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 Z05: Hybrid and Multicomponent Polymer Materials Containing Nanoparticles III |
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Sponsoring Units: DPOLY Chair: Robert Hickey, The Pennsylvania State University Room: Room 128 |
Friday, March 10, 2023 11:30AM - 11:42AM |
Z05.00001: The Effect of Ligand Shell Density on the Diffusion of Nanoparticles in Hydrogel Nanocomposites Paige Moncure The diffusion of poly(ethylene glycol) methyl ether thiol (PEGSH) functionalized gold nanoparticles (NPs) with different ligand densities was measured in polyacrylamide hydrogels to investigate how the NP ligand density affects the diffusion coefficient . The NP core size was held constant, and the NPs were functionalized with mixtures of high molecular weight ligands (either 1 or 2 kDa PEGSH) and short stabilizing ligands (254 Da PEGSH). The ligand density of the large ligand was varied between 1-107 ligands/NP and 0-54 ligands/NP for the 1kDa and 2 kDa functionalized NPs, respectively. The hydrodynamic diameter (Dh) correspondingly increased from 8-12 nm and 8-15 nm for the 1 kDa and 2 kDa functionalized NPs. The diffusion coefficients of the NPs were then measured in gels with mesh sizes from 35-62 nm and decreased as a function of decreasing ligand density. We found that the diffusion coefficients for particles with high ligand densities were well-predicted by the hopping model for diffusion in polymeric gels, but the diffusion coefficients for particles with low ligand densities were higher than predicted based on their Dh. These results suggest that NP ligand densities influence the diffusion process, and that Dh is not a good predictor of diffusion coefficient at low ligand densities. This work brings new insights into the factors that dictate how NPs move through hydrogels and will inform the development of models for applications such as drug delivery in complex viscoelastic biological materials. |
Friday, March 10, 2023 11:42AM - 11:54AM |
Z05.00002: Anomalous Diffusion of Smooth Nanorods in Polymer Nanocomposites Phillip A Taylor, Jiuling Wang, Ting Ge, Thomas O'Connor, Gary S Grest Polymer nanocomposites (PNCs) are diverse, soft materials which comprise a polymer matrix with nanoparticle fillers. PNCs’ tailorable properties have garnered recent interest in applications including plastics, electronics, coatings, and sensors. The structure and dynamics of PNCs determine their viability for specific applications, such as dispersion for enhanced mechanical properties, percolated structures for electrical conductivity, and diffusion of tracers in nanorheology. In this talk, coarse-grained molecular dynamics simulations on the diffusion of thin nanorods in polymer melts as a function of nanorod roughness and aspect ratio will be presented. We observe anomalous nanorod diffusion with decreasing nanorod roughness, which results in nonlinear scaling behavior of diffusion coefficients with nanorod length. The anomalous diffusion for smooth rods is related to non-Gaussian diffusion and the existence of dynamic heterogeneities, quantified in terms of Van Hove correlation functions. The combined effects of nanorod roughness and nanorod diameter is investigated, in which case anomalous diffusion for smooth versus rough nanorods is also observed. This work highlights the ability to tune nanorod roughness and aspect ratio to achieve unique rod dynamics and provides mechanistic insights into the diffusion of anisotropic particles in synthetic and biological media. |
Friday, March 10, 2023 11:54AM - 12:06PM |
Z05.00003: Kinetic distribution and dispersion of nanoparticles in polymer nanocomposites. Greg Beaucage, Kabir Rishi, Ugochukwu O Okoli Dispersion and distribution of nanoparticles in polymer mixing processes are stumbling blocks to the production of nanocomposites. Dispersion, in polymer processing, refers to the structural breakup of agglomerates of nanoparticles while distribution involves spatial randomization. These two features of mixing respond to different viscous flow regimes: laminar flow and turbulent flow. Distributive mixing is difficult in laminar flow, while dispersive structural change can result from either laminar or turbulent flow. In kinetic mixing, agglomerates of immiscible nanoparticles or aggregates on the nanoscale are dispersively broken apart in proportion to the accumulated strain. Parallel to this structural change, turbulent flow, related to the Reynolds number, convectively redistributes the nanoparticles or aggregates. This redistribution optimally leads to the formation of macroscopic filler networks completing a structural hierarchy necessary for ionic and electrical conductivity, tear strength, and modulus enhancement. Both distribution and dispersion depend on the velocity of flow, but they have inverse dependencies on the flow gap size in the simplest geometry. We have adapted the random phase approximation and the van der Waals model to understand kinetic dispersion and distribution in polymer nanocomposites. |
