Mansel Davies

Multiple Relaxation Times in Nonrigid Solute Molecules

This paper describes the first detailed investigation of the dielectric behavior of liquid solutions of large solute molecules possessing small polar groups capable of rotation about a chemical bond. Three hindered hydroxy‐compounds are chosen as examples and their dielectric properties in Decalin solution are measured at frequencies up to 2.4×1010 cps which includes the region of maximum absorption. In each case two distinct absorption regions are obtained, in contrast to the results for the rigid molecule o‐dichlorobenzene, which gives a Debye curve with a single relaxation time.A comparison of the calculated and observed dipole moments supports the theory that in each case the lower frequency absorption is due to the rotation of the main part of the molecule and the higher frequency absorption is due mainly to the independent orientation of the hydroxyl group by rotation about the C–O bond.The activation energies and frequency factors for the dielectric mechanisms are determined, where possible, from t...

Character of absorption in far infra-red by polar molecules in liquid state

The use of the Fourier spectrometer has been extended down to 2 cm–1 and the results of a study of the absorption and dispersion in the liquid and dissolved states of selected polar molecules (methyl chloroform CH3CCl3; chlorobenzene C6H5Cl; benzonitrile C6H5CN; tolune C6H5CH3) from this wave number to beyond 100 cm–1 are reported. It is concluded that the available representations (Record, Powles) of the decay of the dipole relaxation (Debye) absorption due to the inertia factor are inadequate. The further distinct absorption of polar liquids predicted by Poley has been observed for each of the liquids studied. Systematic evaluation of the nature of these absorptions has shown intense features of considerable breadth located in the wave number range 30 to 80 cm–1. Observed data are :[graphic omitted] This (Poley) absorption is of intensity proportional to the molar concentration and is apparently independent of the solvent on dilution. The wide significance of these data is discussed.

Submillimetre- and millimetre-wave absorptions of some polar and non-polar liquids measured by fourier transform spectroscopy

An assessment of the Fourier transform spectrometer indicates the advantages to be gained from its application to be the millimetre-wave region (10 to 2 cm–1). The attainable resolving power is adequate for the study of broad absorptions such as occur in liquids below 100 cm–1. With a mercury arc source, appropriate beam dividers, and an indium antimonide detector at 1 K, continuous refraction (n) and absorption (α) spectra have been obtained below 50 cm–1(to 2 cm–1 in some cases) for some typical polar and non-polar liquids. Results for water, aniline, 1,4-dioxan, cyclohexane, decahydronaphthalene, dimethyl acetylene (2-butyne) and 1-octyne are reported and considered in relation to earlier microwave dielectric data and far infra-red measurements. Water and aniline show strong, almost featureless, absorptions which are probably due to the superposition of three or four processes. The non-polar and weakly-polar liquids show much smaller absorptions : 1.4 dioxan has a profile consistent with a zero permanent electric dipole moment; 2-butyne and 1-octyne show α rising linearly with over the range 5-50 cm–1. The origin of the absorption in non-polar liquids is different from the dominant mechanism in polar liquids although the peak values for both lie in the submillimetre-wave regions. The non-polar absorption peaks occur at frequencies which correlate with those calculated for molecular collisions in the liquids using the formulations of Mie and Bradley.

Dielectric studies of mobility of polar molecules in polystyrene

Dielectric measurements (5Hz–8.5 GHz) at temperatures from –30 to 100°C have been made on polar solutes molecularly dispersed in a polystyrene matrix. Rigid molecules of varying size and shape (camphor, anthrone, cholest-4-en-3-one, tetraphenyl cyclopentadienone) and β-naphthol are considered. By 80° all the molecules show their full dipole moments in polystyrene : the apparent (Eyring) activation energies ΔH*E for molecular dipole relaxations vary from 0.9 kcal mole–1 for camphor to 130 kcal mole–1 for tetracyclone. The apparent ΔH*E over limited temperature ranges themselves reflect changes in the polymer matrix relaxations, and the 130 kcal mole–1 value may well be derived from the glass-transition process. The ΔH*E and ΔS*E correlate linearly and the former is dependent upon the molecular rotational volume. The “whole molecule” and hydroxyl group rotations are well resolved for β-naphthol with ΔH*E values of 11.2 and 0.5 kcal mole–1 respectively.

