Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session M05: Nonequilibrium Structures and Dynamics of Polymeric Materials III |
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Sponsoring Units: DPOLY Chair: Shiwang Cheng, Michigan State University Room: Room 128 |
Wednesday, March 8, 2023 8:00AM - 8:12AM Author not Attending |
M05.00001: Polymers of Intrinsic Microporosity- Molecular Mobility and Physical Aging Revisited by Dielectric Spectroscopy and X-Ray Scattering Farnaz Emamverdi, Glen J Smales, Martin Böhning, Andreas Schönhals Polymer of Intrinsic Microporosity (PIMs) are promising candidates for the active layer in gas separation membranes due to their high permeability and reasonable permselectivity. However, this class of polymers suffers from a significant decrease in separation performance with time due to physical aging. The initial microporous structure approach a denser state via local rearrangements, leading to a reduction of the permeability. In this work, the dielectric behavior of PIM-1 films and their behavior upon hating (aging) were revisited by isothermal frequency scans during different heating/cooling cycles over a broad temperature range between 133 K and 523 K by Broadband Dielectric Spectroscopy. In addition, the obtained results were compared with data of samples that were annealed at ambient temperatures over different time scales. Multiple dielectric processes were observed: several relaxation processes due to local fluctuations and a Maxwell-Wagner-Sillars polarization effect related to microporosity1. The temperature dependence of the rates of all processes follows the Arrhenius law where the estimated activation energy depends on the nature of the process. |
Wednesday, March 8, 2023 8:12AM - 8:24AM |
M05.00002: Size-Dependent Reentrant Mobility of Polymers Driven in a Periodic Potential Won Kyu Kim Barrier-crossing problems of polymers have been extensively addressed to better elucidate complex phenomena widely ranged from biology to soft matter, such as polymer translocation and electrophoresis. Here we revisit a relevant problem, considering potential applications extended to electrodialysis and filtration of polymers, in which the polymers of various flexibilities and lengths selectively cross over spatially periodic energy barriers in three dimensions. To this end, we perform coarse-grained computer simulations in which an external force field (constant bias) drives the polymers as a general source of nonzero flux of the system. Depending on the period of the barrier (L) and the degree of polymerization (N), the polymer flux exhibits unusual reentrance tendencies, particularly found significant for self-avoiding and semi-flexible polymers. Interestingly, for semi-flexible polymers, we find a local enhancement of their mobility as a function of L and N, especially when N is comparable to L, which induces inchworm-like motions of the polymers in a steady state. This reentrant mobility of polymers is further rationalized by approximate theories in one dimension. The results may provide fundamental guidance for developing polymer filtration applications. |
Wednesday, March 8, 2023 8:24AM - 8:36AM |
M05.00003: Physical Aging of Hydroxypropyl Methylcellulose Acetate Succinate Amorphous Solid Dispersions using Fast Scanning Calorimetry Yejoon Seo Amorphous solid dispersions (ASDs) utilize the glassy state to kinetically stabilize drug molecules within a polymer matrix. However, physical aging of the polymer excipient impacts drug stability in ASDs, the extent of which remains unknown. To address this knowledge gap, we employed fast scanning calorimetry (FSC) to probe the physical aging behavior of spray-dried ASDs. Ritonavir was used as the model drug and spray dried with hydroxypropyl methylcellulose acetate succinate (HPMCAS) at 1, 5, and 10 drug weight percent by mass. The high scanning rates of FSC inhibited de-mixing effects at high temperatures, allowing for accurate glass transition measurements. Aging rate calculations showed that despite their expected kinetic stability, ASDs exhibited significant thermodynamic evolution deep in the glassy state (100°C below the glass transition) independent of drug content. However, increased drug content shifted the peak aging rate temperature closer to the glass transition. These behaviors indicated that drug presence has an overall minor influence on HPMCAS physical aging behavior except at temperatures near the glass transition, where ASDs exhibit faster aging rates compared to the pure polymer excipient. |
Wednesday, March 8, 2023 8:36AM - 8:48AM |
