, DOI: 10.1021/la201319h[ACS Full Text], [CAS], Google Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXntlCqtrg%253D&md5=9ea3ca1b4a8edcc48f631a3152519b91Characterization of Polymer-Silica Nanocomposite Particles with Core-Shell Morphologies using Monte Carlo Simulations and Small Angle X-ray ScatteringBalmer, Jennifer A.; Mykhaylyk, Oleksandr O.; Schmid, Andreas; Armes, Steven P.; Fairclough, J. Patrick A.; Ryan, Anthony J.Langmuir (2011), 27 (13), 8075-8089CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)A two-population model based on std. small-angle x-ray scattering (SAXS) equations is verified for the anal. of core-shell structures comprising spherical colloidal particles with particulate shells. First, Monte Carlo simulations of core-shell structures are performed to demonstrate the applicability of the model. Three possible shell packings are considered: ordered silica shells due to either charge-dependent repulsive or size-dependent Lennard-Jones interactions or randomly arranged silica particles. In most cases, the two-population model produces an excellent fit to calcd. SAXS patterns for the simulated core-shell structures, together with a good correlation between the fitting parameters and structural parameters used for the simulation. The limits of application are discussed, and then, this two-population model is applied to the anal. of well-defined core-shell vinyl polymer/silica nanocomposite particles, where the shell comprises a monolayer of spherical silica nanoparticles. Comprehensive SAXS anal. of poly(styrene-co-Bu acrylate)/silica colloidal nanocomposite particles (prepd. by the in situ emulsion copolymn. of styrene and Bu acrylate in the presence of a glycerol-functionalized silica sol) allows the overall core-shell particle diam., the copolymer latex core diam. and polydispersity, the mean silica shell thickness, the mean silica diam. and polydispersity, the vol. fractions of the two components, the silica packing d., and the silica shell structure to be obtained. These exptl. SAXS results are consistent with electron microscopy, dynamic light scattering, TG, helium pycnometry, and BET surface area studies. The high electron d. contrast between the (co)polymer and the silica components, together with the relatively low polydispersity of these core-shell nanocomposite particles, makes SAXS ideally suited for the characterization of this system. Also, these results can be generalized for other types of core-shell colloidal particles.
- 62Rieker, T.; Hanprasopwattana, A.; Datye, A.; Hubbard, P. Particle Size Distribution Inferred from Small-Angle X-Ray Scattering and Transmission Electron Microscopy. Langmuir 1999, 15, 638– 641, DOI: 10.1021/la9810713[ACS Full Text], [CAS], Google Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXotVOmtbw%253D&md5=43193354605bec58cacd8529d5fdfd54Particle Size Distribution Inferred from Small-Angle X-ray Scattering and Transmission Electron MicroscopyRieker, Thomas; Hanprasopwattana, Aree; Datye, Abhaya; Hubbard, PaulLangmuir (1999), 15 (2), 638-641CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Particle size distributions detd. by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) are investigated for samples of interacting hard spheres. Polydispersity in the samples is detd. from the SAXS data by fitting the Porod region to the form factor of a sphere of uniform electron d. smeared by a Gaussian distribution of sphere diams. We find good agreement between SAXS-detd. particle size distributions and those calcd. from TEM image anal.
- 63Pedersen, J. S. Form Factors of Block Copolymer Micelles with Spherical, Ellipsoidal and Cylindrical Cores. J. Appl. Crystallogr. 2000, 33 (3), 637– 640, DOI: 10.1107/S0021889899012248[Crossref], [CAS], Google Scholar63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXkslOisbw%253D&md5=815f89e342650d3dcc702e7e0944882fForm factors of block copolymer micelles with spherical, ellipsoidal and cylindrical coresPedersen, Jan SkovJournal of Applied Crystallography (2000), 33 (3, Pt. 1), 637-640CODEN: JACGAR; ISSN:0021-8898. (Munksgaard International Publishers Ltd.)The form factor of a micelle model with a spherical core and Gaussian polymer chains attached to the surface has previously been calcd. anal. by Pedersen and Gerstenberg. Non-penetration of the chains into the core region was mimicked in the anal. calcns. by moving the center of mass of the chains Rg away from the surface of the core, where Rg is the radius of gyration of the chains. In the present work, the calcns. have been extended to micelles with ellipsoidal and cylindrical cores. Non-penetration was also for these taken into account by moving the center of mass of the chains Rg away from the core surface. In addn. results for worm-like micelles, disk-shape micelles and micelles with a vesicle shape are given.
- 64Muratov, A.; Moussaïd, A.; Narayanan, T.; Kats, E. I. A Percus-Yevick Description of the Microstructure of Short-Range Interacting Metastable Colloidal Suspensions. J. Chem. Phys. 2009, 131, 054902, DOI: 10.1063/1.3179667[Crossref], [PubMed], [CAS], Google Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXps1Oksbg%253D&md5=4100664c2302d742553ecd72a8e3ff21A Percus-Yevick description of the microstructure of short-range interacting metastable colloidal suspensionsMuratov, A.; Moussaid, A.; Narayanan, T.; Kats, E. I.Journal of Chemical Physics (2009), 131 (5), 054902/1-054902/11CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)We present a revised form of the Percus-Yevick approach applicable to dispersions of interacting colloidal particles such as colloid-polymer mixts. and square-well attractive colloids. Our approach is suitable for treating short-range interparticle potentials including excluded vol. hard-sphere repulsion, short-range depletion attraction, and square-well attraction. In all these cases, the Ornstein-Zernike equation for the pair correlation function can be satisfied by a trial function, which generalizes the and ansatz. Structure factors (or x-ray scattering intensities) calcd. by this method are in good agreement with exptl. data for colloid-polymer mixts. over a range of parameters pertaining to the stable fluid phase and the metastable state with moderate attraction. On the same footing, we have detd. the stability limits and analyzed contributions to the scattered intensity from particle aggregates appearing prior to the phase sepn. for sufficiently strong short-range attraction. Similar features are obsd. in the case of square-well attractive colloids when the attraction is turned on. (c) 2009 American Institute of Physics.
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Abstract
Figure 1
Figure 1. Representation of the three main intervals (I, II, and III) that occur during the aqueous emulsion polymerization of a water-immiscible monomer (e.g., styrene) in the presence of a surfactant above its critical micelle concentration. (2,9,16)
Figure 2
Figure 2. (a) Representation of the synthesis of PTFEMA latex particles formed via aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) using an anionic free radical initiator (potassium persulfate, KPS) at 60 °C either in the presence of an anionic surfactant (SDS) or under surfactant-free conditions targeting 5.0% w/w solids. (b) Schematic cross-section of the stirrable reaction cell used for time-resolved small-angle X-ray scattering (SAXS) studies of such formulations. The volume of the reaction solution within this cell is approximately 2.0 mL, which is sufficient to enable post-mortem analysis using 1H NMR spectroscopy, TEM, and dynamic light scattering.
Figure 3
Figure 3. Solution conductivity measurements recorded in situ during the aqueous emulsion polymerization of TFEMA in the presence of SDS surfactant at 60 °C targeting 5.0% w/w solids. The highlighted three time intervals (I, II, and III) are known to occur when such polymerizations are performed in the presence of a surfactant above its CMC (Figure 1).
Figure 4
Figure 4. (a) Conversion vs time curve obtained by 1H NMR spectroscopy and evolution in volume-average particle diameter and polydispersity determined by DLS for the laboratory-scale surfactant-free aqueous emulsion polymerization of TFEMA at 60 °C targeting 5.0% w/w solids. (b) Equivalent data for the laboratory-scale aqueous emulsion polymerization of TFEMA at 60 °C targeting 5.0% w/w solids in the presence of SDS surfactant (2.0 mol % based on TFEMA), where the three regions corresponding to Intervals I, II, and III indicated by solution conductivity measurements (Figure 3) are also shown.
Figure 5
Figure 5. TEM images recorded for PTFEMA latex particles prepared during the aqueous emulsion polymerization of TFEMA at 60 °C in the absence or presence of SDS surfactant. Images a–d correspond to PTFEMA nanoparticles formed during the laboratory-scale synthesis. Images e and f correspond to post-mortem analysis of PTFEMA nanoparticles formed during the in situ SAXS synthesis using the stirrable reaction cell.
Figure 6
Figure 6. SAXS patterns recorded in situ during the aqueous emulsion polymerization of TFEMA at 60 °C targeting 5% w/w solids (a) under surfactant-free conditions and (b) in the presence of SDS surfactant. The onset of particle nucleation is indicated by the arrow. (c) Representative fits for scattering patterns recorded at specific time points for both formulations with data fits represented by either yellow (surfactant-free formulation) or green (SDS formulation) lines, respectively. All scattering patterns are scaled by an arbitrary factor to avoid overlap and improve clarity.
Figure 7
Figure 7. Evolution in I(q) recorded at arbitrary q values during the in situ synthesis and light scattering count rate determined by DLS studies of the equivalent laboratory-based aqueous emulsion polymerization of TFEMA at 60 °C when targeting 5% w/w solids for (a) a surfactant-free formulation and (b) in the presence of SDS surfactant. The onset of particle nucleation is indicated in each case.
Figure 8
Figure 8. Evolution of the PTFEMA latex particle diameter determined by in situ SAXS studies conducted during the aqueous emulsion polymerization of TFEMA at 60 °C targeting 5.0% w/w solids for (a) a surfactant-free formulation and (b) an SDS formulation. The three characteristic time intervals (I, II, and III) identified by solution conductivity measurements for the SDS formulation (Figure 3) are shown for comparison. The Interval II/III boundary for the surfactant-free formulation is also shown.
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ARTICLE SECTIONSThis article references 64 other publications.
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- 2Chern, C. S. Emulsion Polymerization Mechanisms and Kinetics. Prog. Polym. Sci. 2006, 31 (5), 443– 486, DOI: 10.1016/j.progpolymsci.2006.02.001[Crossref], [CAS], Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XkvFykt7s%253D&md5=146081cc2dbc90d88386a2b487c1509cEmulsion polymerization mechanisms and kineticsChern, C. S.Progress in Polymer Science (2006), 31 (5), 443-486CODEN: PRPSB8; ISSN:0079-6700. (Elsevier B.V.)A review. Emulsion polymn. involves the propagation reaction of free radicals with monomer mols. in a very large no. of discrete polymer particles (1016-1018 dm-3) dispersed in the continuous aq. phase. The nucleation and growth of latex particles control the colloidal and phys. properties of latex products. This review article focused on the polymn. mechanisms and kinetics involved in such a heterogeneous polymn. system over the preceding 10-yr period. First, an overview of the general features of emulsion polymn. was given, followed by the discussion of several techniques useful for studying the related polymn. mechanisms and kinetics. Emulsion polymns. using different stabilizers were studied extensively in the last few years and representative publications were reviewed. The performance properties of some specialty polymerizable, degradable or polymeric surfactants and surface-active initiators were also evaluated in emulsion polymn. At present, the particle nucleation process is still not well understood and deserves more research efforts. This article continued to discuss the origin of non-uniform latex particles from both the thermodn. and kinetic points of view. This was followed by the discussion of various reaction parameters that had significant effects on the development of particle morphol. Recent studies on the polymn. in non-uniform polymer particles were then reviewed. Finally, the polymn. mechanisms, kinetics and colloidal stability involved in the versatile semibatch emulsion polymn. were reviewed extensively.
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- 4Asua, J. M. Miniemulsion Polymerization. Prog. Polym. Sci. 2002, 27 (7), 1283– 1346, DOI: 10.1016/S0079-6700(02)00010-2[Crossref], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XksFersLc%253D&md5=9efa5539a9ed9ee9e7e87d223245eb0eMiniemulsion polymerizationAsua, Jose M.Progress in Polymer Science (2002), 27 (7), 1283-1346CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Science Ltd.)A review on miniemulsion polymn., a method which has recently exploded in terms of publications and the development of a wide range of useful polymer materials only accessible through this polymn. technique. In the first part of this article, the fundamental aspects involved in the prepn. and polymn. of monomer miniemulsions are examd. The second part deals with the application of miniemulsion polymn. for the prodn. of specific products.
