Pinning-free Evaporation

How can droplets move easily on a horizontal surface when a droplet of rain doesn’t even slide down a window pane? The answer is that the motion of a droplet on a surface is generally hindered by contact line pinning. This is the liquid equivalent of static friction.

If a water droplet is placed on a SLIPS surface, it’s contact line is not pinned but becomes completely mobile. Although drops readily roll off when the SLIPS is tilted (even by an angle of less than 1°), a droplet placed on a horizontal surface won’t roll off. Instead, it will evaporate over time. However, the profile of the evaporating droplet is rather different to that of a droplet evaporating on a non-SLIPS. The apparent contact angle of the droplet remains constant throughout the evaporation time. The droplet profiles show a spherical cap shape modified by a wetting ridge close to the contact line between the droplet and the surface.