Equation of state and phase separation in binary mixtures of nonadditive chains

Molecular dynamics simulations of equimolar mixtures of hard chains composed of equal size nonadditive segments were performed. Different degrees of polymerization, densities, and nonadditivities were used. Phase separation was investigated and visualized. The equation of state for these mixtures was investigated, and models based on the first order thermodynamic perturbation theory (TPT1) and the polymeric analogue of the Percus-Yevick approximation (PPY) were developed to predict the compressibility factor of the polymer mixtures. The TPT1 model was generally more accurate in predicting the compressibility factor than the PPY model for negative and zero nonadditivity. Phase separation between polymers interacting with positive nonadditivity was observed at high densities.