- 5Tauer, K.; Hernandez, H.; Kozempel, S.; Lazareva, O.; Nazaran, P. Towards a Consistent Mechanism of Emulsion Polymerization - New Experimental Details. Colloid Polym. Sci. 2008, 286 (5), 499– 515, DOI: 10.1007/s00396-007-1797-3[Crossref], [PubMed], [CAS], Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXkvVShsLY%253D&md5=8f1ba1abede03619b48af02d170f7829Towards a consistent mechanism of emulsion polymerization-new experimental detailsTauer, Klaus; Hernandez, Hugo; Kozempel, Steffen; Lazareva, Olga; Nazaran, PanteaColloid and Polymer Science (2008), 286 (5), 499-515CODEN: CPMSB6; ISSN:0303-402X. (Springer)The application of atypical exptl. methods such as cond. measurements, optical microscopy, and nonstirred polymns. to investigations of the classical' batch ab initio emulsion polymn. of styrene revealed astonishing facts. The most important result is the discovery of spontaneous emulsification leading to monomer droplets even in the quiescent styrene in water system. These monomer droplets with a size between a few and some hundreds of nanometers, which are formed by spontaneous emulsification as soon as styrene and water are brought into contact, have a strong influence on the particle nucleation, the particle morphol., and the swelling of the particles. Exptl. results confirm that micelles of low-mol.-wt. surfactants are not a major locus of particle nucleation. Brownian dynamics simulations show that the capture of matter by the particles strongly depends on the polymer vol. fraction and the size of the captured species (primary free radicals, oligomers, single monomer mols., or clusters).
- 6Smith, W. V.; Ewart, R. H. Kinetics of Emulsion Polymerization. J. Chem. Phys. 1948, 16 (6), 592– 599, DOI: 10.1063/1.1746951[Crossref], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaH1cXivFWrtg%253D%253D&md5=e939fd46132dd4c9c432294ed8b1f577Kinetics of emulsion polymerizationSmith, Wendell V.; Ewart, Roswell H.Journal of Chemical Physics (1948), 16 (), 592-9CODEN: JCPSA6; ISSN:0021-9606.As a basis for understanding emulsion polymerization, the kinetics of free-radical reactions in isolated loci is discussed subject to the condition that the free radicals are supplied to the loci from an external source. Three cases of interest are considered: (1) that in which the av. no. of free radicals per locus is small compared with unity, (2) that in which the no. approximates 1/2, and (3) that in which the no. is large. Of these 3 possibilities, the 2nd, in which the free radicals per locus approximate 1/2, is by far the most interesting, as it explains the characteristic features of styrene emulsion polymerization. For this case the av. rate of reaction per locus is independent of the size of the locus, since this rate is simply 1/2 the rate of polymerization of a single free radical. Thus the rate of emulsion polymerization, the concn. of monomer in the loci, and the no. of loci present provide the information needed for calcg. the chain propagation const. for the monomer. A simplified treatment is given for approximating the no. of reaction loci (polymer particles) produced in emulsion polymerization when the rate of polymerization per locus is const. (see case 2). The law obtained indicates that the no. of particles should increase with the soap concn. (3/5 power) and with the rate of formation of free radicals (2/5 power), but should decrease with increasing rate of growth of the free radicals (-2/5 power).
- 7Harkins, W. D. A. A General Theory of the Mechanism of Emulsion Polymerization. J. Am. Chem. Soc. 1947, 69 (6), 1428– 1444, DOI: 10.1021/ja01198a053[ACS Full Text], [CAS], Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaH2sXivVOrsQ%253D%253D&md5=64d871f06a24c6fd81d160078eefa7dfTheory of the mechanism of emulsion polymerizationHarkins, Wm. D.Journal of the American Chemical Society (1947), 69 (), 1428-44CODEN: JACSAT; ISSN:0002-7863.cf. C.A. 40, 3325.3. A mechanism of emulsion polymerization is proposed in which the polymer growth is initiated in soap micelles. This locus ceases to be active at about 13 to 20% yield when 5% soap (based on monomers) is present initially. Further polymerization occurs in the polymer monomer particle. Evidence is presented that indicates that: (1) each double layer of soap is an independent micelle; (2) the micelle increases in size with soap concn.; (3) the crit. concn. for micelle formation is increased by a factor of 2 for each decrease by unity in the no. of C atoms in the soap mol. (4) the principal function of the monomer emulsion droplet is to serve as a storehouse from which the monomer particles diffuse into the aq. phase where they are trapped by soap micelles and polymer particles in both of which they polymerize.
- 8Harkins, W. D. General Theory of Mechanism of Emulsion Polymerization. II. J. Polym. Sci. 1950, 5 (2), 217– 251, DOI: 10.1002/pol.1950.120050208[Crossref], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaG3cXjvFKmtQ%253D%253D&md5=188e533de88e687b7172cdc52b55f2c4General theory of mechanism of emulsion polymerization. IIHarkins, William D.Journal of Polymer Science (1950), 5 (), 217-51CODEN: JPSCAU; ISSN:0022-3832.cf. C.A. 41, 5779e. A general review and elaboration of the author's theory of polymerization which can be summarized as follows: monomer emulsion droplets serve merely as a storehouse of monomer molecules which diffuse into the water phase to soap micelles or polymer particles. With monomers having low H2O soly. (butadiene, styrene, isoprene), the polymer is formed primarily through the growth of free radicals in the monomer-polymer mixture. Almost every latex particle formed is a result of monomer solubilized inside a micelle. The no. of particles initiated within the micelle is a function of the soap concn. and the catalyst activity. Soap seems to stabilize the emulsion by forming a monolayer and giving a charge to the particles. Micelles solubilize a small core of monomer and provide a much larger target for contact with free radicals. Polymer-free radicals grow much larger than expected as a result of using monomer both from the micelle and the surrounding areas. In the mutual formula, 1018 micelles per cc. of H2O phase are present with K dodecanoate or K tetradecanoate.
- 9Thickett, S. C.; Gilbert, R. G. Emulsion Polymerization: State of the Art in Kinetics and Mechanisms. Polymer 2007, 48 (24), 6965– 6991, DOI: 10.1016/j.polymer.2007.09.031[Crossref], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXht12htrnE&md5=e7beca6d356e629ba63b093ff6c2b3e5Emulsion polymerization: State of the art in kinetics and mechanismsThickett, Stuart C.; Gilbert, Robert G.Polymer (2007), 48 (24), 6965-6991CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)A review. Over decades of carefully designed kinetic expts. and the development of complementary theory, a more or less complete picture of the mechanisms that govern emulsion polymn. systems was established. This required means of detg. the rate coeffs. for the individual processes as functions of controllable variables such as initiator concn. and particle size, means of interpreting the data with a min. of model-based assumptions, and the need to perform expts. that had the potential to actually refute a given mechanistic hypothesis. Significant advances were made within the area of understanding interfacial processes such as radical entry and exit into and out of an emulsion polymn. particle, for electrostatic, steric and electrosteric stabilizers (the latter two being poorly understood until recently). The mechanism for radical exit is chain transfer to monomer within the particle interior to form a monomeric radical which can either diffuse into the water phase or propagate to form a more hydrophobic species which cannot exit. Entry is through aq.-phase propagation of a radical derived directly from initiator, until a crit. d.p. z is reached; the value of z is such that the z-meric species is sufficiently surface active so that its only fate is to enter, whereas smaller aq.-phase radical species can either be terminated in the aq. phase or undergo further propagation. For both entry and exit, in the presence of (electro)steric stabilizers, two addnl. events are significant: transfer involving a labile hydrogen atom within the stabilizing layer to form a mid-chain radical which is slow to propagate and quick to terminate, and which may also undergo β-scission to form a water-sol. species. Proper consideration of the fates of the various aq.-phase radicals is essential for understanding the overall kinetic behavior. Intra-particle termination is explained in terms of diffusion-controlled chain-length-dependent events. A knowledge of the events controlling entry and exit, including the recent discoveries of the addnl. mechanisms operating with (electro)steric stabilizers, provides an extension to the micellar and homogeneous nucleation models which enables particle no. to be predicted with acceptable reliability, and also quantifies the amt. of secondary nucleation occurring during seeded growth. This knowledge provides tools to understand the kinetics of emulsion polymn., in both conventional and controlled/living polymn. systems, and to optimize reaction conditions to synthesize better polymer products.
- 10DeFusco, A. J.; Sehgal, K. C.; Bassett, D. R. Overview of Uses of Polymer Latexes. In Polymeric Dispersions: Principles and Applications; Springer: Netherlands, 1997; pp 379– 396.
- 11Vargas, M. A.; Cudaj, M.; Hailu, K.; Sachsenheimer, K.; Guthausen, G. Online Low-Field 1H NMR Spectroscopy: Monitoring of Emulsion Polymerization of Butyl Acrylate. Macromolecules 2010, 43 (13), 5561– 5568, DOI: 10.1021/ma1006599[ACS Full Text], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXmvF2rur0%253D&md5=01e02ca9f095c77330b6c3302a8af8d7Online Low-Field 1H NMR Spectroscopy: Monitoring of Emulsion Polymerization of Butyl AcrylateVargas, Maria A.; Cudaj, Markus; Hailu, Kidist; Sachsenheimer, Kerstin; Guthausen, GiselaMacromolecules (Washington, DC, United States) (2010), 43 (13), 5561-5568CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)The emulsion polymn. of Bu acrylate was monitored by online NMR spectroscopy at 20 MHz 1H frequency. The reaction progress could be followed, monitoring the conversion of the reactant time-resolved without any need of sample prepn. Exptl. data were analyzed with kinetic models for free-radical polymn. The data comprised the polymn. rate in seeded batch emulsion polymns. of Bu acrylate with doubly deionized water and D2O as solvent. The polymn. rate vs. conversion curve behaves compatible with the three rate intervals model, typically obsd. in emulsion polymns. Zero-one kinetics explains the exptl. results appropriately, leading to the detn. of entry and termination rate coeffs.
- 12Chen, X.; Laughlin, K.; Sparks, J. R.; Linder, L.; Farozic, V.; Masser, H.; Petr, M. In Situ Monitoring of Emulsion Polymerization by Raman Spectroscopy: A Robust and Versatile Chemometric Analysis Method. Org. Process Res. Dev. 2015, 19 (8), 995– 1003, DOI: 10.1021/acs.oprd.5b00045[ACS Full Text], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtFSjsLzI&md5=2a87af0b616ebb02275d9f01618d94e2In Situ Monitoring of Emulsion Polymerization by Raman Spectroscopy: A Robust and Versatile Chemometric Analysis MethodChen, Xiaoyun; Laughlin, Ken; Sparks, Justin R.; Linder, Linus; Farozic, Vince; Masser, Hanqing; Petr, MichaelOrganic Process Research & Development (2015), 19 (8), 995-1003CODEN: OPRDFK; ISSN:1083-6160. (American Chemical Society)Emulsion polymn. remains a challenging system for in situ Raman spectroscopic anal. despite extensive research on the necessary instrumentation and chemometric data anal. methods. In this study, we demonstrate a new and facile data anal. method, making in situ Raman spectroscopy a more versatile research tool for monitoring the concns. of monomers in reactions spanning a wide range of compns. The method improvement stems from the use of the homopolymer as an internal std. for the corresponding monomer. Classical least-squares or indirect hard modeling is used for the spectral anal. to det. the spectral responses of major monomers and polymers within the system. Once the relative response factor ratios for a no. of monomer-homopolymer pairs are detd. in the calibration, they can be used to calc. the concn. ratio for such pairs based on reaction spectra. This approach offers two important advantages in detg. the conversion of monomer to polymer. First, because the polymer internal std. will always be present for the corresponding monomer, it is straightforward to compensate for variable signal intensity due to changes in light scattering or instrumental fluctuations. Second, it is possible to calibrate based on a small set of monomer and homopolymer stds. The appropriate pairs can then be selected to establish a calibration method for any polymer product involving a combination of monomers from this set without the need for recalibration. To demonstrate this technique, we provide examples of in situ Raman monitoring for both batch and semibatch emulsion polymns.
