INTEGRAL-EQUATION THEORY FOR THE 4 BONDING SITES MODEL OF ASSOCIATINGFLUIDS .2. DENSITY PROFILES AND ADSORPTION ONTO A SOLID-SURFACE

Density profiles and adsorption isotherms of an associating fluid with four bonding sites near a solid surface are investigated using the Pe rcus-Yevick approximation for the associative Henderson-Abraham-Barker equation. The fluid molecule is represented as a hard sphere with fou r independent attractive sites. The surface is modelled as a hard wall and also as an adhesive wall. The density profiles are obtained both numerically and analytically (as the Laplace transform) as functions o f bulk number density eta and of the reduced inverse temperature beta . The features connected with increasing average number n(b) of bonds are discussed. An analytical expression for the adsorption coefficient is derived. Since the system exhibits critical behaviour, the gaseous and liquid branches of both the adsorption isotherm and density profi les are described separately. The density profiles and adsorption isot herms are compared with Monte Carlo simulation data. In the case of an adhesive surface the competition between the adhesion and association is studied. The formation of several gaseous adlayers at the wail is demonstrated.