Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P52: Polymer Nanocomposites III: Polymer Blends and SolutionsFocus
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Sponsoring Units: DPOLY Chair: Robert Ferrier, Univ of Pennsylvania Room: BCEC 253B |
Wednesday, March 6, 2019 2:30PM - 3:06PM |
P52.00001: Chemical and Dynamic Heterogeneities in Interfaces for Adaptive Polymer Nanocomposites Invited Speaker: Pinar Akcora It is well-known that particle-polymer interactions strongly control the binding and conformations of adsorbed chains on particles. Interfacial layers around nanoparticles consisting of adsorbed and free matrix chains have been extensively studied to reveal their contribution to the overall thermal and mechanical behavior of nanocomposites. Using miscible polymers of different chemistries as adsorbed and matrix layers in composites, the interfacial layer dynamics, hence the mechanical properties can be modulated unusually. We recently showed that when glass transition temperature difference between adsorbed and matrix polymers were large and polymer-polymer interactions were neutral, they reversibly stiffened with temperature. In this talk, I will present the extent of chemical heterogeneity of interfacial layers in adsorbed and polymer-grafted nanoparticles and discuss the role of interfacial layer mixing and chain conformation on the mechanical properties. Low glass-transition temperature composites with different matrix polymers [poly(vinyl acetate), poly(methyl acrylate) and poly(ethylene oxide)] will be discussed with particles of different surface chemistry; and polymers with different architectures. Interfacial layer design strategies in polymer nanocomposites will be outlined. These dynamic and chemical heterogeneities in interfacial layers can be used to design mechanically adaptive polymer nanocomposites. |
Wednesday, March 6, 2019 3:06PM - 3:18PM |
P52.00002: Coexistence Curve and Theta Temperature of Polymer Grafted Nanoparticle (PGN) Solutions Sarah Izor, Tony Dagher, Chris Grabowski, Ali Jawaid, Kyoungwon Park, Richard Vaia PGNs are emerging as an enabling technology, not only for nanocomposite formulation, but also for separations, energy storage, devices and coatings. Their tunability arises from the modularity of the hard-soft architecture, and understanding its impact on phase behavior in small molecules is crucial to fabrication and processing. Unfortunately, minimal data or theoretical insight is available; or how PGNs relate to the role of macromolecular architecture on solution phase behavior. Herein, we discuss the upper critical solution coexistence curve and theta temperature (Θ) of polystyrene (PS)-grafted Au-nanoparticles in cyclohexane. As molecular weight of the PS graft increases (20→50kDa), the coexistence curve shifts to higher temperatures (e.g. Tc~12→20oC @ 10nM (Φ~3e-5)), as determined by spectroscopy, dynamic light scattering, and x-ray scattering. Θ, estimated from extrapolating the low concentration region of the co-existence curve, also increased with graft size (Θ~25–27oC). Overall, these values are less than prior reports of PS stars (Θ~30oC) and linear chains (Θ~33oC ). Understanding the macroscopic and mesoscopic solution behavior of these soft colloids in context to structured macromolecules and curved brushes is essential to their future development. |
Wednesday, March 6, 2019 3:18PM - 3:30PM |
P52.00003: Simulating Nanoparticle Dynamics in Semidilute Polymer Solutions Renjie Chen, Ryan Poling-Skutvik, Arash Nikoubashman, Michael P Howard, Sergei Egorov, Jacinta Conrad, Jeremy C Palmer The dynamics of polymers and particles in nanocomposites are of great interest in materials processing. Particle mobility is well described by the generalized Stokes-Einstein relation when the particles are much larger than the polymers, but less understood when it comes to smaller or comparable sized particles. We investigate this smaller sized regime using advanced particle-based simulation techniques, with the multi-particle collision dynamics (MPCD) scheme modeling solvent-mediated hydrodynamic interactions. We demonstrate that the translational center-of-mass motions of both particles and polymers are sub-diffusive on short times before transitioning into the diffusive regime, and the highly correlated sub-diffusive exponents suggest that not only local polymer relaxations but also polymer center-of-mass motions play a role in the coupling between the dynamics of polymers and nanoparticles. Finally, we perform simulations tuning flexibility of the polymers, and as the persistence length increases, the particle dynamics become more sub-diffusive and decouple from the dynamics of the polymer chain center-of-mass. |
