Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session D18: New Directions in Polymer Nanocomposites III: PropertiesFocus Recordings Available
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Sponsoring Units: DPOLY GSNP Chair: Jinhye Bae, University of California, San Diego Room: McCormick Place W-184D |
Monday, March 14, 2022 3:00PM - 3:12PM |
D18.00001: Influences of "Bonded" and "Unbonded" Monomers on Glass Transition Temperatures in Amorphous Polymer/POSS Composites Reika Katsumata, Walter W Young We report that a fraction of “bonded” or “unbonded” monomers to particle interfaces dictates the composition dependence of the glass transition temperatures (Tg) of polyhedral oligomeric silsesquioxane (POSS)-containing nanocomposites. Although Tg is one of the most critical physical parameters of nanocomposites, confounding interfacial effects make Tg prediction challenging. To this end, we design a model nanocomposite to systematically study Tg of nanocomposites by leveraging the “all interfacial” nature of ultrasmall POSS fillers. An amine-functionalized POSS is loaded into random copolymers of styrene and 2-vinyl pyridine. The POSS forms hydrogen bonds only with 2-vinyl pyridine, which behaves as a “bonded” monomer. The influence of copolymer composition and POSS loading on the Tg of this model composite is successfully explained by modifying the Fox equation. In this presentation, further implications about the different POSS composites will be discussed. |
Monday, March 14, 2022 3:12PM - 3:24PM |
D18.00002: Additive Size Controls the Temperature-Dependence of Relaxation in Bulk Polymers Thomas Q McKenzie-Smith We measure the dependence of bulk, coarse-grained polymer dynamics on the size of spherical additives from the small molecule to nanoparticle size scale. We consider two scenarios for the interactions between the additive and polymer. In both cases, we find a characteristic additive size that is comparable to the monomer size, below which the alpha relaxation time τ of polymers drops sharply. For each additive size, we find that the Localization Model (LM) can relate the temperature dependence of τ to that of the pico-second dynamics quantified by the Debye-Waller factor〈u2〉. We find that the parameters of the LM depend only on additive size, and are independent of the monomer-additive interactions, such that the shapes of the temperature dependencies of dynamic changes can be solely attributed to entropic effects associated with the additive size; interaction strength renormalizes the temperature scale of these dependencies. Further, we find that the LM fit parameters plateau for additives larger than a monomer diameter, suggesting that a ‘nanoparticle limit’ of the LM is reached at a surprisingly small additive size. We also consider how the collective motion is altered by additives, and how these changes are affected by confinement when we examine ultra-thin polymer films. |
Monday, March 14, 2022 3:24PM - 3:36PM |
D18.00003: Dynamic Mechanical Behaviors of Nacre-Inspired Graphene-Polymer Nanocomposites Depending on Internal Nanostructures Zhaoxu Meng, Cho-Chun Chiang, Jane Breslin, Zhangke Yang Nacre, a natural nanocomposite with a brick-and-mortar structure existing in the inner layer of mollusk shells, has been shown to optimize strength and toughness along the laminae (in-plane) direction. However, dynamic responses and deformation mechanisms of layered structures under impact load in the out-of-plane direction, which is the dominant loading from predators, have been much less analyzed. This study investigates the dynamic mechanical behaviors of nacre-inspired layered nanocomposite films using a model system that comprises alternating multi-layer graphene (MLG) and polymethyl methacrylate (PMMA) phases. With a validated coarse-grained molecular dynamics simulation approach, we systematically study the mechanical properties and impact resistance of the MLG-PMMA nanocomposite films with different internal nanostructures, which are characterized by the layer thickness and number of repetitions while keeping the total volume constant. We first use tensile and free vibration tests to characterize the elastic moduli of nanocomposite films depending on nanostructures and illustrate the nanoconfinement effect in the layered structures. We then use ballistic impact simulations to explore the dynamic responses of nanocomposite films. We find that the impact resistance and dynamic failure mechanisms of the films depend on the internal nanostructures. Our study provides insights into the effect of nanostructures on the dynamic mechanical behaviors of layered nanocomposites, which can lead to effective design strategies for impact-resistant films. |
