Microscopic dynamics and topological constraints in polymer melts: A neutron-spin-echo study

Abstract

We have studied the dynamic self- and pair-correlation function on appropriately labeled polydimethylsiloxane melts. For small decays of the scattering function or for small values of the Rouse scaling variable both the results for self and pair correlations are in very good agreement with the Rouse model. For larger values, strong deviations from Rouse dynamics are found indicating the importance of topological constraints. However, no indication for the existence of an intermediate length scale corresponding to the tube diameter of the reptation concept is observed.