Novel reverse micelles partitioning nonaqueous polar solvents in a hydrocarbon continuous phase

Reverse microemulsions have been characterized in isooctane and decane using the surfactant Aerosol-OT (AOT) and the polar solvents formamide, ethylene glycol, acetonitrile, methanal, N,N-dimethylformamide, and 1,2-propanediol. Dynamic light scattering (DLS) experiments show that reverse micelles form in these solutions. The DLS data and steady-state absorption spectra of Coumarin 343 in these solutions reveal that the character of these reverse micelles depends partially upon the solubility of the polar solvent in the hydrocarbon. For formamide and ethylene glycol, which are highly immiscible in the hydrocarbon solvents, changes in micellar size occur for variations in the volume fraction phi of the polar solvent and surfactant in the continuous phase as well as for the traditional changes in w. These reverse micelles with w = 1.1 and phi = 0.006-0.051 exhibit diameters ranging from 5.0 to 26.1 nm. For the solvents acetonitrile, methanol, N,N-dimethylformamide, and 1,2-propanediol, which are slightly miscible with isooctane and decane, micelles form and solubilize some of the polar solvent. However, these solutions do not support micelles with large diameters. Reverse micelles with mole fractions of polar solvent to AOT, w, ranging from 1.1 to 5 exhibit diameters ranging from 2.7 to 9.0 nm, respectively.