Session W18 - Computer Simulation II.
ORAL session, Thursday morning, March 15
Room 308-308, Washington State Convention Center
We present a detailed analysis of cooperative motion and dynamical heterogeneity in a simulated bead-spring model of a low molecular weight polymer melt. We investigate the transient nature and size distribution of clusters of mobile monomers at temperatures T above and approaching the glass transition. We show that the mean cluster size exhibits a time dependent behavior with a peak at intermediate time. The timescale of the peak corresponds to the timescale of the end of the ``caging'' regime. The mean cluster size at the peak time grows with decreasing T. The growing size of clusters underlies the growing range of correlated motion previously reported for this same system (Bennemann, et al., Nature 399, 246 (1999)). We quantify the range of correlation by investigating the time and temperature dependence of the characteristic size and radius of the clusters. The distribution of cluster sizes is found to approach a power law as T decreases with an exponent near 2, similar to behavior reported for a dense colloidal suspension and a simulated binary mixture, demonstrating a potentially universal feature of the dynamically heterogeneous nature of glass-forming liquids.