TIME-RESOLVED FLUORESCENCE QUENCHING MEASUREMENTS OF THE AGGREGATION NUMBERS OF NORMAL SODIUM ALKYL SULFATE MICELLES WELL ABOVE THE CRITICAL MICELLE CONCENTRATIONS

The aggregation numbers, N-A, of normal sodium alkyl sulfate micelles were measured by time-resolved fluorescence quenching in order to test two aspects of a recent proposal by Quina et al. (J. Phys. Chem. 1995 , 99, 17028) that these micelles grow as a power law of the total coun terion concentration, [Na+](aq), in the aqueous phase according to N-A = kappa(2)([Na+](aq))(gamma) where kappa(2) and gamma are constants f or a given detergent. Both the surfactant and any added salt contribut e to [Na+](aq); thus the power law predicts that different combination s of surfactant and salt concentrations leading to the same value of [ Na+], should yield the same value of N-A. This was confirmed, and the values of kappa(2) were determined.