Electrowetting dynamics of sessile droplets in a viscous medium

Electrowetting is a technique that reversibly or irreversibly alters the wetting properties of a droplet on a hydrophobic substrate by applying an electrical field. In this paper, we studied electrowetting dynamics of sessile droplets on a hydrophobic substrate surrounded by viscous liquids. Through this study, we answered the following unanswered questions: the drop's transient response immediately after the actuation, the drop's retraction and resultant dynamics, and the effect of multiple wave actuation on the droplet transition. An overall energy balance approach is extended for analyzing the transient wetting dynamics of droplets from the initial position to the new equilibrium position in viscous media with appropriate governing parameters. The governing nondimensional parameters are the electrowetting number (q), the Roshko number (Ro), the Ohnesorge number (Oh), and the viscosity ratio (mu r) between the droplet and the surrounding medium. This theoretical study, in corroboration with the experimental study, describes the transient evolution of the drop motion from the initial position to the new equilibrium position and predicts the shift from in-phase to out-of-phase drop response for the applied waves.