WHEN: May 19, 2014, from 9:30 am
WHERE: Meeting room, 4th floor, Faculty of Chemistry, Brno University of Technology, Purkyňova 118, Brno
Abstract:
Slow dynamics in supercooled liquids and glasses is of widespread interest for diverse materials classes and scientific disciplines. The common physical feature is the critical importance of rare activated hopping motions which are very sensitive to temperature and external mechanical forces. A new statistical mechanical theory for the alpha relaxation process and shear modulus of equilibrium molecular and polymer liquids will be described that captures the rich experimental phenomenology over 14 decades in time as a consequence of a local activation event and its coupling to the emergent long range elasticity in cold liquids. The approach has been extended to the quenched nonequilibrium polymer glass state based on the experimentally-measurable amplitude of nanometer scale density fluctuations as the central collective variable. Building on this advance, a theory for physical aging and mechanical response under both constant stress (creep) and constant strain rate conditions has been constructed. The nonlinear competition between the effects of aging and mechanical rejuvenation on density fluctuations, relaxation, and mechanical properties will be discussed, and quantitative applications to PMMA glasses presented.
The event has been supported by the EU Seventh Framework Programme under the "Capacities" specific programme (Contract No. 286154 - SYLICA)
