Circular Arc Law Research Articles

Dielectric properties of silicon dioxide/wood composite

For a better understanding of the binding between silicon dioxide and wood as well as the dielectric properties of silicon dioxide/wood composite, dielectric relaxation was measured for untreated wood [Cunninghamia lanceolata (Lamb.) Hook] and for silicon dioxide/wood composite with different weight percentage gain (WPG). Cole–Cole’s circular arc law, distribution spectrum of relaxation time and relation model were applied to the results of relaxation due to motions of the methylol groups. The results were as follows. The generalized relaxation time and e s − e ∞ decreased with increasing WPG. The distribution spectrum of relaxation time decreased more and more and broadened with increasing WPG. The methylol group in the amorphous region of the wood cell wall participated in hydrolysis reaction and condensation reaction caused by tetraethylorthosilicate (TEOS), and there is a cross-link between silicon dioxide and wood. The value of apparent activation energy (ΔE) increased for silicon dioxide/wood composite, and increased with increasing WPG. Activation enthalpy (ΔH) and activation entropy (ΔS) increased, while activation free energy (ΔG) decreased with increasing WPG. The number of hydroxyl groups cut in dielectric relaxation increased with increasing WPG.

Dielectric relaxation of water adsorbed on chemically treated woods

Abstract Changes in the dielectric relaxation due to water adsorbed on eight types of chemically treated woods, as well as untreated wood (Picea sitchensis Carr.), with moisture content (MC) were investigated in the temperature range between −150°C and 20°C and in the frequency range between 100 Hz and 1 MHz. Cole-Cole's circular arc law was applied to the results of dielectric measurements conducted at seven levels of relative humidity (RH), and the relaxation spectra at −75°C were calculated. The theory of rate processes was applied to the dielectric relaxation resulting from the motions of water molecules adsorbed on the untreated and chemically treated woods, and the binding state of adsorbed water was examined. The relaxation magnitude increased with increasing MC, irrespective of the chemical treatment. The distribution of relaxation times decreased in the MC range below 1%, but increased with increasing MC at higher levels. The generalized relaxation time increased up to 5% MC, then decreased. The enthalpy-entropy compensation phenomenon was observed in the dielectric relaxation, which was derived from the adsorption of water molecules on the chemically treated woods. The binding states of adsorbed water and ice were similar. The water molecules adsorbed on wood may have produced a very wide variety of cohesive structures in the chemically treated woods.

Dielectric relaxation due to heterogeneous structure in moist wood

Dielectric properties in three main directions for hinoki wood (Chamaecyparis obtusa) specimens conditioned at various levels of relative humidity were measured in the frequency range from 20 Hz to 10 MHz over the temperature range from −150°C to 20°C. Three relaxations were observed in the specimens conditioned at high levels of relative humidity. The relaxation in the highest frequency range was ascribed to the motions of adsorbed water molecules. The relaxation in the middle frequency range remained unchanged by the ethanol–benzene extraction of specimens. The relaxation location was independent of measuring directions. The relaxation in the lowest frequency range was not detected in the specimens impregnated with methyl methacrylate (MMA). This result suggested that the relaxation was due to electrode polarization. The Cole-Cole circular arc law applied well to two relaxations recognized in the specimens impregnated with MMA. The relaxation magnitude in the middle frequency range was extremely large, and the distribution of relaxation times was very narrow. These characteristics suggested relaxation of the Maxwell-Wagner type resulting from the interfacial polarization in the heterogeneous structure, which included adsorbed water with large electrical conductivity within the insulating cell walls.

