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

Abstract

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 concentrations of the polar component, indicating that strong clustering of polar molecules occurs at these concentrations. The orientational order is also seen to increase very strongly with dipole moment at these concentrations. The pair correlation function for pairs of Lennard-Jones atoms shows little dependence on dipolar strength of Stockmayer molecules at these concentrations. The distribution function for pairs of unlike molecules reflects the increasingly dissimilar character of these molecules as the dipolar strength increases. For large concentrations of Stockmayer molecules, the opposite effect is observed, albeit less pronounced, in that the pair-correlation function for Lennard-Jones atoms shows an increase in local ordering as μ increases, whereas the radial distribution function for Stockmayer pairs remains relatively unaffected with increasing μ. These results are interpreted in terms of a frustation model. Results are given for the variation of the dielectric constant of the mixture with composition and dipolar strength.

Freezing point and solid-liquid interfacial free energy of Stockmayer dipolar fluids: A molecular dynamics simulation study

“…[14][15][16][17][18] Third, the SM/LJ binary fluids can be used to study mixtures of polar and nonpolar fluids. [19][20][21] Fourth, SM clusters can be used to study the effect of dipole strength on structures of polar clusters. 9,22,23 As for the thermodynamic properties of the SM fluids, such as phase equilibria and surface tensions, a) Electronic mail: xzeng1@unl.edu most previous studies have been focused on the liquid-vapor equilibria [24][25][26][27][28][29] while few studies have reported the freezing points.…”

Molecular dynamics study of the thermodynamic and structural properties of methanol and polarizable/non-polarizable carbon tetrachloride mixtures

“…Adachi and Nakanashi 5,6 studied the self-association of methanol in benzene. De Leeuw et al [7][8][9][10] carried out an extensive series of simulations on Stockmayer and Lennard-Jones molecules.…”

Demixing in binary mixtures of apolar and dipolar hard spheres

“…Concerning simulation results, De Leeuw et al 23 studied the phase behavior of mixtures of Stockmayer and LennardJones molecules using molecular dynamics. They found that at high densities a demixing transition takes place.…”