Dynamic characteristics of droplet impact on vibrating superhydrophobic substrate

Abstract

The vibration of solids is ubiquitous in nature and in industrial applications and gives rise to alternative droplet dynamics during impact. Using many-body dissipative particle dynamics, we investigate the impact of droplets on superhydrophobic solid surfaces vibrating in the vertical direction at a vibration period similar to the contact time. Specifically, we study the influence of the impact phase and vibration frequency. We evaluate the influence from the aspects of maximum spreading diameter, the solid–liquid contact time and area, and the momentum variation during the impact. To quantitatively evaluate the solid–liquid contact, we introduce the area-time integral, which is the integral of the contact area over the whole contact time. It is meaningful when the heat exchange between solid and liquid is considered. One characteristic phenomenon of droplets impacting vibrating substrate is that multiple contacts may occur before the final rebound. Unlike previous studies defining the contact time as the time span from the first impact to the final detachment, we define the contact time as the summation of each individual contact time. Using this definition, we show that the discontinuity at the critical impact phase disappears. The fact that the area-time integral also changes continually with the impact phase supports the assumption that the effect of impact phase on the solid–liquid contact may be continuous. Moreover, we show that the probability of impact phase is affected by the vibrating frequency and use it to calculate the weighted averaged outcome when the impact phase is not controlled. This study not only offers insights into the physics of droplet impact on vibrating surfaces but also can be used to guide the design of surfaces to achieve manageable wetting using vibration.