Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y18: Nonequilibrium Structure of Polymeric Materials IIFocus Recordings Available
|
Hide Abstracts |
Sponsoring Units: DPOLY GSNP DSOFT Chair: Yangyang Wang, Oak Ridge National Laboratory Room: McCormick Place W-184D |
Friday, March 18, 2022 8:00AM - 8:12AM |
Y18.00001: The production of polymeric particles via nonsolvent-induced phase separation Rami Alhasan, Tanner A Wilcoxson, Dakota S Banks, Sion Jung, Douglas R Tree Nonsolvent-induced phase separation (NIPS) is frequently employed for producing porous microstructures such as polymer membranes. Because of their ease of manufacture, NIPS-like processes have recently become a method of choice for producing polymeric micro/nanoparticles. Despite their popularity, many questions still surround the process kinetics and its effect on the resultant structure of such particles. At its most basic level, NIPS involves an exchange of a good solvent with a bad one (a nonsolvent) that eventually produces phase separated structures. While simple, predicting microstructure is nontrivial due to the presence of multiple dynamic modes across a wide range of length and time scales. In our study, we overcome this challenge by using a phase-field model of the NIPS kinetics of polymer droplets that phase separate when brought into contact with a bath of nonsolvent. We investigate two separate cases: (i) "rapid precipitation" behavior where the kinetics are determined by the initial mixture, and (ii) "delayed precipitation" behavior where the kinetics involve long-time exchange of solvent and nonsolvent. We perform parameter studies in both cases to investigate the effect of droplet shape and size and of solvent/nonsolvent miscibility on microstructural evolution. |
Friday, March 18, 2022 8:12AM - 8:24AM Withdrawn |
Y18.00002: Stress-induced surface segregation of polymer melts under tension Matthew Melton Polymers at the surface exhibit different molecular mobility from the bulk, leading to many interesting surface related phenomena. In this contribution, we report one stress-induced surface segregation phenomena of polymer melts under uniaxial extension. The basic characteristics of surface segregation under tension is very different from the surface wrinkling previously observed under compressive strains. Scanning electron microscopy and atomic force microscopy have been employed to characterize the surface segregation. The basic characteristics of the surface microstructures and their dependence on the deformation conditions have been investigated and will be discussed in the presentation. |
Friday, March 18, 2022 8:24AM - 8:36AM |
Y18.00003: A Quantitative Approach to Brownian Motions of Polymers under Flow Yangyang Wang, Zhiqiang Shen, Jan-Michael Y Carrillo, Bobby G Sumpter A quantitative method is proposed for studying self-correlations of polymers under flow. Analysis of nonequilibrium molecular dynamics simulations shows that in the flow frame the probability density functions of center of mass displacements can be described by superdiffusive, anisotropic Gaussian distributions. This behavior originates from interactions between centers of mass of polymers, which cannot be properly treated by mean-field models. Additionally, the segmental fluctuations in the polymer frame are strongly suppressed by flow. The origin of this phenomenon will be discussed. |
Friday, March 18, 2022 8:36AM - 8:48AM |
Y18.00004: A Thermodynamically Inspired Method for Quantifying Phase Transitions in Polymeric Liquids with Application to Flow-Induced Crystallization of a Polyethylene Melt Mohammad Hadi Nafar Sefiddashti, Brian J Edwards, Bamin Khomami Thermodynamic-like local atomistic entropy and enthalpy variables are introduced as a means to delineate and quantify phase transitions in atomistic simulations of extensional flow of an entangled polyethylene melt. These variables measure the local ordering and energetics at the monomer level, as opposed to the global system, and hence can be used to detect and quantify flow-enhanced nucleation events on small length and time scales that lead to flow-induced crystallization. The kinetics of the nucleating localized crystals can also be tracked using an atomistic Gibbs free energy composite variable. Based on the assumption that the global crystallization process followed a first-order reversible kinetic rate expression with a lag time, kinetic rate constants were calculated as functions of the Deborah number that allowed quantification of the flow-induced crystallization phenomenon exhibited by the simulated system under planar elongational flow at a temperature high above its quiescent melting point. |
Friday, March 18, 2022 8:48AM - 9:00AM |
Y18.00005: Traveling Coacervate Band Through a Charged Gel Yu-Lin Wang, Murugappan Muthukumar It is well known that coacervates can be formed when polycation solutions and polyanion solutions mix at appropriate pH, ionic strength, and polymer concentration. In this work, we experimentally find a novel coacervation phenomenon where a polyanionic gel is exposed to a solution of polycations. For the system of poly(acrylamide-co-sodium acrylate) and poly(allylamine), we have discovered that the coacervates would initially travel through the gel and form a thin band in the middle of the gel. This band subsequently gives rise to a second band which grows in the opposite direction. Curiously, these two bands subsequently result in a third band which forms between the two pre-formed bands. The rich details on the features of these bands and their growth kinetics will be presented. |
