Volume 78, Number 4, May 2007
Article Number 46007
Number of page(s) 6
Section Condensed Matter: Structural, Mechanical and Thermal Properties
Published online 11 May 2007
EPL, 78 (2007) 46007
DOI: 10.1209/0295-5075/78/46007

On the temperature dependence of thermal diffusion of liquid mixtures

G. Wittko and W. Köhler

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

received 19 February 2007; accepted in final form 12 April 2007; published May 2007
published online 11 May 2007

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 $S_{T}=\alpha (x) \beta (T)+S_{T}^{i}$, and for all but one (dibromohexane/cyclohexane) systems there exists a concentration where ST becomes temperature invariant, corresponding to a zero of $\alpha (x)$. $\beta (T)$ is of similar magnitude for all mixtures investigated. STi neither depends on temperature nor on concentration, and isotopic substitution changes only STi, but not $\alpha (x)$ or $\beta (T)$. For benzene/cyclohexane STi is related to differences of molecular mass and moment of inertia, and $\alpha (x)\beta (T)$ is identified with the chemical contribution to the Soret coefficient.

66.10.Cb - Diffusion and thermal diffusion .

© Europhysics Letters Association 2007