High Rate Micromechanical Behavior of Glassy Polymer Films

Abstract: The nature of the deformation in polymers depends on the ability of the chain segments to respond to the applied load at the imposed loading rate. When the polymer response time is significantly longer than the testing time, the polymer responds in a brittle manner. Polystyrene (PS), for example, is a brittle, glassy solid at room temperature and absorbs little energy during deformation.  When confined in a very thin film, the less entangled, more mobile near-surface regions of free standing films modifies the deformation behavior of high molecular weight polymers.  Here we show unexpected deformation mechanisms at extreme deformation rates created by impact of micron sized projectiles. The supersonic projectiles initiate deformation zones, crazing and adiabatic heating leading to extensive plastic flow of a load-bearing viscoelastic melt prior to perforation and film rupture.  These ductile deformation processes result in high specific energy absorption at extreme strain rates in what is normally considered a brittle material. 

Bio: Ned Thomas’ research interests include polymer physics and engineering of the mechanical and optical properties of block copolymers, liquid crystalline polymers, and hybrid organic-inorganic nanocomposites.  His career started at the University of Minnesota and then moved to the University of Massachusetts where he founded and served as co-director of the Institute for Interface Science and was head of the Department of Polymer Science and Engineering.  In 1988 he became the Morris Cohen Professor of Materials Science and Engineering at the Massachusetts Institute of Technology and was Founding Director of the Institute for Soldier Nanotechnologies.  In 2011, he became Dean of Engineering at Rice University.  Thomas is the recipient of the 1991 High Polymer Physics Prize of the American Physical Society and the 1985 American Chemical Society Creative Polymer Chemist Award. He was elected a Fellow of the American Physical Society  and a member of the American Academy of Arts and Sciences and the National Academy of Engineering.

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