Enhanced air stability of superhydrophobic surfaces with flexible overhangs of re-entrant structures

The stability of air plastron entrapped in a submerged superhydrophobic (SHPo) surface determines the sustainability of the surface properties including drag reduction, self-cleaning, and anti-icing. To increase the stability for high water pressure, various microstructures have been adopted for SHPo surfaces. A re-entrant structure is a typical example to provide high stability for air plastrons. This work proposes flexible overhangs of the re-entrant structures as a new strategy for additional stability. Several SHPo surfaces with re-entrant structures of different sizes are fabricated, and their Young's moduli (E) are controlled from 715.3 kPa to 2509 kPa. Pressurization of water and air diffusion from the plastrons to the surrounding water cause deformation of the air–water meniscus until air plastron disruption starts to occur. The critical water pressure for air plastron disruption is gradually increased as the E of the overhangs decreases. The critical value is also increased as the gap distance between the adjacent overhangs increases. When the water pressure is less than the critical value, the air plastron is also gradually disrupted by the air diffusion. The lifetime elapsed to the air disruption increases by 19%–44% as the value of E decreases. The present results would pave the way for utilizing flexible overhangs of re-entrant structures as a novel approach for increasing the air stability of SHPo surfaces.