Dielectric Relaxation and Phase Transition of Cyclohexanol

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The dielectric properties of cyclohexanol, C_6H_11OH, were measured at frequencies of 0.5-300 kc/s by a capacitance bridge and those of 1000-2000 mc/s by a coaxial line in the range from 90℃ to the liquid air temperature. A common dielectric relaxation was observed both in liquid and in solid states. When log f was plotted against 1/T, a linear relation extending over the two phases was observed ; here T represents the temperature at the peak of ε" at frequency f. The activation energy for the relaxation was determined : U=0.57 eV. No anomaly in dielectric properties was seen at the freezing point. Cole-Cole plot of this relaxation at -70℃ was not a semicircle but a skewed-arc, that is, the low frequency portion of the plot was described by a semicircle with the radius (ε_0-ε_∞)/2, while the high frequency side of it was linear. The empirical equation obtained by Davidson and Cole for the skewed-arc dispersion was found to agree quite satisfactorily with the present experimental results. The phase transition of cyclohexanol in the solid state was observed by dielectric measurement and by differential thermal analysis. The transition was very gradual. When the temperature was kept constant at -80℃, the phase changed gradually in 3 hours (I→II) ; but when it was cooled rapidly (1 deg./min.), no transition occurred down to the liquid air temperature. Instead, the transition (I→II) occurred at about -74℃ on heating. In any case, the low temperature phase changed back to the high temperature one at about -26℃ on heating (II→I). The dipole moment of cyclohexanol was determined by Debye's dilution method to be μ=1.85 D.U.
東北大学の論文

Dielectric Relaxation and Phase Transition of Cyclohexanol

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