Models are proposed for thick-film-coverage adsorption on a general fractal surface. The basic idea is that long-range dispersion forces dominate the thermodynamic behavior. The analysis predicts the coverage to be proportional to [ln($P_0$/P${\left)\right]}^{\left(D\mathrm{-}3\right)/3}$ where P/$P_0$ is the relative vapor pressure and D is the fractal dimension of the surface. Experimental examples for this behavior are presented. They are rough Ag surfaces, giving D=2.30. .AE

• Received 22 September 1988

DOI:https://doi.org/10.1103/PhysRevLett.62.1997