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 A02: Polymer Nanocomposites: DynamicsFocus Live
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Sponsoring Units: DPOLY DSOFT GSNP Chair: Shiwang Cheng, Michigan State University |
Monday, March 15, 2021 8:00AM - 8:12AM Live |
A02.00001: Effects of Heterogeneous Segmental Friction on the Multi-Scale Dynamics of Polymer Nanocomposites Walter Young, Joseph P. Saez, Thomas D. Kumlin, Koji Fukao, Reika Katsumata The multi-scale dynamics of polymers at hard material interfaces are highly sensitive to the chemical composition of the components, but this effect remains poorly understood because chemistry dictates not only polymer-interface interaction strengths, but also morphology, polymer flexibility, etc. This work aims to elucidate the effect of polymer-filler interactions on the segmental and chain dynamics of polymer nanocomposites in a simple model system. Here, heterogeneity in segmental friction and chemical composition is introduced by using an unentangled model random copolymer of styrene and 2-vinyl pyridine (2VP), loaded with octa(aminophenyl) silsesquioxane (OAPS) fillers, which interact weakly with styrene monomers, but strongly with 2VP monomers by hydrogen bonding. The neat copolymer dynamics are independent of 2VP mole fraction in the copolymer. The segmental dynamics of these composites are studied by dielectric loss spectroscopy and differential scanning calorimetry, while the chain dynamics are studied by rheology. We observe that changes in segmental dynamics cannot fully explain the slow-down of chain dynamics. The effect of 2VP content in the copolymer on the multi-scale dynamics of the system will be discussed in this presentation. |
Monday, March 15, 2021 8:12AM - 8:24AM Live |
A02.00002: Viscoelastic Properties of Wrinkled Graphene Reinforced Polymer Nanocomposites – Effect of Interlayer Sliding Among Graphene Sheets Yitao Wang, Jane Breslin, Cho Chun Chiang, Zhaoxu Meng The effect of wrinkles formed in multilayer graphene sheets (MLGS) on the viscoelastic properties of polymer nanocomposites has been largely unknown. Building upon the developed coarse-grained models of MLGS and PMMA coupled with molecular dynamics simulations, we have systematically investigated wrinkled MLGS reinforced PMMA nanocomposites with different numbers of graphene layers and different configurations of the wrinkles. We find that with an increasing level of wrinkling, the modulus and yield strength of the nanocomposites decrease. The reinforcement effect also becomes more significant with increasing number of graphene sheets. Interestingly, the enhancement of modulus and yield strength is not embodied under the out-of-plane shear. However, we observe a sudden stress drop during shear deformation of specific wrinkled MLGS reinforced nanocomposites. We find that these specific nanocomposites also show peculiarly large loss tangent, indicating an increasing level of energy dissipation. It is attributed to the activation of the interlayer sliding among MLGS. Our study demonstrates for the first time that the viscoelastic properties of polymer nanocomposites can be tuned through wrinkle engineering of MLGS. |
Monday, March 15, 2021 8:24AM - 8:36AM Live |
A02.00003: Dynamical Decomposition in Model Polymer Nanocomposites under Creep Entao Yang, James Pressly, Bharath Natarajan, Karen Winey, Robert Riggleman While the elastic properties of polymer nanocomposites (PNCs) have been widely studied, the ability of nanoparticles (NPs) to suppress creep in a polymer matrix has received comparatively less attention. The presence of a slow dynamic layer near the NPs’ surface is widely believed to be the primary mechanism of NP reinforcement. Thus, understanding how the interfacial dynamics, structures, and creep responses change as a function of stress, NP size, and polymer-NP interactions is critical. Here, by introducing a ratio of the interfacial dynamics to the bulk dynamics, we decomposed dynamics in PNCs into two parts: one is structure-dependent and the other is structure-independent. We prove that our decomposition can be further expanded to PNCs under creep, at least within the linear response region. Also, with this decomposition, particles’ free energy barrier for rearrangement can be described as a combination of a packing-related barrier and a packing-unrelated barrier. Our results indicate that both barriers are higher near NPs and decrease with increasing stress, while the packing-independent energy barrier is larger. We also used this model to predict strain-time curves for PNCs under creep, which agree well with the original simulations. |
Monday, March 15, 2021 8:36AM - 9:12AM Live |
