ADSORPTION OF FLUIDS IN DISORDERED POROUS-MEDIA FROM THE MULTIDENSITYINTEGRAL-EQUATION THEORY - ASSOCIATIVE ANALOG OF THE MADDEN-GLANDT ORNSTEIN-ZERNIKE APPROXIMATION

The associative analogue of the integral equation theory developed by Madden and Glandt is applied to a model of methane adsorbed in a silic a xerogel. The integral equations are solved in the associative Percus -Yevick approximation. The associative treatment of strong attraction between fluid particles and matrix species in this model yields a bett er description of the pair distribution functions at intermediate flui d densities and at low temperatures in comparison with the Percus-Yevi ck approximation. In contrast to the Percus-Yevick approximation, the associative Percus-Yevick theory gives solutions for some subcritical temperatures of the bulk fluid. The adlayer structure is discussed in terms of the fraction of bonded species and coordination numbers. The behavior of the distribution functions and internal energy coincides w ith the Monte Carlo simulation data of Kaminsky and Monson. It is show n that the model can be used for the description of different Lennard- Jones fluids in hard sphere matrices. Possible refinements of the theo ry by using the replica Ornstein-Zernike equations of Given and Stell are discussed briefly.