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Materials Science Seminar Series presents Professor David Simmons on Thursday, October 19, from 4 to 5 p.m. The seminar is hosted by Professor Paul Voyles and will be held in MS&E building room 265. Prof. David Simmons will be discussing Insights into the Physics of Glass Formation from Thin Film Dynamics.
A major motivation for research on nanoconfined glass formation has been the hope that confinement and broken symmetry near interfaces might reveal dynamical correlations in glass forming liquids and thus resolve the nature of glass formation itself. An understanding of altered dynamics near interfaces and under nanoconfinement would also empower design of next-generation nanostructured materials. Here, I discuss results establishing a cohesive phenomenology and fundamental understanding of interface and confinement effects on equilibrium dynamics and glass formation at the longest timescales accessible to simulation. This phenomenology is at odds with a number of theories of glass formation as applied near interfaces. On the other hand, it is predicted near-quantitatively by the Elastically Collective Nonlinear Langevin Equation (ECNLE) theory of Schweizer and coworkers, with the long-range 1/z tail emerging from truncation of an elastic activation field and the shorter-ranged exponential log(tau) gradient emerging from a combination of elastic effects and altered local caging. These results establish a predictive understanding of alterations in dynamics near interfaces at the timescales accessible to simulation and accord with experimental studies probing equilibrium dynamics, while providing evidence towards the underlying physics of glass formation more generally.
I additionally will discuss new results pointing towards a role for intrinsic nonequilibrium effects, associated with loss of equilibrium at Tg, in mediating thin film measurements of pseudothermodynamic Tg. These latter findings suggest that nonequilibrium effects may play a key role in mediating the properties of nanostructured materials. Moreover, these effects may explain a number of anomalous phenomena that have been reported at experimental timescales but not thus far in simulation, and thereby may bridge the understanding of surface effects at experimental and simulation timescales.
David S. Simmons is Associate Professor of Chemical and Biomedical Engineering at the University of South Florida. His work, which combines computer simulation, theory, machine learning, optimization, and high-throughput experimentation to advance the understanding and design of polymers and soft materials, has received support from the W. M. Keck Foundation, an NSF CAREER award, and a 3M Non-Tenured Faculty Award, among others. Dr. Simmons received a Ph.D. in Chemical Engineering at the University of Texas at Austin, and his work now focuses on physics and design of glass-forming liquids, sequence-specific polymers, and nanostructured materials.