Structure Relaxation after Temperature Jumps in Homogeneous Polystyrene Poly(styrene-co-bromostyrene) Blends

Abstract

Concentration fluctuations in polymer blends and their change after a temperature jump were studied by time-dependent small angle X-ray scattering experiments. Measurements were conducted on homogeneous mixtures of polystyrene and a partially brominated derivative. Structure factors in thermal equilibrium show the form given by the random phase approximation, thus enabling a direct determination of the χ-parameter and the mean radius of gyration. The T-dependence of χ can be understood as the result of superposed enthalpic contributions and a free volume term. In the T-jump experiments, samples were quenched to temperatures near Tg. Relaxation occurs on the time scale of minutes and is nonexponential, becoming slower with time. Initial relaxation rates increase with increasing scattering vectors q in accordance with theoreticalpredictions.