Molecular dynamics studies of polar/nonpolar fluid mixtures: I. Mixtures of Lennard-Jones and Stockmayer fluids

The results of canonical ensemble molecular dynamics calculations of mixtures of Lennard–Jones and Stockmayer fluids are reported. To study solely the influence of the polarity, the Lennard‐Jones parameters were identical for both components. The excess mixing properties show a strong asymmetry with respect to composition for large dipolar strength. The free energy of mixing is obtained through a thermodynamic integration procedure. The results strongly suggest that, for reduced dipolar strengths μ2>3.15, demixing occurs into a phase rich in polar component and an almost pure Lennard‐Jones fluid. It is shown that perturbation theory yields fairly accurate results for the dipolar energy and free energy of the mixture. For the free energy of mixing, qualitatively correct results are obtained. The structure and orientational correlation functions of the mixture are discussed. The radial distribution function for pairs of polar molecules show a marked increase in local ordering with dipolar strength for low c...