Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B18: New Directions in Polymer Nanocomposites II: DynamicsFocus Recordings Available
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Sponsoring Units: DPOLY GSNP Chair: Robert Hickey, Penn State Room: McCormick Place W-184D |
Monday, March 14, 2022 11:30AM - 12:06PM |
B18.00001: Novel Polymer Nanocomposite Structures Created by Nanoparticle Jamming and Polymer Infiltration Invited Speaker: Russell J Composto Understanding the fundamental polymer science that govern structure-property relationships in polymer nanocomposites (PNCs) remains a key challenge. Herein, we discuss two new directions for controlling PNC morphologies and their resultant properties by (1) arresting nanoparticle (NP) dynamics and (2) infiltrating polymer into scaffolds. First, the interplay between surface enrichment, phase separation, and wetting in PNC films and resulting unique morphologies are investigated using a system of poly(methyl methacrylate) grafted NP (PMMA-NP) in a poly(styrene-ran-acrylonitrile) (SAN) matrix. For PNC films annealed in the one-phase region, surface enrichment of the lower surface energy component (PMMA-NP) occurs, with a homogeneous distribution of NPs remaining in the bulk of the film. In the two-phase region, wetting and phase separation occur simultaneously leading to a tri-layer structure, with two symmetrical PMMA-NP rich wetting layers sandwiching a SAN rich phase containing PMMA-NP pillars that span the two wetting layers. The ‘jammed’ morphologies lead to enhanced mechanical properties and increased thermal stability of the films. Second, a high-filler 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 upon heating PS (P2VP) above its glass transition temperature (Tg). PS and P2VP, having different affinities to the gold scaffold, exhibit different segmental dynamics inside the confined pores as measured through their Tg. The more attractive P2VP shows a 20°C increase in Tg while PS shows only a 6°C increase at comparable molecular weight. Two new approaches are presented that achieve precise control of the structure-property relationships in PNCs and have potential to lead to improved performance for solid polymer electrolytes and gas transport membranes. |
Monday, March 14, 2022 12:06PM - 12:18PM |
B18.00002: Connecting Microscopic Dynamics to Macroscopic Rheology in Dynamic Covalent Composites Grayson L Jackson, Joseph M Dennis, Neil D Dolinski, Michael R Van der Naald, Stuart J Rowan, Heinrich M Jaeger As compared to traditional polymer nanocomposites, incorporation of dynamic covalent chemistry at the filler-matrix interface leads to dynamic covalent composites (DCCs) with self-healing ability and improved stress relaxation. However, it is unclear how dynamic covalent bonds alter particle-scale structure and dynamics and whether these provides additional microscopic mechanisms for stress dissipation. Here, we investigate highly loaded DCCs comprising thiol-coated silica particles dispersed in a fluid matrix of ditopic benzalcyanoacetamide-based Michael acceptors. We explore how particle size and dynamic bond lifetime affect rheological stress relaxation and connect these to microscopic structure and dynamics measured by small-angle X-ray scattering (SAXS) and X-ray photon correlation spectroscopy (XPCS), respectively. We anticipate these structure-property relationships will furnish new handles by which to engineer the properties of stress-responsive composites at the molecular scale. |
Monday, March 14, 2022 12:18PM - 12:30PM |
B18.00003: Effect of Extreme Nanoconfinement and Polymer-Nanoparticle Interactions on the Thermodynamics of Polymer Blends in Dense Nanoparticle Packings Anastasia Neuman, Daeyeon Lee, Robert Riggleman Infiltration of polymer into the interstices of dense nanoparticle (NP) packings leads to the formation of highly loaded nanocomposites with superb mechanical and transport properties. Polymers in such nanocomposites are subjected to physical confinement which alters their glass transition temperature and dynamics. The impact of confinement on polymer blend thermodynamics, particularly within the pores of NP packings, is less understood. Here we present a computational study using self-consistent field theory to understand the thermodynamics of highly confined polymer blends in the interstices of NP packings. Two polymers that undergo macroscopic phase separation in bulk become miscible when subjected to extreme nanoconfinement and the strength of repulsion required to induce phase separation increases significantly as confinement increases. We also explore the impact of polymer-NP interactions on the equilibrium behavior of confined composites. This study shows that confinement alone strongly increases the window of miscibility of polymer blends without inducing any chemical alterations to the system. The ability to create miscible polymer nanocomposites with normally incompatible blends would unlock a myriad of novel properties and applications. |
Monday, March 14, 2022 12:30PM - 12:42PM |
