Energy transitions in superhydrophobicity: low adhesion, easy flow and bouncing

Abstract

The concept of superhydrophobicity was introduced in the 1990s as a result of theinvestigation of the microstructure of extremely water-repellent plant leaves. Since thattime, artificial superhydrophobic surfaces have been developed and implemented,stimulated by advances in nanotechnology, and giving one of the most successful examplesof a bio-inspired technology transferred into engineering applications. Superhydrophobicityis usually defined as the ability of a surface to have (i) a very high water contact angle (CA)and (ii) low CA hysteresis. Here we argue that the ability of a water droplet to bounce off asurface constitutes a third property that is crucial for applications. Furthermore,this property is naturally related to the first two properties, since the energybarriers separating the ‘sticky’ and ‘non-sticky’ states needed for bouncing dropletshave the same origin as those needed for high CA and for low CA hysteresis.