NONIONIC COSURFACTANTS IN AOT REVERSED MICELLES - EFFECT ON PERCOLATION, SIZE, AND SOLUBILIZATION SITE

The effect of nonionic cosurfactants on AOT reversed micellar interfac e and micelle/micelle intel actions was studied. The change on the per colating 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 chaine d alkyl alcohols and poly(oxyethylene) alkyl ethers (C(i)E(j)). If an alcohol was added to the microemulsion, a shift in percolation to high er temperature was observed. The opposite was observed for the C(i)E(j ). The apparent hydrodynamic radius For the same systems Mras determin ed 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 C(i)E(j) had the opposite effect, the apparent hydrodynamic radius increased for bigger head group sizes and higher concentrations. These results were interp reted in terms of a decrease or an increase of the fluidity of the int erface layer. A solubilization site for the cosurfactants is proposed based on this interpretation of the results. Using the experimental re sults and an association model, the clustering enthalpy and entropy we re determined. The clustering process Ras found to be endothermic and entropically driven.