Simulation of polymer dynamics. II. Relaxation rates and dynamic viscosity

Abstract

The stochastic equations of the preceding paper are used to study stress, dielectric, mode and conformational relaxation of chains with threefold symmetric rotation barriers. The modes, qk ∝𝒥bi sinκi where bi is a bond vector, relax independently, insofar as low order time correlation functions are concerned. For stress and dielectric relaxation, most of the theory of mode relaxation in Gaussian chains is directly applicable, with the significant exception that constraints and rotation barriers cause major decreases in relaxation rates from their values for Gaussian chains. This modification suffices to give a large high frequency viscosity limit, which turns out to be a plateau value when a very fast process (of small amplitude in the mode correlations), is incorporated. The rates of passage over barriers show very small effects of chain connectivity, and are well described by Kramers theory. However, the mode relaxation rates show significant dependence on chain length, and approach the conformational relaxation rates quite slowly with increasing chain length.