A02.00004: Nanoparticle Structure and Dynamics in Polymer Nanocomposites Invited Speaker: Michael Hore The physical properties of polymers can be significantly altered both by embedding nanoparticles within them and by grafting them to nanoparticle surfaces. The ability to predict and measure the structure, dynamics, and thermodynamics of grafted polymers is central to purposefully creating new nanocomposite materials. In particular, one powerful technique for studying these aspects of nanocomposites is neutron scattering. This talk will review recent work we have performed to study the behavior of nanoparticles in nanocomposite materials, with a focus on nanorods and nanospheres. Small-angle neutron scattering measurements of poly(ethylene oxide)-grafted Au nanorods, poly(methyl acrylate)-grafted SiO2 nanospheres, and poly(methyl methacrylate)-grafted Fe3O4 nanosheres will be discussed, along with approaches to interpret the scattering results. The conformation of the grafted polymers will be compared between solution and nanocomposite states. Neutron spin echo measurements of the relaxation dynamics of grafted chain will be discussed, and the trends compared to the results of recent dissipative particle dynamics (DPD) calculations done by us. |
Monday, March 15, 2021 9:12AM - 9:24AM Live |
A02.00005: Dynamic Properties of Filled Elastomers Deboleena Dhara, Md Anisur Rahman, Zaid M Abbas, Brian C Benicewicz, Marc Couty, Dimitris Vlassopoulos, Sanat Kumar In response to the increased demand for fuel efficiency and sustainability, companies are seeking advancements in tire technologies to decrease fuel consumption by reducing rolling resistance. In this study, we use polymer grafted silica particles to get better control over the dispersion of the particles in an elastomeric matrix. Previous work in the group has shown that tuning parameters like grafting density and the ratio of matrix to graft chain length results in various dispersion states, which in turn have a direct correlation with reinforcement. Mechanical analysis on melt nanocomposites show that reinforcement is maximized by the formation of a percolating network. On the other hand, the crosslinked composites showed notable enchancement in reinforcement at low grafting density where the sample exhibits sheet like aggregated morphology. With an ultimate goal in mind to understand the reinforcement and hysteresis in rubber tires, we further aim to understand the conditions responsible behind it through the study of Payne effect. |
Monday, March 15, 2021 9:24AM - 9:36AM Live |
A02.00006: Dynamics of Nanorods in Polymer Melts Jiuling Wang, Ting Ge, Thomas O'Connor, Gary Grest The dynamics of nanorods in a polymer matrix is critical to the manipulation of the positions and orientations of nanorods and thus the functions of nanorod polymer composites. We perform molecular dynamics simulations of thin nanorods in polymer melts, where the rod diameter is equal to the monomer size. The simulations demonstrate a large anisotropy between the diffusion in the easy direction along the rod axis and that in the hard direction perpendicular to the axis. The diffusion coefficient D‖ in the easy direction is inversely proportional to the rod length L in both unentangled and entangled polymers, as the rod only experiences the monomeric viscosity. The diffusion coefficient D⊥ in the hard direction first scales as L-2 and then as L-1 with increasing L in unentangled polymers, suggesting that the corresponding viscosity increases linearly with L before saturating at the melt viscosity. D⊥ for sufficiently large L in entangled polymers is strongly suppressed due to the topological constraints. The same viscosity as in the hard direction dictates the rotation. The rotational diffusion coefficient DR first scales as L-4 and then as L-3 as L increases in unentangled polymers. Rotational diffusion is also strongly suppressed for sufficiently large L in entangled polymers. |
Monday, March 15, 2021 9:36AM - 9:48AM Live |
A02.00007: Unusual High-Frequency Mechanical Properties of Polymer Grafted Nanoparticle Melts Mayank Jhalaria, Yu Cang, Yucheng Huang, Brian C Benicewicz, Sanat Kumar, George Fytas We use Brillouin light scattering to characterize the high-frequency mechanical response of polymer-grafted nanoparticle (GNP) melts where the grafted chain molecular weight and grafting density is systematically varied at fixed NP size (diameter, D=16 nm). These measurements parallel recent work (Nano Lett. 2019, 19, 2715) using much larger D=114 nm NPs. The longitudinal sound velocity (and the engineering moduli) in the D=16 nm GNPs follow the effective medium, Wood’s law, in the limit of low NP loadings,φ, but display a steep increase φ>0.05 (shorter grafts). These results are rationalized by the fact that long-enough grafted brushes have a dry zone in the vicinity of the NP core, surrounded by an outer interpenetrated zone. We find that all the modulus results from NPs of different D, but with sufficiently high grafting to ensure the existence of a dry brush layer, fall on an apparently universal curve. These materials have three distinctly different mechanical response regions - the inorganic core, the inner dry region and an outer region which is similar to a neat polymer melt. This conclusion clearly illustrates the critical need to understand the mechanical properties of the dry region if we need to have a quantitative description of these GNP-based systems. |
Monday, March 15, 2021 9:48AM - 10:00AM Live |
