AGGREGATION OF ALKYLAMMONIUM CARBOXYLATES AND AEROSOL-OT IN APOLAR SOLVENTS STUDIES USING ABSORPTION AND FLUORESCENCE PROBES

Using optical probes, the aggregation of 16 different alkylammonium (C10 to C14) carboxylates (C2 to C11) has been investigated in dry benzene, cyclohexane, and carbon tetrachloride, as well as Aerosol-OT in benzene. At the very low concentrations of the absorption (acridine orange and iodine) and fluorescence probes used (octyl-, dodecyl-, and tetradecylammon-ium 8-anilino-l-naphthalenesulfonates), only the iodine probe had a significant effect on the aggregation of the surfactant. Critical micelle concentrations were determined by the Corrin-Harkins method, and in a few cases aggregation numbers and association constants were calculated by Adams' method using vapor pressure osmometric results. For the alkylammonium carboxylates the onset of aggregation is gradual, leading to small aggregates (average aggregation number n = 3) with the monomer population and n dependent on the concentration. In these systems the concept of cmc is used only in an operational sense. For Aerosol-OT the onset of micelle formation is sharper, leading to larger aggregates (n = 10) with the monomer population and aggregation number independent of the concentration. The effects of the solvent, the nature of the probe, and the length of the alkylammonium and counterion chains on the aggregation tendency are discussed. © 1979, American Chemical Society. All rights reserved.