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 $l$ obeys the power-law divergence, $l\propto (T_w-T{)}^{-1\mathrm{}}$, predicted for critical wetting in systems with van der Waals forces.

• Received 5 April 1996

DOI:https://doi.org/10.1103/PhysRevLett.77.1532