Abstract

Electrowetting has been widely used in digital microfluidics as a reliable actuation method due to its considerable advantages such as the absence of heat generation, rapid switching response, flexibility, and low power consumption. Research on the improvement of this method has turned into one of the attractive fields in the design of fluid handling micro devices. This work presents a combined numerical and experimental study to investigate the effect of electrode shape in electrowetting-based microsystems. A new crescent-shaped electrode is proposed which provides a uniform actuation force at the contact line as well as overlap between the adjacent electrodes. The onset of actuation and droplet mobility on electrode arrays have been investigated. The numerical method is based on the Volume of Fluid technique to track the 3-D interface along with the Laplace equation solver to calculate the electric field in the domain. Furthermore, the dynamic behaviour of tri-phase contact line is modeled using the molecular-kinetic theory. Validation experiments were carried out to characterize the droplet actuation on various electrode shapes. The superior performance of the new electrode shape is demonstrated by comparing the droplet velocity and deformation, as well as contact angle distribution with those of a simple flat electrode. Using crescent electrode, the droplet actuation occurs with less deformation and higher velocities. The velocities obtained by using the crescent electrode are up to 4 times at the onset of the actuation and 2 times at the steady state motion of those on the flat electrode. The novel crescent shape can even actuate the droplets which are not placed on the electrode