THE STRUCTURE AND ADSORPTION OF THE 4 BONDING SITES MODEL FOR ASSOCIATING FLUIDS IN DISORDERED POROUS-MEDIA FROM REPLICA ORNSTEIN-ZERNIKE INTEGRAL-EQUATION THEORY

A model for a network-forming associating fluid in which each of the p articles have four sites available for bonding is considered. The mode l possesses liquid-gas transition in the absence of attractive long-ra nge 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-Zerni ke (ROZ) equations are solved with the Percus-Yevick (PY) and hypernet ted chain (HNC) closures and with the ideal network approximation. The pair distribution functions and the structure factors have been obtai ned. The adsorption isotherms have been calculated using a system of h ard spheres adsorbed in a hard-sphere matrix as a reference. The assoc iative 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 env elope with increasing matrix density. The critical temperature and the critical density are sensitive to the density of adsorbent. Both decr ease with increasing matrix density. (C) 1998 American Institute of Ph ysics. [S0021-9606(98)50120-1].