Fractal cluster formation and percolation in supermolecular fluids

Abstract

We have investigated fractal cluster formation near the percolation threshold of water-in-oil microemulsions by various experimental methods. The three-component system water/AOT (surfactant)/isooctane forms a well-defined super-molecular fluid consisting of monodisperse spherical water droplets of ca. 10nm radius in oil, covered by a monomolecular layer of AOT. The system is thermodynamically stable and responds reversibly to changes of the physical parameters.

A steeo conductivity increase by several orders of magnitude in a narror temperature (or concentration) interval clearly demonstrates percolation of the nanodroplets. Dielectric relaxation measurements in the frequency range 100 kHz to 1 GHz reveal the formation of fractal clusters, as the percolation threshold is approached. Their size distribution slow rise times between 100 and 400 μs and strong non-linear field dependence. Analysis of the data yields a shift of the percolation threshold with the electric field, consistent with thre results of the electrooptic experiments.