Regulating droplet impact on a solid hydrophobic surface through alternating current electrowetting-on-dielectric

Abstract

The phenomenon of droplet impact is commonly found in industrial and agricultural processes. The basic characteristics and theories of a droplet impacting solid walls have been extensively studied, but the regulation of the droplet impact phenomenon has not been adequately examined. This study investigates the regulation of droplet impact on a hydrophobic surface based on alternating current electrowetting-on-dielectric (AC EWOD). When a water droplet impacts a virgin Teflon surface at 1.06 m/s, the phenomenon of partial rebound occurs. When an AC voltage is applied to an electrode pair underneath the Teflon layer, the droplet is stabilized on the hydrophobic surface after impact. To investigate the mechanism of influence of the AC signal on the regulation of droplet impact, the variation in the spread diameter and height of the droplet were characterized at different frequencies and amplitudes of the AC signal. An oscillation in the diameter of the droplet was observed in the retraction stage with the application of AC EWOD, which was the dominant effect in neutralizing the retraction kinetic energy and yielded the rebound inhibition effect. A transition diagram between partial droplet rebound and rebound inhibition was plotted in terms of voltage, frequency, and the Weber number, and theoretical analysis was carried out to determine the retraction kinetic energy dissipated by the viscous force when the AC EWOD signal was applied.