If one looks at a leaf of a plant after a rainfall, one sees water droplets of varying sizes. What determines this “wetting” behavior? The answer, known in principle for two centuries, involves the surface tension of the water itself, as well as the two surface tensions at the water-leaf interface (liquid-leaf and vapor-leaf). At the microscopic level, the wetting behavior depends on the relationship between two interactions: the cohesive interaction between two water molecules and the adhesive interaction between a water molecule and the leaf.
In this talk, I will report the first wetting phase transition for water ever to be seen. In studying the wetting transition theoretically, one encounters the least attractive interactions in nature. This transition, in general, can involve liquids as varied as superfluid helium, mercury and water, interacting with alkali metals and graphite surfaces. A fundamental question is this: why are these interactions so weak? From the statistical mechanical point of view, the transition is believed to be described by the two-dimensional Ising model, but this claim has not yet been demonstrated experimentally.