- 13Reis, M. M.; Araújo, P. H. H.; Sayer, C.; Giudici, R. In Situ Near-Infrared Spectroscopy for Simultaneous Monitoring of Multiple Process Variables in Emulsion Copolymerization. Ind. Eng. Chem. Res. 2004, 43 (23), 7243– 7250, DOI: 10.1021/ie034277u[ACS Full Text], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXksVKiu70%253D&md5=78da04166ffc7b72fe6d956d19df1053In Situ Near-Infrared Spectroscopy for Simultaneous Monitoring of Multiple Process Variables in Emulsion CopolymerizationReis, Marlon M.; Araujo, Pedro H. H.; Sayer, Claudia; Giudici, ReinaldoIndustrial & Engineering Chemistry Research (2004), 43 (23), 7243-7250CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)In this work near-IR spectroscopy is used to monitor semicontinuous styrene-Bu acrylate emulsion copolymn. reactions. A set of nine reactions with slightly different formulations was carried out. The results of five reactions were used to fit a SIMPLS model, and the four remaining reactions were monitored in order to evaluate the model performance for estn. of important variables and latex properties such as individual monomer concns. and the av. polymer particle diam. These variables were used to calc. the online monomer conversion, copolymer compn., particle no., and av. no. of radicals per polymer particle.
- 14Silva, W. K.; Chicoma, D. L.; Giudici, R. In-Situ Real-Time Monitoring of Particle Size, Polymer, and Monomer Contents in Emulsion Polymerization of Methyl Methacrylate by near Infrared Spectroscopy. Polym. Eng. Sci. 2011, 51 (10), 2024– 2034, DOI: 10.1002/pen.22100[Crossref], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXpvVChs7c%253D&md5=be110ddabb31e64dfad69c5b4eed6ed1In-situ real-time monitoring of particle size, polymer, and monomer contents in emulsion polymerization of methyl methacrylate by near infrared spectroscopySilva, Wandeklebio K.; Chicoma, Dennis L.; Giudici, ReinaldoPolymer Engineering & Science (2011), 51 (10), 2024-2034CODEN: PYESAZ; ISSN:0032-3888. (John Wiley & Sons, Inc.)This work reports the results of in-situ real-time monitoring of the emulsion polymn. of Me methacrylate by near IR spectroscopy (NIRS) under different feed conditions. Besides the monitoring of the monomer and polymer content, the results show that reasonable ests. can be obtained from the spectra for the av. particle size of the growing polymer particles present in the reaction medium. This is possible because the presence of the particles affects the spectra (through scattering, diffraction, and other mechanisms). Thus, by using appropriate calibration, it is possible obtain reliable models for particle size, in addn. to monitoring the monomer and polymer concns. Exptl. results for emulsion polymns. conducted with various feed monomer conditions indicated that, in the spectral range studied, it is not only possible to monitor the evolution of the monomer and polymer contents, but also to follow the changes in the av. size of the polymer particle. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.
- 15Antonietti, M.; Tauer, K. 90 Years of Polymer Latexes and Heterophase Polymerization: More Vital than Ever. Macromol. Chem. Phys. 2003, 204 (2), 207– 219, DOI: 10.1002/macp.200290083[Crossref], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXitlOisLs%253D&md5=a958ec9506582eb237e913e179c7a4f690 Years of polymer latexes and heterophase polymerization: more vital than everAntonietti, Markus; Tauer, KlausMacromolecular Chemistry and Physics (2003), 204 (2), 207-219CODEN: MCHPES; ISSN:1022-1352. (Wiley-VCH Verlag GmbH & Co. KGaA)A review is given on the historical and possible future development of heterophase polymn. techniques in liq. continuous media to prep. polymer dispersions. The majority of heterophase polymns. is carried out in water as continuous phase and hence, they are belong to green chem. with increasing importance due to environmental reasons. The compartmentalization of the reaction vol. into domains of colloidal size (between a few nm3 and μm3) is the characteristic feature and relates both to the problems and the potential promises of this class of polymers. Special emphasis is placed with regard to the development of new heterophase polymn. techniques, the adoption of new polymn. mechanism to the particular conditions of heterophase polymn., the synthesis of block copolymers and nanoparticulate hybrid structures, the development of new stabilizers and polymn. aids, and the usage of specialty latexes as model systems to learn more about complex matter.
- 16Lovell, P. A.; Schork, F. J. Fundamentals of Emulsion Polymerization. Biomacromolecules 2020, 21 (11), 4396– 4441, DOI: 10.1021/acs.biomac.0c00769[ACS Full Text], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtFKjs7vF&md5=441a1c84f9d2e1771b027bccbd84618bFundamentals of Emulsion PolymerizationLovell, Peter A.; Schork, F. JosephBiomacromolecules (2020), 21 (11), 4396-4441CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)A review. A comprehensive overview of the fundamentals of emulsion polymn. and related processes is presented with the object of providing theor. and practical understanding to researchers considering use of these methods for synthesis of polymer colloids across a wide range of applications. Hence, the overview has been written for a general scientific audience with no prior knowledge assumed. Succinct introductions are given to key topics of background science to assist the reader. Importance is placed on ensuring mechanistic understanding of these complex polymns. and how the processes can be used to create polymer colloids that have particles with well-defined properties and morphol. Math. equations and assocd. theory are given where they enhance understanding and learning and where they are particularly useful for practical application. Practical guidance also is given for new researchers so that they can begin using the various processes effectively and in ways that avoid common mistakes.
- 17O’toole, J. T. Kinetics of Emulsion Polymerization. J. Appl. Polym. Sci. 1965, 9 (4), 1291– 1297, DOI: 10.1002/app.1965.070090410[Crossref], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF2MXptFemtA%253D%253D&md5=e556af63ea1443143afcab995392a596Kinetics of emulsion polymerizationO'Toole, J. T.Journal of Applied Polymer Science (1965), 9 (4), 1291-7CODEN: JAPNAB; ISSN:0021-8995.The quant. theory of free-radical mechanisms in emulsion polymerizations was reexamd. The proposed modifications resulted in a closer resemblance to homogeneous systems. Explicit expressions for the distribution of radicals are also given. The importance of interphase transfer is emphasized.
- 18Ballard, M. J.; Napper, D. H.; Gilbert, R. G. Kinetics of Emulsion Polymerization of Methyl Methacrylate. J. Polym. Sci., Polym. Chem. Ed. 1984, 22 (11), 3225– 3253, DOI: 10.1002/pol.1984.170221141[Crossref], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXisFWjtg%253D%253D&md5=f364d3b67c843aea4999ba49be2c9d8fKinetics of emulsion polymerization of methyl methacrylateBallard, Mathew J.; Napper, Donald H.; Gilbert, Robert G.Journal of Polymer Science, Polymer Chemistry Edition (1984), 22 (11, Pt. 2), 3225-53CODEN: JPLCAT; ISSN:0360-6376.The kinetics of emulsion polymn. of Me methacrylate (I) [80-62-6] at 50° were studied in seeded systems using both chem. initiation and γ-radiolysis initiation. Both steady-state rates and (for γ-radiolysis) the relaxation from the steady state were obsd. The av. no. of free radicals per particle was quite high (e.g., ∼0.7 for 10-3 mol dm-3 S2O62 initiator). The data are quant. interpreted using a generalized Smith-Ewart-Harkins model, allowing for free radical entry, exit, bimol. termination within the latex particles, and aq. phase hetero-termination and re-entry. From this treatment, there results (1) the dependence of the termination rate coeffs. (kt) on the wt. fraction of polymer (wp), (2) lower bounds for the dependence of the entry rate coeff. on initiator concn., and (3) the conclusion that most exited free radicals undergo subsequent reentry into particles rather than hetero-termination. The results for k1(wp) are consistent with diffusion control at temps. below the glass transition point. Comparisons are presented of the behavior of I, Bu methacrylate, and styrene in emulsion polymn. systems.
- 19Heuts, J. P. A.; Gilbert, R. G.; Radom, L. A Priori Prediction of Propagation Rate Coefficients in Free-Radical Polymerizations: Propagation of Ethylene. Macromolecules 1995, 28 (26), 8771– 8781, DOI: 10.1021/ma00130a009[ACS Full Text], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXpsFWqu7w%253D&md5=3c2352025cf1f9d07da38c830b209932A Priori Prediction of Propagation Rate Coefficients in Free-Radical Polymerizations: Propagation of EthyleneHeuts, Johan P. A.; Gilbert, Robert G.; Radom, LeoMacromolecules (1995), 28 (26), 8771-81CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)A method is derived for calcg. Arrhenius parameters for propagation reactions in free-radical polymns. from first principles. Ab initio MO calcns. are carried out initially to det. the geometries, vibrational frequencies, and energies of the reactants and the transition state. Transition state theory then yields the Arrhenius parameters. The lowest frequencies are replaced by appropriate (hindered or unhindered) internal rotors, to better model these modes in the calcn. of frequency factors. It is found that a high level of MO theory (e.g., QCISD(T)/6-311G**) is required to produce reasonable activation energies, whereas satisfactory frequency factors can be obtained at a relatively simple level of theory (e.g., HF/3-21G), because the frequency factor is largely detd. by mol. geometries which can be reliably predicted at such a level. Obtaining reliable frequency factors for quite large systems is thus possible. The overall procedure is illustrated by calcns. on the propagation of ethylene, and the results are in accord with literature exptl. data. Means are also derived for extending the results from propagation of monomeric radicals to propagation of polymeric radicals, without addnl. computational requirements. The method is expected to be generally applicable to those propagation reactions that are not significantly influenced by the presence of solvent (i.e., relatively nonpolar monomers in nonpolar solvents). The calcns. show that the magnitude of the frequency factor is largely governed by the degree to which the internal rotations of the transition state are hindered. They also suggest that there can be a significant penultimate unit effect in free-radical copolymn. Furthermore, the calcns. explain the rate-enhancing effect found upon deuteration of the monomers and explain why the rate coeff. for the first propagation step is larger than that for the long-chain propagation step.
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- 21Gardon, J. L. Emulsion Polymerization. I. Recalculation and Extension of the Smith-Ewart Theory. J. Polym. Sci., Part A-1: Polym. Chem. 1968, 6 (3), 623– 641, DOI: 10.1002/pol.1968.150060318[Crossref], [CAS], Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF1cXhtFGms74%253D&md5=53c600178f7fdf1f5ce36753bb74f5deEmulsion polymerization. I. Recalculation and extension of the Smith-Ewart TheoryGardon, John L.Journal of Polymer Science, Part A-1: Polymer Chemistry (1968), 6 (3), 623-41CODEN: JPSPC3; ISSN:0449-296X.The most important assumptions underlying the Smith-Ewart theory are that the locus of chain propagation is the monomer-swollen latex particle, polymeric chains are initiated by radicals entering from the water phase into the particles, chain termination is an instantaneous reaction between two radicals within one particle, and particles are nucleated by radicals absorbed into monomer-swollen soap micelles. The proportionality const. between the particle no. and the appropriate powers of soap and initiator concns. is defined in terms of independent parameters. Abs. rate equations are presented for the intervals before and after the completion of particle nucleation. To calc. these rates, it is not necessary to have prior knowledge of the exptl. particle no. The conversion at which particle nucleation is complete is calcd. The mol. wt. is defined in terms of independent parameters. Predictions are made for the particle-size distribution. The validity of the theory is confined to specifiable intervals of conversion, to a certain range of monomer-water ratio, and to soap concns. whose upper and lower limits are given. 17 references.
- 22Soh, S. K.; Sundberg, D. C. Diffusion-Controlled Vinyl Polymerization. IV. Comparison of Theory and Experiment. J. Polym. Sci., Polym. Chem. Ed. 1982, 20 (5), 1345– 1371, DOI: 10.1002/pol.1982.170200516[Crossref], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL38XitFygsrk%253D&md5=7a5490842d692b8b742f181b50ff6f33Diffusion-controlled vinyl polymerization. IV. Comparison of theory and experimentSoh, S. K.; Sundberg, D. C.Journal of Polymer Science, Polymer Chemistry Edition (1982), 20 (5), 1345-71CODEN: JPLCAT; ISSN:0360-6376.Bulk polymn. data of methyl methacrylate [80-62-6], ethyl methacrylate [97-63-2], ethyl acrylate [140-88-5], propyl acrylate [925-60-0], vinyl acetate [108-05-4], and styrene [100-42-5] were compared with the predictions of a proposed theory. This theory of polymn. kinetics uses the concepts of free vol. and chain entanglements to describe the relation between chain mobility and chain length dependent termination reactions. Excellent agreement was found between the predictions of the theory and the polymn. rate and mol.wt. data of the 6 polymn. systems studied. Emphasis was placed on the ability to explain the development of higher order mol.wt. avs. (‾Mw, ‾M2, etc.) because they provide the most crucial tests for such a model. No changes were required in the model as it was applied to the different polymn. systems for a variety of reaction conditions. The theory offers a unified understanding of the diverse polymn. behavior displayed by such systems.
