CHI-F INTERACTION PARAMETER AND SINGLE-CHAIN DIFFUSION-COEFFICIENTS OF DEXTRAN POLY(VINYLPYRROLIDONE) WATER - DYNAMIC LIGHT-SCATTERING EXPERIMENTS

Quasi elastic light scattering (QELS) experiments have been performed on poly(vinylpyrrolidone) (PVP)/dextran mixtures in water. The experiments were made at several total polymer concentrations C(T), in the semidilute range (C(T) > C* where C* is the overlap concentration): in the homogeneous and disordered state from about C* to 10C*. At relatively higher concentration, three relaxation modes have been found in the whole range of composition x = C(PVP)/C(T), namely, 0 < x < 1. The slowest one has been interpreted as being the consequence of aggregate formation. The two other frequencies are interpreted in the framework of a model describing the dynamic behavior of ternary polymer mixtures using the random phase approximation (RPA) allowing the determination of the chi(F) interaction parameter and the single-chain diffusion coefficients D(s,i) = kT/N(i)zeta(i), i = 1,2, as well as their polymer concentration dependence. The results show that chi(F) increases rather sharply with the polymer concentration, whereas D(s) decreases. As the concentration increases the variation of D(s) with the concentration is expected and that of chi(F) is interpreted as strong interactions occurring between chains.