Direct observation of the transition from free to constrained single segment motion in entangled polymer melts

Incoherent neutron-spin-echo spectroscopy (NSE) has been employed to directly determine the time-dependent mean-squared segment displacement of a polymer chain in the melt covering the transition from free to constraint Rouse relaxation along the virtual tube of the reptation model. The predicted transition of the time dependence of from proportional to t(1/2) to proportional to t(1/4) is clearly corroborated by the incoherent NSE results. (C) 2004 Elsevier B.V. All rights reserved