THEORY AND SIMULATION FOR ASSOCIATING FLUIDS WITH 4 BONDING SITES

In this paper we present new results from molecular simulation and the ory for associating hard spheres and Lennard-Jones (LJ) spheres with f our association or hydrogen-bonding sites. The association interaction is modelled with a highly anisotropic square well. Results from the f irst-order perturbation form of Wertheim's theory are compared with si mulation results. The agreement between simulation and theory for comp ressibility factor, configurational energy, fraction of monomers, and bonding distribution is good. We also obtained the cluster size distri bution and the average cluster size from simulation. An expression bas ed on the assumptions of the theory and statistical arguments was deve loped for the average cluster size. The agreement between simulation a nd this equation for average cluster size is good for small and modera te strengths of the association potential. Finally the vapour-liquid c oexistence curves for associating LJ fluids were obtained from theory.