Thermodynamics and kinetics of solubilization of naphthalene into anionic micelles

The rate constants for naphthalene entering and exiting from a micelle (k() and k(-), repectively) have been determined by the fluorescence quenching method for 1-dodecanesulfonic acid (DSA) and sodium 1-decanesulfonate (SDe So) micellar solutions at 308.2 K. The first stepwise association constant ((K) over bar (1)) has been determined from the plots of maximum additive c oncentrations for each surfactant solution to obtain a ratio of the k(+) to k(-). The k(-) value for DSA has been found to be much smaller than the on e for SDeSo, although the k(+) value for DSA has been found to be almost th e same for both systems. This indicates that hydrophobic interaction betwee n micelles and naphthalene dictates only in the case where the probe exits into intermicellar bulk solution. (C) 2000 Elsevier Science B.V. All rights reserved.