Mapping between Surface Wettability, Droplets, and Their Impacting Behaviors

Droplet behaviors on solid surfaces will influence numerous droplet-based applications ranging from nonwetting-preferred water-repellent surfaces to wetting-preferred spray coatings. Understanding droplet behaviors is complicated and centered on integrating multiple parameters that include surface properties, droplet initial states, and other boundary conditions. Previous studies have observed that droplet impacting performance by showing their underlying mechanisms is sensitive to either droplet or surface boundary conditions. While the holistic view about droplet behaviors is still missing, here we study the droplet impacting and spreading behaviors by systemically varying surface conditions and droplet input parameters through the combination of optical experiments, simulations, and theoretical approaches. The observation defines three droplet behavior modes: bouncing, semibouncing, and spreading modes through their dynamic phases, where the most contributing parameters can be identified as the combination of initial Weber number and surface wettability. The We-θ phase diagram suggested here will provide a guideline for surface engineering with desired droplet dynamic behaviors.