Application of the density functional method to study phase transitions inan associating Lennard-Jones fluid adsorbed in energetically heterogeneousslit-like pores

A density functional approach is used to study the adsorption of the four-b onding-site model associating Lennard-Jones fluid in slit-like pores with e nergetically heterogeneous walls. The fluid-wall potential is qualitatively similar to that invoked by Rocken, P., Somoza, A., Tarazona, P., and Finde negg, G. H., 1999, J. chem. Phys., 108, 8089, i.e. it consists of a homogen eous part that varies in the direction perpendicular to the wall and a peri odic part, varying also in one direction parallel to the wall. Both parts a re modelled by Lennard-Jones 9,3-type functions. The structure of the adsor bed film is characterized by the local densities of all particles and the d ensities of the monomers. The phase diagrams are evaluated for several syst ems characterized by different corrugation of the adsorbing potential. The adsorbing field is strong enough to allow for the layering transition. As w ell as the formation of the so-called bridge phase that fills the pore spac e over the most energetic parts of the wall and of capillary condensation, the layering transition is observed within the first layer adjacent to the pore walls. If the adsorbing potential due to each pore wall is shifted in phase by pi /2, the bridge phase is not formed.