Droplet impact on hydrophobic and superhydrophobic surfaces with the electrowetting technique

Abstract

A droplet impacting hydrophobic/superhydrophobic surfaces undergoes spreading, recoiling, and rebounding. All these phenomena are affected by the energy exchange between the impacting droplet and the surface. In the present work, an electrowetting technique is implemented to change the droplet interaction with the surface. The droplet impact on hydrophobic and superhydrophobic surfaces combined with alternating current electrowetting on dielectric (AC EWOD) has been numerically investigated. Droplet impact characteristics have been studied for various voltage amplitudes, frequencies, and surface hydrophobicities. These factors strongly affect the droplet dynamics of the impacting droplet. An increase in voltage amplitude enhances the maximum spreading of the impacting droplet. In contrast, it reduces the recoiling rate of the droplet, resulting in partial or complete suppression of the droplet rebound. At a particular voltage amplitude, frequency and hydrophobicity of the surface affect the droplet rebound suppression. Complete rebound suppression has been observed at higher voltage amplitudes and the medium range of frequencies (25–50 Hz). The contact time of the droplet decreases with the increase in surface hydrophobicity at all frequencies, whereas it increases with the voltage amplitude. Contact line velocity and velocity inside the droplet manifest the inertia of the droplet. The droplet is unable to rebound if velocities are very low.