Temperature dependence of the diffusion, thermodiffusion and Soret coefficient of a dilute polystyrene/toluene solution as measured by means of a transient holographic grating technique

Abstract

We have measured diffusion, thermodiffusion and Soret coefficients of a dilute solution of polystyrene in toluene by means of the transient holographic grating technique of thermal diffusion forced Rayleigh scattering over a temperature range from 10 to 50 °C. The results show a systematic deviation from optical beam deflection measurements over a narrower temperature interval of the order of ten percent but the identical temperature dependence. A comparison with previous measurements from our laboratory, new control measurements and literature data does not lead to a clear conclusion about the correct values. From the diffusion coefficient a temperature independent hydrodynamic radius is obtained. Both the Soret coefficient and the viscosity-scaled thermodiffusion coefficient ηDT, for which a universal value has been reported in the case of asymmetric systems with large solute entities, decrease with temperature.