- 23Goodwin, J. W.; Hearn, J.; Ho, C. C.; Ottewill, R. H. Studies on the Preparation and Characterisation of Monodisperse Polystyrene Laticee - III. Preparation without Added Surface Active Agents. Colloid Polym. Sci. 1974, 252 (6), 464– 471, DOI: 10.1007/BF01554752[Crossref], [CAS], Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2MXktlyjuw%253D%253D&md5=01f188ed6ac95910dede33e401f1f182Preparation and characterization of monodisperse polystyrene latexes. III. Preparation without added surface active agentsGoodwin, J. W.; Hearn, J.; Ho, C. C.; Ottewill, R. H.Colloid and Polymer Science (1974), 252 (6), 464-71CODEN: CPMSB6; ISSN:0303-402X.By adjusting the ionic strength, initiator concn., and polymn. temp., monodisperse polystyrene [9003-53-6] latexes with particle sizes 0.1-1.0 μm were prepd. by single-stage polymns. in the absence of surfactants. In a typical polymn., 73 g styrene was added to 670 g H2O contg. NaCl under N with stirring at 60-95°, K2S2O8 initiator was added, and the dispersion was stirred for 24 hr. The total initial ionic strength largely detd. the particle size in the latexes.
- 24Kotera, A.; Furusawa, K.; Kudo, K. Colloid Chemical Studies of Polystyrene Latices Polymerized without Any Surface-Active Agents - II. Coagulation into Secondary Minimum. Colloid Polym. Sci. 1970, 240 (1–2), 837– 842, DOI: 10.1007/BF02160082
- 25Kühn, I.; Tauer, K. Nucleation in Emulsion Polymerization: A New Experimental Study. 1. Surfactant-Free Emulsion Polymerization of Styrene. Macromolecules 1995, 28 (24), 8122– 8128, DOI: 10.1021/ma00128a022[ACS Full Text], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXovFCntr4%253D&md5=4365e2676b666857f3c70c9d6439553eNucleation in Emulsion Polymerization: A New Experimental Study. 1. Surfactant-Free Emulsion Polymerization of StyreneKuehn, I.; Tauer, K.Macromolecules (1995), 28 (24), 8122-8CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)The very early stages of the emulsifier-free emulsion polymn. of styrene were investigated by online monitoring of the optical transmission and the cond. of the reaction mixt. Very careful degassing of the reaction mixt. is crucial to achieve high reproducibility. The higher the residual gas concn. the poorer the reproducibility no matter if the gas is air or N. The results lead to the conclusions that for particle nucleation the rate of initiation in the water phase is very important and that nucleation occurs via cluster formation of water-born oligomers. With the exptl. techniques employed, it was possible to investigate the conversion range from 0.47% to 1.8%. However, it was not possible to detect a particle no. max. Instead of a max., a decrease in the particle no. was obsd. followed by a leveling and another increase, indicating another nucleation step.
- 26Tauer, K.; Deckwer, R.; Kühn, I.; Schellenberg, C. A Comprehensive Experimental Study of Surfactant-Free Emulsion Polymerization of Styrene. Colloid Polym. Sci. 1999, 277, 607– 626, DOI: 10.1007/s003960050433[Crossref], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXksF2jurc%253D&md5=6af92fd7268def774ac44df106f1d115A comprehensive experimental study of surfactant-free emulsion polymerization of styreneTauer, K.; Deckwer, R.; Kuhn, I.; Schellenberg, C.Colloid and Polymer Science (1999), 277 (7), 607-626CODEN: CPMSB6; ISSN:0303-402X. (Springer-Verlag)Comprehensive exptl. results are presented for surfactant-free emulsion polymn. of styrene with water-sol., ionic initiators. Special emphasis is placed on the particle nucleation, the chem. structure of the nucleating species, the change of latex, particle and polymer properties as well as the development of particle morphol. with polymn. time. Under special conditions the appearance in transmission electron microscopy pictures of less electron dense anomalous particles is obsd. The formation of these structures is discussed and possible formation mechanisms presented. Dialysis of the latexes changed their properties drastically as they became unstable to coagulation. The original latexes did not change their properties over several months.
- 27Fitch, R. M. Homogeneous Nucleation of Polymer Colloids. Br. Polym. J. 1973, 5 (6), 467– 483, DOI: 10.1002/pi.4980050606[Crossref], [CAS], Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2cXktlOrsLs%253D&md5=cb8a8fbdaed88e91d569e1e562b8cef3Homogeneous nucleation of polymer colloidsFitch, Robert M.British Polymer Journal (1973), 5 (6), 467-83CODEN: BPOJAB; ISSN:0007-1641.Homogeneous nucleation of polymer colloids was reviewed with 35 refs., and a model for particle formation was based on free radical initiation in a continuous medium and self-nucleation or particle capture was proposed.
- 28Fitch, R. M.; Tsai, C. H. Homogeneous Nucleation of Polymer Colloids, IV: The Role of Soluble Oligomeric Radicals; Polymer Colloids; Plenum Press: New York, 1971; pp 103– 116.Google ScholarThere is no corresponding record for this reference.
- 29Priest, W. Particle Growth in Aqueous Polymerization of Vinyl Acetate. J. Phys. Chem. 1952, 56, 1077– 1083, DOI: 10.1021/j150501a010[ACS Full Text], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaG3sXitFaqtQ%253D%253D&md5=c66d8190bef42c31085c0753e6aaddebParticle growth in the aqueous polymerization of vinyl acetatePriest, W. J.Journal of Physical Chemistry (1952), 56 (), 1077-82CODEN: JPCHAX; ISSN:0022-3654.Electron-microscope observations of latexes produced by the polymerization of vinyl acetate in water showed that in nonmicellar systems (1) the max. no. of primary particles developed is equal to the no. of polymer chains long enough to give water insoly. formed throughout the course of the polymerization and (2) growth takes place by interparticle fusion. The no. of particles present at the completion of the polymerization is the total no. of primary particles less the reduction caused by coalescence during the course of the reaction. Coalescence can be controlled by the use of emulsion stabilizers, the most efficient of which are surfactants such as Na dodecylsulfonate. In the absence of surfactants the particles produced are large (0.1-1.0 μ in diam.), and their size distribution is narrow. Other factors affecting particle size and growth were investigated. Less detailed examn. of the latexes from other slightly water-sol. monomers indicate that the growth mechanism proposed for vinyl acetate is general.
- 30Feeney, P. J.; Napper, D. H.; Gilbert, R. G. Surfactant-Free Emulsion Polymerizations: Predictions of the Coagulative Nucleation Theory. Macromolecules 1987, 20 (11), 2922– 2930, DOI: 10.1021/ma00177a047[ACS Full Text], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXmtFyisL4%253D&md5=b02103930dffcef9f903316b5675eba3Surfactant-free emulsion polymerizations: predictions of the coagulative nucleation theoryFeeney, P. John; Napper, Donald H.; Gilbert, Robert G.Macromolecules (1987), 20 (11), 2922-30CODEN: MAMOBX; ISSN:0024-9297.Equations were given for the formation of latex particles in emulsion polymn. systems in the absence of added emulsifier. The model described the formation of colloidally unstable precursor particles through homogeneous nucleation, followed by their coagulation and propagational growth to form colloidally stable latex particles. Coagulation rates were obtained through DLVO theory and its modifications, with due allowance for the partial attraction that occurred in the coagulation between particles with different radii. Calcns. showed good agreement with the exptl. data of Ottewill et al. for the variation of particle no. d. with initiator concn. and ionic strength.
- 31Pedersen, J. S. Analysis of Small-Angle Scattering Data from Micelles and Microemulsions: Free-Form Approaches and Model Fitting. Curr. Opin. Colloid Interface Sci. 1999, 4 (3), 190– 196, DOI: 10.1016/S1359-0294(99)00033-3[Crossref], [CAS], Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXmslKisLo%253D&md5=e9fc133cbe6eee20dd6aa4d2f6983b10Analysis of small-angle scattering data from micelles and microemulsions: free-form approaches and model fittingPedersen, Jan SkovCurrent Opinion in Colloid & Interface Science (1999), 4 (3), 190-196CODEN: COCSFL; ISSN:1359-0294. (Elsevier Science Ltd.)A review with 51 refs. The free-form methods for analyzing small-angle scattering data have, during the last years, found more widespread use for micelles and microemulsions. Recent developments have made them applicable also to systems with size polydispersity and particle correlations, however, model fitting still constitutes a very important and partly complementary anal. tool.
- 32Pontoni, D.; Narayanan, T.; Rennie, A. R. Time-Resolved SAXS Study of Nucleation and Growth of Silica Colloids. Langmuir 2002, 18 (1), 56– 59, DOI: 10.1021/la015503c[ACS Full Text], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XivVKl&md5=b50de3d1bf12cb9621659ba774bf0904Time-Resolved SAXS Study of Nucleation and Growth of Silica ColloidsPontoni, D.; Narayanan, T.; Rennie, A. R.Langmuir (2002), 18 (1), 56-59CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)This paper reports a time-resolved small-angle x-ray scattering study of in situ Stober SiO2 synthesis. The hydrolysis reaction is initiated by rapidly mixing equal amts. of alc. solns. of NH3 and tetra-Et orthosilicate, using a stopped-flow device coupled to a flow-through capillary cell. Measurements covered the scattering wave vector (q) range of 0.02 ≤ q ≤ 6 nm-1 and time (t) range of 0.1 ≤ t ≤ 1000 s. The combination of high sensitivity, low background, and high dynamic range of the exptl. setup permitted observation of the primary particles of nucleation. During the entire growth process, the measured scattered intensity can be adequately described by a sphere scattering function weighted by a Schultz size distribution function. At the early stages of growth, the fitted radius increased linearly with time, subsequently crossing over to a smaller exponent of between 1/3 and 1/2. The obsd. behavior is consistent with an aggregation process involving primary particles of a few nanometers in size.
- 33Tokumoto, M. S.; Pulcinelli, S. H.; Santilli, C. V.; Craievich, A. F. SAXS Study of the Kinetics of Formation of ZnO Colloidal Suspensions. J. Non-Cryst. Solids 1999, 247 (1–3), 176– 182, DOI: 10.1016/S0022-3093(99)00059-9[Crossref], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXjs1Ohu7g%253D&md5=c8bfd16bfcad19a6b5f6c2a8c7a3eaaaSAXS study of the kinetics of formation of ZnO colloidal suspensionsTokumoto, M. S.; Pulcinelli, S. H.; Santilli, C. V.; Craievich, A. F.Journal of Non-Crystalline Solids (1999), 247 (), 176-182CODEN: JNCSBJ; ISSN:0022-3093. (Elsevier Science B.V.)We have investigated, by in-situ small-angle X-ray scattering (SAXS), the kinetics of formation of zinc oxide colloidal suspensions obtained after refluxing alc. soln. of zinc acetate and catalyzed by lithium hydroxide. The exptl. results demonstrate that the suspensions are composed of colloidal spheroidal particles with a multimodal size distribution. The av. radius of the main mode, approx. 2 nm, is invariant but the no. of these basic particles continuously increases for increasing hydrolysis reaction time. The other two modes correspond to particles with av. radii close to 6 and 10 nm, resp. The larger particles are formed by coagulation of the smaller ones.
