Dielectric Relaxation in Aqueous Solutions of Zwitterionic Surfactant Micelles

Abstract

Abstract The dipolar headgroup of the various investigated surfactants consists of the cationic (H 3 CNCH 3 ) or (‐NH 2 ) group and of the anionic (Co 2 ), (SO 3 ) or (PO 4 ) group; their (single) alkyl chain contains at least 11 (CH 2 ) groups. The complex relative electric permittivity of aqueous 0.28…0.72 molar solutions has been measured at 28…38 frequencies between 50MHz and 39GHz at 25°C. To the measured permittivity vs. frequency spectra have been fitted an empirical relaxation spectral function and a model spectral function. The latter has been especially developed for aqueous solutions of ellipsoidal micelles. From the adjustable parameters of the model spectral function are derived the ellipsoid axial ratio, the number and reorientation time of the hydration molecules, and a correlation number as well as the mobility (or self‐diffusion coefficient) for the diffusive motion of the headgroup's outer ion.