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 TT05: V: Composites, Confinement, and Interfaces in Polymer SystemsFocus
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Sponsoring Units: DPOLY Chair: Kenan Song, Arizona State University Room: Virtual Room 5 |
Tuesday, March 21, 2023 3:30PM - 4:06PM |
TT05.00001: Mechanical reinforcement of nanoparticles: from dispersion to agglomeration Invited Speaker: Wei Yu Polymer nanocomposites have broad applications. The size and shape of nanoparticles and their interaction with polymers determine the mechanical properties of polymer nanocomposites. In this work, we studied the mechanical enhancement and dynamics at different time scales in model polymer nanocomposites with different polymer molecular weights, particle sizes, and different surface properties of nanoparticles. We found the dynamic adsorption-desorption due to weak attractive interaction between nanoparticles and polymers. The adsorped chains may induce additional entanglements with the bulk chains. As a result, the increase of rubbery plateau modulus depends on the number of interaction sites (or effective surface area). These findings are general for both well-dispersed nanoparticles and agglomerated nanoparticles. At a longer timescale, the mechanical enhancement is ascribed to the particle motion or relaxation of agglomerates. A quantitative model was suggested to quantitatively describe the linear viscoelasticity of polymer nanocomposites over a wide range of timescales. |
Tuesday, March 21, 2023 4:06PM - 4:18PM |
TT05.00002: Predicting Polymer Grafted Nanoparticles Assembly using Deep Learning Sachin M Gautham, Tarak K Patra Grafting polymer chains on nanoparticles (NPs)' surfaces is a well-known route to control their self-assembly and distribution in a polymer matrix. Here we propose a DL method to solve this problem. In this method, two deep neural networks (DNNs) learn the effective interaction between a pair of GNPs from the MD trajectory of a cluster of polymer GNPs. The two DNNs represent potential energy surfaces of the centroid and the point of grafting on an NP's surface. We consider a coarse-grained phenomenological model of NPs and polymers to establish and validate the model. CGMD simulation of a cluster of polymer GNP is conducted to generate the training data. We show that the deep learning model predict the energy of polymer GNPs clusters very accurately. We further carry out the deep learning potential of mean force (DL-PMF) based molecular simulation that predicts the self-assembly of many polymer GNPs into various anisotropic superstructures, including percolating networks and bilayers depending on NPsconcentration in 3D. The DL self-assembled structures are consistent with the first principle based actual superstructures of the nanoscopic building blocks. We find this deep learning approach very efficient and accurate in capturing anisotropic interactions, and it predicts long-range anisotropic aggregates of polymer GNPs. We expect that the potential of mean force for systems with atomistic details can be modeled using this DL framework. |
Tuesday, March 21, 2023 4:18PM - 4:30PM |
TT05.00003: Composite Fibers with 1D and 2D Nanoparticle Reinforcement Kenan Song High-performance fibers have been conventionally used in advanced composites for automobile, aerospace, wind energy, and space telescope areas. These fibers include carbon, glass, and aromatic polymer fibers. However, most of these fibers contain a single composition and are uni-functional. Thus, this research will report composite fibers consisting of multilateral with structural properties and multifunctional behaviors that can significantly benefit light-density systems or devices. Nanoparticles of different dimensions and sizes were included in various polymers and fabricated via fiber spinning. The spun fibers showed designable morphologies, such as core-shell, co-axially layered, perpendicular to cross-section layered, and hollow microstructures. The studied parameters include nanoparticle orders, polymer-nanoparticle interactions, and mechanical/functional reinforcement efficiency. The studied systems include polyvinyl alcohol (PVA)/carbon nanotube (CNT), thermoplastic polyurethane (TPU)/graphene nanoplatelet (GNP), polyacrylonitrile (PAN)/carbon nanofiber (CNF), and PVA/boron nitride nanosheet (BNNS) composites. The demonstrations of these composites include structural materials, sensors, smart textiles, and others. |
Tuesday, March 21, 2023 4:30PM - 4:42PM |
TT05.00004: Micrometer Mobile Surface Layer in a Glassy Polymer Ophelia K Tsui, Hailin Yuan, Jinsong Yan, Ping Gao, Sanat K Kumar It is well established that the near-surface dynamics of glassy polymers are enhanced relative to the bulk. However, the distance propagated by these dynamics, ht, is still unsettled. In this study, we measured the mechanical relaxations of free-standing polystyrene films with thickneeses, h, from 5 nm to 186 μm. For h < ~1 μm, the films relaxed faster than the bulk. And the relaxation time decreased with decreasing h below ~100 nm, consistent with the enhanced dynamics originating from a near-surface nanolayer. For h > 1 μm, a bulklike relaxation mode emerged, while the fast mode changed to one that stretched over ~1 μm from the free surface. These findings evidence that the mobile surface region is inhomogeneous, comprising a nanoscale outerlayer and a slower microscale sublayer that relax by different mechanisms. Consequently, measurements probing the enhanced dynamics of different mechanisms may find vastley different values of ht, as shown by the literature. |