- 34Narayanan, S.; Wang, J.; Lin, X. M. Dynamical Self-Assembly of Nanocrystal Superlattices during Colloidal Droplet Evaporation by in Situ Small Angle x-Ray Scattering. Phys. Rev. Lett. 2004, 93 (13), 135503, DOI: 10.1103/PhysRevLett.93.135503[Crossref], [PubMed], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXnvFCitr8%253D&md5=b32afbbcdd0bbdae95190428c9831bddDynamical self-assembly of nanocrystal superlattices during colloidal droplet evaporation by in situ small angle x-ray scatteringNarayanan, Suresh; Wang, Jin; Lin, Xiao-MinPhysical Review Letters (2004), 93 (13), 135503/1-135503/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)The nucleation and growth kinetics of highly ordered gold nanocrystal superlattices during the evapn. of nanocrystal colloidal droplets was elucidated by in situ time-resolved small-angle x-ray scattering. The evapn. rate can affect the dimensionality of the superlattices. The formation of 2D nanocrystal superlattices at the liq.-air interface of the droplet has exponential growth kinetics that originates from interface crushing.
- 35Narayanan, T.; Gummel, J.; Gradzielski, M. Probing the Self-Assembly of Unilamellar Vesicles Using Time-Resolved SAXS. In Advances in Planar Lipid Bilayers and Liposomes; Elsevier B.V.: Amsterdam, 2014; Vol. 20, pp 171– 196.
- 36Brotherton, E. E.; Hatton, F. L.; Cockram, A. A.; Derry, M. J.; Czajka, A.; Cornel, E. J.; Topham, P. D.; Mykhaylyk, O. O.; Armes, S. P. In Situ Small-Angle X-Ray Scattering Studies during Reversible Addition-Fragmentation Chain Transfer Aqueous Emulsion Polymerization. J. Am. Chem. Soc. 2019, 141 (34), 13664– 13675, DOI: 10.1021/jacs.9b06788[ACS Full Text], [CAS], Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsVygtbrO&md5=6cf5c202cb326d41a0e15e84cd87547bIn Situ Small-Angle X-ray Scattering Studies During Reversible Addition-Fragmentation Chain Transfer Aqueous Emulsion PolymerizationBrotherton, Emma E.; Hatton, Fiona L.; Cockram, Amy A.; Derry, Matthew J.; Czajka, Adam; Cornel, Erik J.; Topham, Paul D.; Mykhaylyk, Oleksandr O.; Armes, Steven P.Journal of the American Chemical Society (2019), 141 (34), 13664-13675CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Polymn.-induced self-assembly (PISA) is a powerful platform technol. for the rational and efficient synthesis of a wide range of block copolymer nano-objects (e.g., spheres, worms or vesicles) in various media. In situ small-angle x-ray scattering (SAXS) studies of reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn. have previously provided detailed structural information during self-assembly (see M. J. Derry et al., Chem. Sci. 2016, 7, 5078-5090). However, conducting the analogous in situ SAXS studies during RAFT aq. emulsion polymns. poses a formidable tech. challenge because the inherently heterogeneous nature of such PISA formulations requires efficient stirring to generate sufficiently small monomer droplets. In the present study, the RAFT aq. emulsion polymn. of 2-methoxyethyl methacrylate (MOEMA) was explored for the first time. Chain extension of a relatively short non-ionic poly(glycerol monomethacrylate) (PGMA) precursor block leads to the formation of sterically-stabilized PGMA-PMOEMA spheres, worms or vesicles, depending on the precise reaction conditions. Construction of a suitable phase diagram enables each of these three morphologies to be reproducibly targeted at copolymer concns. ranging from 10 to 30% wt./wt. solids. High MOEMA conversions are achieved within 2 h at 70 °C, which makes this new PISA formulation well-suited for in situ SAXS studies using a new reaction cell. This bespoke cell enables efficient stirring and hence allows in situ monitoring during RAFT emulsion polymn. for the first time. For example, the onset of micellization and subsequent evolution in particle size can be studied when prepg. PGMA29-PMOEMA30 spheres at 10% wt./wt. solids. When targeting PGMA29-PMOEMA70 vesicles under the same conditions, both the micellar nucleation event and the subsequent evolution in the diblock copolymer morphol. from spheres to worms to vesicles are obsd. These new insights significantly enhance our understanding of the PISA mechanism during RAFT aq. emulsion polymn.
- 37Czajka, A.; Armes, S. P. In Situ SAXS Studies of a Prototypical RAFT Aqueous Dispersion Polymerization Formulation: Monitoring the Evolution in Copolymer Morphology during Polymerization-Induced Self-Assembly. Chem. Sci. 2020, 11 (42), 11443– 11454, DOI: 10.1039/D0SC03411H[Crossref], [PubMed], [CAS], Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhvVGgs7rJ&md5=067f3bfb363bace53ee7d9e288afb6ffIn situ SAXS studies of a prototypical RAFT aqueous dispersion polymerization formulation: monitoring the evolution in copolymer morphology during polymerization-induced self-assemblyCzajka, Adam; Armes, Steven P.Chemical Science (2020), 11 (42), 11443-11454CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)Small-angle X-ray scattering (SAXS) is used to characterize the in situ formation of diblock copolymer spheres, worms and vesicles during reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. of 2-hydroxypropyl methacrylate at 70°C using a poly(glycerol monomethacrylate) steric stabilizer. The 1H NMR spectroscopy indicates more than 99% HPMA conversion within 80 min, while transmission electron microscopy and dynamic light scattering studies are consistent with the final morphol. being pure vesicles. Anal. of time-resolved SAXS patterns for this prototypical polymn.-induced self-assembly (PISA) formulation enables the evolution in copolymer morphol., particle diam., mean aggregation no., solvent vol. fraction, surface d. of copolymer chains and their mean inter-chain sepn. distance at the nanoparticle surface to be monitored. Furthermore, the change in vesicle diam. and membrane thickness during the final stages of polymn. supports an 'inward growth' mechanism.
- 38Derry, M. J.; Fielding, L. A.; Warren, N. J.; Mable, C. J.; Smith, A. J.; Mykhaylyk, O. O.; Armes, S. P. In Situ Small-Angle X-Ray Scattering Studies of Sterically-Stabilized Diblock Copolymer Nanoparticles Formed during Polymerization-Induced Self-Assembly in Non-Polar Media. Chem. Sci. 2016, 7 (8), 5078– 5090, DOI: 10.1039/C6SC01243D[Crossref], [PubMed], [CAS], Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xms1Krs7o%253D&md5=2d1c2ec1a0a40ea201ff7892b346fa62In situ small-angle X-ray scattering studies of sterically-stabilized diblock copolymer nanoparticles formed during polymerization-induced self-assembly in non-polar mediaDerry, Matthew J.; Fielding, Lee A.; Warren, Nicholas J.; Mable, Charlotte J.; Smith, Andrew J.; Mykhaylyk, Oleksandr O.; Armes, Steven P.Chemical Science (2016), 7 (8), 5078-5090CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)Reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn. of benzyl methacrylate (BzMA) is utilized to prep. a series of poly(stearyl methacrylate)-poly(benzyl methacrylate) (PSMA-PBzMA) diblock copolymer nano-objects at 90°C directly in mineral oil. Polymn.-induced self-assembly (PISA) occurs under these conditions, with the resulting nanoparticles exhibiting spherical, worm-like or vesicular morphologies when using a relatively short PSMA13 macromol. chain transfer agent (macro-CTA), as confirmed by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies. Only kinetically-trapped spherical nanoparticles are obtained when using longer macro-CTAs (e.g. PSMA18 or PSMA31), with higher mean ds.p. (DPs) for the PBzMA core-forming block simply producing progressively larger spheres. SAXS is used for the first time to monitor the various morphol. transitions that occur in situ during the RAFT dispersion polymn. of BzMA when targeting either spheres or vesicles as the final copolymer morphol. This powerful characterization technique enables the evolution of particle diam., mean aggregation no., no. of copolymer chains per unit surface area (Sagg) and the distance between adjacent copolymer chains at the core-shell interface (ditt) to be monitored as a function of monomer conversion for kinetically-trapped spheres. Moreover, the gradual evolution of copolymer morphol. during PISA is confirmed unequivocally, with approx. 'lifetimes' assigned to the intermediate pure sphere and worm morphologies when targeting PSMA13-PBzMA150 vesicles. Within vesicle phase space, the membrane thickness (Tm) increases monotonically with PBzMA DP. Furthermore, a combination of dynamic light scattering (DLS), TEM and post mortem SAXS studies indicate that the lumen vol. is reduced while the overall vesicle dimensions remain essentially const. Thus the constrained vesicles grow inwards, as recently reported for an aq. PISA formulation. This suggests a universal vesicle growth mechanism for all PISA formulations.
- 39Goodall, A. R.; Wilkinson, M. C.; Hearn, J. Mechanism of Emulsion Polymerization of Styrene in Soap-Free Systems. J. Polym. Sci., Polym. Chem. Ed. 1977, 15 (9), 2193– 2218, DOI: 10.1002/pol.1977.170150912[Crossref], [CAS], Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2sXltlKntLs%253D&md5=be813787d96d6e9e512fa9b86a966d04Mechanism of emulsion polymerization of styrene in soap-free systemsGoodall, A. R.; Wilkinson, M. C.; Hearn, J.Journal of Polymer Science, Polymer Chemistry Edition (1977), 15 (9), 2193-218CODEN: JPLCAT; ISSN:0360-6376.The formation and growth of monodisperse polystyrene latex particles in the absence of added surfactant was studied by sampling polymn. reactions at different times and detg. the surface and bulk properties of the latex. A large no. of nuclei in excess of 5 x 1012/mL were generated during the first minute of reaction, but this decreased due to coagulation until a const. no. (1011-1012/mL) was reached. The rate of polymn. per particle was then proportional to the particle radius. Gel-permeation chromatog. showed that the initial particles consist mainly of material of mol. wt. 1000 with a small amt. of polymer up to mol. wt. 106, and the presence of this low mol. wt. polymer, which in many cases can still be detected after 100% conversion, is indicative of particle formation via a micellization-type mechanism involving short-chain (mol. wt. 500) free-radical oligomers. No.-av. mol. wt. values detd. for the latex particles throughout the reactions show that the mol. wt. increases to a max. of ∼105 as the particles grow. The presence of anomalous regions within the particles was confirmed by transmission electron microscopy, scanning electron microscopy, and gas adsorption studies. It was also possible to re-expose these regions within apparently homogeneous particles by stirring with styrene [100-42-5] monomer, indicating a mol. wt. heterogeneity within the latex particles. The presence of SO4, CO2H, and OH groups upon the latex particle surfaces was detd. by conductometric titrn.
- 40Hawkett, B. S.; Napper, D. H.; Gilbert, R. G. Seeded Emulsion Polymerization of Styrene. J. Chem. Soc., Faraday Trans. 1 1980, 76 (0), 1323– 1343, DOI: 10.1039/f19807601323[Crossref], [CAS], Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3cXksVOhtbY%253D&md5=c48293e078d0b68eea2de5cfdcd579f8Seeded emulsion polymerization of styreneHawkett, Brian S.; Napper, Donald H.; Gilbert, Robert G.Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases (1980), 76 (6), 1323-43CODEN: JCFTAR; ISSN:0300-9599.The kinetics of the seeded emulsion polymn. of styrene [100-42-5] with swollen seed of radii 44-79 nm were measured dilatometrically. Conversion vs. time curves showed an increase in the instantaneous polymn. rate followed by an apparent steady state domain. The kinetic parameters detg. both the entry of free radicals into the latex particles and 1st order loss of free radicals from the particles were detd. directly. The rate coeff. of the latter varied with the inverse square of the swollen particle radius, indicating diffusion control. The magnitude of the obsd. entry rate coeff. coupled with their dependence on initiator concn. indicated that free radical capture by the seed particles was relatively inefficient. The capture rate, however, increased significantly with decreasing initiator concn. for a const. no. of seed particles. The av. no. of radicals per particle can be <0.5 under suitable conditions and, thus, styrene can follow Smith-Ewart case 1 kinetics. A background initiation process requiring no initiator was obsd. and appeared to be the emulsion polymn. equiv. of thermal polymn. of bulk styrene.
