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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 20: Poster: Colloids and Complex Liquids

CPP 20.17: Poster

Dienstag, 12. März 2013, 18:15–20:15, Poster C

Measuring thermal diffusion of binary mixtures using a two color optical beam deflection technique — •Matthias Gebhardt and Werner Köhler — Physikalisches Institut, Universität Bayreuth, D-95440 Bayreuth, Germany

We have measured and analyzed in detail the Soret, diffusion and thermal diffusion coefficients of the binary mixtures of dodecane, isobutylbenzene and 1,2,3,4-tetrahydronaphthalene, the benchmark systems that are currently also investigated on board the International Space Station ISS in the DCMIX program, at various concentrations. The measurements were performed using a two color optical beam deflection technique, which is equipped with two laser diodes one at 405nm and the other at 635nm. With these two wavelengths we can measure one sample and receive simultaneously two deflection signals. The two signals can be used independently to evaluate the transport coefficients in order to verify the results. The measured beam deflection signal is strongly determined by the so called contrast factors. These contrast factors are the derivatives of the refractive index with respect to concentration and temperature, which have to be determined with high accuracy. We use the Lorentz-Lorenz equation and also the modified equation by Looyenga, to calculate the contrast factors using the refractive index, density and molecular polarizability, as described by Li et al [1]. In order to obtain a quantitative agreement with the experimental data, it is necessary to take the temperature dependence of the molecular polarizabilities into account.

[1] W. B. Li et al., The Journal of Chemical Physics 101, 5058 (1994)