Temperature and Composition Dependence of the Structure of Isooctane/AOT Microemulsion L2 Phases with Glycerol and Formamide: A Light Scattering Study

Oil continuous isooctane/AOT microemulsions with a third polar component glycerol or formamide were studied with dynamic light scattering. Both temperature and dispersed phase volume fraction φ were changed. For the glycerol systems, it was found that well below the critical T c and φ c and/or at low glycerol concentrations, the molecular aggregates formed are similar to the aqueous reversed micelles. However an increase of attractive interactions between the droplets is observed, which is related to the formation of clusters. This effect is clearly seen when the φ c is approached, where evidence for the existence of two populations (free reversed micelles and clusters) is obtained. When the φ c is passed, the relaxation rate is fast and becomes single exponential, except for a long tail at lower temperatures, perhaps indicating the approach of a lamellar phase. The formamide system has single-exponential relaxation distribution and linear relationships with ln( φ ) − 1 and does not show any evidence of cluster formation. It is suggested that the bending elastic constants in this system are rather low and saddle-splay structures seem to be preferred, due to different AOT polar head solvation by formamide.