A perturbed Lennard-Jones chain equation of state for polymer mixtures: applications to vapor-liquid and liquid-liquid equilibria

The perturbed Lennard-Jones chain (PLJC) equation of state (EOS) is extende d to polymer mixtures. This equation utilizes the hard-sphere chain mixture as the reference system, while the perturbation term is derived based on t he first-order variational theory. Binary vapor-liquid equilibrium (VLE) da ta of a wide range of polymer mixtures are well described by this model thr ough the use of one binary parameter k(ij). We also show that the PLJC mode l is able to predict liquid-liquid equilibrium of polymer-solvent systems s atisfactorily by introducing an empirical parameter that adjusts the degree of perturbation in the model. All phase equilibrium calculations in this s tudy were performed rigorously by global minimization of Gibbs free energy using a genetic algorithm. (C) 2001 Elsevier Science B.V. All rights reserv ed.