Charles P. Smyth

Microwave Absorption and Molecular Structure in Liquids. IX. Measurement in Organic Halides at 10‐Cm Wavelength

The results of a systematic investigation of dielectric dispersion and absorption in the microwave region are discussed. Simple relations between the complex dielectric constant of an absorptive medium and the complex propagation constant of an electromagnetic wave within the medium are discussed in connection with a new interferometric method for measuring wavelength and absorption index directly within the medium. Results of measurements made at 10 cm wavelength by this method on twenty‐five liquid organic halides are reported. The data of the present and previous measurements on these compounds are discussed in terms of distributions of relaxation times and, on the basis of absolute rate theory, the processes of dipole orientation and viscous flow in these liquids are compared.

Dielectric Relaxation of Rigid Molecules in Supercooled Decalin

The equilibrium dielectric permittivity of pure decalin and the dielectric permittivity and loss of dilute solutions of chlorobenzene, bromobenzene, toluene, tetrahydrofuran, 1‐fluoronaphthalene, 1‐chloronaphthalene, 1‐bromonaphthalene, and 1‐methylnaphthalene in decalin have been measured from 50 Hz to 100 kHz at several temperatures between −135 and −155°C. The equilibrium dielectric permittivity of solutions shows no significant short‐range order tending to align the dipoles preferentially. All the rigid molecules show a broad dispersion region which does not seem to be describable by any simple distribution function. It is shown that the introduction of the solvent as a viscoelastic medium, with frequency‐dependent viscosity, can account for the broad dispersion region. An additional region of dielectric absorption at relatively high frequencies appears to be present in all of these solutions. The Arrhenius plots of the relaxation time are nonlinear, with the activation energy increasing from 25 kcal/...

Microwave Absorption and Molecular Structure in Liquids. LXVIII. Dielectric Behavior at 2.2‐mm Wavelength and Intramolecular Motion in Five Substituted Benzenes and Cyclohexanes

The dielectric constants and losses of anisole, bromocyclohexane, aniline, N,N‐dimethylaniline, and cyclohexanol in the pure liquid state have been measured at 2.2 mm wavelength at temperatures between 20° and 60° and combined with data in the literature to calculate the dielectric relaxation times. Where additional data were needed, measurements were made at wavelengths of 1.2, 3.2, 10.0, and 575 000 cm. A single relaxation region was found for bromocyclohexane, corresponding to dipole orientation by molecular rotation, while cyclohexanol showed three relaxation times like those found for aliphatic alcohols, a long one associated with the hydrogen‐bonded structure of the liquid, an intermediate one presumably corresponding to molecular rotation, and a short one corresponding to hydroxyl‐group rotation. Anisole gave two relaxation times, one for molecular rotation and one for methoxy‐group rotation. Aniline and N,N‐dimethylaniline gave two relaxation times, one of the magnitude to be expected for molecula...

Microwave Absorption and Molecular Structure in Liquids. XXV. Measurements of Dielectric Constant and Loss at 3.1‐mm Wavelength by an Interferometric Method

The theory and apparatus for an interferometric method for the measurement of the dielectric constant and loss of a liquid at 3.1‐mm wavelength are described. The 3.1‐mm wave is obtained as the fourth harmonic from a K‐band reflex klystron. The probable error of the dielectric constant measurements is 0.5%, while that of the loss measurements is 2–5% for high loss liquids. For very low losses, only an upper limit can be obtained because of the small amount of harmonic energy obtainable.Four tetrahalogenated methanes, three substituted benzenes, two methylquinolines, three alcohols, and water have been measured and the results examined in the light of measurements at lower frequencies. All of the liquids but the three alcohols give 3‐mm points lying satisfactorily on Cole‐Cole arc plots drawn through points previously obtained at lower frequencies. The losses observed at 3 mm are, however, some‐what higher than the calculated indicating the probable presence of overlapping absorption regions at still highe...

Microwave Absorption and Molecular Structure in Liquids. LXXIX. Dielectric Behavior and Association of Some Normal Alcohols in n‐Heptane Solution

Dielectric constants and losses at 25°C of 1‐butanol, 1‐hexanol, 1‐heptanol, and 1‐decanol, each at six concentrations from 0.03 to 0.3 mole fraction in n‐heptane, have been measured at wavelengths from 2 mm to 600 m. At the lower concentrations, the dielectric absorption may be resolved into two dispersion regions, characterized by relaxation times τ3 (≈ 3 psec and almost concentration independent) and τ2 (ranging from 25 to 100 psec and concentration dependent). The latter dispersion increases its contribution relative to the former with increasing alcohol concentration. At the higher concentrations a final process with a long relaxation time, τ1 (strongly concentration dependent), appears. This third process corresponds to the principal low‐frequency dispersion already well characterized in pure primary normal aliphatic alcohols. The high‐frequency process, because of its very short relaxation time, is attributed to rotation of the hydroxyl group about its C–O bond, the intermediate process is related ...

