KINETICS OF SOLUTE PARTITIONING AT SURFACTANT MONOLAYERS IN WATER-IN-OIL MICROEMULSIONS

The time scales of the p-nitrophenol (pNP) interfacial association at the curved surfactant monolayers of a dioctyl-sulfosuccinate (AOT) wat er-in-oil microemulsion system were identified and quantified using th e Iodine Laser Temperature Jump (ILTJ) technique. The location of the solute (pNP) was monitored spectrophotometrically as a function of rim e, following a rapid (approximate to 1 mu s) temperature perturbation of the system which shifted the partitioning of pNP between the water and oil phases. The characteristic time assigned to solute association and/or transport was measured to be in the range 0.1 - 1 ms. The equi librium distribution of pNP was determined and used to identify the me chanism responsible for this relaxation time. Our preliminary results for the association of pNP from the aqueous phase to the curved surfac tant interface and transport to the oil are consistent with estimates based on reported results for interfacial resistance offered by surfac tants at planar interfaces. A model that accounts for mass-transfer be tween the water-surfactant-oil regions is proposed to describe the ass ociation and transport of species through the surfactant pseudophase a nd used to analyze the experimental characteristic times.