COUNTERION CONTRIBUTION TO THE DIELECTRIC SPECTRUM OF AQUEOUS-SOLUTIONS OF IONIC SURFACTANT MICELLES

This paper is concerned with the measurement and interpretation of the dielectric relaxation properties of aqueous ionic surfactant micelle solutions without additional salt. The complex permittivities epsilon of cationic and of anionic micelle solutions of hexadecyltrimethylammonium bromide and sodium dodecyl sulfate, respectively, were determined in the frequency range 1 MHz < v < 3 (partly 30) GHz and for several surfactant concentrations choosen between the first and second cmc. The measurements were performed at 25 degrees C. The epsilon (v) spectra were evaluated in terms of an empirical spectral function. The characterizing parameters of that function were discussed in terms of the results of a new theoretical approach for the dynamics of the layer of bound counterions. The proposed model provides information about the degree of dissociation, effective size of the micelles, and mobility of the counterions.