Dielectric Relaxation of Decyltrimethylammonium Bromide-Water-Styrene Oil-in-Water Microemulsion

Complex permittivity measurements of decyltrimethylammoniumbromide+water+styrene microemulsions in the oil-in-water (o/w) region have been made as functions of surfactant (0.0982 ≤ c/mol⋅dm⁻³ ≤ 0.7782) and styrene (0.14 ≤ S ≤ 0.52, where S is the molar ratio of styrene to surfactant) concentrations, in the frequency range ~ 0.2 ≤ γ/GHz ≤ 89, at 298.15 K. Temperature dependence measurements, in the range of 278.15 ≤ T/K ≤ 328.15, were made for one solution, to obtain activation parameters. All the dielectric spectra are described by a summation of five individual Debye relaxation processes over the entire range of concentration at 298.15 K. The two micelle relaxation processes centered around ~ 0.1 and ~ 0.5 GHz are attributed to the radial diffusion of free and tangential diffusion of bound counter ions around the charged micelles. The diffusion coefficient of bound counter ions on the surface of micelles is reduced to almost three times less than in the bulk solution. A significant amount of water molecules are involved in hydrophobic hydration with reduced mobility by the hydrocarbon tail of the surfactant; in addition of a significant amount of water molecules are irrotationally bound by the ionic head group of the surfactant.