Percolation in Nonionic Water-in-Oil−Microemulsion Systems: A Small Angle Neutron Scattering Study

Abstract

Nonionic water-in-oil (w/o)−microemulsions of the type water/c-hexane, n-hexane/Igepal were examined by SANS in both shell and core contrast. Variation of the water to surfactant ratio W0 in the droplet regime yields a linear relation between W0 and the droplet water core radius and R/nm = 0.19 W0 + 0.70. Small angle neutron scattering (SANS) data for W0 = 10 samples show that droplet aggregation occurs with a fractal dimension of D ≤ 1.3 as a percolation-like transition is crossed by decreasing temperature. Data analysis and model calculations, done in both q and r space, are consistent with the formation of linear aggregates of discrete spherical droplets.