Friday, March 10, 2023 12:06PM - 12:18PM |
Z05.00004: Scaling of near-interface dynamics resolved through broadband dielectric spectroscopy with a designed dielectric marker system Shiwang Cheng, Ruikun Sun, Xiaobing Zuo, Xue-Hui Dong Polymers at the interface can exhibit profound alterations in dynamics and mechanical properties compared with the bulk. However, deficiencies in the quantification of gradients of interfacial dynamics impose grand challenges and generate much confusion in the understanding of interfacial dynamics and their connection with the bulk glass transition. In this work, we demonstrate a new dielectric marker system that can be precisely positioned at distance on the order of away from the interface. Broadband dielectric spectroscopy (BDS) is employed to quantify the structural relaxation of the dielectric marker, which reflects salient features of the interfacial dynamics. The ratio of the structural relaxation of the dielectric marker, τd, and the segmental dynamics of polymers away from the interface, τb, follows a power law of τd/τb ~ τb-0.1 over a wide range of temperatures before a deviation is observed at low temperatures approaching the glass transition temperature of the polymer. Implications of the power law observation will be discussed in the presentation. |
Friday, March 10, 2023 12:18PM - 12:30PM |
Z05.00005: Understanding How Grafted Chains Create a Gradient in Local Glass Transition Tg(z) in the Athermal Polystyrene-Silica System James H Merrill, Connie B Roth Surfaces with grafted polymer chains are of fundamental interest to the field of nanocomposites due to their widespread use in controlling dispersion of nanoparticles and likely perturbing local material properties of the matrix. Developing understanding in these materials is limited by the experimental difficulty of measuring how local properties are altered near interfaces. We focus on a model athermal system of polystyrene (PS) matrix chains intermixed with grafted PS chains at a silica interface in a planar film geometry. We investigate how the local glass transition temperature Tg(z) profile near the silica interface is altered by the presence of grafted chains of different lengths using a localized fluorescence method. Right at the silica interface, the Tg(z=0) of the pyrene-labeled PS matrix chains is found to be elevated by approximately 45 K relative to bulk Tg, regardless of grafted chain length and grafting density spanning the mushroom-to-brush transition regime. The independence of Tg(z=0) on these factors suggests that the mechanism for this Tg increase likely involves pinned chain ends inducing locally higher activation barriers for alpha relaxation, in a manner similar to ionomers, vitrimers, and other associating polymers. |
Friday, March 10, 2023 12:30PM - 12:42PM |
Z05.00006: Uncovering the Physical Mechanisms by Which Surface Bound Chains Can Increase the Local Glass Transition of Polymer Matrices Connie B Roth, James H Merrill, Michael F Thees The presence of grafted or adsorbed chains to the surface of nanoparticles is central to our understanding of reinforcement of polymer nanocomposites. However, how these different types of surface bound chains alter the local material properties of the matrix is still unclear. By comparing and contrasting how and when different adsorbed and end-grafted chains alter the local glass transition temperature Tg(z=0) of matrix chains intermixed with these surface bound chains, we uncover two mechanisms by which surface bound chains can increase the local Tg of the matrix. Fluorescence is used to study the local Tg(z=0) of unattached pyrene-labeled PS chains as a function of intermixing time with surface bound PS chains in a model system with a single planar interface. Our efforts are focused on an athermal system of polystyrene (PS) matrix chains intermixed with either adsorbed or grafted PS chains on silica surfaces, making these mechanisms entirely topological in origin. Starting from known pre-adsorbed layers, we can distinguish between the impact of threading small tight loops versus large fluffy loops, and tails versus end-grafted chains. |
Friday, March 10, 2023 12:42PM - 12:54PM |
