Controllable splitting of impacting droplets by hybrid-wettability surface

Abstract

Manipulating droplets by tailoring the surface wettability has recently attracted a great interest of research. In this work, controllable splitting of impacting droplets was realized by a hybrid-wettability surface consisting of a hydrophilic background surface and two intersecting hydrophobic stripes. A three-dimensional VOF-based (volume of fluid) numerical model had been developed to investigate the splitting dynamics, and a dynamic contact angle model had been employed to capture the droplet interface near the triple line. Several key parameters including surface hydrophilicity, stripe hydrophobicity, stripe width, and impact Weber number were examined. On the basis of these parameters, complete impact phase diagrams were constructed. The results showed that there are four possible pathways for impacting droplets, namely no splitting I, no splitting II, splitting I, and splitting II. The conditions for the four pathways were distinguished. Finally, some new methods had been proposed to further control volume ratios of split satellite droplets and splitting time. The results reported in this work provided useful guideline for designing hybrid-wettability surfaces to realize controllable droplet splitting.