On the temperature dependence of thermal diffusion of liquid mixtures

Physikalisches Institut, Universität Bayreuth - D-95440 Bayreuth, Germany

Received: 19 February 2007
Accepted: 12 April 2007

Abstract

Concentration- and temperature-dependent measurements of the Soret coefficient S_T 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. S_T 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 , and for all but one (dibromohexane/cyclohexane) systems there exists a concentration where S_T becomes temperature invariant, corresponding to a zero of . is of similar magnitude for all mixtures investigated. neither depends on temperature nor on concentration, and isotopic substitution changes only , but not or . For benzene/cyclohexane is related to differences of molecular mass and moment of inertia, and is identified with the chemical contribution to the Soret coefficient.