Surface tension and orthobaric densities for vibrating square well dumbbells. I

Abstract

Surface tensions and liquid-vapor orthobaric densities are calculated for a wide variety of vibrating square well dumbbells using discontinuous molecular dynamics simulations. The size of the vibration well, the elongation or bond distance of the two particles of the dumbbell, the asymmetry in size (and interaction range) of the two particles, and the depth of the interaction well are the variables whose effects are systematically evaluated in this work. Extensive molecular dynamics simulations were carried out and the orthobaric liquid-vapor densities are compared with those obtained previously by other authors using different methods of simulation for rigid and vibrating square well dumbbells. Surface tension values are reported for the first time for homonuclear and heteronuclear vibrating square well dumbbells as well as for all the simulated series. The molecular dynamics results of tangent homonuclear dumbbells are compared with those from Monte Carlo simulations also obtained in this work, as a way of checking the order of magnitude of the molecular dynamics results. The size of the vibration well is shown to have a small influence on the resulting properties. Decreasing elongation and the size of the second particle increase critical temperatures, liquid densities, and surface tensions. Moderate increases in the depth of the interaction well have the same effect. For larger asymmetries of the depth of the interaction well on the dumbbell particles, a strong association phenomenon is observed and the main effects are a maximum on the critical temperature for increasing well depth and a decrease in the surface tension.