A numerical and experimental study of flow and instabilities in concentrated colloidal suspensions

This project relates to the numerical and experimental study of the flow properties of concentrated colloidal suspensions on a nanometer scale. A numerical model that successfully describes the behavior of granular systems on a micrometer scale will be ex tended with additional interactions to make it applicable to simulations of nanosized colloids. This model is used to study systems such as (see project description for details) plug flow, quicksand, fluidized beds, an instability in a tube of sand, hydro -fracturing patterns, and a granular Rayleigh-Taylor (GRT) instability. The study of the GRT instability constitutes the major part of the applicants doctoral thesis. The main goal of this project is to extend the successful numerical model by additional interactions, such as Van-der-Waal and Coulomb, which become increasingly important as the particles attain a nanometer size, and apply this model to open questions related to colloidal suspensions. In conjunction with the numerical work experiments will be performed to observe how the real system behaves. A strong interaction between simulations and experiments is an intrinsic quality of this project. Relevant questions to address are how the GRT instability behaves on a nanometer scale and what the ef fects of the new interactions will be. Novel instabilities where the fingers disintegrate instead of merge is a probable observation. The lack of a ordinary surface tension calls on new theories for why the interface in the GRT instability is curved. The existence of other instabilities known from fluid dynamics, such as the Rayleigh instability, will also be investigated by the numerical model. The applicant has been invited by professor Hans J. Herrmann to spend up to three years with his group ``Compu tational Physics of Materials in Civil Engineering'' at the internationally renowned Eidgenössische Technische Hochschule (ETH) in Zürich.