Polymer motions from localization to Rouse dynamics in supercooled melts

Laboratory and simulation studies of relaxation in supercooled polymer melt s provide a view of the approach to the glass transition that is complement ary to that obtained from study of small molecule liquids, because of the a dditional length scales characteristic of macromolecules. Recent molecular dynamics simulations of a supercooled melt of bead-spring polymers have sho wn that the motions of a coarse-grained polymer bead on length scales small er 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 connectiv ity of the polymer becomes significant and molecular motions may be describ ed by the Rouse model. We present calculations of chain dynamics in a super cooled melt from the dynamically disordered Rouse model. This dynamical mea n field model shows qualitative agreement with the simulation data in descr ibing both the short time regime of spatial localization at low temperature and the longer time regimes of Rouse dynamics. (C) 2001 American Institute of Physics.