Electrostatic interactions in ionic microemulsions

We have analyzed the role of electrostatic interactions in ionic microemulsions. Using a recently developed formalism (Daicic, J.; Fogden, A.; Carlsson, I.; Wennerstrom, H.; Jonsson, B. Phys. Rev. E 1996, 54, 3984-3998), we have been able to qualitatively, and in some cases quantitatively, account for a number of experimental observations. We account for (i) the change in the relative stability of lamellar and microemulsion phases as the salt content is varied, (ii) the tilted appearance of the "fish" plot for ionic systems, (iii) the sequence of phases observed as the temperature is changed, (iv) the relative location of the Winsor three-phase area and the lamellar phase, (v) the interrelation between salt content, temperature, and surfactant concentration for the location of balanced conditions, and (vi) the lack of symmetry with respect to an exchange of water and oil at balanced conditions. The overall conclusion is that the Helfrich curvature energy formalism can be successfully adopted for the description of ionic microemulsions, provided that one describes the electrostatic effects using the Poisson-Boltzmann equation at finite film concentrations.