Underwater superhydrophobicity: Stability, design and regulation, and applications

Bioinspired superhydrophobic surfaces have attracted great interest from fundamental research to engineering applications. The stability, design, and regulation of superhydrophobicity, especially in a submerged environment, have been one of the main focuses of recent efforts. This review is dedicated to illustrating the fundamental characteristics of underwater superhydrophobicity, introducing novel and effective strategies for robust design and regulation, and to providing an overview of the state-of-the-art engineering applications in drag reduction and cavitation/boiling control. First, the underlying mechanisms of wetting transition on superhydrophobic surfaces submerged underwater induced by physical phenomena including pressurization, air diffusion, fluid flow, and condensation are reviewed. The influence of the closed/open state of entrapped air cavities is differentiated. Landmark experiments demonstrating wetting transition mechanisms are surveyed. Then, novel strategies for designing robust superhydrophobic surfaces are summarized, including hierarchical, reentrant, lubricant-infused, and mechanically durable structures. Moreover, strategies for superhydrophobicity regulation are introduced, which are classified into two types: self-healing and dewetting, based on the failure regime (surface damage or meniscus collapse). The current state-of-the-art engineering applications in drag reduction and cavitation/boiling control are comprehensively reviewed. Last but not least, remaining challenges for future research are given at the conclusion.