Static and Dynamic Solid-Water Interfaces: charge regulation, diffusio-osmosis and heterogeneous electrokinetics

Abstract

The results presented in this thesis consists of three parts, each with a different view of a solid-water interface. In the first part we consider the case where both the interface and the fluid are static, and investigate the interface between muscovite mica and water for varying salt species and concentration. By combining two experimental techniques, we obtain detailed information of both the number and location of the adsorbed ions, and we construct a model of the interface consistent with all data. In the second part we consider again a static interface but with a dynamic fluid, where water flows from one reservoir to another through a microscopic channel. We construct a theoretical model to predict the transport of water, charge and salt through a channel from one reservoir to the other as a function of the reservoir and channel properties, specifically in the context of reverse electrodialysis, where an electric current is generated by mixing salt and fresh water. We furthermore investigate the transport properties of an array of microscopic channels, i.e. a membrane. We elaborate why the current generated by a membrane is very different from a single channel. In the last part we investigate a system with both a dynamic interface and fluid, as experiments have shown that ions adsorbed in the interface are laterally mobile and are chemically exchanged with the fluid. We show how and why this can significantly alter the transport properties of these microscopic channels.