M05.00004: Applicability of Generalized Stokes Einstein Relation of Mode-Coupling Theory to Near-Critical Polyelectrolyte Complex Coacervate Solutions Vivek M Prabhu, Yuanchi Ma, Paul Salipante, Steven D Hudson, Jack F Douglas Complex coacervate solutions composed of a blend of oppositely charged polyelectrolytes have recently been observed to exhibit liquid-liquid phase separation upon heating or lower critical solution temperature behavior [1], as found in many water-soluble uncharged polymers. It is interesting to consider whether the dynamic critical phenomena of these phase separating fluids is similar to neutral polymers solutions and blends. Despite the additional complexities due to charge fluctuations and associative behavior, we examine whether the mode-coupling theory of Kawasaki and Ferrell [2,3] can describe the wavevector-dependent collective diffusion coefficient (Dc) in near-critical polyelectrolyte complex coacervate solutions, a framework validated in many uncharged near-critical fluid mixtures. We also test the Generalized Stokes-Einstein relationship predicted by this theory for the collective diffusion coefficient, Dc = kB T/ 6 π η ξs, in the long-wavelength limit where ξs is the previously measured static correlation length [1], product of Boltzmann’s constant and temperature (kB T), and η is the viscosity of the fluid mixture independently measured by capillary rheometry. Our observations show that the critical dynamics are remarkably similar to neutral polymer blends in solution and small molecule mixtures near their critical point for phase separation. We hypothesize that relative simplicity found in the dynamic criticality of the coacervate mixtures might arise from the formation of neutral complexes. |
Wednesday, March 8, 2023 8:48AM - 9:00AM |
M05.00005: Suppression of segmental chain dynamics on particle's surface in attractive polymer nanocomposites Antonio Faraone, Jihyuk Kim, Benjamin R Thompson, Taiki Tominaga, Michael Ohl, Erkan Senses, Norman J Wagner The Rouse dynamics of polymer chains in model nanocomposite PolyEthylene Oxide (PEO)/Silica NanoParticles (NPs) was investigated using QuasiElastic Neutron Scattering (QENS). The fraction of segments immobile on the picosecond/nanosecond timescale, as they are physisorbed on the NP surface, was identified. The Rouse rate of the remaining polymer chains decreases as the particle loading increases. This experimental result is analyzed in terms of modified Rouse models for the chains in the NP interphase region. Thus, two chain populations, one bulk like and the other characterized by a suppression of Rouse modes, are identified and the spatial extent of the interphase region is estimated to be ≈2 nm. These finding provide a detailed description of the suppression of the chain dynamics on the surface of NPs. The results are relevant for the fundamental understanding of surface effects and confinement and provide a foundation for the understanding of the rheological properties of well dispersed Polymer NanoComposites (PNCs). |
Wednesday, March 8, 2023 9:00AM - 9:12AM |
M05.00006: Spatial-temporal dynamics at the interface of 3D printed photocurable nanocomposite layers Tad Koga, Benjamin M Yavitt, Lutz Wiegart, Daniel Salatto, ZHIXING HUANG, Sascha Poeller, Manuel Schiel, Maya K Endoh, Stanislas Petrash Additive manufacturing (AM) is used to fabricate polymeric materials into complex three-dimensional (3D) structures. As the 3D structure is built by sequential layer-by-layer deposition of filaments dispensed from a translating nozzle, defects often form at the filament-filament interface. The out-of-equilibrium structural development that occurs during the printing process is difficult to directly measure by quantitative means, limiting our understanding of the physical mechanisms at play. Here, we utilize in-operando X-ray photon correlation spectroscopy (XPCS) measurements with microbeam capability to probe the real-time structural evolution at the filament-filament interface during extrusion 3D printing. We investigate the solidification of a dual cure (UV/thermal) acrylate/epoxy resin during multilayer 3D printing as a rational model by tracking the nanoscale motion of filler particles ("tracers") embedded in the polymer matrix. The spatially and temporally resolved dynamics are measured during the deposition of a single filament as well as during the deposition of a second layer on top of the cured underlayer. The XPCS microrheology approach provides insight into the nanoscale mechanisms that dictate the interfacial crosslinking process between printed filaments and progresses towards overcoming the barriers limiting industrial use of extrusion-based AM. |
Wednesday, March 8, 2023 9:12AM - 9:24AM |
M05.00007: Probing the Structure-Dynamics-Process-Property Relationship of a Curing Epoxy Resin via X-ray Photon Correlation Spectroscopy Leonidas Tsapatsaris, Lutz Wiegart, Stan Petrash, Mikihito Takenaka, Tadanori Koga, Maya K Endoh Industrial adhesives are dispensed as viscous fluids, which then undergo a liquid-solid transition due to the formation of a cross-linked polymer network, known as "curing". However, the development and testing of adhesives is largely empirical owing to the lack of experimental tools to directly probe the internal molecular structure and dynamics of the material during the curing process. Here, we used X-ray photon correlation spectroscopy (XPCS) to investigate the structure/dynamics changes of a commercially available thermally-cured two-component adhesive (epoxy and acrylic resin) under operando conditions closely simulating industrial processing (i.e., nozzle extrusion and thermal-assisted crosslinking). The adhesive contained a small amount of fumed silica fillers for viscosity modification, though as a control we also measured the same epoxy-resin without silica fillers. Numerical analysis of the XPCS data demonstrated direct evidence of non-equilibrium structural and dynamical properties of the cross-linking network during the curing process. We will further discuss the relationship between structure-dynamics of the adhesive during curing, the manufacturing process, and the mechanical properties of the final adhesive. |