Monday, March 14, 2022 3:36PM - 3:48PM |
D18.00004: Deformation of Free-Standing Polymer Nanocomposite Thin Films Jelani Hannah The mechanical properties of polymer nanocomposite thin films are central to their applications as impact mitigating materials and flexible electronics. As a non-contact and substrate-free method, bulge tests (or nanobubble inflation tests) provide many advantages to determine the elastic and viscoelastic behavior of free-standing thin films and they are amenable to cyclic loading and time independent creep measurements. Previous work has extensively utilized interferometric bulge tests. We discuss combining bulge tests with laser scanning confocal microscopy to obtain the 3D profile of bulged films. We apply this technique to obtain the mechanical properties of free-standing polymer nanocomposite thin films (PNCs), which have the potential to be integrated in high demand applications such as drug delivery, energy storage, novel packaging, and membrane filtration. |
Monday, March 14, 2022 3:48PM - 4:00PM |
D18.00005: Particle Dynamics and Rheology of Polymer-Grafted Nanoparticle Composites with Chemical Heterogeneities Di Wu, Pinar Akcora We investigate the effect of chemical heterogeneities and architectures of interfacial chains on mechanical properties of polymer nanocomposites. Magnetite (Fe3O4) nanoparticles adsorbed with flexible poly(methyl methacrylate) (PMMA) chains in poly(methyl acrylate) (PMA) matrices relax at longer times than those of particles with the rigid adsorbed polymer. This confirms our previous results on the reinforcement of highly entangled, packed adsorbed layers around nanoparticles. In the case of grafted Fe3O4 nanoparticle system, particles with short grafts surprisingly exhibit a longer relaxation time than the longer chains, implying a stronger interphase formation in grafted systems. A series of polymer-grafted nanoparticles with different chain lengths at the same graft density are synthesized and their composites with chemically different matrix polymers are prepared to explore the dynamic heterogeneity effect on the mechanical performance of composites. Small-amplitude oscillatory shear (SAOS), temperature sweep, and deformation at large shear experiments are carried out to understand the effect of graft chain conformation and molecular weight effect on the linear viscoelastic behavior and inter-diffusion of the graft-matrix interfacial regions where graft chains become glassy and liquid with temperature modulations around the Tg of graft chains. |
Monday, March 14, 2022 4:00PM - 4:12PM |
D18.00006: The transition to linear-nonlinear dichotomy in rheological responses Xiaorong Wang The term "linear-nonlinear dichotomy" specifies that the viscoelastic behavior is nonlinear in the sense that the storage modulus G' and loss modulus G" depend strongly on the strain amplitude while, in contrast, linearity is implied at each of the strain amplitudes based on the sinusoidal stress response which is simply offset from the oscillatory strain input. This kind of nonlinearity contains two mutually exclusive and contradictory parts that coexist together at the same time. Recently, we analyzed the rheological behavior of a series of particle-filled polymer solutions using the ratio of the third and first harmonics, I3/I1, as a function of the concentration of the polymer in the solutions for a given particle concentration and the analysis of the structural characteristics of the polymer solutions. We found there is a transition to linear-nonlinear dichotomy in the theological responses of these materials at a critical polymer concentration, which is insensitive to strain amplitude, G'/G'0, and filler loading, but very sensitive to the particle size. This transition happens when the mesh size of the entangled polymer network in the matrix becomes smaller than the filler particle size. Here, I will report the milestone results of this research in Tongji, and intend to explain the nature of this unusual nonlinear behavior associated with nanoparticle-filled rubber materials. |
Monday, March 14, 2022 4:12PM - 4:24PM |
