Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M18: Polymer Structure Formation and Dynamics in SolutionFocus Recordings Available
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Sponsoring Units: DPOLY Chair: Svetlana Morozova, Case Western Reserve Univesrity Room: McCormick Place W-184D |
Wednesday, March 16, 2022 8:00AM - 8:36AM |
M18.00001: Structure formation in polyelectrolyte coacervates Invited Speaker: Vivek M Prabhu Measurements on mixtures of oppositely-charged polyelectrolytes potassium-poly(styrene sulfonate) and poly(diallyl dimethyl ammonium bromide) shows liquid-liquid phase separation upon heating, or lower critical solution temperature behavior. The experimental accessibility of the critical temperature occurs for a narrow range of monovalent salt and outlines a temperature, salt concentration and polymer concentration coexistence surface. We show how associative behavior within the homogeneous phase enhances the concentration fluctuations upon approach to the phase boundary. The properties of the ensuing coacervate phase (droplet morphology, interfacial tension) will be discussed in the context of the phase diagram and the kinetics of phase separation. |
Wednesday, March 16, 2022 8:36AM - 8:48AM |
M18.00002: Electrostatic Persistence Length of Collagen Type II Protofibrils and Fibrils Kathryn G Wilcox, Grace Kemerer, Svetlana Morozova Collagen type II is a main structural component of the extracellular matrix and self-assembles into rigid fibrils. The origin of the fibril radial lengthscales is hypothesized to be related to the flexibility, measured by the persistence length, lp, of protofibrils. We have investigated the electrostatic contribution to lp of collagen type II by changing the solution ionic strength (I) of solutions at pH 2, where the collagen is positively charged, and pH 7.4, where collagen has both charges. Using static and dynamic light scattering, lp is determined from the radius of gyration, Rg. In addition to Rg, the hydrodynamic radius Rh, shape factor Rg/Rh, and second virial coefficient A2 of the soluble collagen are reported. In pH 2 solutions, collagen does not form fibrils because of electrostatic repulsion, determined from A2. As electrostatics are screened, both Rg/Rh and lp decrease with I. In pH 7.4 solutions, in part due to electrostatic attraction, collagen forms fibrils. The fibril radii are reported using Scanning Electron Microscopy imaging and are correlated to the size scales, and lp determined from solution scattering. By understanding how collagen type II lp and interactions influence self-assembly, we can better understand the origin of the fibril lengthscales. |
Wednesday, March 16, 2022 8:48AM - 9:00AM |
M18.00003: Free Energy Trajectory and Transition State of Chain Expulsion from a Block Copolymer Micelle Sarah C Seeger, Kevin D Dorfman, Timothy P Lodge Single chain exchange is the dominant relaxation process for block copolymer micelles close to equilibrium, and influences a variety of applications, including drug delivery, oil-based lubrication, and the formation of complex block polymer phases.Methods of studying chain exchange yield information about the system ensemble; however, the molecular-level details of the process are not well understood. We have implemented a simulation method to study the chain exchange process for diblock copolymer micelles in a small-molecule solvent, using dissipative particle dynamics. Our simulation framework utilizes umbrella sampling and the weighted histogram analysis method to compute the free energy profile of chain expulsion. We will present results for the effect of the block lengths of the expelled chain and the interaction energy between the core beads and the solvent, and their effect on the core block conformation at the transition state. Contrary to past models of chain exchange, we see evidence of core block stretching in the expelled chain at the transition state. |
Wednesday, March 16, 2022 9:00AM - 9:12AM |