Friday, March 18, 2022 9:00AM - 9:12AM |
Y18.00006: Stochastic kinetic theory applied to nonequilibrium polymer simulations Patrick T Underhill, Shangren Zhu Stochastic kinetic theories are a relatively new approach for simulating nonequilibrium situations using field equations. We have applied this approach to polymers for the first time. Although it is coarse-grained relative to equilibrium polymer field theory, this approach naturally applies to nonequilibrium situations. It also provides more detail than present in two-fluid models. This new method is particularly important for charged polymers in which fluctuations and correlations of free ions impact structure and phase separation. In this talk, we will introduce the application of stochastic kinetic theories to concentrated polymers. We will quantify the accuracy and show how it can be used to examine dynamics and response to flow. |
Friday, March 18, 2022 9:12AM - 9:24AM |
Y18.00007: Perylene Dye as a Local Thermal and Mechanical Sensor of Local Nanoscale Polymer Matrices Yixuan Han, Connie B Roth Studies on nanoscale materials often require new characterization methods to monitor thermal and mechanical material properties. Fluorescence spectroscopy, with its high sensitivity, allows trace levels of dyes to act as local non-contact probes. Perylene is a robust fluorophore with high quantum yield that has been previously shown to exhibit sensitivity to temperature and pressure, including being used as a local thermometer of the surrounding material. We characterize the temperature dependence of the perylene's emission spectrum doped into a range of different polymers: poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(2-vinyl pyridine) (P2VP), and polycarbonate (PC). We find that with regard to a temperature-invariant reference point, the peak intensity shows a linear response to changes in temperature, where certain polymer matrices result in a stronger perylene sensitivity to temperature. Such qualitatively similar temperature dependencies across different polymers could be indicative of the material's thermal expansion and stiffness of the surrounding polymer matrix. Using a home-built apparatus to apply different pressures, we also characterize the pressure dependence of perylene's emission spectrum to infer the stress response of the system. |
Friday, March 18, 2022 9:24AM - 9:36AM |
Y18.00008: Ab Initio and molecular dynamics simulations of double-bond defects in dipolar polymers Hancheng Qin, Bing Zhang, Xin Chen, Wenchang Lu, Qiming Zhang, Jerry Bernholc Polyvinylidene fluoride (PVDF)-based relaxor ferroelectric polymers have attracted significant attention because of their excellent performance in energy storage, electro-actuators, and electrocaloric solid-state cooling. It has been demonstrated that most of the performance gain originates from conformational changes of the polymer chains under applied electric fields. Recent work shows that new "double bond" (DB) defects can tune the magnitude of the electrocaloric effect. However, there is a lack of understanding of how DBs affect the dynamics of structural changes in an electric field. Here, we apply an accurate DFT method to study ferroelectric polymers by adding DBs as defects into the polymer chains. A phase transition path from the non-polar to the polar phase is introduced, in which DBs reduce the energy barrier, and the polar phase forms much easier even at a low field. Based on the simulations, large electrostriction at low field is also predicted even with ~2 mol% DBs. We also examine the DBs' influence on structure in an external electric field by classical molecular dynamics. Different polymer conformations are investigated to reveal the phase transition process. |
Friday, March 18, 2022 9:36AM - 9:48AM |
Y18.00009: Contrast-variation resonant soft X-ray scattering for partial scattering functions of multicomponent soft matter systems Kristof Toth, Daniel Sunday, Eliot H Gann, Dean M DeLongchamp Resonant soft X-ray scattering (RSoXS) is a powerful synchrotron-based tool for characterization due to its intrinsic element and bond sensitivities, large accessible size scale, and unique bond orientation sensitivity. In small angle scattering, any pattern from more than two isotropic materials can be split into separate contributions from each material that vary with the contrasts of those materials. In small angle neutron scattering (SANS), contrast variation is achieved by synthetically replacing hydrogens with deuterium in a monotonic radiolabeled series and applying a singular value decomposition to obtain partial scattering functions. We propose an analogous quantitative decomposition approach to RSoXS data analysis to isolate and measure the distribution of individual materials within a system by exploiting the energy-dependent scattering length densities (complex indices of refraction) of each component across the soft X-ray energy range. This "stainless," chemistry-specific contrast is created simply by changing the incident X-ray energy, thus eliminating the need for radiolabeling and ensuring a consistent structure factor throughout the process. The decomposed structure functions of a triblock copolymer system are evaluated using GPU-accelerated forward simulations of RSoXS patterns based on real-space models, allowing for the characterization of nontrivial and nonequilibrium structures. This quantitative analysis using RSoXS flips the paradigm from using spectroscopy as a fingerprint to understand variations in a "stack" of RSoXS patterns, to instead "baking in" the energy dependence at an early stage of analysis to produce energy-agnostic partial scattering functions of individual materials and greatly accelerate the extraction of meaningful material structure information in multicomponent soft materials. |