- 41Capek, I.; Lin, S. Y.; Hsu, T. J.; Chern, C. S. Effect of Temperature on Styrene Emulsion Polymerization in the Presence of Sodium Dodecyl Sulfate. II. J. Polym. Sci., Part A: Polym. Chem. 2000, 38 (9), 1477– 1486, DOI: 10.1002/(SICI)1099-0518(20000501)38:9<1477::AID-POLA10>3.0.CO;2-Y[Crossref], [CAS], Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXisFOksr8%253D&md5=d811cf83e95ef8ba1fcfce3358f81fe3Effect of temperature on styrene emulsion polymerization in the presence of sodium dodecyl sulfate. IICapek, Ignac; Lin, Shi-Yow; Hsu, Tien-Jung; Chern, Chorng-ShyanJournal of Polymer Science, Part A: Polymer Chemistry (2000), 38 (9), 1477-1486CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)The batch emulsion polymn. kinetics of styrene initiated by a water-sol. peroxydisulfate, i.e., sodium peroxydisulfate, at different temps. in the presence of sodium dodecyl sulfate was investigated. The curves of the polymn. rate vs. conversion show two distinct nonstationary-rate intervals and a shoulder occurring at a high conversion, whereas the stationary-rate interval is very short. The nonstationary-state polymn. is discussed in terms of the long-term particle-nucleation period, the addnl. formation of radicals by thermal initiation, the depressed monomer-droplet degrdn., the elimination of charged radicals through aq.-phase termination, the relatively narrow particle-size distribution and const. polydispersity index throughout the reaction, and a mixed mode of continuous particle nucleation. The max. rate of polymn. (or the no. of polymer particles nucleated) is proportional to the rate of initiation to the 0.27 power, which indicates lower nucleation efficiency as compared to classical emulsion polymn. The low activation energy of polymn. is attributed to the small barrier for the entering radicals. The overall activation energy was controlled by the initiation and propagation steps. The high ratio of the absorption rate of radicals by latex particles to the formation rate of radicals in water can be attributed to the efficient entry of uncharged radicals and the addnl. formation of radicals by thermally induced initiation.
- 42Wutzel, H.; Samhaber, W. M. Exploring the Limits of Emulsion Polymerization of Styrene for the Synthesis of Polymer Nanoparticles. Monatsh. Chem. 2007, 138 (4), 357– 361, DOI: 10.1007/s00706-007-0605-6[Crossref], [CAS], Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXktlOhurc%253D&md5=a42ee6c054fff2d88550d9a3a04b5b2aExploring the Limits of Emulsion Polymerization of Styrene for the Synthesis of Polymer NanoparticlesWutzel, Harald; Samhaber, Wolfgang M.Monatshefte fuer Chemie (2007), 138 (4), 357-361CODEN: MOCMB7; ISSN:0026-9247. (Springer Wien)Suspensions of polymer nanoparticles in water (latexes) with av. particle diams. between 20 and 80 nm were synthesized by batch emulsion polymn. of styrene using sodium dodecyl sulfate (SDS) as surfactant and potassium persulfate (KPS) as initiator. The influence of surfactant concn., initiator concn., monomer concn., and reaction temp. on the final av. particle diams. and size distributions of the latexes were studied. The no. of particles generated was proportional to the 0.56 power of the emulsifier concn. and to the 0.37 power of the initiator concn. in the whole concn. range which was obsd. Furthermore, the final no. of particles was dependent on the reaction temp. to the 2.06 power. With these correlations the av. particle no. and the av. particle size could be estd., and the results were in good agreement (±6%) with the exptl. values. A redn. of the monomer/water ratio from 1:5 to 1:20 yielded smaller particle diams., while leaving the particle no. unaffected. The lower particle size limits for monomer ratios of 1:10 and 1:15 were estd. with diams. of about 18 and 16 nm.
- 43Li, Y.; Lindsay, S. M. Polystyrene Latex Particles as a Size Calibration for the Atomic Force Microscope. Rev. Sci. Instrum. 1991, 62 (11), 2630– 2633, DOI: 10.1063/1.1142243[Crossref], [CAS], Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXms1ChtL0%253D&md5=d837da10ecaf98a456cd447f8903b24cPolystyrene latex particles as a size calibration for the atomic force microscopeLi, Y.; Lindsay, S. M.Review of Scientific Instruments (1991), 62 (11), 2630-3CODEN: RSINAK; ISSN:0034-6748.A simple method for spreading polystyrene-latex spheres onto mica substrates to form highly cryst. layers is described. These layers can be used as a simple calibration std. for the at. force microscope in the nanometer to micron size range. In particular, they provide simultaneous x, y, and z calibration. A concn. of particles of ∼0.01% is good for forming ordered structures. Two-dimensional polycryst. structures of polystyrene spheres with different packing orders (cubic and hexagonal close-pack) and some defects (vacancies, dislocations, and grain boundaries) were obsd.
- 44Molina-Bolívar, J. A.; Galisteo-González, F. Latex Immunoagglutination Assays. J. Macromol. Sci., Polym. Rev. 2005, 45 (1), 59– 98, DOI: 10.1081/MC-200045819[Crossref], [CAS], Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXit12ktb8%253D&md5=6f44930181bfad9ca02d8ff23d9a3f11Latex immunoagglutination assaysMolina-Bolivar, J. A.; Galisteo-Gonzalez, F.Journal of Macromolecular Science, Polymer Reviews (2005), C45 (1), 59-98CODEN: JMSPCG; ISSN:1532-1797. (Taylor & Francis, Inc.)Latex immunoagglutination assays continue to be widely used in biol. and medicine for the detection of small quantities of an antibody or antigen of interest in fluid test samples. Main characteristics of prepn. and use of these assays are examd. here. Phys. adsorption of proteins onto latex particles surface, with special relevance to Igs, is analyzed with major attention to those factors that influence adsorption: medium conditions such as pH and ionic strength, surface characteristics as type and amt. of charge, or hydrophobicity. Different functionalized latexes for covalent linking are also presented, as well as the corresponding chem. reactions. Techniques for the detection and quantification of the immunoreaction are briefly summarized, including visual observation, light scattering, turbidimetry, nephelometry, and angular anisotropy. Finally, some problems of colloidal stability of these latex assays are analyzed, as well as the different solns. applied by scientists to solve them.
- 45Seelenmeyer, S.; Ballauff, M. Analysis of Surfactants Adsorbed onto the Surface of Latex Particles by Small-Angle X-Ray Scattering. Langmuir 2000, 16 (9), 4094– 4099, DOI: 10.1021/la990998f[ACS Full Text], [CAS], Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXitFGhurY%253D&md5=6881a44ce50678888a1393154855556dAnalysis of Surfactants Adsorbed onto the Surface of Latex Particles by Small-Angle X-ray ScatteringSeelenmeyer, S.; Ballauff, M.Langmuir (2000), 16 (9), 4094-4099CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)A comprehensive study of the process of adsorption of a nonionic surfactant C18E112 onto poly(styrene) (PS) latex particles by small-angle X-ray scattering (SAXS) is presented. The PS latexes (particle radii 35 and 71 nm) employed in this investigation bear no chem. bound surface charges. The anal. of the process of adsorption by SAXS demonstrates that the point of satn. of the surface may be detd. directly from the scattering curves. Free micelles are formed beyond satn., and no second layer of the surfactant is built up at higher concns. of the surfactant. Any assocn. of the micelles with the covered latex particle can be ruled out as well. Moreover, an anal. of the radial structure of the surface layer in terms the zeroth and the second moment of the electron d. of the layers along the radial direction is given. Both moments can directly be obtained from the SAXS data. The zeroth moment of the excess electron d. corroborates the finding that the surfactant is firmly adsorbed onto the surface of the particles. The av. extension of the adsorbed layer (2-4 nm) as express through the second moment increases with the amt. of adsorbed surfactant. This points to a stretching of the chains due to their mutual interaction when the point of satn. of the surfaced is approached.
- 46Akpinar, B.; Fielding, L. A.; Cunningham, V. J.; Ning, Y.; Mykhaylyk, O. O.; Fowler, P. W.; Armes, S. P. Determining the Effective Density and Stabilizer Layer Thickness of Sterically Stabilized Nanoparticles. Macromolecules 2016, 49 (14), 5160– 5171, DOI: 10.1021/acs.macromol.6b00987[ACS Full Text], [CAS], Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFWgsL%252FI&md5=9fed176efbdb916c4bfb8fd962bf6f41Determining the Effective Density and Stabilizer Layer Thickness of Sterically Stabilized NanoparticlesAkpinar, Bernice; Fielding, Lee A.; Cunningham, Victoria J.; Ning, Yin; Mykhaylyk, Oleksandr O.; Fowler, Patrick W.; Armes, Steven P.Macromolecules (Washington, DC, United States) (2016), 49 (14), 5160-5171CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)A series of model sterically stabilized diblock copolymer nanoparticles has been designed to aid the development of anal. protocols in order to det. two key parameters: the effective particle d. and the steric stabilizer layer thickness. The former parameter is essential for high resoln. particle size anal. based on anal. (ultra)centrifugation techniques (e.g., disk centrifuge photosedimentometry, DCP), whereas the latter parameter is of fundamental importance in detg. the effectiveness of steric stabilization as a colloid stability mechanism. The diblock copolymer nanoparticles were prepd. via polymn.-induced self-assembly (PISA) using RAFT aq. emulsion polymn.: this approach affords relatively narrow particle size distributions and enables the mean particle diam. and the stabilizer layer thickness to be adjusted independently via systematic variation of the mean d.p. of the hydrophobic and hydrophilic blocks, resp. The hydrophobic core-forming block was poly(2,2,2-trifluoroethyl methacrylate) [PTFEMA], which was selected for its relatively high d. The hydrophilic stabilizer block was poly(glycerol monomethacrylate) [PGMA], which is a well-known non-ionic polymer that remains water-sol. over a wide range of temps. Four series of PGMAx-PTFEMAy nanoparticles were prepd. (x = 28, 43, 63, and 98, y = 100-1400) and characterized via transmission electron microscopy (TEM), dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS). It was found that the d.p. of both the PGMA stabilizer and core-forming PTFEMA had a strong influence on the mean particle diam., which ranged from 20 to 250 nm. Furthermore, SAXS was used to det. radii of gyration of 1.46 to 2.69 nm for the solvated PGMA stabilizer blocks. Thus, the mean effective d. of these sterically stabilized particles was calcd. and detd. to lie between 1.19 g cm-3 for the smaller particles and 1.41 g cm-3 for the larger particles; these values are significantly lower than the solid-state d. of PTFEMA (1.47 g cm-3). Since anal. centrifugation requires the d. difference between the particles and the aq. phase, detg. the effective particle d. is clearly vital for obtaining reliable particle size distributions. Furthermore, selected DCP data were recalcd. by taking into account the inherent d. distribution superimposed on the particle size distribution. Consequently, the true particle size distributions were found to be somewhat narrower than those calcd. using an erroneous single d. value, with smaller particles being particularly sensitive to this artifact.
- 47Fontenot, K.; Schork, F. J. Batch Polymerization of Methyl Methacrylate in Mini/Macroemulsions. J. Appl. Polym. Sci. 1993, 49 (4), 633– 655, DOI: 10.1002/app.1993.070490410[Crossref], [CAS], Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXltFOqs7o%253D&md5=5e7fba954a959d6858bfd552b10a55afBatch polymerization of methyl methacrylate in mini/macroemulsionsFontenot, K.; Schork, F. J.Journal of Applied Polymer Science (1993), 49 (4), 633-55CODEN: JAPNAB; ISSN:0021-8995.The kinetics of the isothermal batch macroemulsion and miniemulsion polymns. of Me methacrylate at 50° were studied. Hexadecane was used as the cosurfactant or swelling agent. The nucleation mechanisms were different between macroemulsions and miniemulsions. The effect of surfactant, cosurfactant, initiator, shear, and hold time on droplet nucleation was studied. The miniemulsion particles contained more radicals on av. than the macroemulsion particles using certain recipes. This resulted in higher polymn. rates for the miniemulsions at identical particle nos. The latex-particle-size distributions were similar even though the miniemulsion droplets start out with a high polydispersity of ∼1.5. Miniemulsion latexes were more stable under shear. Conductance of emulsions during polymn. was a valuable online tool for investigating particle nucleation and growth.
