DIFFUSION OF POLYSTYRENE LATEX SPHERES IN LINEAR POLYSTYRENE NONAQUEOUS SOLUTIONS

The diffusion of highly cross-linked, nearly monodisperse polystyrene latex spheres of 0.2-mum radius in the presence of linear polystyrene as the matrix polymer in the moderately good solvent N,N-dimethylformamide at 25-degrees-C was determined by quasi-elastic light scattering as a function of matrix concentration and molecular weight. This is the first report of a latex probe in trace amounts diffusing in an organic solvent, and with a matrix polymer chemically similar to the probe. The latex diffusion diminished monotonically with matrix concentration, which varied from moderately dilute solutions into the semidilute regime up to a matrix concentration of 8 times c*. Stokes-Einstein behavior was observed at all matrix concentrations and for both matrix molecular weights (2.15 X 10(5) and 1.1 X 10(6)), within experimental error. In the semidilute region the entanglement relaxation was always much faster than probe motion. The diffusion data fit the scaling law D/D0 = exp(-ac(nu)M(gamma)), with nu equal to 0.99 and gamma equal to 0.49. Comparison is made to diffusion of latex probes in aqueous dispersants, and of silica probes in organic dispersants.