The structure and adsorption of the four bonding sites model for associating fluids in disordered porous media from replica Ornstein–Zernike integral equation theory

Abstract

A model for a network-forming associating fluid in which each of the particles have four sites available for bonding is considered. The model possesses liquid–gas transition in the absence of attractive long-range nonassociative interactions. We have studied the adsorption of the fluid in a disordered porous media that corresponds to an equilibrium configuration of hard spheres. The associative replica Ornstein–Zernike (ROZ) equations are solved with the Percus–Yevick (PY) and hypernetted chain (HNC) closures and with the ideal network approximation. The pair distribution functions and the structure factors have been obtained. The adsorption isotherms have been calculated using a system of hard spheres adsorbed in a hard-sphere matrix as a reference. The associative contribution to the chemical potential follows from Wertheim’s thermodynamic perturbation theory, however, with monomer fraction from the solution of the ROZ equations. The liquid–vapor coexistence curve has been evaluated. We have observed shrinking of the coexistence envelope with increasing matrix density. The critical temperature and the critical density are sensitive to the density of adsorbent. Both decrease with increasing matrix density.