Wednesday, March 8, 2023 9:24AM - 9:36AM |
M05.00008: Surface fluctuations on epoxy resin thin films during the curing process studied by GI-XPCS Taiki Hoshino, Yasushi Okamoto, Atsushi Yamamoto, Hiroyasu Masunaga Epoxy resins are the essential materials for modern industry because of their excellent mechanical properties, chemical resistance, and moldability. In thermosetting epoxy resins, heating temperature and curing time significantly affect the physical properties. Using x-ray photon correlation spectroscopy (XPCS), we have recently studied the dynamics of the curing process in bulk systems and discussed the formation of crosslinked structures and their temperature dependence [1]. On the other hand, the dynamics during the curing process of thin films, which are widely used as semiconductor protective films or adhesives, has not been well studied. In this study, thermal fluctuations on the surface of epoxy resin thin films were investigated by grazing incidence XPCS (GI-XPCS) for understanding the dynamical properties during the curing process. From the measurements, we obtained the capillary wave spectra on the thin films during the thermal curing process and found they slowed down with the reaction process. We analyzed those spectra and showed that they can be explained by the theory of capillary waves for viscous liquids. In addition to these capillary wave spectra for the viscous liquids, we also found a sudden rise and increase in the baseline of the time autocorrelation function at the later stage. Those behavior is assumed to represent the gelation process. Finally, almost no relaxation behavior was observed, indicating that the gelation was almost complete, and the thin films solidified. We succeeded in observing the freezing process of capillary waves during the thermal curing process. This research is widely applicable to the study of the dynamics of the curing process of thin films in non-equilibrium conditions and is expected to lead to various developments in the understanding of the curing mechanisms of various thin films. |
Wednesday, March 8, 2023 9:36AM - 9:48AM |
M05.00009: The study on dispersion of filler in rubber/filler system by ASAXS Shotaro Nishitsuji, Yuki Tanaka, Mizuki Kishimoto, Kiminori Uchida, Yohei Nakanishi, Mikihito Takenaka In rubber/filler system, the dispersion of the filler greatly affects the mechanical properties. Zinc oxide (ZnO) plays an important role in the cross-linking reaction as a vulcanization accelerator, but also affects the dispersion of the filler, so the dispersion of ZnO is also important. In order to investigate the nm order dispersion of filler and ZnO, small angle X-ray scattering (SAXS) is a powerful technique. However, it is difficult to clarify the respective dispersion because the sizes of the dispersion of CB and ZnO are close. To solve this problem, we focused on anomalous small angle X-ray scattering (ASAXS). ASAXS is a technique for performing SAXS measurements with different contrasts by varying the incident X-ray energy near the element-specific X-ray absorption edge. Using this method, the partial scattering function of CB and ZnO in Ethylene Propylene Diene Methylene Linkage(EPDM)/CB/ZnO were obtained. In order to quantitatively estimate the dispersion of the CB, the partial scattering function of CB was fitted using the Unified Guinier/Power-Law Approach. As a result, it was found that the mass fractal dimensions of aggregates of CB differed depending on the kneading process. In addition, the distribution of ZnO changed with the kneading process. |
Wednesday, March 8, 2023 9:48AM - 10:00AM |
M05.00010: Polarized Resonant Soft X-Ray Scattering (P-RSoXS) As a Tool to Measure Structure at Crystalline-Amorphous Interfaces of Semi-Crystalline Polymers. Camille Bishop, Eliot H Gann, Luana Rojas Zurita, Dean M DeLongchamp The structure of the amorphous phase has a significant influence on the macroscopic properties of semi-crystalline polymers. However, the exact structure of the amorphous region can be difficult to quantify, given its less-ordered structure and various chain connectivities. Therefore, it is difficult to define unambiguous processing-structure-function relationships for these systems. In this work, we show the capabilities and potential of polarized resonant soft X-ray scattering (p-RSoXS) to measure chain density and orientation at the crystalline-amorphous interface in polylactic acid (PLA). p-RSoXS exploits the chemically and directionally sensitive interaction between polarized X-rays and oriented chemical bonds, enhancing scattering from specific bond-bond correlations. We use a forward-scattering GPU-accelerated simulation, CyRSoXS, based on high-resolution TEM imaging to identify a real-space model that produces a combination of compositional and orientational scattering that is consistent with experiment. This approach allows us to measure the direction, spatial extent, and magnitude of orientation in polymer chains at amorphous-crystalline interfaces to provide insight into the effect of processing conditions on the structure and properties of semi-crystalline polymers. |
Wednesday, March 8, 2023 10:00AM - 10:12AM |
