DENSITY PROFILES OF A MODEL OF DIMERIZING HARD-SPHERES IN CONTACT WITH A CRYSTALLINE SURFACE - APPLICATION OF WERTHEIM THEORY OF ASSOCIATION

The density profiles of a dimerizing fluid near a crystalline surface are investigated. The model of the bulk fluid is that proposed by Stel l and Zhou, which is a generalization of Wertheim's model for dimeriza tion. The formation of dimers results from the interaction between the intracore attractive sites. The fluid-solid interaction consists of t wo terms. The non-associative term is that proposed by Steele. The dir ectional associative fluid-solid atom interaction is chosen to have a Gaussian form. This provides bonding of the bulk fluid particles with the solid atoms. The solid substrate is assumed to be the graphite bas al plane. The density profiles are studied by using the associative si nglet Percus-Yevick approximation. When the distance from the surface is greater than the dimer length, the effect of crystalline symmetry i s not apparent. The second adlayer tends to disappear when association is present. The relative importance of various positions in the surfa ce unit cell tends to be less when the size of the fluid atom is large r. The dimers prefer to be oriented parallel to the surface but are ti lted from the surface plane when bonded to the carbon atoms. Only a sm all fraction of non-associatively adsorbed dimers have a near-normal o rientation.