Dielectric spectroscopy of micelle hydration and dynamics in aqueous ionic surfactant solutions

The dielectric relaxation of ionic surfactant solutions is discussed by comparing results for cationic (alkyltrimethylammonium halides, CnTAX) and anionic (sodium dodecylsulfate, SDS) model surfactants. It is shown that a careful analysis of the spectra yields quantitative information on the hydration of the formed micelles as well as on their size and on the surface diffusion of the bound counterions. The results are not only self-consistent but can be directly linked to data obtained with other methods. Whereas the surface of SDS micelles is strongly hydrophilic with adsorbed counterions generally separated by a layer of water molecules, the surface of CnTAX micelles is essentially hydrophobic and bound halide ions are directly attached.