PROBE DIFFUSION IN POLYMER-SOLUTIONS IN THE DILUTE SEMIDILUTE CROSSOVER REGIME .1. POLY(ETHYLENE OXIDE)

The Stokes-Einstein relationship has been tested for a system of polystyrene particles sedimenting through solutions of poly(ethylene oxide) (PEO) in the dilute and semi-dilute regimes. The behaviour of three different sizes of probe particles in PEO of molecular weights 112 300, 450 000 and 615 000 was studied by the technique of ultracentrifugation, both in the presence and absence of the non-ionic surfactant Triton X-100. Deviations from Stokes-Einstein behaviour were estimated by comparison of the microscopic viscosity experienced by the particles, calculated from sedimentation measurements, and the macroscopic viscosity of the solution, measured independently. Deviations were found to be greatest for the smallest particles, and in all cases the sense of the deviations were in the sense of the particles experiencing a greater resistance to motion than expected from Stokes-Einstein behaviour.