Generation of transverse fluid currents and forces by an electric field: Electro-osmosis on charge-modulated and undulated surfaces.

As in the usual paradigm for electro-osmosis, an electrolyte fluid confined between two parallel plates is considered, and an electric field E${\ensuremath{\rightarrow}}_{\mathrm{ext}}$ is applied parallel to the plates. Analyzing here the combined effect of charge and shape modulation on the surfaces, E${\ensuremath{\rightarrow}}_{\mathrm{ext}}$ is shown to generate flows in the slab and forces on the plates even if the plates (and thus the fluid) are on average neutral. Furthermore, the corresponding fluid current and plate drag are generically nonparallel to the field, and can be strictly perpendicular to it in well-chosen geometries. \textcopyright{} 1996 The American Physical Society.