B18.00004: Leaching-enabled capillary rise infiltration (LeCaRI) and lateral diffusion of poly(dimethylsiloxane) in nanoparticle packings R Bharath Venkatesh, Daeyeon Lee Capillarity-driven infiltration of polymers into the interstitial voids of nanoparticle packings provides a unique route to prepare highly filled nanocomposites. Additionally, the confinement of large polymer chains in nanopores of the packing alters the dynamics of polymers significantly from their bulk behavior. In this work, we induce infiltration of low glass transition polymers like polydimethylsiloxane (PDMS) from a gel network into the pores of silica nanoparticle packings by leaching-enabled capillary rise infiltration (LeCaRI). The amount of infiltrated polymer is governed by the interplay between two opposing factors: capillary pressure and capillary condensation of water. By using PDMS stamps with patterns, polymer infiltration can be limited to regions within the packing, creating patterned composites. Locally infiltrated polymer spreads laterally via surface diffusion. By tracking the spreading front via ellipsometry, mobility of chains under nanoconfinement can be inferred. We observe that high humidity leads to faster spreading of the polymers within the packings. Results on PDMS spreading behavior including rouse-like scaling of the diffusion coefficient with the molecular weight of the polymer will be discussed. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B18.00005: Measuring Nanoparticle Diffusion in Polymer Melts Using ToF-SIMS Kaitlin Wang, Russell J Composto, Karen I Winey Nanoparticle (NP) dynamics are important for understanding processing of polymer nanocomposites (PNCs) and tuning their membrane, optical, and mechanical properties. Previously, nanoparticle diffusion was measured with ion-beam spectroscopy and single-particle tracking methods that required highly specialized equipment and limited the range and resolution of diffusion measurements to ~500 nm. Here, we measure nanoparticle diffusion in strongly attractive PNC systems using time-of-flight secondary ion mass spectroscopy (ToF-SIMS) on length scales up to 20 μm, which is orders of magnitude larger than previous experiments. Tri-layer polymer-PNC-polymer samples were made, and the cross-section was measured to detect nanoparticle diffusion in polymer melts as a function of diffusion time, temperature, and NP loading. Raw ToF-SIMS data directly provide diffusion profiles that when fit to Fick’s 2nd law finite source to semi-infinite medium solution results in a diffusion coefficient. Our findings match previously reported diffusion coefficients. Our ToF-SIMS method is more accessible and promises to determine molecular weight, particle loading, geometry, and chemistry effects on NP diffusion. |
Monday, March 14, 2022 12:54PM - 1:06PM |
B18.00006: Nanoparticle Avalanches in Filled Rubber Dillon Presto, Suresh Narayanan, Mark D Sutton, Joshua Browns, Quang Ngo, Sergio Moctezuma, Mark D Foster Nanoparticle reinforced rubbers have broad commercial utility, such as use in tire tread technology. However, the complex microscale behavior of the filler particle network and the resulting macroscopic properties are not well understood. Recent X-ray Photon Correlation Spectroscopy (XPCS) experiments performed in-situ on rubbers under strain reveal previously undescribed filler network behavior which is not considered in current physical models of these materials. Rubbers under strain exhibit temporally heterogeneous dynamics, i.e. the particles which constitute the filler network show abrupt speeding up and slowing down, akin to the dynamics of granular systems such as sand and snowpack which exhibit avalanche-like behavior. These nanoparticle “avalanches” significantly influence macroscopic properties such as stress relaxation and the storage modulus of filled rubber. Further, the addition of silane coupling agents to filled rubber and resultant bound rubber layers generated on the filler particle surface strongly suppress the intermittency of the filler dynamics. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B18.00007: XPCS Study of Temporal Dynamic Heterogeneity in a Rubber Nanocomposite Mark D Foster, Dillon Presto, Suresh Narayanan, Joshua Brown, Quang Ngo, Sergio Moctezuma, Mark D Sutton In situ X-ray Photon Correlation Spectroscopy can be used to characterize the temporal heterogeneity in the dynamics of silica filler movement when a highly filled rubber nanocomposite is strained. After a step strain the motions of the filler particles and network do not necessarily develop in a temporally uniform way. The relaxation of the stress can involve sudden slowing down of the particle movement and sudden speeding up of the movement. There are various means of visualizing and describing this intriguing dynamic heterogeneity. The heterogeneity is seen to be less prevalent when a silane coupling agent is added to the rubber. Also, the character of the heterogeneity varies when the type of silica filler is varied. The variation in the intensity and duration of the heterogeneity with direction (e.g. strain direction vs. perpendicular to strain) can also be resolved. |
Monday, March 14, 2022 1:18PM - 1:30PM |
B18.00008: Dynamics of linear alternating polymer-nanoparticle hybrids Shiwang Cheng, Xue-Hui Dong, Dongdong Zhou, Ruikun Sun, Shalin Patil Compared with the linear viscoelastic properties of association polymers, the glassy dynamics of association polymers are much less understood. In this contribution, we study the influence of supramolecular structures on the structural relaxation and the glass transition of a new type of association polymers, the linear alternating polystyrene (PS)-polyhedral oligomeric silsesquioxane (POSS) hybrids (LAPH). The LAPH exhibits inter-connected flower-like micellar supramolecular structures. Broadband dielectric spectroscopy (BDS) and differential scanning calorimetry have been employed to probe the structural relaxation and the glass transition. The glass transition temperature of LAPH is comparable to the PS homopolymer with similar molecular weight of the PS block rather than the whole polymer hybrid chain. Moreover, the LAPH exhibits a much lower fragility index than the PS homopolymer. Since the nanoparticle-nanoparticle association time is much longer than the structural relaxation of the LAPH, one cannot explain the low fragility index of LAPH from the accessible configurational entropy. These observations suggest the supramolecular structures affect strongly the glass formation behaviors of LAPH. