Electrowetting Droplet Actuation in Micro Scale Devices

Abstract

Surface tension is a dominant force for liquid handling and actuation in microscale. Application of an external electric field can change the surface tension between the liquidsolid interface, which reduces the meniscus contact angle and induces motion of a droplet in a microchannel. Numerical simulation of droplet transport in microchannels under electrostatic actuation is investigated. Volume-of-Fluid (VOF) technique is employed, where electrowetting eects are implemented through Lippmann’s relation in the form of modified contact angles at the boundary. Experimental data for steady and transient velocities of droplets in microchannels are used to calibrate the code. Numerical simulation of a zero-leakage microvalve is investigated where a liquid droplet is used as a zero-leakage gate to regulate the flow in a T-junction. The droplet gate is activated by changing its surface tension via an applied electrostatic potential. Numerical simulation is used to predict the droplet behavior and to optimize valve design. It is found that the pressure break-down of the microvalve is significantly aected by the geometry of the T-junction corners. It is expected that such a microvalve design significantly improve the sensitivity and performance of many microfluidic devices.