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CPP: Chemische Physik und Polymerphysik

CPP 26: POSTER Dynamics and Diffusion

CPP 26.1: Poster

Donnerstag, 30. März 2006, 17:00–19:00, P2

Influence of isotopic substitution of cyclohexane on transport coefficients of binary liquid mixtures — •Gerhard Wittko and Werner Köhler — Physikalisches Institut, Universität Bayreuth

In a binary system, a temperature gradient does not only lead to a heat flux but also to a mass flux. The latter effect is known as thermal diffusion, or Ludwig-Soret-effect. The Soret coefficient S_T is a measure for the concentration gradient in the stationary state, where the mass flux due to thermal diffusion is compensated by the mass flux due to Fickian diffusion. Until now there is no microscopic theory on neither thermal diffusion nor diffusion that allows to predict values of S_T or the diffusion coefficient D in liquids from molecular properties. We present experimental results on the influence of the isotopic substitution of protonated cyclohexane by perdeuterated cyclohexane in binary liquid mixtures on D, S_T and the thermal diffusion coefficient D_T. For D we find almost the same value in both the mixture containing protonated and perdeuterated cyclohexane. In contrast to this, S_T of the the mixture containing the heavier isotope is lower than S_T of the mixture containing the lighter isotope by about Δ S_T=1 × 10⁻³K⁻¹ at all mole fractions.