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 L64: Non-linear Polymers, Nanocomposites and BlendsFocus Live
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Sponsoring Units: DPOLY Chair: Erkan Senses, Koc University |
Wednesday, March 17, 2021 8:00AM - 8:36AM Live |
L64.00001: From Single-Chain Nano-Particles to All-Polymer Nano-Composites Invited Speaker: Arantxa Arbe Single-Chain Nano-Particles (SCNPs) obtained by intra-molecular cross-linking of linear macromolecules (precursors) are emerging soft nano-objects showing unique and remarkable physicochemical, rheological, and sensing properties as a result of their locally collapsed structure and ultrasmall size. During last years, we have studied the properties of systems based on SCNPs, including dilute and crowded solutions, bulks and all-polymer nano-composites with SCNPs as fillers (see, e. g. [1]). Diverse techniques have been combined, including small angle scattering, quasielastic neutron scattering and coarse-gained molecular dynamics simulations. Here we present the results on the properties of SCNPs in solution and how they develop upon crowding their environment, with the all-polymer nano-composite as limit. In solution, SCNPs obtained through standard synthesis routes adopt sparse morphologies. Crowding induces compaction of the SCNPs and in the limit case of the nano-composite, the observed conformation of the SCNP resembles that of a crumpled globule. Furthermore, the impact of the presence of SCNPs on the dynamics of an entangled polymer matrix is addressed. In the dynamically asymmetric system investigated, we observe a slowing down of the Rouse-like dynamics as well as a pronounced increase of the explored volume of the (faster) matrix linear chains. The latter effect is attributed to the particular topology (internal compartmentation) of the slow SCNP filler component. |
Wednesday, March 17, 2021 8:36AM - 8:48AM Live |
L64.00002: Estimation of mechanical properties of interfaces in polymer nanocomposites using molecular dynamics Abhishek Shandilya, Linda Feist Schadler, Ravishankar Sundararaman Response mechanisms of interfaces in polymer nanocomposites is unexplored territory. Brush-modified nanofillers interact with the polymer matrix to locally enhance the stiffness. Since experimental observations of such mechanisms is challenging, computer simulations have play an important role. This work demonstrates how molecular dynamics and self-avoiding random walk can model such mechanisms and estimate the local enhancement in mechanical properties. Self-avoiding random walk creates polymer chains either free or tethered to nanofiller surfaces. These model interfaces undergo shear and tensile load using molecular dynamics while local stress and displacement fields are measured. Local elastic modulus is then estimated from the measured stress and displacement. |
Wednesday, March 17, 2021 8:48AM - 9:00AM Live |
L64.00003: Effect of Polymer Topology on Microstructure and Dynamics in Polymer Blends Recep Bakar, Erkan Senses Structure and dynamics of miscible polymer blends have been extensively studied for linear chains in the past. In this work, we used poly(ethylene oxide)-poly(methyl methacrylate) blend system with varying polyethylene oxide architectures (linear, stars, hyper-branched and bottlebrushes) and compositions to explore the effects chain topology on miscibility, glass transition and segmental dynamics of the blend components. XRD results suggest that room temperature miscibility of these polymers can be extended by using compact star shaped polyethylene oxide instead of linear chains that crystallize above 35%. Temperature modulated DSC results showed two distinct glass transitions in intermediate compositions for all systems. The Tg results suggest the possibility to access a previously-unexplored intermediate regime between the conventional linear blends and nanocomposites with hard fillers. Finally, neutron backscattering and broadband dielectric spectroscopy studies unveil a non-monotonic dependence of segmental dynamics on the polymer compactness. |
Wednesday, March 17, 2021 9:00AM - 9:12AM Live |
