We present a study of finger instability observed in a propagating front resulting from dewetting of a thin water film on a mica substrate. The phenomenon results from a longitudinal instability in a thick cylindrical rim along the front, whose unusual properties are determined by domination of long-range van der Waals interaction between the film and the substrate over the effect of curvature. The interpretation is borne out by quantitative measurements and supported by computer simulations.

When a water film evaporates from a mica substrate, an interface similar to a solidification front develops, separating two films of different thicknesses. We show experimentally that the evolution dynamics is controlled mainly by material diffusion through the vapor phase rather than by hydrodynamic flow through the film. Our results illustrate the role of different contributions to pattern formation of volatile liquid films.

We report the first observation of wetting transitions of hep 4 He crystals grown on a metallic substrate. Crystals grown with the [0001] direction perpendicular to the substrate undergo a continuous wetting transition in the range 0.81 < 7 T <0.85 K, whereas crystals grown with the [lOTO] direction perpendicular to the substrate undergo a first-order wetting transition at T= 1.03 K. Our results demonstrate that continuous wetting is possible in a system governed by van der Waals forces.