M18.00004: Label-free characterization of aqueous micelle nanostructure and dynamics via in-situ RSoXS Devin Grabner, Terry McAfee, Thomas Ferron, Phillip Pickett, Charles L McCormick, Isvar A Cordova, Cheng Wang, Brian A Collins Micelles are fundamental to nanocarrier applications from drug delivery to environmental remediation. Their structure and dynamics are of critical importance to their properties and functions but are challenging to measure. Here we demonstrate a novel technique capable of such measurements based on resonant soft X-ray scattering (RSoXS), which uniquely probes organic materials using their intrinsic chemical bonds rather than laborious and disruptive labeling techniques. Our customized microfluidic cell enables RSoXS to be performed in liquid environments, allowing structure and dynamics to be measured in-situ. We have applied this technique to investigate three different molecular weights of a novel amphiphilic statistical copolymer designed for oil spill remediation. By applying a time-resolved dynamic flow experiment, we are able to investigate beyond the large aggregates seen by light scattering and electron microscopy. We can show that the unimeric bridged-core structure is retained despite aggregation at increased concentrations, which is crucial for its application. Further, the only structural dependence of the micelle is due to the molecular weight of the polymer used. Both the core radius and corona thickness are persistent at all concentrations. |
Wednesday, March 16, 2022 9:12AM - 9:24AM |
M18.00005: Chain Conformations and Phase Separation in Polymer Solutions with Varying Solvent Quality Yisheng Huang, Shengfeng Cheng Molecular dynamics simulations are used to investigate chain conformations in polymer solutions. Results show that when the polymer-solvent interaction is unfavorable, the chain collapses as one would expect in a poor solvent. For more attractive polymer-solvent interactions, the solvent quality improves and the chain is increasingly solvated and exhibits ideal and then swollen conformations. However, as the polymer-solvent interaction strength is increased further to be more than about twice of the strength of the polymer-polymer and solvent-solvent interactions, the chain exhibits an unexpected collapsing behavior. Correspondingly, for strong polymer-solvent attractions, phase separation is observed in the solutions of multiple chains. These results indicate that the solvent becomes effectively poor again with very attractive polymer-solvent interactions. Nonetheless, the mechanism of chain collapsing and phase separation in this limit differs from the case with a poor solvent rendered by unfavorable polymer-solvent interactions. In the latter, the solvent is excluded from the domain of the collapsed chains while in the former, the solvent is still present in the pervaded volume of a collapsed chain or in the polymer-rich domain that phase separates from the pure solvent. In the limit of strong polymer-solvent attractions, the solvent behaves as a glue to stick monomers together, causing a single chain to collapse and multiple chains to aggregate and phase separate. |
Wednesday, March 16, 2022 9:24AM - 9:36AM |
M18.00006: Chain-End Attraction Causes Excess Scattering in Simple Polymer Solutions Tyler B Martin, Avanish Bharati, Katie M Weigandt, Steven D Hudson For many decades, researchers have studied polymer solutions using small angle scattering techniques and attempted to explain deviations (i.e., excess scattering) from classical models. While these phenomena are sometimes explained away as uncontrolled experimental factors (e.g., dust), there can be a polymeric origin to the excess scattering, but few interpretable, physics-based models exist to describe it. For example, the Debye-Bueche model provides an ambiguous ‘correlation length’ but no physical origin of low-q excess scattering. In this contribution, we explain two observations of excess scattering in semi-dilute polystyrene solutions: (1) low-q excess scattering indicating long-range concentration fluctuations despite marginally good solvent conditions and (2) excess scattering near qRg = 1, when crowded by contrast-matched chains. To explain these phenomena, we develop a liquid-state theory (PRISM) based scattering model which describes the scattering over all wavenumbers and all concentrations studied. With this model, we demonstrate that both phenomena can be explained by incorporating end-monomer interactions that account for the non-solvency of the acidic methanol end-groups of the polymer. |
Wednesday, March 16, 2022 9:36AM - 9:48AM |
