Untersuchung der Thermophorese negativ geladener Modellkolloide in wässrigen Suspensionen mittels der Thermischen Feld-Fluss Fraktionierung

Thermal field-flow fractionation (ThFFF) is a well-known technique for analytical separations of colloidal dispersions according to their Soret coefficient. The Soret effect describes the direction and the velocity of thermophoresis, resulting in directed migration of particles in a thermal gradient. In this thesis, an improved understanding of the separation mechanism is provided by coupling ThFFF with an electrostatically dominated theory of thermophoresis of charged colloids. Soret effects were studied as a function of temperature and electrolyte composition in the solvent. Charged polystyrene colloids, self-synthesized by surfactant-free suspension polymerization, were compared to commercial standard suspensions. Our results confirmed the excellent ability of ThFFF to separate based on slight differences at the particle-solvent interface. From our experimental data and complementing simulations, we demonstrated that the Soret effect originates to a large extent from specific ion effects, in particular from diffusiophoresis in the salt gradient and from the electrolyte Seebeck effect. In conclusion, thermophoresis of polystyrene beads is fundamentally different from proteins and aqueous polymer solutions, whose thermal diffusion is known to depend on strong non-ionic contributions