How does thermodiffusion of aqueous solutions depend on concentration and hydrophobicity?
Graduate School of Science and Technology, Tokai University, Hiratsuka, 259-1292, Kanagawa, Japan
2 ICS-3 Soft Condensed Matter, Forschungszentrum Jülich GmbH, D-52428, Jülich, Germany
3 Department für Chemie - Physikalische Chemie, Universität zu Köln, 50939, Cologne, Germany
Revised: 15 September 2014
Accepted: 29 September 2014
Published online: 23 October 2014
The thermal diffusion of aqueous solutions of mono-, di-ethylene glycols, poly(ethylene glycol), methanol, and glycerol is investigated systematically as a function of concentration using the Thermal Diffusion Forced Rayleigh Scattering (TDFRS). For all investigated binary mixtures, the Soret coefficient, S T , decays with increasing concentration of the non-aqueous component showing two regions. For aqueous solution of ethylene glycol, at a very low solute content the decay is steep, while it becomes less steep for higher solute concentration. All mixtures show a sign change of S T with concentration. The sign change concentration is discussed with respect to chemical structures of solute molecules and the partition coefficient, log p . It turns out that the number of hydroxyl groups plays an important role. For the investigated aqueous mixtures, we find empirical linear relations between the sign change concentration and the ratio of the number of hydroxyl groups to the number of carbon atoms as well as the partition coefficient, log p .
Key words: Topical Issue: Thermal non-equilibrium phenomena in multi-component fluids
© EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg, 2014