Rayleigh–Brillouin scattering and structural relaxation of polystyrene–cyclohexanes solutions

Publisher Website
Google Scholar
Abstract
An extensive Rayleigh–Brillouin scattering study of polystyrene and cyclohexane mixtures at various temperatures and polymer concentrations has been carried out. The experimental results have been analyzed in terms of the equations of generalized hydrodynamics developed recently by Lin and Wang. Over the entire concentration range, the temperature dependence of the Brillouin frequency and linewidth data can be satisfactorily interpreted in terms of the equations in the recent theory. The pronounced effects of the Brillouin data have been related to a quantity, referred to as the effective structural relaxation time τs for the mixture. The use of the single relaxation time model is justified for Brillouin scattering. It has been found that τs is not significantly affected by the presense of polymer molecules at low polymer concentration, but it increases rapidly with increasing polymer concentration at high concentration. At low polymer concentration, the relaxation frequency τs−1 is fast compared with the sound frequency ωs; and the effects of shear viscosity and thermal relaxation due to internal degrees of freedom are not as important as that of bulk viscosity. At high polymer concentration, the τs data suggest that rapid segmental motion involving only few monomer units in the long polymer chain molecules gives the dominant contribution to the dispersion and attenuation of the hypersonic wave in the polymeric fluid.

This publication has 15 references indexed in Scilit: