Dependence of Fluid Slip Over Superhydrophobic Surfaces on Equilibrium

The relation between contact angle and slip length is explored using molecular dynamics for Couette flow of a Lennard–Jones (LJ) fluid between graphite-like walls. Obtained results vary from the common notion that higher contact angles lead to greater slip and to more effective friction reduction. Effects of varying LJ parameters on contact angle and slip length are investigated parametrically. Results are shown in a 3D map, where the third dimension is the square root of the solid–fluid atom size ratio. Epitaxial layer data help to explain unexpected slip length behavior in relation to the contact angle, and reported inconsistencies between slip length experiments and simulations. Therefore, it seems that solids that can produce favorable epitaxial layering of the fluid will cause larger slip. Dimensional analysis is used to elucidate the contact angle-slip length relationship. The present data can be applied to developing artificial supersolvophobic surfaces that are fundamental to friction drag reduction on interfaces.