2-STAGE CAPILLARY CONDENSATION IN PORES WITH STRUCTURED WALLS - A NONLOCAL DENSITY-FUNCTIONAL STUDY

We present phase diagrams for capillary condensation in chemically str uctured slit pores characterized by two first-order transitions from t he confined ''gas'' over ''liquid bridges'' to ''liquid.'' The split a dsorption is produced by a complex periodic wall potential in one of t he lateral directions that mimics inhomogeneities in real materials. A fter the previous condensation of liquid drops at the most attractive adsorption sites these may combine to form liquid bridges between oppo site walls, separated between them by ''gas gaps.'' Nonlocal density f unctional theory is employed to investigate this stepwise mechanism an d the stability of the liquid bridges phase in function of the thermod ynamic conditions and the pore structure, especially the ratio of the two typical lengths, the corrugation period lambda and the pore width H. Macroscopic predictions for the subcritical phase equilibria and th e critical limit complete the study. The calculations confirm our prev ious results [P. Rocken and P. Tarazona, J. Chem. Phys. 105, 2034 (199 6)] for an Ising lattice-gas model solved in the mean-field approximat ion. (C) 1998 American Institute of Physics. [S0021-9606(98)51020-3].