Broadband Dielectric Properties of Glycerol–Water Mixtures with Salt Additives

In the current study, the dielectric behavior of ternary mixtures composed of glycerol and water with various salt additives is investigated over a frequency range that extends from 0.5 to 20 GHz and at temperatures between 5 and 55 °C. The investigated mixtures consisted of glycerol and water with glycerol volume ratios of 20%, 40%, and 60%. To explore the salt addition’s effect on the dielectric properties, different moderate ionic strengths of glycerol–water mixtures were prepared with NaCl concentrations of 0.10, 0.20, and 0.30 M for the same glycerol volume ratios. The ion-specific effects on the dielectric properties were investigated for prepared mixtures with a 0.10 M concentration of Na2SO3, NaNO3, and KCl for the 20% glycerol ratio to explore ions with different charge density and hydration tendencies. Using dielectric spectroscopy, the frequency dependence of the real (ε′) and imaginary (ε″) dielectric constants was measured, and the associated dielectric parameters were extracted using the Cole–Cole model. This study shows that increasing the salt concentration results in a slight decrease in ε′ while ε″ increases dramatically, especially at lower frequencies, due to enhanced DC conductivity. An isopermittivity behavior is observed in ε′ as the temperature changes across all mixtures, and it is found to be insensitive to the addition of salt, indicating that it is mainly dictated by the glycerol–water dipolar relaxation network. Among the tested mixtures is the 20% glycerol mixture with 0.10 M KCl, which exhibits the highest ε″ value in the low-frequency range, attributed to its relatively high DC conductivity. Additionally, the dielectric properties of mixtures with higher glycerol ratios are found to be less sensitive to the addition of salt due to their high viscosity and the higher structured solvent network, which collectively limit ionic mobility and suppress changes in dielectric response.