A porous superhydrophobic surface with active air plastron control for drag reduction and fluid impalement resistance

Superhydrophobic surfaces are attractive for applications in vehicular locomotion enhancement and biomedical fluid transport. However, under high fluid impalement pressures, these surfaces would lose their function due to the collapse of the air plastron. Here, we developed an effective strategy for robustly maintaining the air plastron under high pressure, by actively controlling the air plastron pressure through a porous superhydrophobic Ti surface. The prepared superhydrophobic surface had hierarchical micro/nano-structures with interconnected micropores, enabling us to supply pressure to the air plastron to counter external impalement pressures, and the air plastron could resist high hydraulic pressures (tested up to 350 kPa). Moreover, active air plastron pressure control and superhydrophobicity were found to have synergic effects in achieving significant drag reduction (92-96% for high speed water jetting), which was impossible with either of them alone. Furthermore, we observed pancake bouncing for droplets impacting our superhydrophobic surface with the active air plastron pressure control, unprecedentedly reducing the droplet contact time by up to 91.5%, thus demonstrating that pancake bouncing is possible even on surfaces with irregular micro-/nano-structures. With these demonstrated features, this study thus provides a simple yet effective approach to robustly maintain the air plastron on superhydrophobic surfaces for applications requiring high impalement resistance.