Microwave Absorption and Molecular Structure in Liquids. LXVI. The Dielectric Relaxation of the Water—Dioxane System and the Structure of Water

The dielectric constants and losses of a series of mixtures of water and dioxane (0.2–0.8 mole fraction) have been measured at wavelengths of 0.217, 1.223, 3.193, and 10.09 cm, and 575 m and temperatures of 1°,10°,25°,40°, and 55°C. The results show that the mixtures have two dielectric relaxation times in contrast to the single time found for water. The results are interpreted as indicating a very rapidly fluctuating structure for pure water in which the molecules are constantly forming, breaking, and reforming hydrogen bonds to their neighbors. At any given instant there are unbonded molecules, as well as singly, doubly, triply, and quadruply bonded molecules, and molecules in all intermediate stages of bonding. However, the fluctuations of structure are so rapid that, averaged over the extremely short time required for dielectric relaxation, the molecules and their immediate environments are approximately the same. In the water—dioxane mixtures, the dioxane molecules alter the environments of some of t...

Microwave Absorption and Molecular Structure in Liquids. LXXVIII. Dielectric and Association Behavior of Six Isomeric Octyl Alcohols in n‐Heptane Solution

The dielectric constants and losses of six isomeric octyl alcohols at concentrations of 0.03–0.35 mole fraction in n‐heptane solution at 25°C have been measured at wavelengths of 0.204, 1.23, 3.23, 9.99, 24.8, and 49.9 cm, and the so‐called static dielectric constants have been measured at 575 m. For three of these alcohols at mole fraction 0.32–0.33, dielectric constant and loss measurements were also made with an RX meter at seven wavelengths from 120 to 600 cm. A new analysis of this measuring system has been carried out to obtain more accurate values of dielectric constant and loss. For those isomers in which the methyl group is attached to the same carbon atom as the hydroxyl group or to the adjacent carbon, the dielectric absorption may be characterized by two relaxation times at all the concentrations employed. The isomers containing a relatively less‐shielded hydroxyl group exhibit an additional low‐frequency relaxation time at the higher alcohol concentrations. In all cases, the magnitude of the ...

Microwave Absorption and Molecular Structure in Liquids. LXX. Dipole Moment, Atomic Polarization, and Dielectric Relaxation in Polymethylpolysiloxanes

Dielectric constants and losses have been measured at wavelengths of 0.22, 1.25, 3.22, 10.01, and 57 500 cm at temperatures of 25°, 40°, and 60° for four liquid polymethylpolysiloxanes of the general formula (CH3)3Si[OSi(CH3)2]xOSi(CH3)3, where x=1, 2, 3, and 5. The data have been used to calculate the small dipole moments, very large atomic polarizations, and two rather small dielectric relaxation times for the molecules. The squares of the dipole moments, the atomic polarizations, and the relaxation times are found to be linear functions of the size of the molecule as measured by x, the number of (CH3)2SiO groups. It is concluded that dipole orientation or relaxation occurs by molecular rotation and by intramolecular motion, which includes group rotation around Si–O bonds and, probably, bending of the Si–O–Si bonds. The bending and twisting of these bonds are the principal causes of the large atomic polarizations, as the absorption frequencies associated with them extend into the far infrared.

Microwave Absorption and Molecular Structure in Liquids. LXV. A Precise Michelson Interferometer for Millimeter Wavelengths and the Dielectric Constants and Losses of Some Low‐Loss Liquids at 2.1 mm

The theory and apparatus for a Michelson interferometer for the precise measurement of dielectric constant and loss of liquids at 2.1‐mm wavelength are described. The probable error of the dielectric‐constant measurements is 0.2%. The probable error of the loss measurements is 2% or ±0.0002, whichever is higher. The dielectric constants and losses of dilute solutions of chlorobenzene in benzene have been measured at 2.1‐mm wavelength at 20° and compared in the light of existing lower‐frequency data. The dielectric constants and losses of several nonpolar and slightly polar liquids have also been measured at 2.1‐mm wavelength at 20°. The presence of appreciable losses in benzene and carbon tetrachloride has been confirmed. Measured losses in cyclohexane and n‐heptane are considerably lower than those in benzene and carbon tetrachloride.

Microwave Absorption and Molecular Structure in Liquids. LXIII. Dielectric Behavior of Rigid Polar Molecules at 2.2‐mm Wavelength and Atomic Polarization

Dielectric constants and losses of fluorobenzene, chlorobenzene, bromobenzene, α‐chloro‐ and α‐bromonaphthalene, thiphene, tetrahydrofuran, and chloroform have been measured at 2.2‐mm wavelength at various temperatures between 20° and 55°C. The results have been used together with the existing lower‐frequency data to construct Cole—Cole arc plots, from which relaxation times, distribution parameters and optical dielectric constants are obtained. In all cases studied the optical dielectric constant e∞ has a value close to the square of the refractive index nD2, and there seems to be no evidence of the additional ultrahigh‐frequency dispersion region suggested by the results of previous workers. The values of e∞ obtained have been used to calculate atomic polarizations which generally agree well with the values determined for the molecules in the gaseous state.