Dynamics of droplet motion induced by Electrowetting

Electrowetting (EW) has drawn significant interests due to the potential applications in electronic displays, lab-on-a-chip microfluidic devices and electro-optical switches, etc. However, current understanding of EW is hindered by the inadequacy of available numerical and theoretical methods in properly modeling the transient behaviors of EW-actuated droplets. In the present work, a combined numerical and experimental approach was employed to study the EW response of a droplet subject to both direct current (DC) and alternating current (AC) actuating signals. Computational fluid dynamics models were developed by using the Volume of Fluid (VOF)-Continuous Surface Force (CSF) method. A dynamic contact angle model based on the molecular kinetic theory was implemented as the boundary condition at the moving contact line, which considers the effects of the contact line friction and the pinning force. The droplet shape evolution under DC condition and the interfacial resonance oscillation under AC condition were investigated. It was found that the numerical models were able to accurately predict the key parameters of electrowetting-induced droplet dynamics.