On the temperature dependence of thermal diffusion of liquid mixtures

Abstract

Concentration-and temperature-dependent measurements of the Soret coefficient ST have been performed for binary mixtures containing benzene and cyclohexane, both of different degrees of deuteration, and dibromohexane. They are discussed together with data on ethanol/water, toluene/n-hexane, and benzene in heptane, tridecane, and 2,2,4-trimethylpentane taken from the literature. ST can be negative or positive and change its sign both as a function of concentration and temperature. For all systems the Soret coefficient can be expressed by the empirical function ST = α(x)β(T ) + S i T , and for all but one (dibromohexane/cyclohexane) systems there exists a concentration where ST becomes temperature invariant, corresponding to a zero of α(x). β(T ) is of similar magnitude for all mixtures investigated. S i T neither depends on temperature nor on concentration, and isotopic substitution changes only S i T , but not α(x) or β(T ). For benzene/cyclohexane S i T is related to differences of molecular mass and moment of inertia, and α(x)β(T ) is identified with the chemical contribution to the Soret coefficient.

Temperature Dependence of Soret Coefficient in Aqueous and Nonaqueous Solutions of Pullulan

“…[20][21][22][23][24][25] It has been revealed that a sign of S T of the polymer in solution can occur as function of the solution temperature as well as of the solvent composition. [26][27][28][29][30] For liquid mixtures composed of small molecules thermally induced sign change of S T have been studied by several researchers [31][32][33][34] , sometime those sign changes could be correlated with structural changes in the liquid mixtures. For polymer solutions and colloidal suspensions sometimes sign changes occur und bad solvent conditions.…”

Systematic study of the thermal diffusion in associated mixtures

“…Only in the case of polar acetone ∆S T is approximately 30% larger but still concentration independent. This investigation has also been extended to a broader temperature range 27 .…”

Study of the thermal diffusion behavior of simple binary mixtures

“…The benzene concentration at which S T changes its sign increases with temperature. The dibromohexane/cyclohexane mixture [185] can also be attributed to this group, while S T does not change its sign with concentration.…”

“…Generally, it was applied to different kind of mixtures: simple fluid mixtures [36,113,75,111,183,185] polymer solutions [34,72,123], micellar solutions [109,110] and colloidal dispersions [33,106]. The advantages of the method are a small temperature difference (∼20 µK) and a small fringe spacing (∼20 µm) which keeps the system close to the thermal equilibrium and allows also the investigation of slow diffusing systems such as polymers and colloids.…”

“…Only in the case of polar acetone ∆S T is approximately 30% larger but still concentration independent. This investigation has also been extended to a broader temperature range [185].…”