Wetting dynamics: a review

University Talks Link: http://talks.is.ed.ac.uk/talk/1003/show

Apart from the fundamental problem of whether a given solid is wetted by a given liquid, many of the practical applications require the precise knowledge of the rates of wetting processes. Particularly, one is often interested to know how fast a liquid can wet a given area of a solid surface. To understand the mechanisms controlling the dynamics of wetting, let us here consider the simplest case: the spreading of a liquid drop on top of a flat solid substrate. When such a liquid drop is placed in contact with the solid, capillary forces drive the interface spontaneously towards equilibrium. As the drop spreads, the contact angle q relaxes from its initial maximum value of 180° at the moment of contact to its equilibrium angle q0 in the case of partial wetting or 0° if the liquid wets the solid completely. At this stage, a unifying approach describing the dynamics of wetting is still missing but  important progress has been achieved rather recently in this direction.

Since the shape of the drop will change versus time, it is clear that dissipation occurs both on a macroscopic scale, due to the reorganization of molecules as described by viscosity, and near the solid, as described by some kind of friction and necessarily dependent on the microscopic characteristics of the system. Considering different channels of dissipation, different macroscopic theories have been developed, and upon certain assumption about the various microscopic characteristics, the behaviour of the liquid can be described.

It is the goal of this presentation to review some recent results based on new experiments and new molecular dynamics simulations to study the details of drop spreading and to provide a review of the physical mechanisms controlling the dynamics of wetting.