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B18.00009: Dynamics of polymer nanocomposites at large deformation Ruikun Sun, Shiwang Cheng, Xiaobing Zuo This work investigates the dynamics and mechanical properties of polymer nanocomposites (PNCs) at large deformation through a combination of small-angle x-ray scattering and rheology. Small-angle x-ray scattering showed clear evidence of the mismatch between the positional rearrangement of nanoparticles at the nanoscale and the macroscopic applied deformation field. The rheological measurements through uniaxial extension showed that PNCs and the neat matrix polymer share almost identical scaling between the overshoot stress and the deformation rates over an exceptionally wide range of stress and deformation rate, indicating negligible influences of the nanoparticles to the disentanglement dynamics. We explain these observations through the hydrodynamic effect of nanoparticles. |
Monday, March 14, 2022 1:42PM - 1:54PM |
B18.00010: 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 I Winey The use of polymer nanocomposites (PNCs) in long-term structural applications requires understanding the mechanisms by which nanoparticles (NPs) affect viscoelastic creep behavior in PNCs. Parameters of interest include NP size, loading, dispersion morphology, and polymer-NP interaction strength. In this study, we examine the creep behavior of silica/poly(2-vinylpyridine) (P2VP) nanocomposites consisting of 13 and 52 nm diameter silica NPs and 200 kg/mol P2VP. Polymer-NP interactions and dispersion quality are controlled by functionalizing the NPs with varying densities of octylsilane. Creep behavior is measured using an accelerated dynamic mechanical analysis (DMA) method and the results are correlated with polymer-NP interaction strength and dispersion. We find that smaller bare NPs delay creep failure by ~10x relative to the larger bare NPs. With octyl-capping, NP dispersion is reduced, shortening the time to creep failure in the small NP systems. For large NPs, the time to creep failure is unaffected by octyl-capping. These results suggest that the dominant reinforcement mechanism is the development of contiguous regions of slowed dynamics via percolated polymer-NP networks, which does not occur for the larger NPs, rather than individual polymer-NP interaction strength. |
Monday, March 14, 2022 1:54PM - 2:06PM |
B18.00011: Morphology and dynamics of Ionic Polydimethylsiloxane-Silica Nanocomposites Argyrios V Karatrantos, Clement Mugemana, Ahmad Moghimikheirabadi, Martin Kröger We designed ionic polydimethylsiloxane (PDMS)-silica nanocomposites from (cationic) ammonium-functionalized PDMS and (anionic) sulfonate-functionalized nanosilicas, with the aim of influencing the distribution and dispersion of the nanoparticles. The impact of the PDMS molecular weight, charge density and charge location on the distribution, dispersion of ionic nanosilicas and on the mechanical reinforcement of the nanocomposites is explored. Self-healing property arises from reversible ionic interactions located at the interface between PDMS matrix and nanosilicas. In addition, we use coarse grained equilibrium molecular dynamics to model ionic nanocomposites and to investigate polymer conformations, entanglements and dynamics for different loadings, for two types of charge-sequenced polymers at two different Bjerrum lengths. We calculate the lifetimes of temporary ionic crosslinks that are created between ionic nanoparticles and polymers. Non equilibrium molecular dynamics is used to investigate the stress - stress behavior, ionic crosslinks and entanglements under deformation. |
Monday, March 14, 2022 2:06PM - 2:18PM |
B18.00012: Kinetics of functional high density polymer nanocomposite formation by tuning enthalpic and entropic barriers. Jaydeep K Basu, Aparna Swain, Nimmi Das Anthuparambil, Sivasurender Chandran Recently various methods have been proposed to prepare high density functional polymer nanocomposites (PNCs) based on either penetration of high density nanoparticles in polymer matrix or capillary rise infiltration of polymer into a dense packing of nanoparticles. The key challenge is to attain high loading while maintaining dispersion to attain maximum possible benefit. Here, we discuss a facile method to prepare polymer grafted nanoparticle (PGNP) based high density functional polymer nanocomposites using thermal activation of a high density PGNP monolayer to overcome entropic or enthalpic barriers to insertion of PGNPs in underlying polymer films. We monitor the temperature dependent kinetics of penetration of a high density PGNP layer and correlate the penetration time to the effective enthalpic/entropic barriers. The experimental results are corroborated by coarse grained molecular dynamics simulations. Repeated application of the methodology used to insert nanoparticles by appropriate control over temperature, time and graft chain properties can lead to enhanced densities of loading in the PNC. Our method can be engineered to produce a wide range of high density PNC membranes for various possible applications including gas separation and water desalination. |
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