Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R52: Polymer Nanocomposites IV: Networks, Elastomers, and GelsFocus
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Sponsoring Units: DPOLY Chair: Jinhye Bae, University of California, San Diego Room: BCEC 253B |
Thursday, March 7, 2019 8:00AM - 8:12AM |
R52.00001: WITHDRAWN ABSTRACT
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Thursday, March 7, 2019 8:12AM - 8:24AM |
R52.00002: Coarse-grained Molecular Dynamics Modeling of Epoxy/CNT Nanocomposites Ralph Romero, Hayden Hollenbeck, Chengyuan Wen, Gary Seidel, Shengfeng Cheng Modeling fracture in a polymer nanocomposite presents a big challenge at the moment. To enable us to model larger systems over longer time scales that can be bridged to those in continuum mechanics models such as peridynamics, we have developed a coarse-grained molecular dynamics (MD) model of epoxy/carbon nanotube (CNT) nanocomposites. The polymer is described as bead-spring chains with bonded and nonbonded interactions parametrized with atomistic MD simulations. A CNT is represented similarly as a bead-spring chain but with each bond treated as a rod with finite length and radius. Such a treatment leads to a jointed-tube model in which the corrugation issue associated with traditional coarse-grained models of CNTs is removed and the represented CNT behaves as a filament with finite radius. The CNT-CNT and CNT-polymer interactions are further trained with atomistic MD modeling. Using the coarse-grained model, we study the behavior of CNTs in an epoxy matrix including dispersion and bundling and the fracture properties of the epoxy/CNT nanocomposites. |
Thursday, March 7, 2019 8:24AM - 8:36AM |
R52.00003: QM/MM hybrid simulations of critical failure at the interface in CNT/polymer nanocomposites. Jacek Golebiowski, Arash A Mostofi, Peter Haynes, James R Kermode Functionalized carbon nanotube (CNT)/polymer composites have received significant interest as promising structural materials with applications in the most demanding areas of industry such as aerospace and ballistic protection. Developing a fundamental understanding of failure mechanisms at the CNT/polymer interface is essential to improving their properties. Here, we use a quantum mechanics/molecular mechanics (QM/MM) hybrid approach to show how chemical structure at the CNT/polymer interface determines its strength and propose candidate chemistries to guide further experimental work. |
Thursday, March 7, 2019 8:36AM - 8:48AM |
R52.00004: A new strategy for tire tread stocks with high performances Aihua He, Xinping Zhang, Riguo Wang, Hao Wang The desire tire tread stocks require satisfied comprehensive performances including good wet-skid resistance, low rolling resistance, good abrasion resistance and excellent anti-fatigue propertie. In our work, trans-1, 4-poly (butadiene-co-isoprene) copolymer rubber (TBIR) as novel reactive functional rubber is introduced into traditional SSBR and SSBR/BR recipes. Owing to the reinforcement effect of TBIR on the blended polymer matrix, TBIR inclusion could not only inhibit the aggregation of silica during ageing process, but also improve the filler dispersion in the rubber matrix. Furthermore, the TBIR in the form of lamellar fibrils could inhibit crack initiation and deviate crack propagation direction. Consequently, the vulcanized elastomer nanocomposites exhibit significantly improved comprehensive properties, such as enhanced mechanical strengths, outstanding fatigue resistance, improved abrasion resistance and lower rolling resistance with other properties remaining unchanged. |
Thursday, March 7, 2019 8:48AM - 9:00AM |
R52.00005: The Linear-Nonlinear Dichotomy Behavior for Filled Rubbers in LOAS Shan Jiang, Xiaorong Wang Filled rubbers display an unusual linear-nonlinear dichotomy of their rheological responses under large amplitude oscillatory shears, where the amplitude of stress output deviates strongly from the linear dependence of strain, but the time-dependence of stress remains sinusoidal. Increasing the cross-linking density in the rubber matrix tends to favor this quasi-sinusoidal responses. Rising the usage of processing oil in a rubber compound tends to disfavor this dichotomy behavior. Varying the amount of reinforcement fillers seems to be ineffective, as long as the filler loading exceeds its percolation threshold. These observations suggest that the topological structure of polymer chain network in the matrix plays an important role in the linear-nonlinear dichotomy rheology. The agglomeration of fillers and the overall characteristics of the fractal structures of filler clusters may have a less important influence on this phenomenon. A summary of recent research activities at Tongji on this subject will be given. |
Thursday, March 7, 2019 9:00AM - 9:12AM |
