Neutron spin-echo investigations on the dynamics of polymer systems

Abstract

Neutron spin-echo spectroscopy allows the observation of long-range internal relaxation mechanisms of macromolecules simultaneously in space and time. Thereby, it facilitates a microscopic study of molecular models applied for the explanation of macroscopic viscoelastic properties of polymer materials. After an outline of the method, we discuss experimental results on chain relaxation in polymer melts. We show that in the short time regime, the Rouse model describes perfectly well both the time dependences of the self and the pair correlation function. For longer times and stronger decay of the dynamic pair correlation function we observe distinct deviations from the Rouse model towards slower relaxation. However, other than predicted by the tube models the data do not reveal evidence for the existence of a microscopic length like the tube diameter or the entanglement distance but follow the time momentum transfer scaling behaviour of the Rouse-model. Thereafter we discuss aspects of the dynamics of polymer networks. We present neutron spin-echo results on the motion of labelled cross-links in a model network. These measurements reveal a surprisingly high mobility of the cross-links and are in qualitative agreement with the predictions of the phantom network theory.