- 48Reimers, J. L.; Schork, F. J. Predominant Droplet Nucleation in Emulsion Polymerization. J. Appl. Polym. Sci. 1996, 60 (2), 251– 262, DOI: 10.1002/(SICI)1097-4628(19960411)60:2<251::AID-APP13>3.0.CO;2-8[Crossref], [CAS], Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xhs12lsLc%253D&md5=7661a6176082e19e1c739c8e4aac5a89Predominant droplet nucleation in emulsion polymerizationReimers, J. L.; Schork, F. J.Journal of Applied Polymer Science (1996), 60 (2), 251-62CODEN: JAPNAB; ISSN:0021-8995. (Wiley)Emulsions stabilized against diffusional degrdn. by incorporating a polymeric cosurfactant have been produced and polymd. The presence of large nos. of small droplets shifts the nucleation mechanism from micellar or homogeneous nucleation, to droplet nucleation. When an efficient cosurfactant is used, this process is referred to as miniemulsion polymn. The polymer, however, is a poor cosurfactant. Its advantage is that, unlike most cosurfactants, it is innocuous in the recipe. Results indicate that even a poor cosurfactant (polymer) is adequate to stabilize small droplets against diffusional degrdn. long enough to nucleate them into polymer particles. The dependence of the concn. and mol. wt. of the cosurfactant on the droplet size and distribution is investigated. Droplet diams. range from 19.5 to 141.2 nm with polydispersities of about 1.023. The polymeric cosurfactant affects the mechanism of nucleation. Online conductance measurements are used to successfully differentiate between nucleation mechanisms. The obsd. reaction rates are dependent on the amt. of polymeric cosurfactant present.
- 49Santos, A. F.; Lima, E. L.; Pinto, J. C.; Graillat, C.; McKenna, T. Online Monitoring of the Evolution of the Number of Particles in Emulsion Polymerization by Conductivity Measurements. I. Model Formulation. J. Appl. Polym. Sci. 2003, 90 (5), 1213– 1226, DOI: 10.1002/app.12657[Crossref], [CAS], Google Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXntFylur8%253D&md5=686e4b8bc29f1168f16f7f089a2854dbOnline monitoring of the evolution of the number of particles in emulsion polymerization by conductivity measurements. I. Model formulationSantos, A. F.; Lima, E. L.; Pinto, J. C.; Graillat, C.; McKenna, T.Journal of Applied Polymer Science (2003), 90 (5), 1213-1226CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)A cond. meter is an inexpensive instrument that can easily be installed in polymn. reactors. This instrument can be used to monitor ionic species without time-consuming calibrations. A probe is inserted into the media, providing in situ measurements of cond. in real time. For emulsion polymn. reactions, the cond. meter can respond to changes in the ionic surfactant concn., allowing the detn. of surfactant dynamics in the media. The surfactant concn. can then be related to the changes in the surface area of the polymer particle phase, which can be linked to nucleation or coagulation phenomena. In this study, a cond. meter was coupled to a calorimetric reactor to provide in situ and online measurements of cond. during the emulsion polymn. of styrene, with sodium dodecyl sulfate as an anionic surfactant and with potassium persulfate as a free-radical initiator. A semiempirical model was built to describe the cond. signal as a function of the latex compn. and the reactor temp. The model was inverted and combined with the available cond. signal, conversion, and temp. measurements and was able to accurately predict the no. of polymer particles in the latex and the surfactant concns. in the many phases, without online measurements of the particle size.
- 50Banthia, A. K.; Mandal, B. M.; Palit, S. R. Dye-Partition Method of Analysis of End Groups in Nonpolar Polymers Re-Examined: Sulfate End Groups in Persulfate-Initiated Polystyrene. J. Polym. Sci., Polym. Chem. Ed. 1977, 15 (4), 945– 957, DOI: 10.1002/pol.1977.170150416[Crossref], [CAS], Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2sXhsFKitbc%253D&md5=01c96e1c19f6c7c3269d2e4ff004b5c6Dye-partition method of analysis of end groups in nonpolar polymers re-examined: sulfate end groups in persulfate-initiated polystyreneBanthia, Ajit K.; Mandal, Broja M.; Palit, Santi R.Journal of Polymer Science, Polymer Chemistry Edition (1977), 15 (4), 945-57CODEN: JPLCAT; ISSN:0360-6376.Sulfate, sulfonate, and isothiouronium salt end groups in polystyrene (I) [9003-53-6] prepd. using K2S2O8, Na2SO3-Cu+2-O2, and FeCl3-thiourea initiators, resp., were estd. by the dye partition method. While the persulfate-initiated polymers contained very low amts. of sulfate end groups (0.05-0.3 per polymer mol.), the other 2 initiator systems yielded polymers with about 2 salt end groups per polymer mol. The low amt. of sulfate end group in persulfate-initiated I is in conformity with the initiation mechanism of A. Ledwith and P.J. Russell (1976) for persulfate-initiated emulsion polymn. of styrene, and supports earlier findings that polymer polarity does not affect the results of end-group anal. by the dye-partition technique.
- 51Ghosh, P.; Chadha, S. C.; Mukherjee, A. R.; Palit, S. R. Endgroup Studies in Persulfate-Initiated Vinyl Polymer by Dye Techniques. Part I. Initiation by Persulfate Alone. J. Polym. Sci., Part A: Gen. Pap. 1964, 2 (10), 4433– 4440, DOI: 10.1002/pol.1964.100021013
- 52Tauer, K.; Deckwer, R. Polymer End Groups in Persulfate-Initiated Styrene Emulsion Polymerization. Acta Polym. 1998, 49 (8), 411– 416, DOI: 10.1002/(SICI)1521-4044(199808)49:8<411::AID-APOL411>3.0.CO;2-D[Crossref], [CAS], Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXlslOjs7w%253D&md5=d21634e040f866d772d6ef48df835109Polymer and groups in persulfate-initiated styrene emulsion polymerizationTauer, K.; Deckwer, R.Acta Polymerica (1998), 49 (8), 411-416CODEN: ACPODY; ISSN:0323-7648. (Wiley-VCH Verlag GmbH)MALDI-TOF-MS investigations of the polymer inside the particles at the end of a persulfate-initiated emulsifier-free emulsion polymn. of styrene reveal, beside sulfate groups, a variety of different end groups of the polymer mols. almost independent of the buffer concn. employed during the polymn. The results support at least the existence of the following end group combinations: H-H, H-OH, K+-OO-OH, K+-OO-K+-OO, HO-OH, K+-OS3-H, K+-OSO3-OH, and K+-OSO3-K+-OSO3. These results lead to conclusions concerning particle nucleation and radical entry. As non-micellar particle nucleation is governed by the soly. of waterborne oligomers, chains started with radicals formed by side reactions in the aq. phase obviously play an important role in particle nucleation. Concerning radical entry, the results suggest that surface activity of the entering radicals is not a prerequisite.
- 53Pedersen, J. S.; Gerstenberg, M. C. Scattering Form Factor of Block Copolymer Micelles. Macromolecules 1996, 29 (4), 1363– 1365, DOI: 10.1021/ma9512115[ACS Full Text], [CAS], Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XltlWjsA%253D%253D&md5=e6f549fc773b455a50c0d6e157ca4981Scattering Form Factor of Block Copolymer MicellesPedersen, Jan Skov; Gerstenberg, Michael C.Macromolecules (1996), 29 (4), 1363-5CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)The form factor of a micelle model with a spherical core and Gaussian polymer chains attached to the surface was calcd. anal. and the results were compared to Monte Carlo simulations. Excluded vol. interactions between the core and the polymers were introduced in the simulations. The expansion of the coils due to this effect can be mimicked in the anal. calcns. by moving the center of mass of the chains away from the surface of the core. The anal. expression for the form factor has been used for analyzing small-angle scattering data.
- 54Li, T.; Senesi, A. J.; Lee, B. Small Angle X-Ray Scattering for Nanoparticle Research. Chem. Rev. 2016, 116 (18), 11128– 11180, DOI: 10.1021/acs.chemrev.5b00690[ACS Full Text], [CAS], Google Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlsF2qsrw%253D&md5=659565f88b80ce6994bb98c07f034eb2Small Angle X-ray Scattering for Nanoparticle ResearchLi, Tao; Senesi, Andrew J.; Lee, ByeongduChemical Reviews (Washington, DC, United States) (2016), 116 (18), 11128-11180CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)X-ray scattering is a structural characterization tool that has impacted diverse fields of study. It is unique in its ability to examine materials in real time and under realistic sample environments, enabling researchers to understand morphol. at nanometer and angstrom length scales using complementary small and wide angle X-ray scattering (SAXS, WAXS), resp. Herein, we focus on the use of SAXS to examine nanoscale particulate systems. We provide a theor. foundation for X-ray scattering, considering both form factor and structure factor, as well as the use of correlation functions, which may be used to det. a particle's size, size distribution, shape, and organization into hierarchical structures. The theory is expanded upon with contemporary use cases. Both transmission and reflection (grazing incidence) geometries are addressed, as well as the combination of SAXS with other X-ray and non-X-ray characterization tools. We conclude with an examn. of several key areas of research where X-ray scattering has played a pivotal role, including in situ nanoparticle synthesis, nanoparticle assembly, and operando studies of catalysts and energy storage materials. Throughout this review we highlight the unique capabilities of X-ray scattering for structural characterization of materials in their native environment.
- 55Narayanan, T.; Wacklin, H.; Konovalov, O.; Lund, R. Recent Applications of Synchrotron Radiation and Neutrons in the Study of Soft Matter. Crystallogr. Rev. 2017, 23 (3), 160– 226, DOI: 10.1080/0889311X.2016.1277212[Crossref], [CAS], Google Scholar55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXisVaks78%253D&md5=15e7445b1320185847e34352e9d3b5c8Recent applications of synchrotron radiation and neutrons in the study of soft matterNarayanan, Theyencheri; Wacklin, Hanna; Konovalov, Oleg; Lund, ReidarCrystallography Reviews (2017), 23 (3), 160-226CODEN: CRRVEN; ISSN:0889-311X. (Taylor & Francis Ltd.)The broad range of applications of synchrotron and neutron scattering in the investigation of soft condensed matter is reviewed. Appropriate combinations of these techniques allow probing the structure and dynamics of these complex systems from sub-nm to micron size scales and picoseconds to seconds and longer time ranges. Applications include a myriad of systems such as polymers, colloids, surfactants, phospholipids, biol. macromols. and functional materials both in bulk and at interfaces. Most studies are performed in situ under the real thermodn. state of the given system and large ensemble averaged information is readily obtained. The new generations of synchrotron and neutron sources open possibilities for investigating more complex soft matter systems in hitherto unexplored dynamical states.
- 56Takahashi, R.; Miwa, S.; Sobotta, F. H.; Lee, J. H.; Fujii, S.; Ohta, N.; Brendel, J. C.; Sakurai, K. Unraveling the Kinetics of the Structural Development during Polymerization-Induced Self-Assembly: Decoupling the Polymerization and the Micelle Structure. Polym. Chem. 2020, 11, 1514– 1524, DOI: 10.1039/C9PY01810G[Crossref], [CAS], Google Scholar56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtVektrk%253D&md5=85cb40c5284055c0b9b46c8bed6f5f50Unraveling the kinetics of the structural development during polymerization-induced self-assembly: decoupling the polymerization and the micelle structureTakahashi, Rintaro; Miwa, Shotaro; Sobotta, Fabian H.; Lee, Ji Ha; Fujii, Shota; Ohta, Noboru; Brendel, Johannes C.; Sakurai, KazuoPolymer Chemistry (2020), 11 (8), 1514-1524CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)Upon extending a hydrophobic polymer chain from the end of a preceding hydrophilic chain in aq. solns., the resultant block copolymers may eventually undergo self-assembly. Further chain propagation continues in the newly formed hydrophobic polymer rich domain. This process is often referred to as polymn.-induced self-assembly (PISA). Its kinetics are detd. by the polymn. and the micelle formation/growth, which may influence each other, possibly leading to a highly complex process of structural development. In this study, we examd. PISA in aq. soln. on the reversible addn. fragmentation chain transfer (RAFT) dispersion polymn. of poly(N-acryloylmorpholine)-b-poly(N-acryloylthiomorpholine). Using in situ small-angle X-ray scattering (SAXS) and NMR spectroscopy (NMR), the polymn. and micelle formation were obsd. In the anal., because the time scale of the micelle formation/growth is much shorter than that of the polymn., the polymn. and micelle formation/growth can be decoupled. Thus, these were sep. analyzed in depth, and a combination of the kinetics of RAFT polymn. and the simple scaling theory of the micellar structures can quant. describe the overall micellar structural development during PISA. This study provides an unprecedented insight into the processes underlying PISA and deepens our quant. understanding of it.
