Drop splashing on a rough surface: How surface morphology affects splashing threshold

We investigate the drop splashing threshold ST of water on a rough surface. Surface roughness has been known to facilitate drop splashing, but a counterexample has been observed. Here, we suggest a possible explanation of how surface morphology affects drop splashing. We focus on the air flow during the splashing event and estimate ST on a rough surface. To demonstrate this effect, experiments using well-designed surfaces were conducted, and the results agree with our relation. This work shows that surface morphology can both suppress and facilitate drop splashing, and presents a method to predict ST on surfaces with different morphologies.