Effects of droplet volume, electrode geometry, and surface tension on the threshold actuation voltage of a droplet on coplanar electrodes

Abstract

Actuation voltage is critical for droplet motion on coplanar electrodes via electrowetting on dielectric. In this study, we derive an electromechanical model including threshold actuation voltage, as well as liquid (surface tension, droplet volume, electrical conductivity) and device parameters (electrode width, applied frequency, relative permittivity, and thickness of materials) on a one-plate structure. In addition, the effects of the three most important parameters (droplet volume, electrode geometry, and surface tension) on the threshold actuation voltage of the droplet on coplanar electrodes were investigated experimentally. The effects of electrode geometry, surface tension, and droplet volume on liquid actuation voltage can also be successfully explained based on the theoretical model. This study covers a wide range of droplet volume and surface tension for liquid actuation voltage. Different solutions—DI water, NaCl solution, and water–ethanol mixtures—are used to verify the threshold actuation voltage of liquids in our model. The model’s results are in good agreement with experimental results. Our findings can be utilized to obtain the threshold actuation voltage for various solutions on coplanar electrodes.