Determination of the monomer-micelle exchange frequency of a paramagnetic surfactant

Abstract

For the first time, EPR spectra have been obtained which unambiguously distinguish between paramagnetic surfactants in monomeric and micellar environments. The frequency with which the paramagnetic surfactant 2,2,6,6- tetramethylpiperidine-oxidedodecyldimethylammonium bromide exchanges between micellar and aqueous environments increases from about 10⁵ s^–1 at 24°C to 1.7 × 10⁶ s^–1 at 68°C. From these data an enthalpy of activation for the micellization process of approximately 9.5 kcal/mol has been determined.