Reversible Electrowetting of Liquid-Metal Droplet

In this paper, we study in detail the electrowetting behavior of a liquid-metal droplet (mercury) on top of a dielectric insulating layer experimentally. 74° of the contact angle change (from 141° to 67°) is achieved by applying a voltage of 180V to a mercury droplet on a Parylene surface. By using a very thin Teflon AF coating, low contact angle hysteresis (2°) and highly reversible electro-wetting are reported. The dynamic responses of the droplet to a voltage stair and a voltage pulse are video-captured and analyzed by using a high-speed camera. The electrowetting has very fast rise/fall time, which is suitable for application in MEMS devices. By using a high-k material as the insulating layer along with a thin Teflon AF coating, a very large contact angle change of 40° (from 150° to 110°) is achieved with only 30V. Saturation of the electrowetting behavior is also observed and discussed. Applications of the electrowetting effect of a liquid-metal droplet in MEMS devices are discussed.