Tuesday, March 21, 2023 4:42PM - 4:54PM |
TT05.00005: Mechanism of Enhanced Adhesion Strength of Multi-layer Films via Multi-block Copolymer Compatibilizers: Coarse-Grained Simulation Study Umi Yamamoto, Keiichiro Nomura, Christopher J Ellison Multi-layer films of immiscible polymers, such as poly(ethylene terephthalate) and poly(ethylene), have been realized by introducing multi-block copolymer (MBCP) compatibilizers leading to the enhancement of interfacial adhesion strength. However, the mechanism of the enhanced adhesion, while several candidates have been proposed, remains elusive. Here, we present a coarse-grained simulation study to investigate the mechanism of the enhanced adhesion due to the MBCP compatibilizers. Starting from a binary polymer blend of A (repulsive) and B (attractive) homopolymers mixed with MBCPs composed of A and B, we first form a bilayer where MBCPs are localized at the A-B interface. Then, the adhesion strength of the bilayer is quantified by applying uniaxial elongation to the bilayer and obtaining a stress-strain curve. We report how block length, number of blocks, concentration of MBCPs, etc. affect the adhesion strength and discuss the importance of having entanglements between the MBCP blocks and the homopolymers in each layer. This study, if the miscibility of MBCPs is simultaneously optimized, provides a way to design optimal multi-component materials with satisfactory adhesion strength from arbitrary combinations of raw materials. |
Tuesday, March 21, 2023 4:54PM - 5:06PM |
TT05.00006: Kinetics of Polymer Expansion Released from a Confined Cavity Pai-Yi Hsiao Understanding releasing mechanism of genetic materials such as DNA or RNA chains from a viral capsid is important. It helps researchers to design efficient vectors for gene therapy and drug delivery. In this study, we develop a two-stage model to explain expansion phenomena of an enclosed chain freely released from a cavity. In the first stage, the chain is presumed to expand with a spherical structure while in the second stage, it expands like a coil. The kinetic equation for the evolution of the chain size is derived in the two stages via Onsager's variational principle. The theory is then verified by performing extensive Langevin dynamics simulations. We find that the expansion process is dominated by the second stage, and the variation of chain size follows the predicted curve which depends on the chain length. It allows us to define the principal expansion time for the process. Scaling analysis shows that the chain does undergo a coil expansion in the second stage but in the first stage, the presumed spherical structure is not truly held. Nonetheless, the variation of the chain size can be still approximated by the derived equation for the first stage. The characteristic time and the associated scaling exponents are analyzed in detail and compared with the theory. A universal route for the chain expansion is proposed at the end. |
Tuesday, March 21, 2023 5:06PM - 5:18PM |
TT05.00007: Capillary Filling of Polymer Chains in Nanopores Jiajia Zhou, Jianwei Zhang, George Floudas We performed molecular dynamics simulations with a coarse-grained model to investigate the capillary filling dynamics of polymer chains in a nanopore. Short chains fill slower than predicted by the Lucas-Washburn Equation but long chains fill faster. The analysis shows that a viscous area is generated by the strong adsorption of polymer chains next to the pore walls that reduces the pore radius and slows down imbibition. This region can be negligible at the macroscopic scale but cannot be ignored at the nanoscale. Reduction of the entanglements is the main factor behind the reversing dynamics because it induces a lower effective viscosity and leads to a faster filling. This effect is enhanced for longer chains. The observed increase in the mean square radius of gyration during capillary filling provides a clear evidence of chain orientation, that leads to the decrease in the number of entanglements. Finally, we propose an equation that accounts for the effect of chain length on the capillary filling dynamics of polymer chains in nanopores. |
Tuesday, March 21, 2023 5:18PM - 5:30PM |
TT05.00008: Forced-assembly of triblock copolymers at the transitioning interfaces from liquid-air to solid-air Sungsook Ahn The nature of an interface specifies properties such as adhesion, interfacial fracture toughness, friction/wear, adsorption, wettability, compatibility with adjacent phases and the like. Based on a mean field approach in polymer mixtures, entangled Individual polymer coils coerce the characteristic segmental interactions while the connectivity of the segments along the chain increases the scales in space, time, and temperature domains as compared to those of liquids. In this point, the interfacial phenomena of phase coexistence and segregation in polymer films can be described in terms of the orientation of the polymer chains to the interface, morphology and the chain diffusion dynamics, dominated by the chain length and the process kinetics. |
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