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

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.