Thermodiffusion, diffusion and Soret coefficients of binary polymeric mixtures in toluene and cyclohexane

Abstract

We present the results of experimental study on measuring the thermodiffusion, molecular diffusion and Soret coefficients of polystyrene (4,880 g/mol) in the pure solvents toluene and cyclohexane at 298 K and atmospheric pressure. The experiments have been carried out for a wide range of concentrations, starting from the diluted state with 2 % polystyrene mass fraction (proposed in the DCMIX4 project) up to the semidilute regime of 20 % polystyrene mass fraction. In addition, we present a complete characterisation of the thermophysical properties of the analysed mixtures. Thermodiffusion, molecular diffusion and Soret coefficients of binary polymeric samples have been measured by combining the traditional thermogravitational column technique, the thermogravitational microcolumn and the optical beam deflection method. In toluene, the obtained experimental results are consistent with literature, showing that the magnitude of the mass transport thermoproperties decrease significantly with increasing polystyrene concentration, which is a first indication of an approaching glass transition in the concentrated regime. The results for thermodiffusion and molecular diffusion coefficients in cyclohexane as a function of concentration exhibit a similar trend. Nevertheless, the Soret coefficient seems to show an opposite tendency for the two solvents, increasing in magnitude for cyclohexane, at least up to the analysed polystyrene concentration.