Concentration fluctuation effects on chain orientation dynamics of polymer blends in the critical region

Abstract

Dielectric relaxation spectroscopy has been employed to investigate the normal mode relaxation of polyisoprene I chains in binary polystyrene/polyisoprene (S/I) blends over a broad temperature range in the one and two phase region. The normal mode relaxation time in the homogeneous phase near the transition is faster than expected on the basis of the average bulk composition and the distribution of relaxation times becomes bimodal in the transition region. A concentration correlation model is proposed to account for the new experimental findings in the framework of Rouse chain dynamics and mean-field static behavior. The computed normal mode relaxation times compare well with the experiment for an effective composition averaged over a microscopic scale O(nm).