Patterning electro-osmotic flow with patterned surface charge

This Letter reports the measurement of electro-osmotic flows (EOF) in micro channels with surface charge patterned on the 200 mu m scale. We have inves tigated two classes of patterns: (1) Those in which the surface charge vari es along a direction perpendicular to the electric field used to drive the EOF; this type of pattern generates multidirectional flow along the directi on of the field. (2) Those in which the surface charge pattern varies paral lel to the field; this pattern generates recirculating cellular flew, and t hus causes motion both parallel and perpendicular to the external field. Me asurements of both of these flours agree well with theory in the Limit of t hin double layers and low surface potential.