Dielectric Analysis on Aqueous Solutions by a High-Precision Double-Logarithmic-Derivative Method for Relaxation Frequency Calculation

In this paper, cooling dielectric spectra of NaCl and KCl aqueous solutions with different concentrations from 10°C to -60°C were first measured and the corresponding crystallization and dielectric relaxation behavior were analyzed. Subsequently, by establishing a high-precision double-logarithmic-derivative method, dielectric relaxation frequencies contained in dielectric spectra were accurately calculated. Furthermore, with the help of this proposed method, the relaxation polarization time τ and the activation energy Ea of water molecules in composite ice formed by low-temperature aqueous solutions with different concentrations were calculated and analyzed. The results indicate that the accuracy of relaxation frequency identification reaches 2.10-4.67 times that of classical methods. As the concentration ratio β increases, the relaxation time τ of water molecules in composite ice formed by low-temperature solution rapidly decreases and the activation energy Ea significantly increases when 0 < β ≤ 0.5. When β1, τ slowly increases and E_a gradually decreases. The E_a-β curves of NaCl composite ice and KCl composite ice show maximum values at β NaCl=0.56 and β KCl=0.62, respectively.