Controlled Fabrication of Salvinia-Inspired Heterogeneous Surfaces for Recoverable Underwater Air-Water Interfaces

Stabilizing the air-water interface (AWI) on underwater material surfaces is essential for enabling long-term interfacial functionality. However, conventional superhydrophobic surfaces fail to preserve this composite interface under pressure fluctuations or extended immersion, underscoring the need for alternative stabilization strategies. Here, inspired by the hierarchical architecture of Salvinia, we developed a deterministic fabrication strategy that couples femtosecond-laser-induced self-growth of micropillars on thermally shrinkable polystyrene (PS) with an asymmetric scanning method. This method produces eggbeater-like structures with precisely controlled geometry and spatial arrangement. Localized hydrophilic tips were further introduced with micrometer-scale precision, yielding biomimetic Salvinia surfaces (BSSs) that integrate air-retaining superhydrophobic regions with hydrophilic domains capable of pinning the AWI. The BSSs exhibited enhanced contact-line pinning, improved resistance to liquid penetration, and reversible recovery of the AWI under pressure perturbations. They sustained repeatable interfacial recovery over 60 negative-pressure cycles and preserved AWI stability under complex hydrodynamic disturbances. These results demonstrate that combining controlled microgeometry with localized wettability heterogeneity provides a robust and effective strategy for regulating AWI evolution on submerged surfaces.