Scalable Conversion of Superhydrophobic Surfaces to <i>Salvinia</i> Surfaces

Abstract The underwater functionality of superhydrophobic (SHPo) surfaces relies on the presence of a thin trapped air layer, or plastron, yet maintaining this plastron in uncontrolled environments remains a major challenge. Here, a scalable method is reported to convert SHPo surfaces into Salvinia surfaces by selectively coating polydopamine (PDA) on the top surfaces of microstructures. The success is enabled by identifying and overcoming a previously unrecognized barrier unique to PDA coating on SHPo surfaces. Pressure fluctuation experiments demonstrate that the converted Salvinia surfaces have markedly enhanced plastron stability compared with SHPo counterparts of identical microstructure. Complementary mathematical analysis and numerical simulations establish how micrograting and micropost geometries govern plastron stability, providing a design guideline for SHPo and Salvinia surfaces.