Dielectric Relaxation of Aqueous NaCl Solutions

Abstract

The complex dielec. permittivity of aq. sodium chloride solns. has been detd. in the frequency range 0.2-20 GHz with a com. dielec. measurement system based on a vector network analyzer. NaCl solns. of 0.1-5 mol/kg (mass fraction 0.005-0.23) were investigated at 5, 20, 25, and 35°. An improved calibration procedure of the dielec. measurement system for conducting samples was developed. The complex permittivity spectra have been represented by a Cole-Cole relaxation time distribution. Where possible, the obtained fitting parameters, static permittivity ε and relaxation time τ, and distribution parameter α, are compared with literature data to assess the performance of the instrument, which was found to be comparable to that of time domain and waveguide systems. Effective solvation nos. were deduced from the effect of NaCl concn. on ε. The data suggest that in addn. to the irrotational bonding of water mols. by Na+ ions, kinetic depolarization under slip boundary conditions dets. the soln. permittivity. A three-state model is proposed to describe the concn. dependence of τ.