Solubilization of Water in Aerosol OT / Cosurfactant / Mineral Oil Systems

Abstract

: Turbidity measurement was found to be a simple and effective method to evaluate the solubilization of water in Aerosol OT (AOT) / cosurfactant / mineral oil systems. The systems showed greater ability to solubilize water when the mineral oil was a long chain hydrocarbon with a carbon number between C10 and C12. Because these hydrocarbons do not easily penetrate the monolayer of the reversed micelles, the effective volume of the monolayer does not increase and the micellar size is maintained. The most suitable cosurfactants were sorbitan trioleate (Span 85) and sorbitan monolaurate (Span 20), and each increased the solubilization of water by a different mechanism. It seems that Span 85 acts on the lipophilic groups of the AOT molecules, thickening the monolayer of the reversed micelle to prevent the mineral oil from penetrating it, thereby promoting formation of larger, stabler reversed micelles. Meanwhile, Span 20 may form reversed micelles with the AOT molecules, weaken-ing the electrostatic interaction between the hydrophilic groups to allow formation of larger and stabler reversed micelles.