Dielectric study on pure and KOH-doped tetrahydrofuran clathrate hydrates

Abstract

Complex dielectric permittivities of pure and KOH-doped (x = 1.8 x 10⁻⁴) tetrahydrofuran clathrate hydrates were measured in the temperature range 20–260 K and in the frequency range 20 Hz-1 MHz. The relaxation time of the water reorientational motion was found to decrease drastically as a result of the doping; e.g., the relaxation time of the doped sample was 10⁻⁹ times shorter than that of the pure sample at 70 K. The activation enthalpy of the motion was reduced to 7.4 kJ mol⁻¹. On cooling the crystal, the value ofɛ′ decreased suddenly at the 62 K phase transition to theε _∞2 value of the pure sample and at the same timeɛ″ disappeared. No dispersion effect due to the guest reorientation was observed below the transition. These data indicate that both the host and guest molecules become ordered or, at least, change their mobility drastically. In the pure sample, a relaxation phenomenon ofε ₀₂ was found around the glass transition region. The relaxation times agreed well with those derived from the enthalpy of relaxation in a calorimetric study.