EFFECT OF TEMPERATURE AND COUNTERION ON THE MICELLE FORMATION PROCESS STUDIED BY POSITRON-ANNIHILATION TECHNIQUES

The positron annihilation technique was applied to the study of the micelle formation process in micellar systems Aerosol OT and dodecylammonium propionate (DAP) in apolar solvents, such as benzene and isooctane. At certain surfactant concentrations abrupt changes in the number of thermal o-Ps atoms formed can be observed. The surfactant concentration at which this effect can be seen is widely temperature independent in Aerosol OT solutions while a significant shift to higher surfactant concentrations can be found with increasing temperature in DAP solutions. The effect of the nature of the counterion on the mechanism of micelle formation is further investigated by substituting the counterion Na+ in Aerosol OT by tetraalkylammonium ions, N+H4, N+(CH3)4, and N+(C2H5)4. The results are discussed in terms of the pseudophase model and multiple equilibrium model for micelle formation. © 1979 American Chemical Society.