Impurity-Induced Localized Superhydrophobicity Breakdown

A hitherto unknown mechanism for the breakdown of superhydrophobicity, which is the prerequisite for various interface-related applications and phenomena, is reported. When a droplet impacts onto a sphere placed atop a superhydrophobic surface with a droplet-sphere offset, even though the sphere decelerates the droplet, a smaller impact speed than in the case without a sphere impact speed is required for superhydrophobicity breakdown. When the inertia-powered liquid-vapor interface that wraps the sphere with no contact with the sphere surface dominates over the capillarity-driven resistance to interface deformation and the spontaneous spreading of the contact line on the sphere, an air cavity forms near the sphere bottom, and the cavity-collapse-induced jet toward the substrate is revealed to be the reason.