In this work, we present the effect of NH4OH, Al(NO3)3, and ZrOCl2 on the structure of reverse micelles for the system AOT/water/isooctane. An analytical approach, coupled with experimental results from dynamic light scattering, have been used to gain insight on the reverse micelle structure under different electrostatic environments (i.e., ionic systems of varying charge and concentration). A change in slope in the average reverse micelle size with respect to salt concentration is observed at low values of salt concentration and this is used to estimate the Stern layer ion occupancy at the surfactant interface. In addition, the hydrodynamic radii obtained have been corrected with surface charge density estimates. Furthermore, the water core sizes and Stern layer ionic occupancy have been used to determine the electrical double layer thickness and the core zone. The calculations support the formation of an onion-type reverse micelle structure that contains a core, an electrical double layer zone with two overlapping electrical potentials, a Stern layer, and an outer surfactant layer. In all systems, as salt concentration is increased up to the critical concentration, the reverse micelle core zone approaches a value close to 2 nm, as illustrated in the figure. Preliminary results on a AOT/ethanol/heptane system will also be presented and correlated to the model developed for the AOT/water/isooctane system.

Structure and stability of reverse micelles with salt additions: Experimental and modeling insights

251st National Meeting (2016)

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