Wednesday, March 6, 2019 3:30PM - 3:42PM |
P52.00004: Interphase structures and dynamics near nanofiller surfaces in polymer solutions Tadanori Koga, Deborah Barkley, Maya Endoh, Michihiro Nagao, Takashi Taniguchi, Jan-Michael Carrillo, Bobby G Sumpter, Maho Koga, Tomomi Masui, Hiroyuki Kishimoto We report the structures and dynamics of hydrogenated polybutadiene (PB) chains bound to carbon black nanoparticle surfaces in polymer solutions composed of deuterated PB and deuterated toluene using small-angle neutron scattering and neutron spin echo techniques together with molecular dynamics (MD) simulations. The experimental results showed that the swollen bound chains exhibit the so-called breathing dynamics at polymer concentrations (c) below and above the overlap polymer concentrations. Interestingly, the collective dynamics slowed down by a factor of 2 compared to that in pure d-toluene when the chain lengths of the bound and matrix polymer are equal. However, when the free polymer chains were longer than the bound chains, the decrease in collective dynamics was not as significant. MD simulations showed that the matrix chains, whose length is equal to that of the bound chains, can be accommodated in the bound layer effectively and are “strangulated” by the bound chains, while the longer matrix chains only partly penetrate into the bound chains and the diffusion behavior was hardly affected compared to that in bulk. |
Wednesday, March 6, 2019 3:42PM - 3:54PM |
P52.00005: Dynamics of polymer-grafted nanoparticles controlled by soft confinement Ali Slim, Ryan Poling-Skutvik, Jacinta Conrad, Ramanan Krishnamoorti The efficacy of polymer-grafted nanoparticles (PGNPs) in applications depends on their transport within complex soft matrices featuring heterogeneities similarly sized to the PGNPs. Further, the deformability of the grafted polymers leads to soft interactions that may alter the dynamics, depending on the relative size of the grafted polymer and particle core. When the radius of gyration Rg of grafted polymer is much smaller than NP radius RNP, dynamics of PGNPs are expected to be similar to a hard sphere. Conversely, when Rg is much larger than RNP, PGNPs behave like a dendritic polymer or a star. In the intermediate regime where Rg and RNP are comparable, the structure and dynamics become influenced by both the hard (NP-NP) and soft (polymer-polymer) interactions. This regime is not well understood. Using a “grafting-to” method, we attach linear polystyrene chains to comparably sized spherical particles and disperse them in polystyrene dissolved in 2-butanone. We probe the structure and dynamics of our system using a combination of neutron and X-ray scattering. Our results show that grafted corona compresses and dynamics deviate from predictions of hard spheres in polymer solutions, suggesting an introduction of a soft potential due to grafted-free polymer interactions. |
Wednesday, March 6, 2019 3:54PM - 4:06PM |
P52.00006: Initial solvent driven non-equilibrium behavior of polymer nanocomposites with varying size ratios between nanoparticles and polymers Sol Mi Oh, Mozhdeh Abbasi, Kay Saalwaechter, So Youn Kim The adsorbed polymer layer near particle surface is important in polymer nanocomposites (PNCs) as it controls particle stability and resulting polymer properties. Therefore, extensive studies have been carried out to characterize the structure of adsorbed polymers and detailed adsorbed polymer-particle interactions; the adsorbed polymer near nanoparticle surfaces is known to have different mobility and conformation from the polymer in bulk. However, most of studies are discussed in their equilibrium states although polymers and nanoparticles may not reach the equilibrium state during the processing PNC. Processing of PNC requires initial mixing of polymer and particles in solutions and subsequent solvent evaporation; thus, polymers are often kinetically trapped because of their slow dynamics. Here, we investigate the role of initial casting solvent on the adsorption layer at interfaces and the resulting rheological property of PNCs where we systemically vary the size ratios between particles and polymers and show the casting solvent changes the thickness of immobilized polymer layer and polymer conformation on nanoparticle surfaces. |
Wednesday, March 6, 2019 4:06PM - 4:18PM |
