  When the theoretical values of the interfacial tension -resulting from the
homogeneous distribution of ionic surfactant molecules amongst the interface of
emulsion drops- are plotted against the total surfactant concentration, they
produce a curve comparable to the Gibbs adsorption isotherm. However, the
actual isotherm takes into account the solubility of the surfactant in the
aqueous bulk phase. Hence, assuming that the total surfactant population is
only distributed among the available oil/water interfaces, one can calculate
what surface concentration is necessary to reproduce the experimental values of
the interfacial tension. A similar procedure can be followed using the zeta
potential of the drops as a standard for a given set of salt and surfactant
concentrations. We applied these procedures to the case of hexadecane/water
nanoemulsions at different salt concentrations. This information was used to
compute typical interaction potentials between non-deformable nanoemulsion
drops. The results indicate that there are significant differences between the
surfactant population expected from macroscopic adsorption isotherms, and the
actual surfactant popula- tion adsorbed to the surface of nanoemulsion drops.
