Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J34: Dillon Medal SymposiumPrize/Award
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Sponsoring Units: DPOLY Chair: Richard Register, Princeton University Room: 506 |
Tuesday, March 3, 2020 2:30PM - 3:06PM |
J34.00001: Structured Polymer Colloids by Flash NanoPrecipitation Invited Speaker: Rodney Priestley Colloids with internal and external structure have shown great promise in applications ranging from biosensors to optics to drug delivery, where the overall particle structure is paramount to performance. The growing demand for such nanomaterials motivates the development of a scalable processing platform for their production. Here, we demonstrate that Flash NanoPrecipitation (FNP), a rapid and inherently scalable colloid precipitation technology, can be used to prepare structured colloids from homopolymers, polymer mixtures and block copolymers. As revealed by a combination of experiments and simulations, by varying key process parameters and functional groups within the polymers, a range of structured colloids can be produced without any modification to the FNP process. Finally, in one application, we demonstrate how ionomer-based Janus colloids can be used to stabilize Pickering emulsions. |
Tuesday, March 3, 2020 3:06PM - 3:18PM |
J34.00002: Exploiting supramolecular associations in interpenetrating networks and elastomers LaShanda Korley Supramolecular interactions may hold the key to the development of network systems with tunable mechanics and modulated architecture, such as observed in the muscle protein titin. It is the dynamic nature of these physical associations that we have exploited in the design of tough supramolecular materials that super-impose covalent and non-covalent interactions to tailor tensile response. We have developed supramolecular elastomers and interpenetrating network (IPN) systems that probe the interplay of non-covalent and covalent interactions in structural organization and mechanical response. By tailoring physical associations via control of self-assembly and composition, we have demonstrated enhanced supramolecular dynamics driven by architecture and toughness enhancements due to phase behavior. Recently, non-covalent interaction strength, network regularity, and chemoresponsiveness have been utilized as handles to derive gradient materials and to induce actuation behavior. |
Tuesday, March 3, 2020 3:18PM - 3:30PM |
J34.00003: Droplet aggregates as model systems for connecting granular systems to continuum mechanics: how few is too few? Kari Dalnoki-Veress, Jean-Christophe Ono-dit-Biot, Johnathan Hoggarth In recent years we have developed a method to produce microscopic monodisperse oil droplets in an aqueous environment. With an attractive interaction between the droplets, monodisperse droplets form perfect crystalline aggregates, while a blend of small and large droplets allows us to prepare a disordered glass. By carefully tuning the adhesion forces between the droplets, the aggregates provide model systems for studying various physical phenomena that are not accessible by investigating molecular systems. Here I will provide a brief overview of experiments we have carried out to address two fundamental questions. How does a system transition from crystal to glass, when blending large and small droplets? And secondly, how does a system transition from a few particles, to many particles, where continuum models are valid. These experiments enable us to study the transition from few-to-many, and crystal-to-glass. |
Tuesday, March 3, 2020 3:30PM - 3:42PM |
J34.00004: Evolution of polymer conformation during droplet-to-particle formation Joao Cabral Motivated by ubiquitous spray drying approaches in the manufacturing of polymer particles and composites, we experimentally investigate the mechanism and kinetics of particle formation by controlled solvent extraction and evaporation of polymer solution droplets. We employ microfluidics and acoustic levitation to precisely handle the polymer droplets in controlled environments. We then couple our experimental platforms with small angle neutron scattering (SANS) to elucidate chain conformation under equilibrium conditions and along the particle formation pathway, supplemented by optical and electron microscopies that characterise overall external and internal particle morphologies. We examine three model systems: two water-soluble polymers, poly(vinyl alcohol) and semi-flexible polyelectrolyte sodium carboxymethyl cellulose, and high-glass transition, semicrystalline poly(2, 6-diphenyl-p-phenylene oxide). We investigate the roles of composition (with respect to c* and c**), molecular mass, viscosity, and salt addition. Equipped with this knowledge, we then predictively design and fabricate polymer particles and capsules with prescribed dimensions, shape, porosity, microstructure and dissolution profile, and discuss complementarity with ‘flash nanoprecipitation’ methods. |
Tuesday, March 3, 2020 3:42PM - 3:54PM |
