Measurements of Interdroplet Attractions and the Onset of Percolation in Water-in-Oil Microemulsions

Both the percolation thresholds and the attractive interdroplet interactions for water-in-oil microemulsions made with sodium 1-(4'-heptylnonyl)benzenesulfonate (SHBS), isobutyl alcohol, water, and NaCl with octane, decane, dodecane, and tetradecane have been measured. We find for this particular microemulsion formulation that percolation occurs when the attractive interdroplet interaction is 2.0±0.3 kT. The existence of a critical value of the interdroplet interactions of the same magnitude for other microemulsion mixtures also rationalizes many observations in the literature. Thus we confirm experimentally that the strength of the microscopic interdroplet interactions is directly related to the macroscopic percolation threshold.