M18.00007: Unraveling the Side Chain Effects on Chain Conformation of Donor-Accepter Conjugated Polymers Zhiqiang Cao, Zhaofan Li, Miao Xiong, Guorong Ma, Luke Galuska, Song Zhang, Michael Ocheje, Gage Mason, Changwoo Do, Kunlun Hong, Ting Lei, Simon Rondeau-Gagné, Wenjie Xia, Xiaodan Gu The less studied chain conformation of donor-accepter conjugated polymers (D-A CPs) hinders the fundamental understanding of their optical and electronic properties. Here, we systematically studied the effect of side-chain length and branch point on the chain conformation of diketopyrrolopyrrole (DPP) and isoindigo (IID) based polymers. Using small-angle neutron scattering (SANS) measurements, we find that chain rigidity of DPP-based polymers increases with side-chain length, which directly correlates with increased charge carrier mobility until the insulating alkyl sidechains are bulky enough to hinder efficient intermolecular charge carrier transport. The chain rigidity of IID-based polymers increases when moving the branch position farther away from the backbone. The trend of the solution optical bandgap changes is in accordance with an odd-even effect of the branching point. Using atomistic molecular dynamics (MD), we examined how side-chain structure can be modified to control chain conformation which further validated the experimental results. This work fills the fundamental gaps in our knowledge of the most basic relationships between polymer structure and chain conformation. |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M18.00008: Structure-based Coarse Graining of Homopolymer Solutions: Designing the Implicit-Solvent Model with PRISM Theory Yan Wang, Jiawei Zhang, Qiang Wang, Baohui Li, Suyu Wang Implicit-solvent (IS) models are widely used in molecular simulations of polymer solutions, with the advantage of dramatically saving the amount of computation and the hope of faithfully reproducing some properties of the corresponding explicit-solvent (ES) model. In practice, however, an IS model often gives qualitatively different results from the corresponding ES model. In this work, we take a simple model system of homopolymer solutions as an example to examine the features of the effective pair potential between polymer segments in the IS model that is designed, using the well-developed polymer reference interaction site model (PRISM) theory, to reproduce the pair correlation functions between polymer segments in the corresponding ES model. To assess the accuracy of the PRISM theory, we also quantitatively compare its predictions with Monte Carlo simulation results. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M18.00009: Computational Study Linking Polysulfamide Chain Design to the Hydrogen Bonding Induced Chain Aggregation Zijie Wu, Jiun-Wei Wu, Quentin Michaudel, Arthi Jayaraman Recent advances in sulfur(VI) fluoride exchange (SuFEx) click chemistry have led to a new family of polymers - poly-N, N’-disubstituted sulfamides [Chem. Sci., 2020, 11, 7807-7812] that are analogous to polyureas. Before these polymers can replace polyureas in many commercial applications, we need better fundamental understanding of poly-N, N’-disubstituted sulfamides. We present a computational study of polysulfamide chains and their assembly driven by hydrogen bonding interactions between the sulfamide groups. These computations support experiments that show different extents of chain crystallinity for varying aliphatic and aromatic chemical substitutions on either side of the sulfamide groups. Using a coarse-grained model that captures directional interactions in polymers and molecular dynamics simulations we link the contour length, bulkiness, and flexibility of the substituted chemistries on either side of the sulfamide group to the morphology (e.g., positional and orientational order among the chains) in the polysulfamide aggregates. We will conclude this talk with a sensitivity analysis based on the variations in the chain design parameters and the resulting change in positional and orientational order of the polysulfamide chains in the chain aggregates. |
Wednesday, March 16, 2022 10:12AM - 10:24AM |
M18.00010: Compositional and environmental dependence of random heteropolymer behavior in solution Shayna Hilburg, Ting Xu, Alfredo Alexander-Katz Synthetic random heteropolymers (RHPs) have proven capable of protein stabilization and mimicry in a variety of applications. Using MD simulations, we develop a comprehensive view of how RHP statistical sequences behave in solution. Our work shows multiple dynamic modes and heterogeneous surfaces in water, properties which scale predominantly with composition rather than particular sequence motifs. Through an introduction of organic solvents and small molecules, we characterize these statistically derived properties when electrostatic and polar interactions are changed. We observe environmentally-dependent driving forces to compact globular assembly or chain extension with significant activation barriers when transferring to organic solvent. Finally, we demonstrate that mixing solvents and small molecules alter not only the driving forces to assembly, but also introduce high energy interfaces that strongly impact polymer conformation. These results enable predictable modification and processing of these RHPs in addition to providing a synthetic perspective that can relay behavioral relationships back to the biomolecules that inspire them. |
