Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F03: Polymer Nanocomposites: Structure and PropertyFocus Live
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Sponsoring Units: DPOLY DSOFT Chair: Robert Hickey, Pennsylvania State University |
Tuesday, March 16, 2021 11:30AM - 12:06PM Live |
F03.00001: Molecular Dynamics Simulations of Polymer-Grafted Nanoparticle Monolayers Invited Speaker: Lisa M. Hall Inorganic nanoparticles with polymers grafted to their surface, known as hairy nanoparticles or polymer-grafted nanoparticles (PGNs) are a means to create functional materials with a controllable nanoscale structure. A thin film of PGNs on a surface can self assemble into a mechanically robust hexagonally packed structure with a precise spacing, leading to interesting optical properties, improved dielectric breakdown strength, or other desirable features. To guide design of future materials, one needs to connect the molecular-scale structure and resulting material properties to parameters that can be controlled during PGN synthesis, including particle size, graft length, and grafting density. Here, we use coarse-grained molecular dynamics (MD) simulations to show how these factors interact to set the interparticle spacing, interpenetration and entanglements of polymers on adjacent particles, and mechanical properties of PGN monolayers. Specifically, we graft Kremer-Grest chains of N=160 (lightly entangled) to spherical nanoparticles of 10 times the monomer diameter. We consider a series of high to moderate graft densities such that nanoparticle surfaces are sterically protected from directly interacting. Lower graft density leads to greater interpenetration of canopies on adjacent particles and thus a greater number of interparticle entanglements per chain, which corresponds to greater mechanical toughness, both for PGN monolayer melts on a smooth surface and for freestanding glassy films. We compare the crazing behavior of glassy PGN films under deformation to that of analogous homopolymers, finding that the PGNs lead to a more regular craze structure. |
Tuesday, March 16, 2021 12:06PM - 12:18PM Live |
F03.00002: Chain Conformations in Model Polymer-Grafted Nanoparticle Monolayers Nicholas Liesen, Lisa M. Hall Neat polymer-grafted nanoparticles (PGNs) are promising materials consisting of only nanoparticles (NPs) with polymer chains grafted to their surface. The presence of only grafted polymer mitigates demixing issues observed in NP-filled polymer composites. These materials can have a well-defined nanoscale structure and desirable mechanical, optical, and electronic properties. Mechanical properties can depend sensitively on graft density through changes to polymer brush conformation, interpenetration, and degree of entanglement. |
Tuesday, March 16, 2021 12:18PM - 12:30PM Live |
F03.00003: Effects of Chain Length on the Structure and Dynamics of Semi-Dilute Nanoparticle-Polymer Composites Ari Liu, Hamed Emamy, Jack Douglas, Francis Starr We use molecular dynamics simulations to study how chain length affects the structure and dynamics of polymer-nanoparticle (NP) composites at a semi-dilute NP concentration with an ideal dispersion of NPs. By varying both chain length and NP concentration, we examine regimes where chain size (i.e. chain radius of gyration Rg) is small compared to the NP separation d (Rg/d < 1), as well as cases where Rg/d > 1, so that chains can “bridge” between the NPs. Generally, we find that polymers slightly elongate near the NP interface and the chains tend to align their longest axis with the NP interface. Chains that bridge between NPs must significantly elongate when the NP separation is large compared to the chain dimensions. These bridging chains have a longer relaxation time than non-bridging chains, but surprisingly they do not make a substantial contribution to the overall composite relaxation for the conditions studied. Accordingly, the variation of glass transition temperature Tg with chain length essentially mirrors the trend for the reference pure polymer melt, where Tg increases with chain length and roughly saturates at large mass. Overall, for the conditions studied, bridging chains are found to have a surprisingly small impact on the composite properties. |
Tuesday, March 16, 2021 12:30PM - 12:42PM Live |
F03.00004: Nanoscale Structure-Property Relations in Self-Regulated Polymer Grafted Nanoparticle Structures John McClimon, Shawn Maguire, Connor R Bilchak, Austin Wesley Keller, Sage Fulco, Kevin Turner, Russell John Composto, Robert W Carpick Using a model system of poly(methyl methacrylate) grafted silica nanoparticles (PMMA-NP) and poly(styrene-ran-acrylonitrile) (SAN), we generated unique polymer nanocomposite morphologies by balancing the degree of phase separation and wetting within the films. Depending on the annealing temperature, the thin films undergo different stages of phase evolution, resulting in homogenously dispersed systems at low temperatures and three-dimensional bicontinuous structures of PMMA-NP pillars sandwiched between two PMMA-NP wetting layers at high temperatures. Using a combination of atomic force microscopy (AFM), AFM nanoindentation, and optical microscopy, we show that these self-regulated structures lead to nanocomposites with increased modulus, hardness, and thermal stability compared to analogous PMMA/SAN blends. These studies demonstrate the ability to reliably control nanocomposite surface morphologies, which have attractive technological applications where surface-dependent properties such as wettability, durability, and the friction are important. |
