Splitting dynamics of droplet impact on ridged superhydrophobic surfaces

Droplet splitting is a fascinating interfacial phenomenon, which shows great potential in applications such as fluid dispending and liquid spraying. Splitting behaviors of droplet impact on structured superhydrophobic surfaces are highly transient and complex, but the underlying mechanism is far from clear. Here, we report the splitting dynamics on ridged superhydrophobic surfaces through experimental and theoretical investigations. As the Weber number increases, three splitting modes appear in sequence: non-splitting, departure splitting, and contact splitting. Based on the movement of the liquid film behavior on the ridge along the axial direction, the splitting time consists of durations of three stages: axial spreading, axial retraction, and oscillation retraction, and it decreases with the increasing Weber number. A theoretical model is further established to predict the splitting time, where the law of the axial spreading and retraction is revealed. Splitting dynamics can be regulated by the geometric shape of the ridge. Droplet splitting is inhibited on the rectangular ridge, while the splitting time and contact time are effectively reduced on the semi-cylindrical and triangular ridges. This work is expected to provide fundamental support for diverse applications related to droplet splitting and offer guidance for the design of superhydrophobic surfaces.