TEMPERATURE-DEPENDENCE OF SOLVENT VISCOSITY, SOLVENT THERMAL-CONDUCTIVITY, AND SORET COEFFICIENT IN THERMAL FIELD-FLOW FRACTIONATION

In this work equations are presented to describe solute concentration profiles in thermal field-flow fractionation that account for the effe ct of the temperature drop across the solute zone on the thermal and o rdinary diffusion coefficients. The influence of this effect, together with the effects of the temperature dependence of the solvent viscosi ty and solvent thermal conductivity, on the conversion of retention da ta into thermal diffusion data were studied. The systematic error made when the ratio of the thermal and ordinary diffusion coefficient (alp ha/T) is assumed to be constant can be considerable and is larger for systems with low retention (e.g., for low molecular weight or small th ermal diffusion). For the two systems studied (polystyrene in THF and in ethylbenzene), it was found that the temperature dependence of the solvent viscosity is of much greater importance than the temperature d ependence of the solvent thermal conductivity. When all three paramete rs are considered to be independent of the temperature, the results ar e still quite acceptable. This is due to the fact that the effect of t he temperature dependence of the solvent viscosity is counteracted by the combined effects of the temperature dependence of the solvent ther mal conductivity and of alpha/T.