Thermodynamic Evaluation of the Polydispersity of Droplet Microemulsions

Abstract

By exploiting our previously presented multiple chemical equilibrium approach to the theory of Winsor II microemulsions (Eriksson, J. C.; Ljunggren, S. Progr. Colloid Polym. Sci. 1990, 81, 41.) we derive relations which enable an evaluation from thermodynamic data of the polydispersity of Winsor II type microemulsions as well as of corresponding one-phase (ternary droplet) microemulsions. We find that, quite generally, a size polydispersity ( R /R max ) in the range 0.1-0.2 is to be anticipated for such microemulsion and, moreover, that the absolute width of the size distribution to a large extent is determined simply by the value of the interfacial tensio, γ∞, of the planar, surfactant-laden oil/water interface. The shape and surfactant film packing density flucuations also influence the peak width but to a lesser extent. Furthermore, we show how the curvature-related bending constant k 2 =2k c +k c can be evaluated from the overall volume fraction of droplets