Vapour-liquid equilibria of binary mixtures containing Stockmayer molecules

Using Gibbs ensemble Monte Carlo simulations, we investigated the vapour-liquid equilibria of a number of binary mixtures, some containing Lennard-Jones (LJ) and Stockmayer (SM) components, and others containing two SM components with different reduced dipole moments. Our results show that the phase coexistence properties of the mixtures are sensitive to the difference between the reduced dipole moments of the two components: an increase in this difference causes the phase envelope to widen for both the LJ-SM and SM-SM mixtures. Comparison of our results to vapour-liquid equilibria data simulated using an angle-averaged approximation of the long-range dipolar interaction, the Keesom potential, suggests that the Keesom potential is not suitable to approximate the dipolar interactions for mixtures when the dipolar interaction is dominant.