EQUATION OF STATE FOR POLYMER SYSTEMS

We developed an equation of state for systems containing chain-like mo lecules. The equation consists of three contributions. As a reference, we first adopted the equation for hard-sphere-chain fluids (HSCF) der ived through the r-particle cavity-correlation function of sticky hard spheres. The HSCF equation has a simple form similar to the Camahan-S tarling equation and has been satisfactorily tested by computer-simula tion results for chain fluids with a wide range of chain length. Secon dly, for the perturbation, we used the square-well (SW) equation. Thir dly, for molecules with specific oriented interactions such as hydroge n bonding, we introduced a contribution from chemical association (ASS ). The corresponding expression for association comes naturally from t he sticky model used in deriving the reference equation. The ASS term was well tested with computer-simulation results for associated molecu les. The equation of state was widely tested by fitting experimental v apor-liquid equilibrium data. For Liquid-liquid equilibria, we adopted a lattice model developed previously as a high-pressure limit that vi rtually serves as a mixing rule. (C) 1998 Elsevier Science B.V. All ri ghts reserved.