Numerical simulation of droplet shapes on rough surfaces

It has been demonstrated that surface roughness causes superhydrophobicity. Our objective is to develop a numerical tool and study the relationship between the roughness characteristics and the apparent contact angle and motion of liquid drops on rough surfaces. As a first step we consider a stationary drop on a substrate with a simple geometry of horizontal grooves. A public domain software is modified to numerically investigate the 3D equilibrium drop shapes on a rough surface. We observe that a drop of given volume and actual contact angle attains different equilibrium positions on a rough substrate. The energies and the apparent contact angles of each equilibrium state are different. The actual contact angle in our simulations was ≥ 90°. It was also seen that for higher values of actual contact angles the liquid tends to move out of the grooves thus leading to the formation of a composite surface of contact on the substrate.