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

Specific salt effects on thermophoresis of charged colloids

We study the Soret effect of charged polystyrene particles as a function of temperature and electrolyte composition. As a main result we find that the Soret coefficient is determined by charge effects, and that non-ionic contributions are small. In view of the well-known electric-double layer interactions, our thermal field-flow fractionation data lead us to the conclusion that the Soret effect originates to a large extent from diffusiophoresis in the salt gradient and from the electrolyte Seebeck effect, both of which show strong specific-ion effects. Moreover, we find that thermophoresis of polystyrene beads is fundamentally different from proteins and aqueous polymer solutions, which show a strong non-ionic contribution

Physicochemical characterization of nanoparticles and their behavior in the biological environment

Whilst the physical and chemical properties of nanoparticles in the gas or idealized solvent phase can nowadays be characterized with sufficient accuracy, this is no longer the case for particles in the presence of a complex biological environment. Interactions between nanoparticles and biomolecules are highly complex on a molecular scale. The detailed characterization of nanoparticles under these conditions and the mechanistic knowledge of their molecular interactions with the biological world is, however, needed for any solid conclusions with regards to the relationship between the biological behavior of such particles and their physicochemical properties. In the present article we discuss some of the challenges with characterization and behavior of nanoparticles that are associated with their presence in chemically complex biological environments. Our focus is on the stability of colloids as well as on the formation and characteristics of protein coronae that have recently been shown to significantly modify the properties of pristine particles. Finally, we discuss the perspectives that may be expected from an improved understanding of nanoparticles in biological media