Z05.00007: Atomistic Simulation Studies of Polymer / Silica Nanocomposites Anastassia Rissanou, Alireza F Behbahani, Albert J Power, Patrycja Polinska, Craig Burkhart, Vagelis Harmandaris The conformations and the dynamics of polymer chains in polymer/silica nanocomposites are studied through atomistic molecular dynamics simulations. Two polymers have been utilized: A) Poly(butadiene), where the effect of the stereochemistry of PB chains is addressed by simulation of cis-1,4-PB/silica and trans-1,4-PB/silica nanocomposites. The model systems contain 30wt % silica nanoparticles. The dimensions of PB chains, excluding a small fraction of chains that wrap around the NP, are not affected. The dynamics of PB chains in the nanocomposites is very heterogeneous and a coupling between the dynamics and the conformation of PB chains is observed. B) Poly(ethylene oxide), where the effect of spatial confinement, induced by the nanoparticles on the polymer structure and dynamics is studied. Investigation of the static properties of the nanocomposites reveals a heterogeneous polymer density layer at the vicinity of the interface. For small volume fraction of silica nanoparticles, the polymer dynamics is consistent with the presence of a thin adsorbed layer of slow dynamics which attains the bulk dynamics far away from the nanoparticle. For high volume fraction of nanoparticles (strong confinement) the dynamics of all polymer chains are predicted slower than that in the bulk. |
Friday, March 10, 2023 12:54PM - 1:06PM |
Z05.00008: Glass transition and viscoelastic properties of polymer nanocomposites with integrated interface design Shalin Patil, Ruikun Sun, Xiaobing Zuo, Xuehui Dong, Dongdong Zhou, Shiwang Cheng Polymer nanocomposites (PNCs) are important lightweight materials with tunable functionalities that have been widely used in energy, environment, medication, and infrastructure. It has been proposed more than 20 years ago that controlling the interface of PNCs can lead to a rational design of PNCs with desired macroscopic properties. Two decades of active research have not been able to achieve the goal of the precise design of interfaces in PNCs. In this contribution, we combine chemical synthesis and interface design for new types of polymer-nanoparticle hybrids. With a combination of broadband dielectric spectroscopy, differential scanning calorimetry, and rheology, we show the glass transition and viscoelastic properties of the polymer-nanoparticle hybrids can be rationally tuned to the extent not accessible in other types of polymer nanocomposites. These new results could lead to alternative strategies of interface design of polymer nanocomposites for desired macroscopic properties. |
Friday, March 10, 2023 1:06PM - 1:18PM |
Z05.00009: Polymer Infiltration Kinetics Inside Nanoporous Gold: Effect of Molecular Weight and Polymer-Gold Interaction Energy Weiwei Kong, Anastasia Neuman, Robert A Riggleman, Russell J Composto Polymer composites are widely studied because they combine the best properties of the filler, typically inorganic, and matrix polymer. Usually, polymer nanocomposites (PNC) are fabricated by adding inorganic nanofillers to a polymer matrix. However, high loading is difficult due to particle aggregation followed by kinetic arresting of the morphology. In this work, a high-filler (ca. 50 vol%) PNC is created by infiltrating polystyrene (PS) or poly(2-vinylpyridine) (P2VP) into a nanoporous gold scaffold exhibiting a bicontinuous structure with nanoscale pores. Infiltration occurs through capillary forces by heating PS (P2VP) above its glass transition temperature. If infiltration is dictated by reptation, the infiltration time should scale as MW3.4. However, in our studies, polystyrene infiltration time is faster than expected, scaling as MW1.7. We have also observed that P2VP, which has an affinity with gold, infiltrates at a slower rate when compared with a similar MW as PS. To investigate the enhanced kinetics observed within nanopores, molecular dynamics is used to simulate capillary rise infiltration into bicontinuous nanoporous. The impact of polymer-surface interactions, pore size, chain length, and degree of entanglement are explored. Aside from the enhanced kinetics, the interconnected structure of these composites could facilitate high ion (electron) conductivity, thus enabling enhanced performance for batteries and flexible electronics. |
Friday, March 10, 2023 1:18PM - 1:30PM |
Z05.00010: Tube Dilation in Polymer Composite Melts by Oligomer Addition Yi Feng, Pinar Akcora Dispersion of attractive nanoparticles in polymer melts is critically important for enhancing mechanical properties of nanocomposites. Adding oligomers into nanocomposites enables their easy processability, particularly at high particle loadings. Here, we prepared a series of plasticized poly(methyl acrylate) (PMA)-SiO2 (15 nm in diameter) nanocomposites at various oligomer volume fractions at the confined and unconfined particle limits. We observed that as oligomer amount increased in composite at the unconfined state, plateau modulus and terminal relaxation time decreased, whereas entanglement relaxation increased only slightly, which led to a decrease in the apparent entanglement density. At the confined state (with 13.8 vol% loading), the nanoparticle entanglement at terminal region predominated with oligomer addition. The dilation scaling exponent of GN is found to be 2.3 and 4 for loadings at 13.8 vol% and 6 vol%, respectively. In summary, we demonstrate that adding nanoparticles into polymer melt shrinks the host chain tube diameter by nanoparticle induced geometrical confinement; and oligomer inclusion increases the entanglement molecular weight of the confined host chains, hence, enlarges the reptation tube diameter. By combining the tube shrinkage and dilation effects of nanoparticles and oligomer, the plasticized polymer composites at confined states with enhanced fluidity is achieved. |
