NUCLEATED WETTING FILMS - THE LATE-TIME BEHAVIOR

We examine the late-time wetting behavior of the system hexadecane plu s acetone after the coalescence of nucleated wetting droplets into a u niform wetting film. The experimental results at large reduced tempera tures (t > 7 X 10(-4)) fall into two distinct wetting layer thicknesse s of 43.1+/-2.7 nm and 29.5+/-2.0 nm. We identify the similar to 43.1 nm layer with a nonequilibrium wetting state that exists after the nuc leated wetting droplets have coalesced into a uniform wetting film. Th is nonequilibrium state has a lifetime of a few hours before it collap ses into a film of thickness similar to 29.5 nm, which we believe corr esponds to an equilibrium wetting layer. The collapse of the nonequili brium wetting film is explained in terms of a hydrodynamic instability where the film is in a regime that is unstable to long-wavelength cap illary wave fluctuations on the adjacent critical interface. The magni tude of the equilibrium wetting film gives reasonable quantitative agr eement with the dispersion theory of Dzyaloskinskii, Lifshitz, and Pit aevskii [Adv. Phys. 10, 165 (1961)]. At small reduced temperatures (t < 7 X 10(-4)) critical adsorption effects within the wetting layer bec ome significant.