Tuesday, March 16, 2021 12:42PM - 12:54PM Live |
F03.00005: Strain hardening from deformation-induced nanoparticle-nanoparticle interaction of polymer nanocomposites Ruikun Sun, Matthew Melton, Xiaobing Zuo, Shiwang Cheng Understanding the structure-property relationship of polymer nanocomposites (PNCs) during deformation is crucial for PNC processing. In this work, we investigate the roles of external deformation on the nanoparticle-nanoparticle interactions through a combination of small-angle x-ray scattering and rheology. We found the applied uniaxial extension brought together the NPs at the transverse stretching and catalyzes the percolation transition of nanoparticles. The percolated nanoparticle network thus leads to a strong surge in the elongation viscosity at yielding, leading to an unexpected strain hardening at large deformation. Interestingly, the yield strain, εY, and yield stress, σY, of the percolated nanoparticle network follow a scaling of εY ~ (dε/dt)0, and σY ~ (dε/dt)0.5 regardless of the loading of NPs, where the dε/dt is the Hencky strain rate. These observations manifest the unconventional roles of external deformation on modulating the nanoparticle-nanoparticle interaction, enabling advanced structures and properties control of PNCs. |
Tuesday, March 16, 2021 12:54PM - 1:06PM Live |
F03.00006: Correlating Polymer Morphology to Rheological Properties in PEO / SiO2 nanocomposites Kiriaki Chrissopoulou, Sokratis Kogchylakis, Spiros Anastasiadis Polymer nanocomposites, comprised of a polymer matrix and inorganic additives, possess improved and often innovative physicochemical properties compared to conventionally filled systems. In this work we report on the rheological behavior of series of poly(ethylene oxide) / silica, PEO/SiO2, nanocomposites through oscillatory shear rheology measurements. The nanohybrids were synthesized by dispersing spherical SiO2 nanoparticles of two different radii within high molecular weight PEO at different compositions to investigate the effect of the additive on the material rheological properties. Dynamic time and strain sweep tests verify the material thermal stability and linear viscoelastic behavior whereas dynamic frequency sweeps probe its dynamic response. In these nanohybrids, PEO crystallinity was found to depend on the degree of spatial confinement that the nanoparticles impose as well as their adsorption capacity. The effect of nanoparticle size and concentration on the behavior is examined to correlate the morphological changes to the materials rheological response in an attempt to better understand the structure-properties relationship. Acknowledgements: This research has been co-financed by EU and Greek national funds (Action RESEARCH – CREATE - INNOVATE, MIS: 5030174). |
Tuesday, March 16, 2021 1:06PM - 1:18PM Live |
F03.00007: Using in situ polymerizations to create polymer/inorganic nanoparticle hybrid materials Jacob LaNasa, Robert Hickey Control of particle dispersion within a matrix is a critical consideration when designing hybrid polymer/inorganic nanoparticle materials. Reaction induced phase transitions (RIPT) have been effective in achieving stable and metastable states in polymer and hybrid material systems. However, the influence of factors such as particle miscibility, translational diffusion, and polymerization rate on dispersion require exploration. Here, poly(cyclooctadiene) (PCOD) functionalized nanoparticles are dispersed within poly(styrene) and poly(methyl methacrylate) matrices by an in situ polymerization of a monomer and polymer-functionalized particle solution. The in situ polymerization arrests particle mobility as the matrix increases in chain length and is paired with an in situ grafting of the matrix chains to “soften” the enthalpic differences between components. The approach presented here is able to achieve a range of dispersion states dependent on graft chemistry and the rate of polymerization in different matrix chemistries. |
Tuesday, March 16, 2021 1:18PM - 1:30PM Live |
F03.00008: Structure of Polymer-Grafted Nanoparticle Melts Jiarul Midya, Michael Rubinstein, Sanat Kumar, Arash Nikoubashman The structure of neat melts of polymer-grafted nanoparticles (GNPs) is studied via coarse-grained molecular dynamics simulations. We systematically vary the chain length and grafting density at fixed NP radius, and study in detail the shape and size of the GNP coronas. For sufficiently high grafting density, chain sections close to the NP core are extended and form a dry layer. Further away from the NP there is an interpenetration layer, where the polymer coronas of neighboring GNPs overlap and the chain sections have almost unperturbed conformations. To better understand this partitioning, we develop a two-layer model, representing the grafted polymer around a NP by spherical dry and interpenetration layers. This model quantitatively predicts that the thicknesses of the two layers depend on one universal parameter, x, the degree of overcrowding of grafted chains relative to chains in the melt. Both simulations and theory show that the chain extension free energy is non-monotonic with increasing chain length at fixed grafting density, with a well defined maximum. This maximum is indicative of the crossover from the dry layer-dominated to interpenetration layer-dominated regime, which may have some connection to variety of anomalous transport properties of these GNPs. |
