Fig. 1.

Water on textured hydrophobic surfaces can exist in either the Cassie or the Wenzel state. (A) In the Cassie state, water is unable to penetrate the surface texture (blue) so that a water droplet (red) sits on a cushion of air, contacting only the top of the pillars. As a result, there is minimal contact between water and the solid surface, leading to a small contact angle hysteresis and a large contact angle, which are critical in conferring superhydrophobicity to the surface. Also shown is a simulation snapshot of the pillared surface that we study here (Right), which consists of square pillars arranged on a square lattice and is made of atoms (blue spheres) arranged on a cubic lattice. The textured volume, V, as well as the dimensions that characterize the pillared nanotextured surface are highlighted; the width of the pillars is W = 2 nm, their height is H = 4.5 nm, and the interpillar spacing is S = 4 nm. (B) In the Wenzel state, water wets the texture, so that there is extensive contact between water and the solid surface, leading to a large contact angle hysteresis and a smaller contact angle; in this state, the surface is no longer superhydrophobic. We define the normalized density, ${\rho }_{\text{n}}$, in the textured volume to be the number of waters in V, normalized by the corresponding number of waters in the Wenzel state.