Directional transport of water droplet on a programmed electrowetting-on-dielectric device

Electrowetting is a powerful method for directional transport of droplet in space. Its applications in fluid management include water collection, phase separation, and interface control. However, a long-distance transport of the droplet under efficient control is challenging due to complicity of this active method. In this study, we design an experimental setup with a programed open electrowetting-on-dielectric (EWOD) device to achieve continuous transport of a water droplet. A self-controlled software is introduced into the EWOD device. The droplet is transported by electrowetting at a high velocity of about 0.19 m/s. The velocity of droplet transport increases with the applied voltage (V); however, it is close to saturation at about V = 250V. The calculated contact line friction coefficient (ς) is as high as 1.2 Pa·s when V = 200V because the contribution of pinning effect is significant. The ς value reduces to below 0.2 Pa·s when V ≥ 230V and is little dependent on the voltage. The velocity of droplet transport follows a non-monotonic trend with the increase in droplet volume. It reaches the maximum when the volume is about 1.5 μL. The EWOD device shows a good anti-gravity ability. The transport velocity of the droplet decreases with the tilted angle of the chip while the length-to-width ratio of the droplet increases. The droplet can be transported effectively until the tilted angle is as large as 55 °.