Kinetics of surfactant-mediated breakdown of N-(4-nitrophenyl)perfluorononanamide aggregates in aqueous solutions

MARIANA A. FERNANDEZ; ALEJANDRO M. GRANADOS; RITA H. DE ROSSI; A.M. GRANADOS; OMAR A. EL SEOUD

LANGMUIR

American Chemical Society

Año: 2002 vol. 18 p. 8786 - 8791

0743-7463

Breakdown of aggregates of N-(4-nitrophenyl)perfluorononanamide (1) by micelles of the following ionic and nonionic surfactants has been studied by UV-vis and 1H NMR spectroscopy, surface tension, and conductivity measurements: dodecyltrimethylammonium bromide, DTABr, and dodecyltrimethylammonium chloride, DTACl, cetyltrimethylammonium bromide, CTABr, sodium dodecyl sulfate, SDS, polyoxyethylene(23)lauryl ether, Brij-35, and perfluorononanoic acid, 2, as well as mixtures of DTACl plus 2 and/or its methyl ester. Deaggregation of 1 occurs at surfactant concentrations higher than their critical micelle concentrations, and is characterized by two processes, whose overall rate constants are k1obs and k2obs. The former depends on concentration of the surfactant monomers in bulk solution, and is attributed to the formation of dimers between 1 and surfactant monomer. The latter rate constant is attributed to insertion of these dimers in the micellar pseudophase. Both steps depend on the structure, packing, and charge of the micelle and/or the mixed micelle.