A Perturbed Hard-Sphere-Chain Equation of State for Polymer Solutions and Blends Based on the Square-Well Coordination Number Model

Abstract

Based on the concept of a perturbed hard-sphere-chain (PHSC), where the square-well fluid is the reference system, a perturbation term is developed from the coordination number model for pure and mixture square-well fluids proposed by this group. Consequently, we derive a new PHSC type equation of state (EOS), which is of much simpler formulation and is even easier to use. The EOS has been extensively tested in terms of a large data bank, consisting of the properties of 37 normal fluids and solvents, 67 polymers. The correlation accuracy for the saturated properties is within the errors in common EOS approach. In particular, the grand average deviation for correlating the liquid densities for 67 polymers is 0.19%, which is of the same accuracy as that for commonly used lattice model EOSs. In all of the calculations, the EOS needs only three temperature- and composition-independent parameters. In addition, the new EOS is used for 40 sets of vapor−liquid equilibrium (VLE) calculations of polymer−solvent systems. Three typical liquid−liquid equilibrium (LLE) systems have been investigated by using the EOS, including both the upper critical solution temperature and the lower critical solution temperature polymer−solvent and polymer blend systems. The calculated binodal and spinodal curves are in good agreement with experimental data. All of the VLE and LLE calculations need conventional mixing rules and only a binary interaction parameter.