Molecular Interaction and Infra‐Red Absorption Spectra PART I. METHYL ALCOHOL

A study has been made of the absorption spectra between 3μ and 15μ of methyl alcohol at varying concentrations in solution. Clear indications are obtained of at least two new bands outside the 3μ region which arise from the associated molecules. The data allow of a further discussion of the vibrational assignments in methyl alcohol and it is hoped that some of the uncertainties in that respect have now been removed.

Far infra-red absorptions of non-dipolar liquids. Part 1.—Experimental measurements, quadrupole interpretation and model calculations

The far infra-red absorption spectra of a number of non-dipolar liquids have been obtained using the NPL-Grubb Parsons cube interferometer, adapted to employ phase modulation. Marked improvement in the precision and reproducibility of the absorption measurements has been achieved. The characteristic absorption of non-dipolar liquids in the far infra-red has then been evaluated in terms of an “effective” quadrupole moment of the molecules involved. The quadrupole moments so calculated agree with available literature values, thus supporting the view that the submillimetre-wavelength absorption of non-dipolar liquids largely has its origins in a quadrupole-induced dipole appearing in the molecules.Model calculations show there is adequate “dipole strength” induced by the quadrupole field of a neighbouring non-dipolar molecule to account for the absorptions observed. The approximations involved in point multipole representations of adjacent-molecule interactions are estimated by comparison with the better approximations of local-charge models.

High field dielectric measurements in water

High field dielectric measurements of the “Piekara factor” have been carried out for pure water at 293 K. The measurements have been made possible by the development of a new technique capable of measuring permittivity changes ΔIµ/Iµ as low as 10–5 in samples with conductivities as high as 10–2Ω–1 m–1. Reproducible results with water having conductivities in the range 1 to 4 × 10–5Ω–1 m–1 gave ΔIµ/E2=–(1.00 ± 0.15)× 10–15 m2 V–2. The results are interpreted in terms of the low field dipole polarization factor Rp and the non-linear field effect correlation factor RS. The behaviour is that of the “classical” non-linear effect of a negative ΔIµ due to permanent dipoles.

Dielectric relaxation in clathrates

Dielectric parameters (permittivity and loss factors) have been measured for clathrates based on ice (gas hydrates), quinol and Dianins compound with particular attention to the frequency and temperature ranges displaying the reorientational dipole dispersion of the guest molecules. Many such processes conformed to the simple Debye form. Enthalpies (in kcal mole–1) and entropies (in cal mole–1 deg.–1) of activation for this reorientation were evaluated from Eyrings rate equation, and effective dipole moments (in D) for the guest were derived from the Bottcher-Onsager equation.[graphic omitted] Most of these ΔH*E are less than those for the reorientation of the same or similar molecules in inert solvents. In Dianins compound, permittivity data were obtained and the freedom of the dipole to reorient assessed for single molecules of o-C6H4Cl2, C6H5NO2,C6H5CN, C6H5CH2CN, t-C4H9CN, and for two molecules of HCOOH, CH3COOH, CH3NO2, and (CH3)2CO per cavity; for (CH3CN)2 per cavity, ΔH*E= 2.10±0.15; ΔS*E=–2.9; µ= 7.0D; (CH3CH2CN)2 and (CH3OH)n gave extended absorptions. The possible resonance form of small-molecule absorptions is considered.

Dielectric and optical studies of a nematogen (4,4-n-heptyl-cyanobiphenyl)

The permittivity, refractive index, molecular dipole moment, dielectric relaxation parameters and molecular Kerr constant are reported for the nematogen 4,4-n-heptyl-cyanobiphenyl (HCB) in the nematic phase, in the pure isotropic phase and in benzene solutions. The anisotropy of molecular polarizability is less than in benzene. Kirkwood–Bordewijk g-factors show significant dipole antiparallelism in the isotropic and nematic phases: in the latter it is much larger parallel to the director axis than perpendicular to it. The two major (orthogonal) component activation enthalpy and entropy terms for dipole reorientation (Bauer) in the nematic phase (including benzene solutions) are compared with those in the isotropic media: in the pure nematic ΔHB(‖)= 60 ± 8 kJ mol–1; ΔHB(⊥)= 6 ± 2 kJ mol–1. The current theoretical representations of the nematic phase are examined using the experimental data. The occurrence of pre-transitional molecular interaction in benzene solutions (above 3 mol dm–3) and in the pure isotropic phase can be detected.

Total dielectric saturation observed in a dipolar solution

Abstract Measurements of dielectric saturation have been made in a solution of poly(benzyl-L-glutamate in dioxan. dioxan. Almost complete saturation has been obtained, the data following Langevin function at high fields. Anomalous behaviour is observed at low fields.