Viscosity anomaly and charge fluctuations in dilute AOT microemulsions with X < 20

An experimental investigation of the viscosity and microstructure of AOT/water/n-decane inverse microemulsions examines the maximum in the low shear viscosity as a function of the molar ratio of added water to surfactant, X, at a fixed Volume fraction of droplets. Dilute viscometry and dynamic and static Light scattering link the phenomena directly to a maximum in the attraction between droplets around X = 8. The strength of the attraction is quantified by static Light scattering and compared with estimates via Baxter's adhesive hard sphere model from the viscometric and dynamic light scattering data. Together these confirm the connection, though the latter values exceed those from static light scattering, presumably due to an inaccurate treatment of hydrodynamic interactions. The exchange of ions between droplets is demonstrated to produce an attraction of sufficient strength and appropriate dependence on X with much less than one charge per droplet.