Sequence of Two Wetting Transitions Induced by Tuning the Hamaker Constant

We report an ellipsometry study of the wetting of hexane on water. By adding salt to the water, we are able to tune the Hamaker constant of this system. This allows us to demonstrate, for the first time, that two rather than one wetting transitions can exist in a single system. Upon increasing the temperature, a discontinuous (first-order) transition from a microscopic film to a mesoscopic film occurs, followed by a continuous (critical) wetting transition that leads to a thick adsorbed film. The latter is due to the Hamaker constant which changes sign with temperature. The first-order transition temperature changes by the same amount as the critical wetting temperature upon changing the Hamaker constant.