Herman Farber

Microwave dielectric relaxation of some liquid ethers

Abstract Complex permittivities, at 25°C, in the frequency range 4-68 GHz, for the liquids 1–3 Dioxolane, dimethoxymethane, 2–2 dimethoxypropane and 1–2 dimethoxyethane are reported. The data for these liquids may be analyzed, within experimental error, by a single Debye relaxation process (up to the investigated frequency of 68 GHz). Correlations between the shear viscosity and the microscopic relaxation time for the above liquids and for methoxy compounds containing rigid aromatic frames have been attempted. It is concluded the major contribution to the observed relaxation times for the liquids investigated containing methoxy groups, is molecular tumbling rather than methoxy group rotation.

Microwave dielectric relaxation of water in hydrated melts: system Ca(NO3)2.4H2O

The microwave complex permittivities of hydrated melts of composition Ca(NO3)2 3.9 H2O, in the frequency range 8.2–79 GHz, and temperature range 40–55°C, are reported. The real and imaginarry coefficients of the complex permittivity show a dielectric relaxation process, which can be described in most of the frequency range by a Debye function for a single relaxation. Some deviation becomes apparent, however, at the upper end of the frequency range investigated. Eyring plots of the inverse of the relaxation time vs the inverse of temperature give the activation parameters for the process. The latter is interpreted as due to the rotation of water in the melts, all the water being probably coordinated with the cations. Compared to the activation parameters in pure water one notices an increase in both the enthalpy and entropy of activation. An increase in the activation energy in concentrated aqueous LiCl has been already reported in the literature.

Microwave dielectric relaxation of methyl and ethylcellosolve

Abstract The complex dielectric permittivity of methyl and ethylcellosolve at 25°C and in the frequency range 1–90 GHz are reported. The real and imaginary coefficients of the permittivity show a relaxation profile with frequency that can be interpreted either by a Cole-Davidson distribution function or by the sum of two discrete Debye-relaxation processes. Preference for the latter description is given not on the basis of an optimum of a numerical fit, but rather on the proposal that the two Debye processes are related to H-bond breaking, as for the alcohols, and to alkoxy and/or molecular tumbling respectively. Evidence of the above hypothesis is given by reporting the complex permittivity of methylcellosolve-dimethoxyethane mixtures in the whole composition range. It is shown that the relaxation contribution e0-e∞1, attributed to the lower Debye relaxation process (and assigned to the H-bond breaking process) is proportional to the molarity of methylcellosolve up to the pure liquid. This shows that by substituting the OH group by the methoxy group, the effect attributed to (e0-e∞1) decreases and disappears when no -OH groups are present as for pure dimethoxyethane. Further, by taking the position that the contribution e0-e∞1 is to be dealt with as in liquid mixtures, the apparent dipole moment μ∼3 Debyes is calculated by the Bottcher theory. This figure is comparable to the values of μ calculated by the Onsager theory for the alcohols. The above seems to suggest that although the Cole-Davidson distribution function may fit the relaxation profile numerically, it eludes (by its own nature) the molecular description of the dielectric relaxation processes.

Microwave Dielectric Relaxation of Lithium Salts in Media of Low Permittivity at t=25°C

This paper reviews data (taken in our laboratory) of complex permittivities of solutions of lithium salts at U.H.F. and microwave frequencies. The solvents used were tetrahydrofuran, dimethyl- and diethylcar-bonate.