R52.00006: Controlling Microstructure in Thermoplastic Polyurethane/Graphene Oxide Nanocomposites via Rigid Segment Length Brandy Grove, Shaghayegh Khani, Ricardo Andrade, Guilhermino Fechine, Joao Maia Thermoplastic Polyurethane (TPU) is a commercially and academically interesting polymer with a wide range of applications. Engineering the micro-structure of the block-copolymers is of crucial importance for achieving desired mechanical properties. Incorporation of nanofillers such as graphene and graphene oxide platelets provides a means to control the phase separation for this material. Dissipative Particle Dynamics (DPD) are preformed to study the phase separation of systems with these nanofillers and determine how much difference functionality makes in a variety of TPUs with hard segments of different lengths. Platelet nanofillers act as a nucleating agent in TPUs with shorter hard segments, inducing local order; as the hard segment length becomes longer, the ordered local structures formed by hard segments break down. Functionalized nanofillers do not aid or hinder the nucleation in TPUs with short hard segments, but may enhance order in TPUs with moderately longer segment length, particularly with a hard segment to nanofiller length that is 1/3 the length of the nanofiller size. |
Thursday, March 7, 2019 9:12AM - 9:48AM |
R52.00007: Interphases in polymer nanocomposites - recent insights from NMR studies Invited Speaker: Kay Saalwaechter The outstanding performance of modern elastomers is dominated by reinforcement arising from nanometric fillers. The compounds’ peculiar thermo-mechanical properties cannot be explained without consideration of an interphase, i.e., a region of polymer with modified properties [1]. Our, and many others’, work supports a consensus picture of adsorbed components with locally increased Tg, reaching the bulk value over a gradient zone of a few nm [1-3]. This talk focuses on more recent results, mostly obtained by proton low-resolution NMR, that challenge the generality of this picture. |
Thursday, March 7, 2019 9:48AM - 10:00AM |
R52.00008: Compatibility/Dispersion in Multi-Hierarchical Polymer Nanocomposites Greg Beaucage, Kabir Rishi, Alex McGlasson, Michael Chauby, Vikram K Kuppa Commercial polymer nanocomposites such as reinforced elastomers differ significantly from model nanocomposites. Successful commercial products display a complex multi-level hierarchical, nano- to macro-scale structure. We have studied these structures using TEM, small-angle x-ray scattering, and rheology. The multi-hierarchical structure in carbon black reinforced polybutadiene will be described as a function of processing conditions. The filler network in this compound displays a nanoscale aggregate network within nano-clusters that percolate on the micron scale. The nanoscale network develops due to thermodynamic incompatibility of carbon black and polybutadiene which is mitigated by the accumulated strain. The network clusters are limited in size due to incompatibility. On increasing concentration, percolation of these network clusters is observed in scattering, TEM and dynamic rheology. Through this work control over this complex multi-hierarchical structure will be achieved through manipulation of compatibility/incompatibily and processing history. |
Thursday, March 7, 2019 10:00AM - 10:12AM |
R52.00009: Fabricating Polymer Network Nanocomposites for Recyclabilty with Full Property Recovery and the Sometimes Complex Roles of Polymer-Nanofiller Interfaces Xi Chen, Lingqiao Li, John Torkelson Polymer network nanocomposites cannot be recycled for high-value applications because permanent covalent cross-links prevent melt-state reprocessing. We have developed novel dynamic covalent cross-linking methods that yield recyclabiity of polymer networks with full recovery of cross-link density. In the fabrication of network nanocomposites, filler surface functionality can provide challenges. With addition-type reversible covalent cross-linking, e.g., a controlled radical polymerization method, surface functionality (e.g., hydroxyl groups) has no significant effect on reprocessability. However, with step-growth-type dynamic covalent cross-linking, e.g, a hydroxyurethane cross-link, surface functionality has deleterious effects. With hydroxyl or amine functionality which can participate in hydroxyurethane chemistry, silica nanoparticles speed the reprocessing but modestly reduce cross-link density and property recovery. Silica nanoparticles with superhydrophobic surfaces (absence of functionality) impact reprocessing kinetics but not recovery of cross-link density. We will also discuss how filler surface functionality combined with dynamic covalent cross-linking may yield novel, well-dispersed nanocomposite networks with especially robust properties. |
Thursday, March 7, 2019 10:12AM - 10:24AM |
