Experimental Observation of Critical Wetting

An ellipsometry study of the wetting behavior of pentane on water reveals that at a well-defined temperature Tw a continuous transition from a thin to a thick adsorbed film takes place. We present evidence that the transition is due to a Hamaker constant that changes sign with temperature at Tw, and verify that the wetting layer thickness l obeys the power-law divergence, l∝(Tw-T)^-1, predicted for critical wetting in systems with van der Waals forces.