Lubrication effects on droplet manipulation by electrowetting-on-dielectric (EWOD)

Abstract

Electrowetting has the potential to realize stand-alone point-of-care devices. Here, we report droplet-migration characteristics on oil-infused electrowetting-on-dielectric substrates. We prepare sparse micropillars to retain the oil layer in order to exploit the layer as a lubricating film. A physical model of the droplet velocity is developed, and the effects of the lubrication, the oil viscosity, the droplet volume, and the thickness of solid and liquid dielectric layers are discussed. It is found that the droplet velocity is scaled as U≈E2, which differs from a relationship of U≈E3, which is predicted from the dominant drag force for droplets sliding down on liquid-infused surfaces by gravity. Furthermore, our device achieves droplet velocity (19 μl) of ∼1 mm s−1 at the applied voltage of 15 V. The velocity is approximately tenfold as high as the same condition (applied voltage and oil viscosity) on porous-structure-based liquid-infused surfaces. The achieved high velocity is explained by a lubrication-flow effect.