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 concentrations, to determine the functional dependence of the aggregation number on the detergent and added common counterion concentrations. Six members of the sodium alkyl sulfate family with different alkyl chain lengths including octyl, nonyl, decyl, undecyl, dodecyl, and tetradecyl were studied. In all cases, the growth of the aggregates with added salt and surfactant concentrations was found to obey the power law proposed by Quina et al. (J. Phys. Chem. 1995, 99, 17028) namely, NA = κ2 ([Na+aq])γ, where NA is the aggregation number and [Na+aq] is the total counterion concentration in the aqueous phase (supplied by the surfactant and the added salt). The constants κ2 and γ were determined for each of the sodium alkyl sulfates.