Electrokinetics in reactive and conical channels: Not-so-linear transport of charge, fluid, and salt

Abstract

Transport of charge, fluid, and salt in electrolytes is critical for biology, where it nurtures cells, and also for industry, where it is used to purify our drinking water. Not only is transport in electrolytes important, but it also exhibits a rich variety of transport phenomena due to the intricate connection between ionic and fluidic transport. Striking examples are electro-osmotic flow, where a voltage difference drives flow, and streaming current, where a pressure difference drives charge transfer. In straight, micrometer, channels this transport usually exhibits a linear relation between driving force and transport rate. However, in this thesis we investigate transport in reactive and conical channels for which surprisingly transport is nonlinear. We show that flow alters the surface chemistry of a dissolving channel and that electrostatic surface-ion interactions induce nonlinear reaction kinetics. Finally we consider the influence of pressure and geometry on current rectification by conical pores. These nonlinear transport phenomena not only open up new signal-processing and chemical analysis methods, but also affect mineral transport by groundwater.