P52.00007: Solvent-Induced Self-Assembly of Triblock Copolymers for Creating Polymer Nanocomposite Gels Chao Lang, Yifan Xu, Jacob A LaNasa, Manish Kumar, Robert Hickey The self-assembly of ABA triblock copolymers has been a focus of many studies over the years because of their possible applications in thermoplastic elastomers, solid electrolytes, and drug delivery systems. Triblock copolymers exhibiting ABA-type polymer architectures will self-assemble into either flower-like micelles or physically-crosslinked gel networks when added to B-block selective solvent. Although the two final states, micelles and gels, are well-established, controlling the self-assembly process to design specific nanostructures, while incorporating inorganic nanoparticles has yet to be fully established. Here, we present a recently developed method for creating nanostructured nanocomposite hydrogels by quickly injecting a solution containing ABA amphiphilic triblock copolymers and hydrophobic nanoparticles into water. During the ABA polymer/nanoparticle solution injection process, the nanoparticles aggregate within the physically-crosslinked hydrophobic A-block domains. By adding hydrophobic gold nanoparticles to the initial polymer solution, we are able to incorporate plasmonic properties into the nanostructured gels. The research presented here highlights the great potential in kinetic manipulation of self-assembled structures for making polymer nanocomposite gels. |
Wednesday, March 6, 2019 4:18PM - 4:30PM |
P52.00008: Nanoparticle Jamming at Liquid Interfaces Studied by In Situ Scanning Electron Microscopy Yige Gao, Paul Kim, Satyam Srivastava, Alexander Ribbe, Thomas Russell, David Hoagland Functionalized with polymer ligands, nanoparticles can segregate to liquid interfaces, where their two-dimensional organization and dynamics depend on nanoparticle areal fraction. Here, these organization and dynamics were imaged for PEGylated silica nanospheres on ionic liquids, the latter’s nonvolatility facilitating high resolution scanning electron microscopy at vacuum. An in situ liquid cell varied surface area and thereby areal fraction, and particle interactions were well approximated as those of hard spheres. A focus was high areal fraction nanoparticle mixtures approaching and/or exceeding the threshold for jamming; such mixtures were prepared for nanospheres of different diameter and nanospheres mixed with nanorods, and in both cases, composition was varied. By image analysis, quality of mixing and nanoparticle organization were assessed through orientational and translational order parameters. For uniform nanospheres, when compressed beyond jamming, surface wrinkling and buckling were observed, and when held jammed for large times before decompression, cracking was noted; throughout the imaging, individual nanospheres could be tracked to the resolution of a few nanometers. |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P52.00009: Self-assembly of Janus rods in binary blends of polymers. Part I: phase behavior under equilibrium Shaghayegh Khani, Felipe Leis Paiva, Arman Boromand, Veronica Calado, Argimiro Secchi, Joao Maia Janus rods due to their shape anisotropy and amphiphilic nature result in superior properties when incorporated into multi-phase polymer systems. Self-assembly of these particles at the interface of binary polymer blends can provide a means for fabrication of advanced functional materials. In this presentation we will discuss the interplay between the entropic and enthalpic factors that determine the self-assembled structure of Janus rods at the interface of two immiscible liquids. We have performed molecular simulations to investigate the role of individual parameters. Janus rods orientation is controlled by the entropic factors such as aspect ratio and concentration as well as the interfacial energy which also has consequences on the dynamics. Their interfacial assembly is also shown to be highly influential in altering the phase separation process in binary polymer blends. Janus rods exhibiting hexagonally-packed, liquid crystalline-like structures favor faster phase separation kinetics, while Janus rods of higher aspect ratio that are tilted at the interface aggregate side-by-side; are able to hinder phase separation kinetics. |
Wednesday, March 6, 2019 4:42PM - 4:54PM |
P52.00010: Self-assembly of Janus rods in binary blends of polymers. Part II: phase behavior under shear flow and relaxation Felipe Leis Paiva, Shaghayegh Khani, Arman Boromand, Veronica Calado, Argimiro Secchi, Joao Maia Janus particles are highly active at the interface of immiscible fluids and thus they can self-assemble into different structures when incorporated into multiphase systems. In Part I, we performed mesoscale Dissipative Particle Dynamics simulations to investigate the influence of individual parameters on the structures formed by Janus rods at the interface of two immiscible liquids. In particular, we showed how interfacial orientation and self-assembly of Janus rods are highly influential in controlling the phase separation process when added to a polymer blend. Moreover, we also monitor herein the microstructures formed by these systems under flow conditions and upon relaxation after flow cessation. We verified in our simulations various stabilizing effects provided by Janus rods of higher aspect ratio that present a tilted configuration at the interface. We also studied the Janus aggregate-breakup process during shear and how these interfacial aggregates rebuild upon flow cessation. The results of this study can be used for designing new approaches for directing nano-particles into desired morphologies by applying shear flow. |
