Droplet Retention on Superhydrophobic Surfaces: A Critical Review

Abstract Wetting phenomena and superhydrophobic surfaces are ubiquitous in nature and have recently been explored widely in scientific and engineering applications. The understanding and control of surface superhydrophobicity are not only fundamentally intriguing but also practically important to provide unique and regulated functionalities to natural species and industrial applications. Here, the fundamentals of wetting phenomena are critically reviewed that especially apply to superhydrophobicity, putting an emphasis on the clarification of contact angles, the quantification of droplet retention force, and the role of contact line. The fundamentals of how the droplet retention is determined by the surface features are discussed and advanced analytical models for the prediction of contact angles and retentive forces are introduced. Applications are further discussed whose functionalities largely depend on the droplet retention, including directional droplet transport, anti‐icing, and water harvesting.