Molecular theory of surface tension

Abstract

Values of the surface tension and surface excess internal energy of a number of simple liquids are obtained by numerical integration of the Kirkwood-Buff-Fowler equations. All calculations are based on the Lennard-Jones potential with parameters which are known to reproduce the thermodynamic properties of the bulk liquids. Agreement between theoretical and experimental values of surface tension at the triple point is good, except for neon, and it is concluded that the Kirkwood-Buff-Fowler treatment is numerically more satisfactory than had previously been supposed. On the other hand, poor results are obtained for surface energy because the variation of surface tension with temperature is greatly underestimated. Furthermore, the results on surface energy are thermodynamically inconsistent with those on surface tension. Agreement with experimental data on surface tension at higher temperatures can be achieved by taking into account the non-zero width of the liquid-vapour transition region. By forcing agreement in this way the temperature-dependence of the surface thickness of liquid argon is estimated.