J34.00005: Gelation of Methylcellulose Chains Versus Methylcellulose Fibers Timothy Lodge, Sveta Morozova, S. Piril Ertem, McKenzie Coughlin, Frank S Bates Upon heating in aqueous solutions, MC reversibly self-assembles into ~ 7–10 nm fibrils that percolate, resulting in physical gelation. We have chemically crosslinked both MC solutions at room temperature, and MC physical fibril gels at 80 °C, and compare the swelling and shear modulus properties. Hydroxyl moieties on MC were substituted with allyl groups, with a degree of substitution of about one pendant double bond per nine anhydroglucose repeat units. The allyl groups undergo crosslinking in the presence of a photo-initiator and UV light. Chemically crosslinking MC fibril gels at 80 °C results in opaque solid materials, and locks in the fibril structure, which persists even on cooling to room temperature. The shear modulus G' increases modestly with temperature, and the volume fraction scaling is consistent with previous results for fibril gels. On the other hand, chemically crosslinking MC solutions at room temperature leads to clear, solid hydrogels which no longer form fibrils. Instead, swelling measurements show that the MC gels shrink by an order of magnitude when the temperature is increased from 25 °C to 80 °C. The equilibrium polymer volume fraction and G¢ are consistent with established theories for crosslinked polymer chains. |
Tuesday, March 3, 2020 3:54PM - 4:06PM |
J34.00006: Non-linear Deformation of Polymer Grafted Nanoparticles Ramanan Krishnamoorti Linear viscoelastic properties of polymer grafted nanoparticles indicate that the systems behave like elastic solids with elastic moduli that scale with concentration of the nanoparticles and with the molecular weight of the polymer chains grafted to the particles. We studied the non-linear viscoelastic properties of such polymer grafted nanoparticle melts through a systematic examination of steady shear behavior and the recovery after cessation of flow. The local re-arrangement of particles and the formation of slip-planes and the regenearation of local order upon cessation of flow dominate the flow and recovery properties of these nanocomposites. |
Tuesday, March 3, 2020 4:06PM - 4:18PM |
J34.00007: Harnessing nanoparticle vibrations to probe surface mobility and glass transition Eunsoo Kang, Bartlomiej Graczykowski, George Fytas, Katelyn Randazzo, Rodney Priestley Advances in polymer nanoparticle synthesis and assembly techniques have enabled new applications, from drug delivery carriers to novel coatings. However, the polymer dynamics, especially at the particle surfaces of architected colloids, must be understood in order to realize their potential. Brillouin light spectroscopy as a direct probe of the particle surface mobility via nanoparticle vibrations, reveal the correlation between the glass transition behavior and surface dynamics and the presence of a low frequency mode extremely sensitive to particle-particle interactions. These are enabled by the surface mobility which can be engineered by different shell architecture layers. We demonstrate that a thin shell layer is able to eliminate the effect of enhanced particle surface mobility and drastically modify the structure of nanoparticle assembly. Surface mobility is strongly affected by the application of pressure modifies enabling a facile soldering of the colloidal film. |
Tuesday, March 3, 2020 4:18PM - 4:30PM |
J34.00008: Non-Equilibrium Effects in Polymer Nanocomposites Sanat Kumar We have previously shown that the polymer nanocomposites, especially those that involve pure polymer-grafted nanoparticles,have a solid-like mechanical response with extraordinarily long relaxation times. In parallel with these efforts here we show that the structure and dynamics of these materials (and apparently for all nanocomposites) relax over similarly long times. The implications of these results for our understanding of this class of hybrid materials will be explored. |
Tuesday, March 3, 2020 4:30PM - 4:42PM |
J34.00009: Programming surface energy driven Marangoni convection to pattern polymer films Christopher Ellison The Marangoni effect describes how fluid flows in response to gradients in surface energy. We recently developed a method for photochemically preprograming surface energy patterns in glassy polystyrene (PS) thin films. Patterned UV irradiation through a mask selectively dehydrogenates PS, increasing surface energy in the UV exposed regions compared to the unexposed regions. After heating the film to the liquid state, transport of polymer occurs from regions of low surface energy to regions of high surface energy. This method can be harnessed to rapidly manufacture polymer films possessing prescribed three-dimensional topographies reflective of the original light exposure pattern without solvent washes or etching procedures. To better understand this phenomenon, a theoretical model will be presented that reveals the physics of this process, its limits and ways to apply it efficiently for various target metrics. |
Tuesday, March 3, 2020 4:42PM - 4:54PM |
