Recherches Sur La Thermodiffusion En Phase Liquide

Abstract

The authors have studied the thermal diffusion of associated solutions by the thermogravitational method. Experiments have been carried out with the following mixtures: methanol—benzene; ethanol—cyclohexane; cyclohexanol—cyclohexane and ethanol—dioxane. The S o r e t coefficient D′/D was found to vary considerably with concentration contrarily to what had been observed with perfect solutions as reported in a previous paper. In an inert solvent, such as benzene or cyclohexane, the sign of D′/D was reversed when passing from low to high concentrations: the alcohol accumulated in the bottom reservoir when its concentration was weak, in the top reservoir when its concentration was strong (this was not due to the “forgotten” effect) .There seems to be a close relation between this sign reversal of D′/D and the association itself. Experimental results were interpreted with the help of the theory developped in a previous paper and it was shown that: 1. 1) The interaction between a molecule of alcohol and a neighbouring molecule of solvent was, in all cases examined, greater than between two molecules of solvent. 2. 2) The reversal observed with inert solvents was related to an entropy increase due to destruction of complexes which took place when a molecule of alcohol and a molecule of inert solvent exchanged their position.