Cooperative motion and self-diffusion in dilute and semidilute poly-vinylpyrrolidone solutions

Abstract

After a general introduction to the technique of dynamic light scattering, measurements from aqueous polyvinyl-pyrrol-idone solutions in a concentration range up to 6 c* are reported, where c* is the coil overlapping concentration. In dilute solutions only one diffusion process was observed. Above c*, however, the time correlation function decays in two steps, and the slow mode gains quickly influence with increasing concentration. The fast and slow diffusion coefficients follow power laws of the type D ~ (c/c*)exp with exponents of 0.60 and −1.50 for the fast and the slow modes. These exponents are lower in value than 0.75 and −1.75 as was predicted by de Gennes for semidilute solutions on the basis of scaling concepts. The mean square radius of gyration was found to increase sharply above c* in contrast to the prediction for reptating chains, where the radius should slightly decrease. The experimental findings are interpreted being caused by the motion of loosely entangled clusters. © 1984 IUPAC