A two-dimensional model associating fluid with spherically symmetric intracore square-well shell. Integral equations and Monte Carlo simulation study

Abstract

The structure and thermodynamics of a monolayer of an associating fluid in the framework of the primitive model of Cummings and Stell is studied by using a two-dimensional approximation. The model permits formation of dimer species for small values of the bonding length parameter, the formation of chains, if the bonding length is slightly larger, and also the vulcanization of species for bonding length values close to the diameter of particles. The structure and thermodynamics of the model that are of interest for statistical mechanics of surface chemical reactions, are studied by computer simulations in the canonical, grand canonical and isobaric ensembles and from the two-dimensional Ornstein—Zernike-like or Wertheim's Ornstein—Zernike integral equation. We have shown that the theory is satisfactory for the case of dimerization if the fluid density is low. For higher densities one must apply a correction for the cavity distribution functions to describe the fraction of unbonded species more adequately. For the case of chain formation the theory just resembles trends following from the simulation data. For the model with vulcanization of species we have obtained the fractions of differently bonded particles and have shown that chemical ordering of species is manifested in the antiphase oscillations of the pair distribution functions of species.