A02.00008: Magnetic Heat Generation Mechanisms of Iron Oxide–Poly(ethylene oxide) Nanocomposites Donovan Weiblen, Deniz Rende, Pinar Akcora, Rahmi Ozisik Remote triggering of smart materials such as shape memory polymers and nanocomposites for drug delivery are research areas of continued interest. Magnetically susceptible nanoparticles (NPs) generate heat when exposed to an alternating magnetic field (AMF), making these NPs an ideal candidate for use in smart nanocomposites. Current work studies the dependence of heat generation mechanisms and interfacial heat transfer on the matrix molecular weight and NP concentration in iron oxide (Fe3O4)–poly(ethylene oxide), PEO, nanocomposites. Understanding the rotational dynamics of magnetic NPs is important in the application areas of these nanocomposites. The relative importance of Brownian and Neel relaxation processes is determined by altering the polymer matrix viscosity. Single core amine coated 10–nm–diameter Fe3O4 NPs were dispersed at concentrations less than 1% by weight in PEO matrices with varying molecular weights. Altering the matrix viscosity by varying the molecular weight of the PEO allows for consistent intermolecular interactions between the NPs surface groups and the PEO. The viscoelastic properties of these materials were also studied via nanoindentation. |
Monday, March 15, 2021 10:00AM - 10:36AM Live |
A02.00009: Structure and dynamics of polymer nanocomposites with different interactions Invited Speaker: Anne-Caroline Genix Polymer nanocomposites (PNCs) are made by the dispersion of hard fillers in a polymer matrix, where the fillers are usually added to enhance mechanical properties. Such materials attract industrial interest and their investigation is essential for the improvement of their performances. The latter are strongly related to the structural properties of PNCs: the dispersion state of nanoparticles (NPs) in the polymer melt is governed by the mixing protocols (solid phase mixing or solvent casting) and thermodynamics of the system (i.e., particle miscibility) which influence both filler-filler and filler-polymer interactions. |
Monday, March 15, 2021 10:36AM - 10:48AM Live |
A02.00010: Effect of polymer-nanoparticle interaction strength on viscoelastic creep attenuation in polymer nanocomposites James Pressly, Entao Yang, Eric J Bailey, Tia Denby, Bharath Natarajan, Robert Riggleman, Karen Winey Successful use of polymer nanocomposites (PNCs) in infrastructure applications requires a thorough understanding of the mechanisms affecting viscoelastic creep behavior in PNCs, including nanoparticle size, loading, and polymer-nanoparticle interaction strength. In this study, we examine the long-term creep behavior of a model nanocomposite system consisting of 13 and 52 nm diameter silica nanoparticles (NPs) dispersed in a matrix of 200 kg/mol poly(2-vinylpyridine) (P2VP). The polymer-nanoparticle interaction strength is controlled by functionalizing the nanoparticle surface with varying densities of methoxy(dimethyl)octylsilane. to achieve a range of nanoparticle surface chemistries, resulting in a variety of systems from strongly attractive bare-silica/P2VP composites to weakly attractive densely functionalized octyl-silica/P2VP composites. The long-term viscoelastic creep behavior of the composites is measured using dynamic mechanical analysis (DMA). The results are correlated to observations of the nanoparticle dispersion within the PNC, as quantified using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), as well as NP surface energy measurements via inverse gas chromatography (IGC). |
Monday, March 15, 2021 10:48AM - 11:00AM Live |
A02.00011: Solvent induced phase behavior of binary polymer-grafted nanoparticle blends Wenjie Wu, Maninderjeet Singh, Xiaoteng Wang, Yue Zhai, Zongyu Wang, Tanguy Terlier, Krzysztof Matyjaszewski, Michael R Bockstaller, Alamgir Karim Polymer-grafted nanoparticles (PGNPs) have attracted much attention in recent years for their potential applications, from nanoelectronics to tough materials with tunable enhanced mechanical properties. However, recent study of poly (methyl methacrylate) silica (PMMA-SiO2) and poly(styrene) silica (PS-SiO2) blends reveal that thermal annealing cannot coarsen the phase separation of large PGNPs, due to the lack of mobility of the large masses involved. This can be resolved through liquid-enabled phase-separation as a facile approach. To this end, we developed a method to coarsen the in-plane and out-of-plane surface patterns, to over 3 and 20 times respectively, by using a direct solvent immersion annealing (DIA) method. By varying the solvents in the DIA solution, interchangeable phase-separated and homogeneous blend morphologies are formed, and the magnitude of the phase separated surface patterns are in the order of the interfacial tension relative to surface tension, similar to homopolymer melt mixtures. Depth profiling by ToF-SIMS reveals that the switchable phase separation state persists within the films. Such homopolymer matrix free PGNP-only blend systems are novel, and these switchable transitions are not readily obtainable by thermal annealing. |
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