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. © 1991 American Institute of Physics.