D18.00007: Dispersion of modified fumed silica in elastomeric nanocomposites Ugochukwu O Okoli, Kabir Rishi, Greg Beaucage, Hendrik K Kammler, Alex M McGlasson, Michael Chauby, Vishak Narayanan, James Grammens Surface modification of silica can enhance dispersion in elastomers by improved filler/polymer interactions. Surface modification is usually achieved with silane coupling agents. It is also possible to deposit carbon directly during pyrogenic synthesis. Carbon coated and chemically modified pyrogenic silica fillers were dispersed in styrene-butadiene (SBR) rubber to explore their differences. Surface carbon content, the extent of dispersion, and rheological properties were explored. X-ray scattering indicated that the in-flame and chemically modified fillers displayed good dispersion in the SBR matrix as quantified by the second viral coefficient. Pristine pyrogenic silica aggregates at concentrations above a critical value display correlations in nanocomposites due to the presence of silanol groups on the surface as demonstrated in our previous work. In the present study, flame synthesized fumed silica with sufficient surface carbon monolayers mitigate the charge repulsion due to silanol moieties, removing aggregate correlations. This led to improved properties. The rheological behaviour of the nanocomposites displayed a balance between lower rolling resistance and enhanced wet grip. Variations in the dispersion and its impact on rheological properties were also explored. |
Monday, March 14, 2022 4:24PM - 5:00PM |
D18.00008: Mechanical Dissipation in Polymer-Grafted Nanoparticle Assemblies Invited Speaker: Richard A Vaia Macroscopic assemblies of polymer-grafted nanoparticles (PGNs) (i.e. single component nanocomposites) are being assessed for a broad range of structural, separation, electronic, and optical technologies. Elucidating the relationship between PGN design (graft density, graft length, and nanoparticle size), hierarchical structure (composition, shape, arrangement, spacing, and distribution of organic and inorganic constituents), and processing (rheology, solubility, wettability, mesoscopic self-assembly) is crucial to optimize performance. In all cases however, mechanical robustness is paramount. Herein, we will discuss recent experiments and simulations to understand the impact of PGN design on entanglements among adjacent neighbors, and the subsequent impact on plasticity and failure at low and extreme deformation rates. These studies point toward an optimal PGN design at intermediate graft density that maximizes inter-canopy entanglements throughout the polymer region. This architecture affords sub-Tg, bulk energy dissipation processes within the polymer, such as cavitation and crazing, and enables the nanoparticle core to act as a low relaxation rate crosslink, creating a secondary mesoscale nodal network. The most favorable entanglement arrangement likely depends on strain rate, and whether maximum strength or energy dissipation is required. Future concepts are required to increase entanglement density, and thus decrease the canopy (polymer) volume fraction, as well as elucidate the impact of hierarchical structures on mechanical dissipation, such as those comprised of multiple and/or anisotropic PGNs. |
Monday, March 14, 2022 5:00PM - 5:12PM |
D18.00009: Nanostructure Heterogeneity and the Excess Free Volumes in Polymer-grafted Nanoparticle Membranes Sophia Chan, Masafumi Fukuto, Kevin Yager, Marcus Noack, Guillaume Freychet, Yucheng Huang, Brian C Benicewicz, Sanat K Kumar Polymer-grafted nanoparticle (PGN) membranes display significantly enhanced gas permeabilities relative to neat polymer analogs. Independent experiments have shown that the underlying cause is an increased free volume in the PGNs. However, there is no understanding of how free volume manifests in macroscale PGN properties. We use small-angle x-ray scattering with a micro-focused beam coupled with the evolving tools of artificial intelligence to measure the distribution of distances between neighboring nanoparticle centers for densely grafted poly(methyl acrylate)-grafted-silica nanoparticles (PMA-g-SiO2) melts across macroscale areas (i.e., 4 mm x 4 mm). Based on these, we present remarkable correlated trends between the standard deviations of these nanostructure distributions and gas permeability enhancements. For the PMA graft molecular weight with the highest gas permeability enhancement, we found a broad distribution of nanostructure distances, suggesting a reduced penalty for creating such spatial heterogeneities. We posit that these results reflect the ability of these materials to tolerate density fluctuations, providing a molecular underpinning of the free volume trends. |
