Time-Dependent Effects Near the Percolation Threshold in Water-in-Oil Microemulsions

Abstract

The three-component system water/surfactant(AOT)/oil(i-C₈) forms in a certain range of compositions and temperatures (see Fig. 1) thermodynamically stable microemulsions consisting of nanometer-sized water droplets (ND) covered by a monomolecular layer of surfactant and dispersed in oil /1/. The nanodroplet radius is controlled by the ratio w₀ = [H₂O]/[AOT] and has a typical value of 10 nm. The nanodroplets are spherically symmetric and rather monodisperse, as has been established both experimentally and theoretically (see e.g. /2/). The spontaneous formation and thermodynamic stability of these emulsions is due to the “ultra-low” interfacial tension of the order of k_BT/4πR² (R = radius of spherical water droplet) of the oil/water interface in the presence of surfactant(s). This is a consequence — to a first approximation — of a compensation of Coulombic, lateral dispersion and curvature energy contributions.