Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 20: POSTERS Driven Soft Matter

CPP 20.16: Poster

Wednesday, February 27, 2008, 16:00–18:30, Poster A

Isotope and isomer effect in thermal diffusion of binary liquid mixtures — •Steffen Hartmann, Gerhard Wittko, and Werner Köhler — Physikalisches Institut, Universität Bayreuth

A temperature gradient induces a diffusive mass flow in a multicomponent system, which is counterbalanced in the stationary state by the Fickian mass diffusion. The occuring concentration gradient can be described by the Soret coefficient, defined as the ratio of the thermal and the Fickian diffusion. There still exists no rigorous theory for thermal diffusion in liquids and a few transient holographic grating experiments have been performed in which well definied parameters are systematically varied. The isotopic substitution leaves most molecular parameters unchanged and mainly affects the molecular mass and moment of inertia. Deuteration of one component leads to a change of the Soret coefficient, which is independent of concentration and temperature. For many binary mixtures there exists a certain concentration where the temperature dependence of the Soret coefficient vanishes. In contrast to the isotope effect, the change of the Soret coefficient due to isomeric substitution depends on the concentration.