Droplet rebound on superhydrophilic surfaces: toward self-cleaning functionality

Droplet rebound is commonly associated with superhydrophobic surfaces. we demonstrate that even flat superhydrophilic surfaces can support bouncing behavior, provided a microscopically thin air cushion persists between the droplet and the substrate during impact. Using high-speed imaging and interferometry, combined with numerical modeling, we reveal that the evolution of this transient air film governs the post-impact response. Depending on the impact parameters, we observe three distinct regimes: complete rebound, partial rebound, and spreading. The duration over which the air film remains intact is identified as a critical factor, decreasing with greater inertial loading. We construct a theoretical model based on gas-layer fluid–structure interaction, which predicts the film rupture time as a function of gas viscosity and film thickness. The model agrees closely with experimental results and provides a regime diagram that delineates the boundaries between rebound behaviors. As a practical implication, we find that this air film–mediated rebound can facilitate self-cleaning even on hydrophilic surfaces. Droplet impact can dislodge pre-deposited particles, and the removal efficiency depends sensitively on particle size, wettability, and surface coverage. These findings expand the applicability of droplet impact–based cleaning mechanisms beyond superhydrophobicity, offering new design strategies for surface maintenance using vapor-mediated interactions