R52.00010: Intrinsic temperature dependence of plasmonic resonances in gold nanorod polymer nanocomposites David Lioi, Sarah Izor, Vikas Varshney, William Kennedy Optical scattering in plasmonic polymer nanocomposites is strongly influenced by the dielectric properties of both matrix and particles. Since changes in temperature can affect each constituent in fundamentally different ways, interpretation of optical scattering spectra as a function of temperature is not straightforward. Here we present a systematic experimental and analytical study of the optical scattering of gold nanorods embedded in an epoxy matrix. We demonstrate that the temperature dependence of scattering spectra from gold-polymer nanocomposites depends on the relative thickness of the surrounding ligands or inorganic coatings that are typically used to stabilize nanorods in polymer matrices. Using empirical fits for the dielectric functions of gold, epoxy, and coating materials we show that it is possible to correct for temperature effects in the interpretation of scattering spectra. This can greatly enhance the precision and accuracy of material state sensing applications that rely on the plasmonic response of gold nanorods in polymers. |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R52.00011: The Impact of an Emergent Hierarchical Filler Network on Nanocomposite Dynamics Kabir Rishi, Greg Beaucage, Vikram K Kuppa, Alex McGlasson, Jan Ilavsky The performance of nanoscale-filled elastomers is related to the structure of the aggregated filler network in addition to interfacial chemical affinity and filler dispersion. This structure emerges due to a competition between the thermodynamically driven filler immiscibility and the kinetically driven mixing process. A hierarchical filler network model evidenced in x-ray scattering is linked to the dynamic response at low strains in the linear viscoelastic regime. The primary nanoscale network that percolates locally at ~5 vol % displays a mesh-size, which is related to the changes in the dynamic spectrum at frequencies below the Einstein-Smallwood enhancement associated with the elastomer within the network pores in the high frequency region. The secondary micron-scale network associated with the Payne effect and bulk electrical conductivity that percolates globally at ~20 vol %, influences the gel-like dynamic response at very low frequencies. The hierarchical filler network is described by two crossover frequencies in the dynamic spectrum and two related structural scaling regimes. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R52.00012: Defect-Mediated Assembly of Liquid Crystal Elastomer Nanocomposites Xinfang Zhang, Hao Yu, Yubing Guo, Taras Turiv, O D Lavrentovich, Qi-Huo Wei One holy grail in making polymer nanocomposites is to be able to place the filling particles into designable positions or orientations. In this talk, we will present a new strategy to self-assemble liquid crystal elastomer nanocomposites by employing topological defects in liquid crystals. We show that topological defects with pre-designed shapes and topology can be created by using a photopatterning technique to control the molecular orientations at the boundaries. Nanoparticles dispersed in the liquid crystals are attracted and self-assembled to these topological defects to minimize the elastic energy of the system. With carefully designed molecular orientations, we show the self-assembly of the nanoparticles into loops and web-networks in liquid crystal polymers. |
Thursday, March 7, 2019 10:48AM - 11:00AM |
R52.00013: Mesoscale modeling of polymer bigels using Janus particles Shensheng Chen, Xin Yong Polymeric gels composed of chemical-distinct networks may have unique mechanical properties and potential applications in various areas. Nanocomposites of polymer and colloidal particles also draw great attention due to their enhanced strength, stimuli responsiveness, and rheology. To guide the rational design for a bigel contains hydrophilic and hydrophobic networks with predictive properties, we utilize dissipative particle dynamics (DPD) to simulate a model system that incorporate chemistry, physical absorption, and material characterization. To enable the coexistence of hydrophilic and hydrophobic networks, we use Janus particle with corresponding surface chemistries to attract different polymers. A bell model is used to simulate the reversible physical absorption and desorption. Our results show that a bigel is formed when the hybrid polymers are integrated with a high concentration of Janus particles. The bigel exhibits increased Young’s modulus and shear thinning behavior. More importantly, the bigel recovers to a homogenous network in a short time after deformation. This integrated approach provides a general path towards functional network materials with enhanced mechanical properties and potential applications in drug delivery and wound dressing. |
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