Microgroove convexity is critical for robust gaseous layers on hierarchically-structured superhydrophobic surfaces

Gaseous layers (plastrons) trapped on the surfaces of immersed hydrophobic surfaces are critical for their function. Fibrillar morphologies offer a natural pathway, yet they are limited to a narrow range of liquid-surface systems and are vulnerable to pressure fluctuations that irreversibly destroy the plastron. Inspired by the convexly grooved surfaces of water fern (Salvinia) leaves that support their fibrous outgrowths, we study the plastron formation on 3D-printed dual-scale surfaces with elliptical interconnected microgrooves. The groove curvature stabilizes a seed gas layer (SGL) that facilitates plastron formation and restoration for all immersed hydrophobic surfaces. Computations and theoretical calculations reveal that the SGL storage capacity that sets the plastron robustness follows from the liquid menisci adaption to the groove geometry and pressure, and it can be further tuned using separated grooves. Our study highlights groove convexity as a key morphological feature for the design of multi-scale immersed surfaces for robust superhydrophobicity.