J. Crossley

Dielectric Relaxation of Some Aliphatic Ketones in Cyclohexane Solution

The dielectric constant and loss data, measured at seven microwave frequences, for seventeen aliphatic esters in cyclohexane solution at 25°C have been analyzed for mean relaxation times and Cole‐Cole distribution parameters. The relaxation times for ethyl esters are slightly longer than those for corresponding methyl esters. In both cases, however, the relaxation time does not lengthen significantly as R in RCOOR′ is increased from C5 to C22. It would appear that the dielectric absorption of aliphatic esters is similiar to that for aliphatic ketones and is dominated by an intramolecular relaxation process.

Reorientational motions of dipolar solutes in glassy o‐terphenyl

The low frequency (102–105 Hz) dielectric relaxation behavior of small dipolar molecules dispersed in supercooled o‐terphenyl has been studied below the glass transition temperature. Broad asymmetric loss curves are obtained for both rigid and nonrigid solute molecules. The relaxation times and Eyring activation enthalpies for molecular and intramolecular group reorientation processes are compared with the analogous values for the same solutes in a polystyrene matrix.

The nature of the β process for polar solutes in four glassy forming solids

Dielectric constant and loss data have been obtained for several rigid dipolar substituted benzenes in up to four glass forming solvents. Measurements were made between 10 and 105 Hz from about 80 K up to room temperature. The broad loss curves were analyzed to give relaxation times which were then used to determine Eyring activation enthalpies ΔHE. For the glassy systems dipole reorientation, at temperatures well below the glass transition, Tg is essentially independent of the solvent and is identified as a β process. The ΔHE values of the β process increase appropriately with molecular size but are largely independent of the glassy medium. The β process for these systems is ascribed to molecular relaxation which may possibly occur in a ‘‘solvent cavity.’’

Dielectric relaxation of 1‐alkenes

Dielectric constants and losses have been measured for 1‐hexene, 1‐octene, 1‐decene, 1‐dodecene, 1‐tetradecene, 1‐pentadecene, 1‐hexadecene, 1‐heptadecene, and 1‐octadecene as pure liquids at up to 10 frequencies between 1 and 140 GHz at 25°C. The mean relaxation times, τ0, and viscosities, η, increase significantly with increasing chain length; however, the parameter τ0/η reaches a maximum for 1‐dodecene and then decreases with increasing chain length. The results are compared with those obtained for other n‐alkyl compounds containing a polar end group.

Dipole reorientation of solute molecules dispersed in organic glasses

Dielectric loss curves (102–105 Hz) have been obtained for a variety of organic molecules dispersed in a six‐ring polyphenyl ether over a range of temperatures below the glass transition. Characteristic broad loss curves were obtained for rigid molecules, such as nitrobenzene, and molecules, such as 1,4‐dimethoxybenzene, which contain a rotatable polar group that can contribute to the dielectric absorption. Eyring activation enthalpies determined from the temperature dependence of the relaxation times for these systems are compared with earlier results using o‐terphenyl and polystyrene glasses. The time scale of the group relaxation of a particular solute molecule in different organic glass solvents seems to be fairly independent of the nature of the solvent despite substantial differences in their glass transition temperature.

Dielectric Relaxation of Aliphatic Amines in Cyclohexane Solution

Dielectric constants and losses have been obtained for n‐butyl‐, n‐hexyl‐, n‐nonyl‐, 2‐nonyl‐, 5‐nonyl‐, n‐decyl‐, n‐undecyl‐, N‐methyl‐n‐octyl‐, N, N‐dimethyl‐n‐octyl‐, and N, N‐diethyl‐n‐octylamines in cyclohexane solution at 25°C at up to 10 frequencies in the range 1.0–145 GHz. Static dielectric constants have also been measured at 2 MHz. Primary amines are characterized by short relaxation times which are almost independent of the size of the alkyl group and the location of the −NH2 group. Considerably longer values are obtained for the secondary and tertiary amines. The results are discussed in terms of the relative importance of dipole reorientation by intramolecular and whole molecule rotations.

Macroscopic viscosity and the dielectric relaxation of 1-butanol and 1-decanol

Abstract Dielectric constants and losses have been measured at eight microwave frequencies between 1 and 35 GHz for 1-butanol and 1-decanol in paraffin oil and paraffin oil- n -heptane mixtures at 25 °C. The data have been analyzed in terms of two relaxation times and their dependence on viscosity and concentration is examined. The dielectric relaxation behaviour of these alcohols is not affected to any appreciable extent by increased macroscopic viscosity.

Dielectric relaxation processes of some almost spherical dipolar organic molecules

Dielectric constant and loss measurements have been made, between 10 and 105 Hz, on seven dipolar substituted methanes from liquid nitrogen temperature up to and above the melting point. All these components have been examined in the pure solid state, four in cis‐decalin and one in carbon tetrachloride. Two detailed studies have been made on the influence of concentration on the loss factor maximum value. All of the substances gave broad loss curves which were analysed to give relaxation times and activation enthalpies. Six compounds yielded an α process in the pure solid state. In the case of 1, 1, 1‐trichloroethane in the pure solid state, cis‐decalin, and carbon tetrachloride the β process may probably be ascribed to molecular relaxation.

Microwave absorption and molecular structure. LXXXII. The dielectric relaxation mechanisms of benzyl‐ and benzoylpyridines

Dielectric constant and loss measurements have been made at six frequencies between 0.6 and 150 GHz for 2−, 3−, and 4−benzoylpyridine and 2− and 4−benzylpyridine in benzene solution. The data have been analyzed for mean relaxation times τ0. The τ0 values for the benzoylpyridines indicate that their dielectric absorptions are dominated by the reorientation of the molecule as a whole. It was possible to analyze the data for the benzylpyridines in terms of two relaxation times which may be associated with whole molecule and intramolecular reorientation processes.

Relaxation processes of 9‐fluorenone and benzophenone in o‐terphenyl solution

Dielectric absorption studies have been made on both 9‐fluorenone and benzophenone in o‐terphenyl solution at several temperatures above the melting point of o‐terphenyl in the frequency region 1 to 6 GHz. These relaxation data may be explained in terms of molecular relaxation of individual solute molecules. This is to be contrasted with the behavior of these systems as supercooled liquids where the absorption may be accounted for in terms of an α process which involves cooperative motion. It seems likely that,between the glass transition temperature and the melting point, the motion of regions of the solvent govern the relaxation process of the solute. Above the melting point, however, local solute–solvent motion as involved in the customary dielectric relaxation process of a solute at low concentration in a nonpolar solvent predominates.