The influence of solid–liquid interactions on dynamic wetting

The molecular-kinetic theory of dynamic wetting has been extended to take specific account of solid–liquid interactions. By equating the work of adhesion with the surface component of the specific activation free energy of wetting, equations have been derived which show the way in which solid–liquid interactions modify both the driving force and the resistance to wetting. For a liquid meniscus advancing across the surface of a solid, these two effects have opposing consequences. Thus, strong interactions increase both the driving force and the resistance, while weak interactions decrease the driving force and the resistance. Because of the form of the relationships, the two effects do not simply cancel out. As a result, the maximum rate at which a liquid can wet a solid may exhibit its own maximum at some intermediate level of interaction. Data taken from both experimental and molecular-dynamics simulations are shown to support these findings, which have significant implications for any process where wetting dynamics are important, such as coating.