Dielectric response of liquid water and aqueous solutions: two-fluid behavior

Dielectric response of pure water and aqueous chlorides solutions at very high frequencies, greater than 1 GHz, can fully be accounted for only considering the relaxation spectral function as the weighted sum of two independent single-parameter Debye functions. Two different relaxation modes are assigned to a collective mode and to an individual mode each having its own relaxation time, steady-state dielectric constant and high-frequency residual permittivity. The observed static permittivity is the result of a superposition of the dielectric constant of the two populations and varies accordingly. This also explains the variation of the dielectric constant with the concentrations in aqueous solutions. Our results are fully compatible with the results shown in the literature showing that in electrolytic solutions, except for the case of LiCl, the dispersion and absorption are higher than in pure water. We attribute the LiCl odd behavior (it is more transparent than pure water to THz radiation) to its high chaotropic effect on interacting dipoles.