Surfactant- and salt-induced growth of normal sodium alkyl sulfate micelles well above their critical micelle concentrations

Time-resolved fluorescence quenching measurements were performed on normal sodium alkyl sulfate micelles, well above their critical micelle concentrat ions, to determine the functional dependence of the aggregation number on t he detergent and added common counterion concentrations. Six members of the sodium alkyl sulfate family with different alkyl chain lengths including o ctyl, nonyl, decyl, undecyl, dodecyl, and tetradecyl were studied. In all c ases, the growth of the aggregates with added salt and surfactant concentra tions was found to obey the power law proposed by Quina ct al. (J. Phys. Ch em. 1995, 99, 17028) namely, N-A = kappa(2) ([Na-aq(+)])(gamma), where N-A is the aggregation number and [Na-aq(+)] is the total counterion concentrat ion in the aqueous phase (supplied by the surfactant and the added salt). T he constants kappa(2) and gamma were determined for each of the sodium alky l sulfates.