Experimental observation of critical wetting

An ellipsometry study of the wetting behavior of pentane on water reveals that at a well-defined temperature T-w 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 T-w, and verify that the wetting layer thickness I obeys the power-law divergence, l proportional to (T-w - T)(-1), predicted for critical wetting in systems with van der Waals forces.