Investigation of the soret effect in aqueous and non-aqueous mixtures by the thermal lens technique

Polyakov, P.; Wiegand, S.

doi:10.1039/b810860a

Journal Article

PreJuSER-3412

Investigation of the soret effect in aqueous and non-aqueous mixtures by the thermal lens technique

Polyakov, P.FZJ* ; Wiegand, S.FZJ*

2009
RSC Publ. Cambridge

Physical Chemistry Chemical Physics 11, 864 - 871 (2009) [10.1039/b810860a]

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Please use a persistent id in citations: http://hdl.handle.net/2128/4652 doi:10.1039/b810860a

Abstract: In the present work we investigate the thermal diffusion behavior of three different binary mixtures with a thermal lens (TL) setup. In the setup used in this study we avoid the addition of a dye for systems, such as aqueous mixtures, with a weak absorption band at a wavelength of 980 nm. In some aqueous systems with a complex phase behavior the addition of dye significantly affects the apparent measured thermal diffusion properties. The studied systems are dimethylsulfoxide (DMSO) in water, the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate (EMIES) in butanol and a non-ionic surfactant hexaethylene glycol monododecyl ether (C(12)E(6)) in water. The Soret coefficients of the selected systems cover a range of two orders of magnitude. For DMSO in water with a very low Soret coefficient of the order of S(T) approximately 10(-3) K(-1) we find for a low DMSO content (c = 0.33) a reasonable agreement with previous measurements, while the weak thermal lens signal for the DMSO-rich mixture (c = 0.87) leads to 20% too large Soret coefficients with an uncertainty of more than 30%. Secondly we studied a liquid salt 1-ethyl-3-methylimidazolium ethylsulfate (EMIES) in butanol with a roughly ten times higher Soret coefficient of S(T) approximately 10(-2) K(-1). For this system we performed additional measurements with another experimental technique, the classical thermal diffusion forced Rayleigh scattering (TDFRS), which requires the addition of a small amount of dye to increase the absorption. In the entire investigated concentration range the results obtained with the TL and classical TDFRS technique agree within the error bars. As a third system we studied a non-ionic surfactant hexaethylene glycol monododecyl ether (C(12)E(6)) in water with a Soret coefficient of the order of S(T) approximately 10(-1) K(-1). For this system we find good agreement with previous measurements. We conclude that the TL technique is a reliable method for systems with a strong optical contrast and fairly large Soret coefficient of the order of S(T) approximately 10(-2) K(-1).

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Note: The authors thank Jan Dhont for his constant interest in this work and his support. We also appreciate discussions with Hui Ning and the technical help of Hartmut Kriegs. We would like to thank the Deutsche Forschungsgemeinschaftfor the financial support (WI 1684).

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