THERMODYNAMIC EVALUATION OF THE POLYDISPERSITY OF DROPLET MICROEMULSIONS

By exploiting our previously presented multiple chemical equilibrium a pproach to the theory of Winsor II microemulsions (Eriksson, J. C.; Lj unggren, S. Progr. Colloid Polym. Sci. 1990, 81, 41.) we derive relati ons which enable an evaluation from thermodynamic data of the polydisp ersity of Winsor II type microemulsions as well as of corresponding on e-phase (ternary droplet) microemulsions. We find that, quite generall y, a size polydispersity (sigma(Rmax)) in the range 0.1-0.2 is to be a nticipated for such microemulsions and, moreover, that the absolute wi dth of the size distribution to a large extent is determined simply by the value of the interfacial tension, gamma infinity, of the planar, surfactant-laden oil/water interface. The shape and surfactant film pa cking density fluctuations also influence the peak width but to a less er extent. Furthermore, we show how the curvature-related bending cons tant k(2) = 2k(c) + (k) over bar(c)> can be evaluated from the overall volume fraction of droplets.