Probe diffusion in poly (vinyl acetate) / toluene solutions

The technique of forced Rayleigh scattering has been used to examine the tracer diffusion of probe photochromic dyes, azobenzene and methyl red, in poly (vinyl acetate)/ toluene solutions, as a function of polymer concentration (0–96% by weight) and temperature (5–45°C). It is demonstrated that the dye diffusivity can be quantitatively scaled to the solvent diffusivity, thus permitting direct application of predictions for two‐component systems. The results have been interpreted using the free volume theories of Fujita and Vrentas and Duda. While both approaches are able to describe the concentration dependence extremely well, the Vrentas‐Duda expression has the virtue of being employed without any freely adjustable parameters. However, neither theory is particularly successful in predicting the observed temperature dependence.