Wednesday, March 16, 2022 10:24AM - 10:36AM |
M18.00011: Revisiting the Lennard-Jones Implicit Solvent model for the Simulation of Dilute Polymer Solutions Hao Guo, Kun Qian, Mesfin Tsige Polymer chains in dilute solution usually exhibit different types of conformation and scaling behaviors based on solvent quality. In the Flory-Huggins theory, the conformation of a polymer chain in dilute solution can be directly connected to an excluded volume,ν, resulting in a universal scaling behavior and verifying the scaling behavior has been a subject of numerous experimental and computational studies. Different types of implicit solvent models have been developed to make simulations faster and to correlate the quality of solvent with excluded volume easier. In experiments, temperature is commonly used to control the quality of solvent. In the Lennard-Jones (LJ) implicit solvent model, temperature (T) or polymer-polymer interaction parameter (eij) or the LJ cutoff distance (rc) can be independently varied to change the quality of solvent. The equivalency of these three approaches has never been tested through simulations, to the best of our knowledge, and will be the primary focus of this presentation. |
Wednesday, March 16, 2022 10:36AM - 10:48AM |
M18.00012: Synthesis and characterization of sulfoxide-functional polyethers in low temperature aqueous environments Nathaniel A Lynd Polymeric materials provide a low-toxicity, low osmolality, and high functionality alternative to small molecule colligative antifreeze agents such as solutions of dimethylsulfoxide (DMSO) or glycerol. Polymers can be designed that are inherently non-toxic and produce high post-thaw recovery of mammalian cells after frozen storage at –196 ºC. In this presentation, I will describe our efforts in the design and synthesis of improved cryoprotective polymeric materials and how design has been guided by investigation of polymer-water-ice-cellular interactions, and also post-thaw viability assays of model cell lines. Significantly, materials have been synthesized that increase the extent of the unfrozen fraction of aqueous solutions upon cooling, increase solution glass-transition temperature, and that also affect the kinetics of cellular dehydration during freezing; these factors are believed to be important in affecting polymer-mediated post-thaw recovery of mammalian cells. However, many fundamental questions remain. |
Wednesday, March 16, 2022 10:48AM - 11:00AM |
M18.00013: Monitoring Polymerization of Conjugated Polymers on Nanoparticles: A SANS Study Lilin He, Sofia Fanourakis, Sharona Q Barroga, Jem Valerie Perez, Debora F Rodrigues Ferromagnetic nanoparticles have shown promising applications in water treatment due to their large surface area, high reactivity, stability and reusability. However, their dissolution in aqueous environment greatly diminishes the usability as photocatalysts. Coating of conductive polymers on the surface of photocatalysts can reduce the dissolution without compromising the material’s photocatalytic properties. In this work, polypyrrole (PPy) and polyaniline (PANI) were coated on the surface of two magnetically separable MoO3/Fe3O4 nanocomposites with different surface chemistries. We used small-angle neutron scattering (SANS) technique to in situ monitor the polymerization kinetics by taking advantage of neutron’s sensitivity on light elements. The scattering results reveal that PPy polymerization initiated faster yet had a slower rate than PANI. This study shows that the polymerization of PPy was more affected by the base material properties than PANI. These findings can be explained by different polymerization mechanisms of the two polymers. The ultimate size of polymer chains grafted on nanoparticles largely depended on the concentration and the surface properties of the nanoparticles. These observations provide valuable insights on the polymerization mechanisms of two conjugated polymers on the surface of nanocomposites. |
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