Square-well chains: Bulk equation of state using perturbation theory and Monte Carlo simulations of the bulk pressure and of the density profiles near walls

Abstract

Equations of state are obtained for square-well chains via perturbation theory about the hard chain system. The molecules are modeled as a pearl necklace of freely jointed spheres that interact via a site–site square-well intermolecular potential. The local structure of the reference fluid (required in perturbation theory) is obtained from polymer reference interaction site model (polymer–RISM) theory. The theory is compared to Monte Carlo simulation data for the pressure of square-well chains obtained from simulations of the fluid between walls. At high temperatures the density profiles are characterized by the packing/entropic effects observed in hard chains; as the temperature is lowered the attractions cause a severe depletion of sites from the region near the walls. The agreement of the theory with the simulation data for the compressibility factor is good for square-well 4-mers and 8-mers but not as good for square-well 16-mers.