The dynamics of directional transport of a droplet in programmable electrowetting channel

Abstract

Directional fluid transport by electrowetting is an effective method for fluid management both on Earth and in the space environment. Exact control of the process is always hard because the fundamental dynamics of fluid flow and interface are not well understood. In this study, we examine the process of a sensible droplet transported directionally in an electrowetting channel. The electrodes of the channel are programmed to actuate the droplet at the most effective manner. We build a numerical model based on the phase field method, and a dynamic contact angle model is incorporated in the model. Based on simulated results, the basic process of droplet deformation and motion is explained. Three different stages are observed when the droplet starts to move in the electrowetting channel. The droplet can be transported at a high velocity of 17 mm/s at a voltage of V = 80 V. A wide range of influence factors, including voltage, droplet size, friction factor, pinning force, channel height, gravity level, and tilted angle of the channel, are considered. The contact line friction increases almost linearly with the contact line friction coefficient and the pinning force, both retarding the motion of the droplet at parabolic relations. With an increase in the gravity level, the transport velocity of large droplet decreases. However, the droplet smaller than the capillary length shows quite good anti-gravity capability, which can be transported smoothly even when the channel is tilted by 90° in a normal gravity.