Transient study of droplet oscillation characteristics driven by an electric field

Electrowetting technology, a microfluidic technology, has attracted more and more attention in recent years and has broad prospects 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 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, including the perspective of pressure variation and force balance inside the droplet. The results show that when the alternating current frequency increases from 50 Hz to 500 Hz, the amplitude of the oscillation waveform after droplet stabilization is 0.036 mm, 0.016 mm, 0.013 mm and 0.002 mm, while the relevant droplet oscillation period T is 11 ms, 4 ms, 2 ms and 1 ms, 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 an eddy current, in which the number of vortices matches the resonance mode. A high resonance mode corresponds to a small droplet amplitude, while there are more vortices with a smaller size.