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Understanding and Design of the Glass Transition in Nanostructured Materials: From Computational Insights to Evolutionary Algorithms

Speaker: David Simmons, University of Akron
Series: CBE Departmental Seminars
Location: Elgin Room (E-Quad A224)
Date/Time: Wednesday, September 27, 2017, 4:00 p.m. - 5:00 p.m.

The origin of the precipitous dynamic arrest known as the glass transition is a grand open question of materials science and condensed matter physics. This ubiquitous phenomenon can drive solid-like behavior in materials as diverse as polymers, bulk metallic glasses, small organic molecules, and inorganic solids. For this reason, fundamental understanding and rational control of the glass transition would enable transformational advances in material technologies, with applications ranging from energy storage to flexible electronics to robust structural materials. This is especially true in the many promising materials that incorporate internal or external nanostructure, which frequently exhibit large modifications in glass formation behavior relative to bulk homogeneous materials. Technologically relevant examples range from nanostructured block polymeric ionic liquids of interest in next-generation batteries to semicrystalline polymers that are among the largest-scale commercial polymers in the world. Despite the importance of these effects in determining material properties and performance, an understanding of the glass transition and its alterations near interfaces remains elusive.

By employing a new strategy for efficient molecular dynamics simulations in the glass formation range, here we identify universal mechanistic aspects of the glass transition in materials ranging from polymers to metals. Results reveal that the glass transition is accompanied by a quantitatively universal particle localization transition that may represent an underlying mechanism of solidification. We further employ these simulations to probe the validity of several leading theories of glass formation. Extending the resulting insights to nanostructured materials, we present an emerging unified understanding of near-interfacial alterations in glass formation and dynamics in materials as diverse as thin films, nanocomposites, ionomers, block copolymers, and semicrystalline polymers. This new picture casts all of these systems as specific instances of a general tendency toward broad dynamic interphases in polymers and other glass forming materials – a natural consequence of an emergent length scale of cooperative dynamics. Ultimately, we describe how these new insights, together with design tools including evolutionary algorithms, machine learning, and high-throughput experiments, can enable rational design of materials with targeted glass formation behavior for next-generation material technologies.