L64.00004: Dispersion, Glass Transition and Dynamics in Nanocomposites with Non-linear Polymers Saeid Darvishi, Muhammad Anwaar Nazeer, Seda Kizilel, Erkan Senses We prepared nanocomposites of spherical nanoparticles and polymer matrices with various architectures (from linear to stars and hyper-branched) to understand the effect of polymer topology on the composite microstructure, thermal and rheological behavior. Two different sizes of nanoparticles and wide range of concentrations from a few percent up to fifty percent (by volume) were systematically investigated using DSC, rheology, static and dynamic light scattering, x-ray scattering, and neutron scattering. The results show that chain compactness is the key factor for determining the glass transition and the rheological behavior of these nonlinear polymer nanocomposites. Compact polymers induce less reinforcement compared to the loose linear chains due to less penetrability and weaker inter-chain entanglements of compact architectures. In all cases, the differences in mechanical reinforcement are amplified in the confined regime where the dynamics is controlled primarily by the surface bound polymers. These results are corroborated with the polymer segmental dynamics measured using quasielastic neutron backscattering. |
Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L64.00005: Large changes in the hydration and mechanical properties of dendritic phytoglycogen nanoparticles with chemical modification Michael Grossutti, John Dutcher Phytoglycogen is a glucose-based polysaccharide nanoparticle with a highly branched, dendritic architecture. We used ellipsometry at different relative humidities (RH) to compare the equilibrium RH-driven swelling of ultrathin films of native and chemically modified phytoglycogen, as well as dextran and hyaluronic acid. Our analysis allowed us to compare the hydration force decay length λ and bulk modulus K of the films. We also used attenuated total reflection infrared spectroscopy to investigate the hydrogen bond structure of the hydration water in the polysaccharide films. By combining ellipsometry and infrared spectroscopy, we find that structuring of the hydration water hydrogen bond network correlates with both λ and K.These measurements provide insight into the relationship between the hydration water structure and mechanical properties of polysaccharides, suggesting that a more ordered water hydrogen bond network leads to a shorter λ and larger K. Significantly, we find that chemical modification of phytoglycogen dramatically alters its hydration and mechanical properties, highlighting opportunities to tailor its properties for different applications. |
Wednesday, March 17, 2021 9:24AM - 10:00AM Live |
L64.00006: Influence of Polymer Topology on Glass-Formation Invited Speaker: Jack Douglas There is a growing interest in controlling the molecular topology of polymers to engineer the properties of materials for diverse technological applications and for the insights that topology variations can make into the nature of chain entanglement, polymer crystallization, glass-formation, etc. To gain insights into the influence of topological constraints on glass-formation, we perform molecular dynamics simulations on melts of star polymers having f equivalent arms, polymers with grafted side-groups, and knotted ring polymers having fixed minimal crossing number mc and examine basic thermodynamic and dynamic properties of these model glass-forming liquids as a function of their fundamental topological invariants, f and other branching induces and mc for the knotted polymers. We find that increasing topological complexity, as quantified by f and mc, leads to a tendency for polymers to adopt a more symmetrical and compact conformational shapes, a general tendency that also exists in solution. Topologically constrained polymers exhibit increasing rigidity with increased topological complexity, i.e., topological rigidification, a primary molecular factor influencing Tg and fragility. Increasing topological complexity in these melts allows us to progressively ‘tune’ these fundamental properties of polymeric glass-forming materials, indicating that the manipulation of polymer topology offers a powerful means to tune polymer material properties in their condensed state. The applicability of the string model of glass-formation in providing a unified description of these topologically complex fluids is explored. |
Wednesday, March 17, 2021 10:00AM - 10:12AM Live |
L64.00007: Isomeric and Non-isomeric Structures of ABm-type Hyperbranched Polymers: An Approach Using Combinatorics Surbhi Khewle, Ravi Anand Singh, Neeldhara Misra, Pratyush Dayal
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Wednesday, March 17, 2021 10:12AM - 10:24AM Live |
