ELCTROOSMOSIS ON INHOMOGENEOUSLY CHARGED SURFACES

The electro-osmotic flow generated by an electric field (E) over right arrow(ext) in a fluid bounded by surfaces bearing a charge varying in space is considered. Focusing on a slab geometry, I characterize the formation of steady convective rolls and describe their morphology as a function of the slab thickness. These rolls can be used to generate net currents and forces, even for zero average surface charge density. Moreover, the current (or the force) can be perpendicular to the applied field, opening the way to a variety of microscopic electromechanical devices.