Transient study of droplet oscillation characteristics driven by an electric field

Abstract

Electrowetting technology, one of the microfluidic technologies, has attracted more and more attentions in recent years, and it has a broad prospect in terms of microdroplet drive. In this paper, the dynamic contact angle theory is used to develop a numerical model to predict the droplet dynamic contact behavior and the internal flow field under electrowetting. In particular, based on the established computational model of droplet force balance, the dynamic process of a droplet under electrowetting is analyzed, with the perspective of pressure variation and force balance inside the droplet. The results show that when the alternating current frequency increases from 50Hz to 500Hz, the amplitude of the oscillation waveform after droplet stabilization is 0.036mm, 0.016mm, 0.013mm, 0.002mm, while the relevant droplet oscillation periods T are 11ms, 4ms, 2ms, 1ms, respectively. It is also found that the initial phase angle does not affect the droplet oscillation amplitude. In addition, the pressure on the droplet surface under alternating current electrowetting increases rapidly to the maximum value, with resonant waveform oscillation, and the droplet will present different resonance modes under voltage stimulation. The higher the resonance mode is, the smaller the droplet oscillation amplitude is, and the streamline at the interface will present eddy current, in which the number of vortices matches the resonance mode. The high resonance mode corresponds to the small droplet amplitude, while there are more vortices with smaller size.