PROBE DIFFUSION IN POLYMER-SOLUTIONS UNDER THETA AND GOOD CONDITIONS

Quasielastic light scattering was used to measure the diffusion coefficient of 67-nm-diameter polystyrene latex spheres through aqueous solutions of M(w) = 1.39 x 10(5) (hydroxypropyl)cellulose at temperatures of 41-degrees-C (near-theta conditions) and 10-degrees-C (good-solvent conditions). At both temperatures, D was described well by a stretched exponential form exp(-alphac(nu)), with nu almost-equal-to 1 under theta conditions but nu almost-equal-to 3/4 in a good solvent. The observed solvent-quality dependence of nu is quantitatively predicted by several models of probe diffusion, including hydrodynamic scaling and the de Gennes-Langevin-Rondelez transient gel model.