ABSTRACT
To describe the superhydrophobic phenomena, it is first fundamental to well understand the Young equation, which gives the apparent contact angle of a liquid droplet on a "smooth" substrate. This contact angle depends on three surface tensions: the solid–vapor, the solid–liquid, and the liquid–vapor interface. The presence of surface structures or roughness is necessary to obtain superhydrophobic properties. Indeed, two equations are very often used to explain the effect of surface roughness on the surface wettability. When a water droplet follows the Wenzel equation, the liquid enters all the surface roughness in contact leading to a full solid–liquid interface. It was also reported in the literature that superhydrophobic properties can be reached from intrinsically hydrophilic polymers. This possibility is not allowed with the Wenzel equation but can be predicted with the Cassie–Baxter equation. The Cassie–Baxter equation can also be used to predict superoleophobic properties even if the materials are intrinsically oleophilic.