Wednesday, March 6, 2019 4:54PM - 5:06PM |
P52.00011: Fabrication and Optical Properties of Polymer-Grafted Gold Nanorod Assemblies Jason Streit, Kyoungweon Park, Joon-Jae Yi, Richard Vaia Precise, large-scale assembly of polymer-grafted nanoparticles (PGNs) has shown great promise for the scalable manufacturing of sensors, energy storage devices, and photonic elements. Different than traditional ligand-coated nanoparticles, PGNs are stabilized by high molecular weight polymers at relatively low grafting densities. In this regard, PGNs behave as soft colloids, possessing favorable processing properties typical of polymer systems while still retaining the ability to pack into ordered structures. Herein, we demonstrate that large scale, highly uniform monolayer films of gold-polystyrene nanorods can be fabricated from PGN inks within a few seconds using a simple flow-coating technique. Using a combination of AFM, SEM, and GISAXS, we observe nanorod positional and orientational order dependent on coupling between processing conditions, polymer canopy, and surface energy. Additionally, optical extinction measurements reveal strong plasmonic coupling between the gold nanorods which can systematically be tuned by varying film morphology. With fundamental understanding of structure-processing relationships, we demonstrate optical notch filters using laser-induced reshaping of resonant nanoparticle subpoulations. |
Wednesday, March 6, 2019 5:06PM - 5:18PM |
P52.00012: Constructing conductive composites by spinodal decomposition of miscible polymer blends with graphene nanoplatelets Yangming Kou, Xiang Cheng, Chris W Macosko Conductive polymer composites (CPCs) enjoy broad industrial applications such as electrostatic discharge (ESD) protection. Herein, we construct CPCs by solution-blending graphene nanoplatelets (GNPs) in a miscible blend of poly(methyl methacrylate) (PMMA) and poly(styrene-co-acrylonitrile) (SAN). By inducing PMMA/SAN spinodal decomposition via annealing above the lower critical solution temperature (LCST), we obtain spatially regular, cocontinuous polymer domains where high aspect ratio GNPs preferentially localize within the SAN phase to form a conductive network. Compared to the traditional CPC manufacture approach of blending carbon black into a homopolymer, our approach lowers the percolation threshold required to enhance electrical conductivity. At 1 wt% GNP loading, our blend shows a bulk electrical conductivity of up to ~10–8 S/cm upon phase separation, suitable for ESD protection. To understand the structure-property relations of our CPCs, we develop TEM image analysis methods to quantitatively characterize the final PMMA/SAN/GNP blend morphology and GNP localization, allowing us to address important questions such as how the state of GNP dispersion within the blend affects the coarsening length scale and domain size distribution throughout the composite. |
Wednesday, March 6, 2019 5:18PM - 5:30PM |
P52.00013: Molecular dynamics simulation of spherical PEO brush: Curvature and Grafting Density Effect Elena Dormidontova, Udaya R Dahal Nanoparticle modification by polyethylene oxide (PEO) is commonly used to ensure nanoparticle solubility, dispersion and protection from undesirable interactions. Using atomistic molecular dynamics simulations, we studied spherical PEO brushes grafted to gold nanoparticles of different radii and with varying grafting densities. We analyzed the scaling behavior of the radial polymer volume fraction, which is found to follow the Daoud-Cotton model, except for low grafting density when PEO adsorption onto gold surface is observed. We also investigated PEO hydration in the spherical brush and determined the existence in the surface vicinity of a dehydrated or low hydration zone, which substantially expands with an increase of grafting density and/or decrease of nanoparticle radius of curvature. The implications for water exchange within the polymer brush and with the surrounding solution will be discussed. |
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