Pressure-Induced Plastron Collapse and Drag Reduction on Surfaces with Mushroom-Shaped Re-entrant Microstructures

Superhydrophobic surfaces can reduce underwater skin-friction drag by sustaining a lubricating plastron at the solid–liquid interface. Their practical use, however, is limited by plastron collapse under elevated hydrostatic pressure. Inspired by the micro/nanotopography of springtail cuticles, we constructed a molecular dynamics model of a superhydrophobic surface with mushroom-shaped re-entrant microstructures (MSRM) that markedly improves pressure resistance and drag-reduction performance. The Cassie-to-Wenzel transition was identified from abrupt changes in the solid–liquid interfacial interaction energy. The critical plastron-collapse pressure increased nearly linearly with the projected microstructure area fraction, whereas enhanced hydrophobicity raised both the critical pressure and the critical contact angle. Within the parameter range examined, projected area fraction exerted a substantially stronger influence on plastron stability than surface wettability. A theoretical model was developed to describe the combined effects of projected area fraction, wettability, and characteristic size on the plastron-collapse pressure. Among the morphologies considered, the MSRM surface exhibited the highest initial Cassie-state critical pressure and the largest slip velocity, demonstrating favorable overall plastron stability and drag-reduction performance. The T-shaped microstructure exhibited two successive wetting thresholds associated with its upper and lower cap edges, suggesting a route toward multilevel pinning designs. These findings will provide a molecular-scale basis for the design of durable superhydrophobic drag-reducing surfaces.