At eight temperatures T between 0 and 60 °C and at five mole fractions x e of ethanol (0 < x e ≤ 1) the complex (electric) permittivity of ethanol/water mixtures has been measured as a function of frequency ν between 1 MHz and 24 GHz. At 25 °C the ethanol permittivities are completed by literature data for the frequency range 200 MHz to 90 GHz. The spectra for ethanol and for the ethanol/water mixtures are compared to permittivity spectra for water which, at some temperatures, are available up to 900 GHz. All spectra of the ethanol/water system can be well represented by the assumption of two relaxation regions. The relaxation time τ 1 of the dominating relaxation process varies between 4 ps (x e = 0, 60 °C) and 310 ps (x e = 1, 0 °C). The relaxation time τ 2 of the second relaxation process is smaller. Evaluation of the extrapolated low frequency (“static”) permittivity yields a minium in the effective dipole orientation correlation of the ethanol/water system at 0.2 ≤ x e ≤ 0.4. In this composition range, other parameters also exhibit extrema, indicating a microheterogeneous structure of the mixtures and the existence of precritical concentration fluctuations. Interesting, the activation enthalpy ΔH 1 ⧧ and entropy ΔS 1 ⧧ of the dominating dielectric relaxation process also display a distinct maximum at around x e = 0.22. These activation quantities have been obtained from Eyring plots of the relaxation time τ 1 at different mixture compositions. The relaxation parameters of the ethanol/water system are discussed in terms of a wait-and-switch model of dipole reorientation.

At different temperatures T (0 °C ≤ T ≤ 60 °C) and mole fractions x of ethanol (0 ≤ x ≤ 1) the complex (electric) permittivity of ethanol/n-hexanol mixtures has been measured as a function of frequency ν between 1 MHz and 18 GHz. Within this frequency range of measurement the dielectric spectra reveal two relaxation regions. The relaxation time of the dominating relaxation process varies between τ1 = 63 ps (x = 1; 60 °C) and τ1 = 2.8 ns (x = 0; 0 °C). The relaxation time τ2 of the second process is smaller (5 ps ≤ τ2 ≤ 109 ps). The extrapolated static permittivity ε(0) of the alcohol systems is evaluated to show that there is a noticeable effect of permanent electric dipole orientation correlation. The relaxation terms are discussed in the light of hydrogen bond fluctuations and modes of reorientational motions of alcohol molecules. A remarkable result is the finding that the activation enthalpy associated with the dominating relaxation process can be represented by a sum of contributions from interactions between the hydrogen bonding OH-groups and between the methylene as well as methyl groups of the alcohol molecules. This finding suggests intermolecular interactions between the aliphatic groups to play a siginificant role in the dynamics of the molecular reorientations.

For an abrupt transition from a coaxial to circular waveguide with a dielectric interface in the plane of discontinuity, the input admittance has been calculated as a function of frequency and of relevant geometrical and electrical quantities. The calculations have been performed applying a mode matching technique. A simple lumped-element representation has been derived from the theoretical considerations which was found to provide an excellent description of the input admittance of the discontinuity over a wide range of values of the parameters of interest. Network parameters are discussed for transitions that are most suited as sample cells for dielectric measurements in both the time domain and the frequency domain. Results from test measurements are reported to show the agreement of our numerical predictions with precise capacitance values of other authors and also to demonstrate the sensitivity and accuracy attainable with such cells.