Evaluation of the Soret Coefficient for polystyrene in decalin by means of Thermal Field Flow Fractionation

One of the most appealing features of FFF (Field-Flow Fractionation) techniques is their capability of easily finding out direct mathematical relationships between the retention parameter and physico-chemical parameters of the analytes. In the case of thermal FFF applied to macromolecules in solution, these parameters are the Soret coefficient and the molar mass. In this work, a rich set of retention data for polystyrene in a mixture of cis and trans decalin, in a wide range of temperatures and molar masses, is used for finding out an empirical relationship between Soret coefficient, temperature, and molar mass using a refined approach of handling thermal FFF data. This law is then statistically tested and very good agreement between experimental and predicted values of Soret coefficient is found. The importance of this law lies in the fact that it makes possible a truly universal calibration of the polystyrene-decalin system on any thermal FFF apparatus in the investigated ranges of temperatures and molar masses. The thermodiffusion coefficient of polystyrene in cis + trans decalin is evaluated for various molar masses at the temperature of 333 K and a slight dependence of this parameter on molar mass at that temperature is observed