QUASI-ELASTIC LIGHT-SCATTERING AND VISCOELASTICITY OF POLYSTYRENE IN DIETHYL PHTHALATE

A comprehensive quasielastic fight scattering study of polystyrene (PS) in diethyl phthalate has been carried out. The homodyne intensity-intensity correlation function of the scattered light is measured as a function of polymer concentration and molecular weight. In the semidilute and concentrated concentration regimes, the time correlation function deviates from a single-exponential shape. The deviation is interpreted as arising from two types of modes, one associated with cooperative diffusion and the other with the viscoelasticity of the polymer solution. The experimental results are interpreted in terms of a recently developed hydrodynamic theory without assuming the transient gel model of de Gennes and Brochard. The concentration dependence of the osmotic modulus is obtained from the static light scattering experiment. Using both theory and experiment, we have obtained the osmotic modulus, the cooperative diffusion coefficient, the longitudinal modulus, and the friction coefficient as a function of polymer concentration. This work furnishes an alternative point of view for the interpretation of the dynamic light scattering data of the polymer solution in the semidilute and concentrated regimes.