Induced-charge electro-osmosis around metal and Janus spheres in water: Patterns of flow and breaking symmetries

We establish experimentally the flow patterns of induced-charge electro-osmosis (ICEO) around immobilized metallic spheres in aqueous electrolyte. The AC field modifies local electrolyte concentration and causes quadrupolar flows with inward velocities being smaller than the outward ones. At high fields, the flow becomes irregular, with vortices smaller than the size of the sphere. Janus metallo-dielectric spheres create dipolar flows and pump the fluid from the dielectric toward the metallic part. The experimentally determined far-field flows decay with the distance as r-3.