Micelle and Microemulsion Properties of Cesium Di-Dodecyl-Dimethylsulfosuccinate, Cs-AOT

Cesium di-2-ethylsulfosuccinate (Cs-AOT) micelles in aqueous solutions and Cs-AOT/water/n-decane microemulsions were investigated, at 22 ± 0.1 °C, by small angle neutron scattering (SANS). The critical micelle concentration of Cs-AOT is ∼2 mM, comparable to that of Na-AOT. However, their solution properties and micellar structures were found to be very different. The solubility of Na-AOT in water is approximately 1 wt %, and the micelles grow from spherical (at a concentration of about 0.1 wt %) to oblate objects with eccentricity equal to about 0.8 (at a concentration of 1 wt %), whereas Cs-AOT is largely soluble in water, over 30 wt %, and its micelles are disklike at 1 wt %. As the surfactant concentration increases, micelles may go through an L3 region, and enter the lamellar phase. Cs-AOT/water/n-decane microemulsions, with a [water]/[Cs-AOT] = 29.1, form isotropic L2 phases only at very low Cs-AOT + water volume fractions (below 0.0165), whereas Na-AOT has a large L2 region. These differences are probably due to the degree of charge condensation near the AOT polar headgroups. A theoretical description is needed to better understand this behavior.