Electric instability of cassie droplets on super-lyophobic pillar surface: Pull-in versus electrowetting

This paper presents for the first time the modeling and experimental efforts to classify the electric instability modes of the Cassie-state droplets on super-lyophobic surface. The shape of the liquid-air interface on overhanging pillar structure, under the influence of the electric field, has been directly captured using a high-precision laser displacement meter. We develop a force-balance model with which a geometry-dependent boundary curve identifying the two competing modes of the Cassie-to-Wenzel transition: 1) pull-in of the liquid-air interface, and 2) electrowetting-limited process. The validity of our model has been successfully demonstrated through the present experiments.