Monday, March 14, 2022 5:12PM - 5:24PM Withdrawn |
D18.00010: Molecular Weight Dispersity as Design Parameter to Enable Brush Particle Hybrid Materials with Enhanced Fracture Toughness and Inorganic Content Ayesha Abdullah, Jaejun Lee, Yuqi Zhao, Zongyu Wang, Michael R Bockstaller Polymer-tethered (or 'brush') particles (BPs) have been pursued as building blocks for one-component electronic and optical hybrid materials. However retention of application capability involves high inorganic fraction, along with mutually exclusive properties such as high modulus and toughness. |
Monday, March 14, 2022 5:24PM - 5:36PM |
D18.00011: Strain energy density based effective potential for polymer grafted spherical nanoparticles Subhadeep Pal, Sinan Keten Polymer-grafted nanoparticles (PGN) form single-component nanocomposites that have gained significant popularity as they allow for superior control over ordering and mechanical properties. However, the design space for PGNs is huge and it is challenging to find optimal molecular parameters that yield a particular mechanical outcome. To overcome this issue, we have developed a strategy to convert the strain energy density obtained from coarse-grained molecular dynamics (CG-MD) simulations to the form of an effective interparticle potential. The double exponential potential can capture the interaction between spherical nanoparticles and circumvent the need to explicitly model grafted chains. Upscaling to a single particle representation increases the computation speed by approximately four orders of magnitude relative to coarse-grained models and enables us to investigate the design space (consisting of polymer chain length, grafting density, nanoparticle radius) with less computational cost and without losing the underlying physics. This novel framework is foundational for micron-scale modeling of single and multi-component polymer-grafted nanoparticle composite films under mechanical loads, including microballistic impact. |
Monday, March 14, 2022 5:36PM - 5:48PM |
D18.00012: Role of Solvent-quality in the Processing of Polymer Nanocomposites on Their Microstructure and Rheological Properties Tae Yeon Kong, So Youn Kim The physical properties of polymer nanocomposites (PNCs) generally rely on the microstructures, namely the spatial organization of nanoparticles (NPs) in a polymer matrix. Thus, enormous efforts have been made to control the structure of NPs and thus to obtain desired properties of PNCs. One of the effective methods is to change the initial solvent quality. The initial dispersing solvent is not present in a final state of PNCs but is known to alter their microstructures and mechanical properties, varying polymer chain structures and dynamics, especially at interfaces. |
Monday, March 14, 2022 5:48PM - 6:00PM |
D18.00013: Superdiffusive thermal transport in polymer-grafted spherical nanoparticle melts Bohai Liu, Mayank Jhalaria, Sanat K Kumar, Xiangfan Xu, George Fytas We use a thermal bridge method to measure the thermal conductivity κ in densely packed polymer-grafted spherical nanoparticle (GNP) membranes as a function of the polymer degree of polymerization, N, at fixed grafting density and NP size (radius 8 nm). While κ expectedly increases with NP loading ϕ<0.05 (long grafts) it unexpectedly decreases at higher ϕ’s (short grafts). This pinning behavior is rationalized by a crossover from a homogeneous mixture of NP in interpenetrated long grafts to percolating “hard spheres” of short grafts on NPs. In the latter dry polymer zone, heat transport occurs through stretched grafts. Representation of κ (N) by a modified Maxwell model leads to κPMA ~ N1/2 corroborating the notion of superdiffusive phonon transport in stretched (one-dimensional) short grafts. This structural transition in GNP’s also explains the enhanced elasticity of the same GNP melts for short grafts as revealed by Brillouin light spectroscopy. Utilizing the sound velocities, the increase of κ with N can be attributed to an enhanced phonon mean free path for short grafts. The manifestation of the GNP topology to diverse physical quantities can help to understand the properties of the dry region necessary for quantitative description of the GNP based materials. |
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