1999-03-19
11:15 at ML F39

How do molecules move near the liquid/glass transition?

M. Hediger

Department of Chemistry, University of Wisconsin, USA,

How do molecules move near the liquid/glass transition? Evidence for spatially heterogeneous dynamics in polymeric and low molecular weight glass formers

In the last seven years, experiments from many laboratories have been interpreted as indicating spatial heterogeneity in the dynamics of glass-formers as Tg is approached from above, i.e., it is believed that time scales for motion in one re gion of space may be orders of magnitude faster than those in another region some nanometers away. Given this background, answers to the following questions are desired: How large are these heterogeneities? How long do they last? How much do the dynamics vary between the fastest and slowest regions? Why do these heterogeneities arise? To address the first three questions, we present optical experiments which measure the rotational and translational motion of probe molecules in polymeric and low molecular weight glass formers. As an answer to the final question, we will present a simple model consistent with these observations based upon equilibrium density or entropy fluctuations.