Thermal diffusion: An Unsolved Puzzle in Soft Matter Physics
Dr. Simone Wiegand, Forschungszentrum Jülich GmbH
The separation of the components in binary and multicomponent mixtures in a temperature gradient is one of the unsolved problems in physical chemistry. Nevertheless the effect is used in polymer and colloid analysis in the so-called thermal field flow fractionation. Very recently it has also been utilized to study the bio molecular binding reactions. In order to gain a deeper understanding of the underlying mechanism we study systematically bio- and soft matter in a temperature gradient.
We investigated various low molecular weight structures such as sugar molecules, sugar surfactants, nucleotides, fd-viruses and microemulsions by a holographic grating method called infrared thermal diffusion forced Rayleigh scattering (IR-TDFRS). Open questions such as the radial dependence of the thermal diffusion coefficient and its relation with the interfacial tension are considered. Additionally, empirical correlations with the ratio of the thermal expansion coefficient and the kinematic viscosity for polar and non-polar substances are discussed. Additionally we developed a new micro thermogravitational column with optical detection. The new developed set-up is presented and its strength and weakness in comparison with other methods is discussed. As first systems we investigated the so-called benchmark systems, which have been measured by five different groups and methods.