Nonionic Cosurfactants in AOT Reversed Micelles: Effect on Percolation, Size, and Solubilization Site

Abstract

The effect of nonionic cosurfactants on AOT reversed micellar interface and micelle/micelle interactions was studied. The change on the percolating temperature induced by these cosurfactants was determined for several water contents, micelle concentration, and cosurfactant type and concentration. Two types of cosurfactants were used, linear chained alkyl alcohols and poly(oxyethylene) alkyl ethers (CiEj). If an alcohol was added to the microemulsion, a shift in percolation to higher temperature was observed. The opposite was observed for the CiEj. The apparent hydrodynamic radius for the same systems was determined using dynamic light scattering. The apparent hydrodynamic radius of the alcohol-containing microemulsions was only slightly dependent on the concentration and chain size of the alcohol. The CiEj had the opposite effect, the apparent hydrodynamic radius increased for bigger head group sizes and higher concentrations. These results were interpreted in terms of a decrease or an increase of the fluidity of the interface layer. A solubilization site for the cosurfactants is proposed based on this interpretation of the results. Using the experimental results and an association model, the clustering enthalpy and entropy were determined. The clustering process was found to be endothermic and entropically driven.