Micelle formation by sulfonates in a nonpolar solvent

Abstract

The micellar properties of oil-soluble sulfonates in benzene have been studied by the fluorescence depolarization method. In moist benzene, the dinonylnaphthalene sulfonates of barium and sodium aggregate to form micelles of 7 to 8 and 12 to 13 monomers, respectively; the size of these micelles is not sensitive to water concentration. The critical range for micelle formation of these sulfonates is estimated at 1 × 10 −6 to 1 × 10 −7 formula weight per liter. A barium petroleum sulfonate was found to aggregate in micelles of 34 to 35 monomers. The difference between the sizes of micelles of the two types of sulfonates is explained in terms of the geometries of the respective monomers. The formation of Rhodamine B-sulfonate complexes has been observed, requiring a slight revision of previously developed methods for treatment of the data. The micellar nature of these substances in nonpolar solvents supports a previously published explanation of their effectiveness in reducing the corrosion potentials of acids in lubricating oils.