Friday, March 10, 2023 1:30PM - 1:42PM |
Z05.00011: Gelation dynamics during photocrosslinking of polymer nanocomposite hydrogels Michael C Burroughs, Tracy H Schloemer, Daniel N Congreve, Danielle J Mai Polymer nanocomposite hydrogels exhibit mechanical properties that depend on material composition and processing route. The gelation kinetics of network-forming polymer solutions in the absence and presence of silica-coated nanocapsules were investigated using in situ dynamic rheology measurements. Network-forming polymers comprised either 4-arm or 8-arm star polyethylene glycol (PEG) with terminal anthracene groups, which dimerize under irradiation with ultraviolet (UV) light. Upon UV exposure, 4- and 8-arm PEG-anthracene solutions exhibited rapid gel formation as indicated by the crossover from liquid-like to solid-like behavior during in situ small-amplitude oscillatory shear rheology. Adding nanocapsules to PEG-anthracene solutions resulted in faster gelation than nanocapsule-free PEG-anthracene solutions with equivalent effective polymer concentrations. The final elastic modulus of nanocomposite hydrogels increased with nanocapsule volume fraction, signifying synergistic mechanical reinforcement by nanocapsules. Overall, these findings quantify the impact of nanocapsule addition on the gelation kinetics and mechanical properties of polymer nanocomposite hydrogels, which are promising materials for applications in optoelectronics, biotechnology, and additive manufacturing. |
Friday, March 10, 2023 1:42PM - 1:54PM |
Z05.00012: Spatially resolving energy dissipation in molecular dynamics of polymer nanocomposites Pierre Kawak, Harshad Bhapkar, David S Simmons Compared to nanoparticle-free elastomers, elastomeric nanocomposites have a larger toughness and feature an unusual mechanical response. This reinforcement is linked to an enhanced ability of nanocomposites to dissipate energy. Despite these materials' prevalence, the molecular mechanisms controlling this reinforcement remain poorly understood. In an effort to resolve this, here we describe a new approach to quantifying the location of dissipation in molecular dynamics simulations of nanoparticle-filled melts of bead springs. We describe analyses of our data that differentiate between multiple hypothesized mechanisms of enhanced dissipation in elastomeric nanocomposites. A better understanding of the origins of enhanced dissipation will lead to better lifetime prediction of many industrial products and enable new materials combining toughness with targeted functionalities such as high or low thermal or electrical conductivity, permeability, or ion conductivity - advances relevant to energy storage, thermal management, and separations. |
Friday, March 10, 2023 1:54PM - 2:06PM Author not Attending |
Z05.00013: Role of growing nanoparticle architecture on dewetting of polystyrene thin films Mithun Chowdhury, Jotypriya Sarkar, Fariyad Ali, Mithun Madhusudanan, Anindya Dutta, Sivasurender Chandran The flow properties and performance of polymer films have attracted significant intellectual and technological interest. It is well known that the dispersion of nanoparticles enhances the range of properties that polymers have to offer. While there are many reports exist on spherical nanoparticles, our understanding of the role of other complex architectures is only limited. Motivated by this lacuna, we report the dewetting dynamics of polystyrene films incorporated with CdSe nanotetrapods with variable arm lengths. Results were compared with films incorporated with CdSe quantum dots. In line with the earlier reports, the addition of CdSe quantum dots slowed down the dewetting of polymer nanocomposite (PNC) films. However, intriguingly, the addition of CdSe nanotetrapods resulted in enhancement of dewetting and the extent of enhancement scaled with the arm length of the tetrapods. These results reveal the importance of nano-architecture on the stability and in turn the performance of polymer films. We tentatively interpret the results via the differences in the phase separation induced by the architecture of the nanoparticles. |
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