The Refractive Index of Perfluorinated Surfactant Solutions

Abstract

AbstractThe refractive index of several perfluorinated surfactant solutions was measured as a function of the concentration. The plot of the refractive index against the concentration for each surfactant shows a sharp break at the cmc. For several systems the slope of the refractive index changed even its sign. The extent of this change is much bigger for perfluorinated surfactants than the change that is shown by hydrocarbon surfactants. It is shown by density measurements that the difference of the refractive index increment above and below the cmc is due to the difference of the partial molar volumes of the surfactant molecules in the monomer and in the micellar state. It is thus possible to determine volume changes in surfactant systems by means of the measurement of the refractive index.