3-D thermodynamic analysis of superhydrophobic surfaces.

Some microtextured surfaces strongly repel water. In particular, surfaces with contact angle (CA) higher than 150 degrees are called superhydrophobic surfaces and many studies to obtain such surfaces have been reported. However, none of them could be a guide to achieve superhydrophobicity and the thermodynamic mechanisms are not well understood. In this study, two types of 3-D models--pillar-textured surfaces and cavity surfaces--were selected and thermodynamically analyzed focusing on the surface free energy. By calculations, equilibrium CA, free energy wall (FEW), and CA hysteresis are obtained. Based on these calculations, the factors to determine the sliding angle are indicated. Additionally, based on these results, one example of the optimal geometry for superhydrophobic surfaces is proposed.