When and how surface structure determines the dynamics of partial wetting

The motion of a three phase contact line, as in a droplet spreading over a dry surface, is ubiquitous in nature and common in technology, but is still not well understood. As has been recently shown, line friction may play an important role in rapid dynamic wetting. Recognizing this as a sometimes dominating factor, we identify the possible scenarios for dynamic wetting of a partially wetting fluid, given the fluid and substrate properties. In doing so, we also reconcile the seemingly different interpretations of dynamic wetting that have been put forward in the recent literature.