A visual measurement of contact angles in a molecular-dynamics simulation

We have simulated a liquid-vapor interface which is confined by two parallel walls. Initially, a liquid slab is positioned perpendicular to the walls. The liquid-vapor interface deforms to a cylindrical surface which makes a definite contact angle with the walls. The angle could be varied between 0 and π by changing the solid-fluid interaction strength, showing the presence of both a wetting and a drying transition. The angle is related to the strengths of the wall-liquid, wall-vapor and liquid-vapor surface tensions via Young's law. A previous simulation positioned the liquid parallel to the walls and measured the surface tensions. Compared with the contact angles deduced from those measurements, the visually measured angles in this experiment give a different location of the drying transition.