Electrically Driven Continuous Motion of a Water Droplet Over a Single Active Electrode

Abstract

This paper studies electrically-driven continuous motion of a liquid droplet placed on a dielectric surface using a single active electrode. In an experiment, an open electrowetting-on-dielectric (EWOD) configuration is used with a bottom active electrode and a top ground wire placed horizontally above just touching the drop. Simulations have been carried out in a two-dimensional coordinate system using COMSOL© along with a constant contact angle model arising from the Young-Lippmann equation at the three-phase contact line. The computational model mimics the experimental arrangement of a sessile droplet sitting on a dielectric-coated active electrode. The top ground wire electrode is placed horizontally over the droplet instead of being vertically inserted into it. The ground wire leads to initial spreading, followed by continuous motion along the electrode. Droplet spreading stops before it loses contact with the top ground wire. This constraint determines the shape of the drop and its resulting motion. Experimentally recorded images are further compared with numerical simulation.