- 57Ballauff, M. SAXS and SANS Studies of Polymer Colloids. Curr. Opin. Colloid Interface Sci. 2001, 6 (2), 132– 139, DOI: 10.1016/S1359-0294(01)00072-3[Crossref], [CAS], Google Scholar57https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXktFWnsLY%253D&md5=9ce2496b9042232cbaf4d14400c977faSAXS and SANS studies of polymer colloidsBallauff, M.Current Opinion in Colloid & Interface Science (2001), 6 (2), 132-139CODEN: COCSFL; ISSN:1359-0294. (Elsevier Science Ltd.)The anal. of latex particles by small-angle scattering (small-angle X-ray scattering, SAXS; small-angle neutron scattering, SANS) is reviewed with 42 refs. Small-angle scattering techniques give information on the radial structure of the particles as well as on their spatial correlation. Recent progress in instrumentation allows to extend SANS and SAXS to the q-range of light scattering. Moreover, contrast variation employed in SANS and SAXS studies may lead to an unambiguous detn. of the radial scattering length d. of the particles in situ, i.e. in suspension. Hence, these techniques are highly valuable for a comprehensive anal. of polymer colloids as shown by the examples discussed herein.
- 58Wagner, J.; Härtl, W.; Hempelmann, R. Characterization of Monodisperse Colloidal Particles: Comparison between SAXS and DLS. Langmuir 2000, 16 (9), 4080– 4085, DOI: 10.1021/la991125o[ACS Full Text], [CAS], Google Scholar58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXhvFKms7w%253D&md5=0f379dc7d152f980e999a0a123e71077Characterization of monodisperse colloidal particles: comparison between SAXS and DLSWagner, Joachim; Haertl, Wolfram; Hempelmann, RolfLangmuir (2000), 16 (9), 4080-4085CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Fluoroalkyl (meth)acrylate polymer colloids with low refractive index are prepd. via emulsion polymn. The characterization is done using small-angle X-ray scattering and dynamic light scattering. The independently obtained particle size distributions are in remarkable mutual agreement and give evidence for the monodispersity of our particles. The small-angle scattering signal of such monodisperse samples is influenced by the resoln. of the exptl. setup. We discuss a method to take such instrumental contributions into consideration and show that the divergence of the primary beam is the most important factor using a pinhole camera with flat single-crystal monochromator.
- 59Bolze, J.; Ballauff, M.; Kijlstra, J.; Rudhardt, D. Application of Small-Angle X-Ray Scattering as a Tool for the Structural Analysis of Industrial Polymer Dispersions. Macromol. Mater. Eng. 2003, 288 (6), 495– 502, DOI: 10.1002/mame.200390046[Crossref], [CAS], Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXltlWitL0%253D&md5=177da42a2d945f20cf343318865d3a1cApplication of small-angle X-ray scattering as a tool for the structural analysis of industrial polymer dispersionsBolze, Joerg; Ballauff, Matthias; Kijlstra, Johan; Rudhardt, DanielMacromolecular Materials and Engineering (2003), 288 (6), 495-502CODEN: MMENFA; ISSN:1438-7492. (Wiley-VCH Verlag GmbH & Co. KGaA)Small-angle X-ray scattering (SAXS) was applied for the structural anal. of an industrial polymer dispersion in water (synthetic latex). For the prepn. of the spherical latex particles under investigation, butadiene, styrene, and acrylic acid were used as monomers in a seeded emulsion polymn. process. The product is widely used as a film-forming agent for coatings in the paper-making industry. It was demonstrated that by measuring the SAXS curves at different contrasts the overall particle size, mass d., polydispersity, and degree of heterogeneity can be estd. with a good accuracy, even without the necessity of a detailed fitting procedure. In particular, one obtains information about the spatial distribution of the various monomer units within the particles. Five isoscattering points could be obsd. in the contrast variation measurements and the scattering curves at all contrasts could be modeled with a fully consistent set of fit parameters. It is thus safe to conclude that the contrast agent sucrose does not affect the particle structure. A quant. fitting of the exptl. data set revealed that a significant amt. of the poly(acrylic acid) was preferentially located in a thin shell of ca. 2 nm thickness around the core of the particles, that was mainly formed by poly(styrene-co-butadiene). The obtained results were fully consistent with addnl. measurements of the particle mass d., of the hydrodynamic particle radius by dynamic light scattering, and of the particle surface charge by potentiometric titrn. It was concluded that SAXS is a highly useful tool for characterizing the structure of industrial latexes.
- 60Ballauff, M.; Bolze, J.; Dingenouts, N.; Hickl, P.; Pötschke, D. Small-Angle X-Ray Scattering on Latexes. Macromol. Chem. Phys. 1996, 197 (10), 3043– 3066, DOI: 10.1002/macp.1996.021971001[Crossref], [CAS], Google Scholar60https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xmt1WisLc%253D&md5=80f028fd6854b055abd25f84c1f2267fSmall-angle x-ray scattering on latexesBallauff, Matthias; Bolze, Joerg; Dingenouts, Nico; Hickl, Peter; Poetschke, DominicMacromolecular Chemistry and Physics (1996), 197 (10), 3043-3066CODEN: MCHPES; ISSN:1022-1352. (Huethig & Wepf)Recent small-angle x-ray scattering (SAXS) studies of polymer latexes are reviewed with 106 refs. to show that SAXS can be used to study the structure and interactions of polymer latexes with great accuracy.
- 61Balmer, J. A.; Mykhaylyk, O. O.; Schmid, A.; Armes, S. P.; Fairclough, J. P. A.; Ryan, A. J. Characterization of Polymer-Silica Nanocomposite Particles with Core-Shell Morphologies Using Monte Carlo Simulations and Small Angle X-Ray Scattering. Langmuir 2011, 27 (13), 8075– 8089, DOI: 10.1021/la201319h[ACS Full Text], [CAS], Google Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXntlCqtrg%253D&md5=9ea3ca1b4a8edcc48f631a3152519b91Characterization of Polymer-Silica Nanocomposite Particles with Core-Shell Morphologies using Monte Carlo Simulations and Small Angle X-ray ScatteringBalmer, Jennifer A.; Mykhaylyk, Oleksandr O.; Schmid, Andreas; Armes, Steven P.; Fairclough, J. Patrick A.; Ryan, Anthony J.Langmuir (2011), 27 (13), 8075-8089CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)A two-population model based on std. small-angle x-ray scattering (SAXS) equations is verified for the anal. of core-shell structures comprising spherical colloidal particles with particulate shells. First, Monte Carlo simulations of core-shell structures are performed to demonstrate the applicability of the model. Three possible shell packings are considered: ordered silica shells due to either charge-dependent repulsive or size-dependent Lennard-Jones interactions or randomly arranged silica particles. In most cases, the two-population model produces an excellent fit to calcd. SAXS patterns for the simulated core-shell structures, together with a good correlation between the fitting parameters and structural parameters used for the simulation. The limits of application are discussed, and then, this two-population model is applied to the anal. of well-defined core-shell vinyl polymer/silica nanocomposite particles, where the shell comprises a monolayer of spherical silica nanoparticles. Comprehensive SAXS anal. of poly(styrene-co-Bu acrylate)/silica colloidal nanocomposite particles (prepd. by the in situ emulsion copolymn. of styrene and Bu acrylate in the presence of a glycerol-functionalized silica sol) allows the overall core-shell particle diam., the copolymer latex core diam. and polydispersity, the mean silica shell thickness, the mean silica diam. and polydispersity, the vol. fractions of the two components, the silica packing d., and the silica shell structure to be obtained. These exptl. SAXS results are consistent with electron microscopy, dynamic light scattering, TG, helium pycnometry, and BET surface area studies. The high electron d. contrast between the (co)polymer and the silica components, together with the relatively low polydispersity of these core-shell nanocomposite particles, makes SAXS ideally suited for the characterization of this system. Also, these results can be generalized for other types of core-shell colloidal particles.
- 62Rieker, T.; Hanprasopwattana, A.; Datye, A.; Hubbard, P. Particle Size Distribution Inferred from Small-Angle X-Ray Scattering and Transmission Electron Microscopy. Langmuir 1999, 15, 638– 641, DOI: 10.1021/la9810713[ACS Full Text], [CAS], Google Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXotVOmtbw%253D&md5=43193354605bec58cacd8529d5fdfd54Particle Size Distribution Inferred from Small-Angle X-ray Scattering and Transmission Electron MicroscopyRieker, Thomas; Hanprasopwattana, Aree; Datye, Abhaya; Hubbard, PaulLangmuir (1999), 15 (2), 638-641CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Particle size distributions detd. by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) are investigated for samples of interacting hard spheres. Polydispersity in the samples is detd. from the SAXS data by fitting the Porod region to the form factor of a sphere of uniform electron d. smeared by a Gaussian distribution of sphere diams. We find good agreement between SAXS-detd. particle size distributions and those calcd. from TEM image anal.
- 63Pedersen, J. S. Form Factors of Block Copolymer Micelles with Spherical, Ellipsoidal and Cylindrical Cores. J. Appl. Crystallogr. 2000, 33 (3), 637– 640, DOI: 10.1107/S0021889899012248[Crossref], [CAS], Google Scholar63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXkslOisbw%253D&md5=815f89e342650d3dcc702e7e0944882fForm factors of block copolymer micelles with spherical, ellipsoidal and cylindrical coresPedersen, Jan SkovJournal of Applied Crystallography (2000), 33 (3, Pt. 1), 637-640CODEN: JACGAR; ISSN:0021-8898. (Munksgaard International Publishers Ltd.)The form factor of a micelle model with a spherical core and Gaussian polymer chains attached to the surface has previously been calcd. anal. by Pedersen and Gerstenberg. Non-penetration of the chains into the core region was mimicked in the anal. calcns. by moving the center of mass of the chains Rg away from the surface of the core, where Rg is the radius of gyration of the chains. In the present work, the calcns. have been extended to micelles with ellipsoidal and cylindrical cores. Non-penetration was also for these taken into account by moving the center of mass of the chains Rg away from the core surface. In addn. results for worm-like micelles, disk-shape micelles and micelles with a vesicle shape are given.
- 64Muratov, A.; Moussaïd, A.; Narayanan, T.; Kats, E. I. A Percus-Yevick Description of the Microstructure of Short-Range Interacting Metastable Colloidal Suspensions. J. Chem. Phys. 2009, 131, 054902, DOI: 10.1063/1.3179667[Crossref], [PubMed], [CAS], Google Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXps1Oksbg%253D&md5=4100664c2302d742553ecd72a8e3ff21A Percus-Yevick description of the microstructure of short-range interacting metastable colloidal suspensionsMuratov, A.; Moussaid, A.; Narayanan, T.; Kats, E. I.Journal of Chemical Physics (2009), 131 (5), 054902/1-054902/11CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)We present a revised form of the Percus-Yevick approach applicable to dispersions of interacting colloidal particles such as colloid-polymer mixts. and square-well attractive colloids. Our approach is suitable for treating short-range interparticle potentials including excluded vol. hard-sphere repulsion, short-range depletion attraction, and square-well attraction. In all these cases, the Ornstein-Zernike equation for the pair correlation function can be satisfied by a trial function, which generalizes the and ansatz. Structure factors (or x-ray scattering intensities) calcd. by this method are in good agreement with exptl. data for colloid-polymer mixts. over a range of parameters pertaining to the stable fluid phase and the metastable state with moderate attraction. On the same footing, we have detd. the stability limits and analyzed contributions to the scattered intensity from particle aggregates appearing prior to the phase sepn. for sufficiently strong short-range attraction. Similar features are obsd. in the case of square-well attractive colloids when the attraction is turned on. (c) 2009 American Institute of Physics.
Supporting Information
Supporting Information
ARTICLE SECTIONSThe Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.0c11183.
Full experimental details for PTFEMA particles; further characterization data including aqueous electrophoresis, additional SAXS patterns, optical microscopy images of monomer droplets recorded at various TFEMA conversions, and GPC analysis of PTFEMA chains; and details and examples of the supporting analysis, along with the hard sphere scattering model used to analyze the PTFEMA latexes (PDF)
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