(166c) Ion Conservation and Its Consequences for Electro-Osmosis and Electrophoresis

I will discuss electrokinetic flows, in which applied electric fields exert forces upon ionic clouds that surround charged surfaces, forcing the surrounding fluids into motion. Such effects have been known for two centuries, and a rational theory has been around for one. Given this history, one has no right to expect new surprises to emerge. Developments in micro- and nano-fluidic systems, however, have subjected the classic theory to new tests, and challenged our understanding of even the most basic concepts in this arena. I will describe cases in which the "standard model" of coupled ion transport and viscous flows are inadequate to explain measured phenomena, and will describe various mechanisms by which such discrepancies might arise. In particular, I will describe cases where non-uniform ion transport along surfaces -- e.g. nanoscale roughness, variable surface charge, or inhomogeneous slip -- changes even the qualitative features of electrokinetic flows.