Static and spontaneous electrowetting

摘要

There has been recent renewed interest in electrocapillary and electrowetting phenomena given its potential for microfluidic actuation and manipulation. Different approaches, in which a variety of electrode configurations have been adopted, however, have dominated the developments in this field. These different approaches have given rise to rich and varied behavior, which has often led to some overlap and confusion in the literature. In this axticle, we delineate the different observations and elucidate the relationship between these phenomena by re-stressing classical concepts and examining their limitations. Paxticular emphasis is placed on the distinction between static and spontaneous electrowetting. In the former, a static change in the liquid-solid macroscopic contact angle results when a dielectric film-coated planar plate electrode is employed. In the latter, a spontaneous thin front-running electrowetting film is pulled out ahead of the macroscopic drop with the use of planar parallel line electrodes. This dynamically evolving electrowetting film advances much faster than the macroscopic drop itself and behaves in a self-similar manner analogous to gravity spreading films.