(485a) Electrokinetic Flows Over Rough Surfaces

Electrokinetic flows arise when externally-applied electric fields force the (charged) ionic clouds that screen charged surfaces, exerting a body force upon the fluid and driving it into motion. Classic studies of this phenomenon have typically involve electrophoresis, in which solid particles move electrokinetically through an electrolyte, and electro-osmosis, in which an electrolyte is driven to flow relative to surfaces. While the vast majority of studies of these phenomena have involved surfaces that are effectively smooth, we demonstrate that even nanometer-scale roughness can have a dramatic effect upon the electrokinetic flow over surfaces. Since such roughness routinely occurs with microfabricated metal electrodes (i.e. evaporated or sputtered), the effects we discuss have broad implications for microfabricated (AC or DC) electrokinetic systems. We illustrate with simple and intuitive physical arguments as well as more detailed calculations and experiments.