J34.00010: Influence of Pore Morphology on the Diffusion of Water in Triblock Copolymer Membranes Dipak Aryal, Michael P Howard, Rituparna Samanta, Segolene Antoine, Rachel A Segalman, Thomas Truskett, Venkatraghavan Ganesan Understanding the transport properties of water in self-assembled block copolymer morphologies is important for furthering the use of such materials as water-purifying membranes. In this study, we used coarse-grained dissipative-particle-dynamics (DPD) simulations to clarify the influence of pore morphology on the self-diffusion of water in linear-triblock-copolymer membranes. We considered representative lamellar, cylindrical, and gyroid morphologies and present results for both the global and local diffusivities, as well as the structural characteristics of water in the pores. Our results suggest that the diffusivity of water in the confined, polymer-coated pores differs from that in the unconfined bulk. Explicitly, in confinement, the mobility of water is reduced by the hydrodynamic friction arising from the hydrophilic blocks coating the pore walls. We demonstrate that in lamella and cylindrical morphologies, the latter effects can be rendered as a universal function of the pore size relative to the brush height of the hydrophilic blocks. |
Tuesday, March 3, 2020 4:54PM - 5:06PM |
J34.00011: Enhanced Conductivity via Homopolymer-Rich Pathways in Block Polymer Composite Electrolytes Thomas Epps, Melody A Morris The BP electrolyte polystyrene-block-poly(oligo-oxyethylene methacrylate) [PS-b-POEM] was blended with POEM homopolymers of varying molecular weights to explore the impact of polymer additives on ion conductivity. The incorporation of a higher molecular weight homopolymer additive promoted a ‘dry brush-like’ homopolymer distribution within the BP self-assembly and led to higher lithium salt concentrations in the more mobile homopolymer-rich region, increasing overall ionic conductivity relative to the ‘wet brush-like’ and unblended composites. Furthermore, using 7Li solid-state nuclear magnetic resonance spectroscopy, we found a temperature corresponding to a transition in lithium mobility (TLi mobility) that was a function of blend-type. TLi mobility was found to be 39 °C above Tg in all cases. Interestingly, the ionic conductivity of the blended BPs was highest in the ‘dry brush-like’ composites even though these composites had higher Tgs than the ‘wet brush-like’ composites, suggesting that homopolymer-rich conducting pathways formed in the ‘dry brush-like’ assemblies had a larger influence on conductivity than the greater lithium ion mobility in the ‘wet brush-like’ blends. |
Tuesday, March 3, 2020 5:06PM - 5:18PM |
J34.00012: Comparison of macroscopic and microscopic measurements of segmental dynamics in aging polymer glasses Mark Ediger, Josh Ricci, Trevor Bennin, Enran Xing Optical probe reorientation experiments and mechanical stress relaxation measurements in the linear response regime were performed during aging of glasses of poly(methyl methacrylate) (PMMA) and poly(D,L-lactide) (PLA). For each polymer, across all aging times and temperatures, an excellent correlation is observed between the relaxation times for mechanical and optical experiments with the two observables showing a power law relationship with an exponent near one. For PMMA, relaxation times for the two observables in crosslinked and uncrosslinked materials follow the same correlation. The probe reorientation method has previously been utilized to track changes in segmental dynamics during nonlinear deformations. Our new experiments validate the conclusion that probe reorientation is a good reporter of segmental dynamics in the glass, in the linear response regime. The strong agreement between macroscopic and microscopic measurements of mobility in the aging polymer glasses contrasts to recent work on colloidal and metallic glasses. |
Tuesday, March 3, 2020 5:18PM - 5:30PM |
J34.00013: Confinement Effects on Dye Diffusivity in Polymer Films Depend on Polymer Molecular Weight: Relation to Fragility-Confinement Effects John Torkelson, Tong Wei, Tian Lan We studied the translational diffusivity of 9,10-bis(phenylethynyl)anthracene (Ddye) in supported, polystyrene (PS) films. Relative to bulk films and near Tg, Ddye is reduced by 80 - 90% in 100-nm-thick, high molecular weight (MW) PS (400 kg/mol) films. These results are associated with fragility-confinement effects, with fragility decreasing in films with decreasing thickness below ~ 200 nm. Fragility reflects the breadth of the cooperative segmental relaxation distribution: that breadth narrows with confinement. The thickness dependence of Ddye reflects the time scales associated with the fast relaxation tail of that distribution. At thickness below ~200 nm, the distribution narrows, with the shortest relaxation times shifting to longer times, leading to a reduction in Ddye. We also studied Ddye in low MW PS (6 kg/mol). Because 6 kg/mol PS exhibits much lower bulk fragility than high MW PS, confinement has a much-reduced effect on low MW PS fragility: both fragility and Ddye in 100-nm-thick low MW PS films are unchanged from bulk. Thus, for thicknesses where fragility-confinement effects are observed (high MW PS), Ddyealso exhibits confinement effects. By suppressing fragility-confinement effects by using very low MW PS, confinement effects on Ddye are also suppressed. |
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