Messungen dielektrischer Eigenschaften bei hohen Drücken und tiefen Temperaturen III: Die statische und komplexe Dielektrizitätszahl von Cyclopentanol

Abstract

The static permittivity ε of liquid and solid cyclopentanol has been determined as a function of temperature (+ 50 to ‐ 80 °C) and pressure (up to 3 kbar). From these and PVT data the Kirkwood correlation factor g has been calculated. Plots of g as a function of temperature intersect at g = 2.6 and at the “cross‐over‐temperature” of 30 °C. The calculations have also been extended to the plastic phases (SI, SII) of cyclopentanol, because their permittivity (especially that for SII) exceeds that for the liquid considerably. There is a drastic decrease of ε to values about 2.5 at a lower SII/SIII transition. The increase of ε at the freezing point is larger as should be expected according to the Onsager equation. The temperature dependence of g at constant volume is negative. Also the dielectric relaxation has been studied for the plastic phases of cyclopentanol up to frequencies of 10 MHz. The complex permittivity has been evaluated with the help of the Cole‐Cole equation, showing only a small deviation from a simple Debye‐mechanism (α ≤ 0.05). The relaxation times τ about 1000 bar vary from 10−5 s (‐70°C) to 3 · 10−8 s (‐ 10°C) in solid cyclopentanol, τ being discontinuous at the SI/SII transition. Activation volumes (5–7 cm3 mol−1) and activation energies (40 kJ mol−1) have been derived from the pressure and temperature dependence if τ.

Dielectric spectroscopy on two orientationally disordered crystals: NPA (CH2OHC(CH3)3) and TCE (CH2OHCCl3)

“…NPA presents g values larger than unity for the whole temperature range. This is a typical value in chain [32,33], alicyclic [19][20][21][22][23] and branched [3,24] alcohols indicating a preferred parallel correlation of the dipoles. However, for TCE, the g values are always lower than 0.5.…”

“…This fact would not be surprising, taking into account that the possibility of formation of hydrogen bonds is greater than for NPA and NPG. A more exhaustive revision of the values of activation enthalpies for the ODIC state of alicyclic alcohols, like cyclopentanol, cyclohexanol, cycloheptanol [19][20][21][22][23][24] and other branched alcohols like neohexanol, neooctanol, . .…”