Tuesday, March 16, 2021 1:30PM - 1:42PM Live |
F03.00009: Strong Preparation Effects on the Morphology and Gas Transport Properties of Polymer Grafted Nanoparticle Membranes Sophia Chan, Mayank Jhalaria, Yucheng Huang, Brian C Benicewicz, Masafumi Fukuto, Ruipeng Li, Sanat Kumar Processing conditions and morphology have long been known to dictate the macroscopic properties of polymer nanocomposites due to the incompatibility between hydrophilic nanofillers and hydrophobic polymers. In an attempt to remedy the incompatibility, we chemically grafted the polymer to the nanoparticle and found these polymer grafted nanoparticle (PGN) films yielded significantly high enhancements of gas permeabilities relative to that of the neat polymer. However, in subsequent preliminary data, we were surprised to find that the morphology and property (gas transport) of PGNs are still sensitive to preparation methods. Here, the preparation-morphology-property relationships of polymer grafted nanoparticles are explored. Different conditions including casting methods, choice of solvent, and temperature annealing conditions are investigated for their effects on heterogeneities within morphology using X-ray scattering, and from there, gas transport properties using both the constant-volume / variable-pressure permeation cell and the quartz crystal microbalance. |
Tuesday, March 16, 2021 1:42PM - 1:54PM Live |
F03.00010: Direct visualization of the nanoparticle rearrangement of polymer nanocomposites under deformation by scanning electron microscopy Matthew Melton, Shiwang Cheng Understanding the influence of the external deformation on the microstructure rearrangement of polymer nanocomposites is crucial for polymer nanocomposites processing. Although small angle scatterings provide an important characterization on the dispersion state of NPs, they offer little insights on the structural changes of the PNCs at the single nanoparticle level that directly link to the polymer-nanoparticle interaction. In this work, the roles of the external deformation on the spatial rearrangement of individual particles or nanoparticle clusters will be mapped out through a combination of scanning electron microscopy and rheology. While the affine deformation of PNCs holds macroscopically, the presence of nanoparticles significantly modifies the movement of the trace particles deviating from the applied strain field. These results imply a strong distortion and highly heterogeneous deformation field for PNCs at the nanoscale and highlight the complex polymer-nanoparticle interactions at the nanoscale. |
Tuesday, March 16, 2021 1:54PM - 2:06PM Live |
F03.00011: Mesostructured Metal Superconductors via Block Copolymer Nanocomposites: Quantum Metamaterials from Soft Matter R. Paxton Thedford, Sol Michael Gruner, Ulrich Wiesner Three-dimensionally mesostructured superconductors have unique properties compared to thin film or bulk analogues, but their investigation has been limited by the lack of facile synthesis methods. Though largely unexplored in this application, block copolymers (BCPs) can serve as structure-directing agents to tune material architectures and, by extension, properties over scales on the order of characteristic lengths in superconductors (10s of nm). Here we will report on a versatile approach to mesostructured metal superconductors via block copolymer nanocomposite formation. Results indicate quantum metamaterials behavior, with evidence that properties such as the coherence length or magnetic vortex formation and pinning change substantially in a 3D periodic bicontinuous double gyroid mesostructure. The work suggests the emergence of a new field of soft matter self-assembly directed quantum materials promising new physical phenomena and quantum material properties. |
Tuesday, March 16, 2021 2:06PM - 2:18PM Live |
F03.00012: Enhancing the Fracture Toughness of Polymer-Infiltrated Nanoparticle Films via Polymer Bridging and Entanglement Yiwei Qiang, Daeyeon Lee, Kevin Turner The mechanical properties of disordered nanoparticle (NP) packings can be significantly improved through capillary rise infiltration (CaRI) of polymers to enhance the interactions between the NPs. While results from previous nanoindentation-based fracture measurements suggest that polymer infiltration can toughen NP packings, it is challenging to fully understand how the relative size of polymer and nanoparticles and the extent of confinement affect the toughness. In the present work, a thin-film fracture testing method based on the double cantilever beam (DCB) specimen is developed and used to investigate the fracture properties of polymer-infiltrated nanoparticle films. In the DCB specimen, a crack is propagated in NP films over distances of tens of millimeters, allowing for highly accurate measurements of toughness in a mode I (tensile opening) configuration. The fracture toughness of the polymer-infiltrated NP films is found to be strongly dependent on polymer molecular weight (MW) and NP size. Low MW, unentangled polymers, effectively toughen small NP packings; whereas high MW, entangled polymers, show enhanced toughening in large NP packings. Possible toughening mechanisms, including confinement-induced polymer bridging and polymer entanglement, will be discussed. |
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