M05.00011: XPCS Study of Dynamic Strain Response of Rubber Nanocomposite Containing Functionalized Chains Mark D Foster, Dillon Presto, Hakan Aras, Suresh Narayanan, Sergio Moctezuma, Mark D Sutton Coupling agents are widely used in rubber nanocomposites to improve macroscopic properties for targeted applications. We have shown using In situ X-ray Photon Correlation Spectroscopy how the coupling agents change the filler nonequilibrium microdynamics response to dynamic strain. The incorporation of functionalized chains provides an additional means of modifying the filler-polymer interface to tailor properties. We present the microdynamics seen by XPCS for nanocomposites in which a fraction of lower molecular weight rubber chains are incorporated into the network as polymeric additives. The microdynamics differ for the case in which these short chain additives are end-functionalized and the case in which they are not functionalized. The macroscopic properties as measured with Dynamic Mechanical Analysis are considered in light of the insights into the nonequilibrium microdynamics provided by XPCS. |
Wednesday, March 8, 2023 10:12AM - 10:24AM |
M05.00012: Cooperative Adsorption of Polymer Chains on Solid Surfaces Yuma Morimitsu, Hisao Matsuno, Yukari Oda, Satoru Yamamoto, Keiji Tanaka The adsorption of polymer chains in different phases onto the surfaces is a ubiquitous phenomenon in natural systems, composite materials, and thin-film devices. It is the key to triggering bioreactions, improving the storability of materials, improving the material's mechanical properties, and so on. Polymer chains generally form interfacial layers where their aggregation states and thermal molecular motions differ from the bulk. In this study, we visualize well-defined double-stranded DNAs (dsDNAs) with three lengths using atomic force microscopy and molecular dynamics simulations to clarify the adsorption mechanism of polymer chains onto solid surfaces. Initially, short and long dsDNAs show individual and cooperative adsorption, respectively. Cooperative adsorption involves the intertwining of multiple chains. The dependence of adsorption on the chain affects the formation of the interfacial layer, realizing different mechanical properties of DNA/filler bulk composites. These findings will contribute to developing light and durable polymer composites and films for various industrial, biomedical, and environmental applications. |
Wednesday, March 8, 2023 10:24AM - 10:36AM |
M05.00013: Direct Observation of In-plane Diffusion of Isolated Polymethacrylates Chains on Solid Surfaces Masayuki KAWANO, Yuma Morimitsu, Satoru Yamamoto, Daisuke Kawaguchi, Keiji Tanaka Polymer composites have attracted a great deal of attention as light-weight structural materials with excellent mechanical properties. It has been widely accepted that the polymer adsorbed layer on the filler surface is a key to controlling the performance of the material. Although there is no doubt that the interaction between polymer and solid surface is of importance to designing it, the effect of the interaction on the dynamics of chains on the surface is not yet fully understood. Therefore, we visualized the in-plane diffusion of poly(methyl methacrylate) (PMMA) and poly(tert-butyl methacrylate) (PtBMA) chains on solids using atomic force microscopy. We also tackled the effect of condensed surface water on the in-plane chain diffusion. The diffusion of PMMA chains was not observed regardless of the thickness of the water layer. On the other hand, PtBMA chains diffused on a wet surface, while they did not on a well-dried surface. These results imply that the presence of the bulky side group alters the interaction with the solid surface having the condensed water layer. |
Wednesday, March 8, 2023 10:36AM - 10:48AM |
M05.00014: Structural and dynamical heterogeneities of isotactic polypropylene adsorbed onto carbon fiber Yashasvi Bajaj, ZHIXING HUANG, Jan-Michael Carrillo, Yohei Nakanishi, Kiminori Uchida, Kazuki Mita, Takeshi Yamada, Bobby G Sumpter, Maya K Endoh, Tadanori Koga Carbon fiber (CF) reinforced polymers (CFRPs) have been widely used in various industries. One of the most important parameters that controls the macroscopic property of CFRPs is the interface between a polymer matrix and CF. There is growing evidence to suggest the formation of a bound polymer layer (BPL), i.e., polymer chains that physically adsorb onto a filler surface. However, this interface is always in contact with the thicker part of a polymer matrix, rendering its understanding a difficult task. Therein, we used CF-reinforced isotactic polypropylene (iPP) as a rational CFRP. To characterize the iPP BPL on the CF surface, we extracted it from the CFRP using solvent-rinsing with p-xylene. The physical and thermal properties of the BPL were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), while its microscopic structures and dynamics were probed by quasi-elastic neutron scattering (QENS) above the melting temperature. Subsequently, we employed atomistic molecular dynamics (MD) simulations to complement the QENS results and reveal details that were not accessible experimentally. In this talk, we will discuss the flattening process of the backbone and side groups at the interface and resultant heterogeneities in the structures and dynamics of the BPL. |
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