LIGHT-SCATTERING STUDY OF FLUCTUATIONS IN CONCENTRATION, DENSITY, AND LOCAL ANISOTROPY IN POLYSTYRENE DIOXANE MIXTURES

Static and dynamic light scattering was applied in a comprehensive study of the different modes of relaxatory motion in polystyrene-dioxane mixtures, comprising the whole range of different compositions from dilute solution to plasticized melts. For the analysis of data measured in the presence of the nearly elastic anomalous excess scattering usually encountered in concentrated solutions and the melt, a generalized Siegert relation was used. Analysis of depolarized dynamic scattering data obtained for the PS-rich mixtures indicates a simple Vogel-Fulcher temperature dependence for the relaxation rates of the anisotropy fluctuations with T(g) as the only relevant parameter. The dynamics observed in polarized scattering continuously changes its character, being dominated at low temperatures and high concentrations by density fluctuations and in the limit of high temperatures and low concentrations by concentration fluctuations. Density and anisotropy fluctuations show identical relaxation rates.