Friday, March 18, 2022 9:48AM - 10:00AM |
Y18.00010: Bottom-up Ultra-coarse-graining of Homopolymers for Inhomogeneous Systems Fabian Berressem, Arash Nikoubashman We study the coarse-graining of homopolymers into single spherical beads, focusing on simulations of thin polymer films and droplets. Accurately representing these inhomogeneous systems by a coarse-grained model is challenging due to the large density variations at the interfaces. Using models interacting solely through pair potentials parametrized in the bulk typically leads to unstable systems. Hence, we follow an alternative approach, where we include higher order interactions through a local-density-dependent potential parametrized using relative entropy minimization. We defined the local density as the overlap integral of the monomer distributions around the centers of mass, effectively incorporating a density dependent contact interaction. Our coarse-grained model reproduces stable polymer films and droplets. There are some (minor) quantitative differences compared to the reference simulations, namely a slight broadening of the interfaces accompanied by a smaller surface tension, which are due to the (fixed) spherical polymer shape in the coarse-grained model. We further look into substituting some of the model parameters obtained via reference simulations by analytical expressions, reducing the computational effort necessary for parametrizing the coarse-grained model. |
Friday, March 18, 2022 10:00AM - 10:12AM |
Y18.00011: Polymeric Structural Symmetry Breaking and Conformational Search Driven by Anisotropic Dispersion Interactions Mario Galante, Alexandre Tkatchenko The modeling of conformations and dynamics of (bio)polymers is of primary importance for understanding physicochemical properties of soft matter. Although short-range interactions such as covalent and hydrogen bonding control the local arrangement of polymers, non-covalent interactions play a dominant role in determining the global conformations. Here we focus on how the inclusion of many-body effects [1] in van der Waals dispersion affects the outcome of the geometry optimization and molecular dynamics simulations of model polymers. We find that delocalized force contributions are key to explore the conformational landscape, as they induce an anisotropic polarization response which efficiently guides the conformation towards globally optimized structures. This is in contrast with the commonly used pair-wise approach, where the structure-independent atomic polarizabilities lack information on the global geometry. We show that such local approximation causes the conformational search to be obstructed by conformations with unphysically limited spatial symmetry, while the many-body formalism strongly reduces the roughness of the potential energy landscape. |
Friday, March 18, 2022 10:12AM - 10:24AM |
Y18.00012: The non-ideal preparation state of polymer (model) networks Michael Lang, Toni Müller We show that the phantom modulus can be split into two major contributions: the cycle rank of the active network structure and a correction resulting from non-ideal chain conformations at the instance of cross-linking. The correction contains several contributions related to loop formation, an effective repulsion between network junctions, and an excess strain of chains that develops towards the end of the reactions, if reaction partners become sparse. This challenges the text-book assumption that network strands are incorporated into the network with the same conformations as a free chain inside the reaction container. Our results are relevant for developing a better understanding of rubber elasticity and its dependence on the network formation process. |
Friday, March 18, 2022 10:24AM - 11:00AM |
Y18.00013: The role of hydrodynamics in flowing semidilute solutions of ring/linear polymer blends Invited Speaker: Charles E Sing It is important to understand the dynamics of semidilute polymer solutions at a molecular level, because out-of-equilibrium polymer conformations that arise due to strong processing flows can impact both rheology and eventual material properties in a variety of applications. Despite this practical importance, it remains a challenge to predict how concentration, flow, hydrodynamic interactions (HI) and architecture all govern the dynamics of semidilute polymer solutions. This is particularly true in simulation, where it is computationally expensive to include long-range HI effects that are necessary to accurately model the dynamics of polymer solutions. We developed an iterative conformational-averaging (CA) method for performing these calculations, circumventing computational bottlenecks to enable the large-scale simulation of polymer solutions in flow. CA calculations demonstrate the importance of HI in semidilute solutions, revealing the effect of 'local flows' that enhance conformational fluctuations. We demonstrate these effects in the context of ring/linear blends, where there is a competition between topological 'hooking' and chain length effects that showcase the complicated role of polymer architecture in conformational dynamics during both startup and steady-state flows. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700