  A model for the limiting surface tension of surfactant solutions (surface
tension at and above the critical micelle concentration, cmc) was developed.
This model takes advantage of the equilibrium between the surfactant molecules
on the liquid/vacuum surface and in micelles in the bulk at the cmc. An
approximate analytical equation for the surface tension at the cmc was
obtained. The derived equation contains two parameters, which characterize the
intermolecular interactions in the micelles, and the third parameter, which is
the surface area per surfactant molecule at the interface. These parameters
were calculated using a new atomistic modeling approach. The performed
calculations of the limiting surface tension for four simple surfactants show
good agreement with experimental data (~30% accuracy). The developed model
provides the guidance for design of surfactants with low surface tension
values.
