Some aspects of the adsorption of a Lennard-Jones gas on a rough surface

We study the adsorption, including wetting, of a Lennard-Jones gas on a rou gh surface consisting of rough layer on a smooth substrate with which the g as interacts via a 9-3 potential. The rough layer is two molecular diameter s thick and consists of a disordered quenched matrix of hard spheres. As we ll as interacting with the other matrix spheres by the hard-sphere potentia l, the matrix molecules interact with the gas molecules by the hard-sphere potential. Hence, on average, the degree to which the gas molecules can app roach the substrate depends only on the density of the matrix layer. The de nsity of this rough layer has a significant effect. As the density of the m atrix layer increases, the adsorption isotherms pass from wetting to a prew etting transition, and, if the layer is dense enough, to partial wetting. I t is interesting that the prewetting transition remains first order. (C) 19 99 American Institute of Physics. [S0021-9606(99)71001-9].