Reversible Electrowetting of Liquid-Metal Droplet

This paper reports experimental investigations on the electrowetting effect of liquid metals, e.g., mercury, on dielectric films. Largest contact angle change of $74deg$ (from $141degto67deg$⁠) is achieved on top of a Parylene film. Highly reversible electrowetting with very low hysteresis $(2-4deg)$ is demonstrated on the Teflon®-coated surfaces. The actuation voltage for $30deg$ contact angle change (from $148degto118deg$⁠) is largely reduced to $25V$ by using a high-dielectric-constant tantalum oxide film as the dielectric layer. The effect of trapped charges in the dielectric film on the electrowetting is observed and measured. The rise and fall times of the electrowetting actuation are inversely proportional to the droplet diameter and as short as $0.1-0.2ms$ for a $50μmdia$ droplet. The actuation reliability is tested, and a long-time operation is achieved in an oil environment.