Programmable Control of Two-Phase Fluid Interface Relative Motion in Electrowetting Device

Electrowetting is a highly recognized way to control droplet movement on a solid surface and induce motion in the oil/water interface. It is still challenging to manipulate liquid/liquid interface dynamics due to the electro-capillary instability caused by the electric field in the electrowetting system. Here a dielectric bridge is induced near the oil/water interface by constructing a conductive micropillar (CMP) directly on the hydrophobic surface in an electrowetting system. The CMP height can be adjusted by regulating the wettability of the hydrophobic surface. The electric-field gradient induced by CMP can precisely control the rupture position and guide the contraction direction of the oil film. For application, the CMPs are added in the full-color electrowetting display panel, and the average transmittance can increase 25% at white state due to the consistent oil contract direction. The rupture voltage is reduced, and the response time of the electrowetting display is also improved. The COMSOL simulation results are consistent with experimental results indicating the oil rupture position is controlled by the electric field strength. Combing with program patterning, the authors demonstrate a new display function in an unpatterned indium-tin oxide-based electrowetting display. These findings will benefit most switchable electrofluidic applications and devices with two-phase liquid.