L64.00008: Field-theoretic simulations of core-shell bottlebrush copolymers Christian Tabedzki, Robert Riggleman The unique structure of bottlebrush polymers, featuring a linear polymer backbone grafted densely with polymer side-chains, allows for the creation of interesting and unique morphologies. By combining structurally dissimilar backbone and grafts, core-shell bottlebrushes serve as candidates for materials with unique combinations of properties, such as mechanically rigid backbones combined with conductive grafts, a combination which could be useful as membranes in battery applications. In this talk, we present a field-theoretic model for the structure of bottlebrush copolymers and explore how architecture alters the traditional block copolymer phase diagram. We accomplish this via our recently developed theoretically informed Langevin dynamics (TILD) package for LAMMPS, in which the non-bonded forces are calculated using density fields in lieu of particle-based interactions. The TILD simulations capture the fluctuating version of the model, which is compared to the analytic RPA predictions for the ODT boundaries. Finally, we provide insight into the changes in the chain conformations and relate them to the shifts in the phase boundaries we observe. |
Wednesday, March 17, 2021 10:24AM - 10:36AM Live |
L64.00009: When does a polymer chain become a soft nanoparticle? Jacob Fischer, Lu Han, Tomonori Saito, Mark Dadmun As the variety of nanoparticles increases, understanding the impact of particle deformability, morphology, and topology on its global properties becomes essential. With this in mind, we have synthesized soft polymeric nanoparticles ranging in crosslink densities of 0.1-10.7%. An interesting question arises with nanoparticles with such low crosslinking densities: at what point do these polymers transition from a molecule to a nanoparticle? Comprehensive analysis of small angle neutron scattering studies of these nanostructures in dilute solution provides structural characteristics that identify transitions from polymer chain-like behavior to particle-like behavior. These analyses include elucidating the Porod exponent in q-ranges that describe the interior structure of the nanoparticle, as well as analysis of dimensionless Kratky plots. These results show that PEHMA samples with crosslink density greater than ~ 0.81% present a particle like structure signified by a Porod exponent greater than 3, and clear presence of a peak in the Kratky plot. PS samples showed similar behavior, however a low molecular weight 0.81% crosslinking density sample exhibited clear chain-like characteristics suggesting that molecular weight may also influence morphological identity. |
Wednesday, March 17, 2021 10:36AM - 10:48AM Live |
L64.00010: Enhancing the Dielectric Breakdown Strength of Solid-State Polymer Capacitors by Chain End Manipulations Alamgir Karim, Maninderjeet Singh, Wenjie Wu, Mei Dong, David Tran, Karen L. Wooley, Nihar Pradhan, Dharmaraj Raghavan The need for high power density, flexible, pulsed power and lightweight energy storage devices requires the use of polymer film-based dielectric capacitors. The maximum energy storage density of a dielectric capacitor is proportional to the square of breakdown voltage. Chain ends contribute adversely to the electrical breakdown of polymer dielectrics at high electric fields. In this work, we enhanced the dielectric breakdown voltage and hence the energy density of the polymer capacitor by using well-ordered high molecular weight block copolymers (BCP), in which the chain ends are segregated to narrow zones. The well-ordered and easily processable BCP capacitors exhibit an energy density more than 5 J/cm3, which is higher than that of industrial used biaxially oriented polypropylene. Cyclic homopolymers (no chain ends) and linear homopolymers having chemistry-controlled chain ends also show enhanced dielectric breakdown strength, resulting in higher energy density compared to linear counterparts. These novel insights into manipulating chain end distribution such as in BCPs and with molecular topology to increase the energy density of polymers will address next-generation energy demands. |
Wednesday, March 17, 2021 10:48AM - 11:00AM Live |
L64.00011: Amphiphilic model gels composed of complementary tetra-functionalized star polymers Reinhard Scholz, Carolin Bunk, Lothar Jakisch, Frank Böhme, Michael Lang In this work, we compare the synthesis and structure of model networks built from tetra-PEG and tetra-PCL star polymer solutions with computer simulations. Covalent networks at stoichiometric conditions result from selective coupling of amine end groups on PEG branches with benzoxazinone end groups on PCL, for varying polymer volume fractions and molecular weights of the stars. |
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