We examine the late-time wetting behavior of the system hexadecane plus acetone after the coalescence of nucleated wetting droplets into a uniform wetting film. The experimental results at large reduced temperatures (t>7×${10}^{\mathrm{-}4}$) fall into two distinct wetting layer thicknesses of 43.1±2.7 nm and 29.5±2.0 nm. We identify the ∼43.1 nm layer with a nonequilibrium wetting state that exists after the nucleated wetting droplets have coalesced into a uniform wetting film. This nonequilibrium state has a lifetime of a few hours before it collapses into a film of thickness ∼29.5 nm, which we believe corresponds to an equilibrium wetting layer. The collapse of the nonequilibrium wetting film is explained in terms of a hydrodynamic instability where the film is in a regime that is unstable to long-wavelength capillary wave fluctuations on the adjacent critical interface. The magnitude of the equilibrium wetting film gives reasonable quantitative agreement with the dispersion theory of Dzyaloskinskii, Lifshitz, and Pitaevskii [Adv. Phys. 10, 165 (1961)]. At small reduced temperatures (t<7×${10}^{\mathrm{-}4}$) critical adsorption effects within the wetting layer become significant.

• Received 11 February 1993

DOI:https://doi.org/10.1103/PhysRevE.50.2827