Spreading dynamics of droplets impacted on an oscillating substrate

Droplet impact on oscillating substrates is ubiquitous in many natural and industrial processes. For example, impact, spreading, and subsequent atomization of rain droplets on beating insect or bird wings and on fluttering leaves govern the spread of pathogens and cellular matters from these surfaces. In industrial applications, oscillating substrates are often used to control atomization, heat transfer, and solidification mechanisms in printing, spraying, or coating processes. Recognizing the importance of the dynamics that arise from the coupling between droplet-transport and substrate motion, in this work, we present an experimental investigation of the spreading of a droplet impacting on a sinusoidally oscillating hydrophobic substrate. The work particularly focuses on the maximum spread of droplets as a function of various parameters of the substrate oscillation. We will show that the maximum spread for impacts on vibrating substrates differs from the impact on static substrates. Specifically, we will elucidate how the frequency, amplitude of vibration, and the phase at the impact significantly affect the outcome. Subsequently, the work will present a scaling analysis to connect the spreading dynamics with an average velocity of the substrate.