Liquid dielectrophoresis controlled detachment and re-attachment of bubbles*

Air bubbles attached to surfaces in liquids can block flow in channels, amplify shear wall stress, and form dry patches in heat exchangers. Here we present a new method of controlling the wetting, detachment, and re-attachment of an air bubble in a dielectric liquid through an interface-localized form of liquid dielectrophoresis. We show the contact of the bubble with the surface obeys a dielectrowetting equation, analogous to electrowetting. Moreover, the bubble can be completely detached on demand from the surface with the application of a voltage to a patterned electrode on the surface. Once detached, bubbles are free to float beneath the surface and can be prevented from re-attaching to the surface by a thin liquid layer maintained by an applied voltage. The thickness of this liquid has a logarithmic dependence on the magnitude of the voltage, which we accurately describe by a theory that considers the energy balance due to liquid-dielectrophoresis and buoyancy of the liquid-bubble system. The critical re-attachment voltage is shown to depend on the material parameters of the liquid, and on the geometrical parameters of the electrode pattern.