Polymer motions from localization to Rouse dynamics in supercooled melts

Abstract

Laboratory and simulation studies of relaxation in supercooled polymer melts provide a view of the approach to the glass transition that is complementary to that obtained from study of small molecule liquids, because of the additional length scales characteristic of macromolecules. Recent molecular dynamics simulations of a supercooled melt of bead–spring polymers have shown that the motions of a coarse-grained polymer bead on length scales smaller than the bead diameter closely resemble dynamics in a supercooled simple liquid, in which molecules are spatially localized in accordance with the predictions of mode coupling theory. On longer length scales, the connectivity of the polymer becomes significant and molecular motions may be described by the Rouse model. We present calculations of chain dynamics in a supercooled melt from the dynamically disordered Rouse model. This dynamical mean field model shows qualitative agreement with the simulation data in describing both the short time regime of spatial localization at low temperature and the longer time regimes of Rouse dynamics.