Dielectric relaxation due to the heterogeneous structure of wood charcoal

Delignified hinoki wood and cellulose as well as hinoki and lauan woods were carbonized at 590°C for 1 h. The dielectric properties of these specimens were measured at 20°C in a frequency range of 20 Hz to 1 MHz. Inflection points in the dielectric constant (e′) versus the logarithm of frequency (log f) curves as well as in the logarithm of the electric conductivity (log σ) versus log f curves for all specimens prepared were recognized. Peaks in the dielectric loss and the imaginary part of the complex conductivity versus the log f curves were detected in the frequency location corresponding to the inflection point in the e′ and log σ versus log f curves. It was considered that this relaxation was responsible for the interfacial polarization observed in heterogeneous materials because no permanent dipoles existed in the specimens carbonized above 500°C. The Cole–Cole circular arc law was applied to account for this relaxation. Similar average relaxation times were obtained for all specimens. These results suggested that the observed relaxation was ascribed to interfacial polarization at microscopic levels in the cell walls.

Dielectric relaxation spectra of chemically treated woods

AbstractThe changes in the dielectric properties of absolutely dried Sitka spruce (Picea sitchensis Carr.) wood caused by chemical treatments were investigated. Eight kinds of chemical treatments with various levels of weight percentage gain (WPG) were performed. Through the application of the Cole–Cole circular arc law to the results of the dielectric measurements in the frequency range of 1 kHz to 1 MHz at −60°C, the relaxation spectrum was calculated. The relaxation magnitude (ε0 − ε∞) was reduced by formalization, acetylation, propylene oxide, and phenol–formaldehyde resin treatments, in which chemical reactions occurred between the OH groups in the cell wall and the added reagents. On the other hand, the generalized relaxation time (τm) decreased with increasing WPG, except for acetylation, for which τm decreased up to a WPG level of 20% and then increased. In poly(ethylene glycol) impregnation, (ε0 − ε∞) decreased with increasing WPG up to about 50% and then increased, whereas τm linearly decreased with increasing WPG. No significant changes in these parameters were recognized for the wood methyl methacrylate composite and heat treatment. With the steam treatment, τm increased. The distribution of the relaxation times was broad in acetylation and narrow in propylene oxide treatment and poly(ethylene glycol) impregnation. However, it remained almost unchanged in the other treatments. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 37–43, 2005

Dielectric relaxation due to interfacial polarization for heat-treated wood

The dielectric properties of totally dried sugi ( Cryptomeria japonica) wood block and powder specimens treated at various temperatures up to 800 °C were measured in the range from 20 Hz to 1 MHz and from −150 to 20 °C. Relaxation ascribed to the motion of methylol groups was detected in specimens treated at temperatures below 300 °C and its magnitude decreased with increasing temperature. The electric conductivity decreased with increasing temperature up to 400 °C. Another form of relaxation was recognized for block specimens treated at temperatures between 500 and 600 °C. Cole–Cole’s circular arc law was applied to the experimental results. The relaxation magnitude was 60–75 and 24–28 in the longitudinal and radial directions of the block specimens, respectively. Identical relaxation was also observed in the powder specimen. The electric conductivity began to increase remarkably from 500 °C. These results suggested that a small volume fraction of particles with large conductivity is formed at microscopic levels in the cell walls. It is considered that this relaxation is due to interfacial polarization.

Dielectric properties of chemically treated wood

Dielectric properties along the grain for absolutely dried untreated and seven kinds of chemically treated Sitka spruce (Picea sitchensis Carr.) woods were measured. Cole-Cole's circular arc law was applied to the results of the relaxation due to the motions of methylol groups. The following changes were caused by chemical treatments. In polyethylene glycol (PEG) impregnation, the distribution of relaxation times became very narrow, the generalized relaxation time (τm) was considerably decreased, and the relaxation magnitude (e0 − e∞) was slightly increased. In acetylation, the distribution of relaxation times became very broad, τm was considerably increased, and (e0 − e∞) was remarkably decreased. In propylene oxide treatment, the distribution of relaxation times became slightly narrow and τm was decreased. τm was slightly decreased in formalization, phenol-formaldehyde (PF) resin treatment and wood methyl methacrylate (MMA) composite. (e0 − e∞) was decreased in formalization and PF-resin treatment and was hardly changed in wood-MMA composite and heat treatment. The distribution of relaxation times was almost unchanged in formalization, PF-resin treatment, wood-MMA composite and heat treatment.

Dielectric properties of nematic liquid crystals in the ultralow frequency regime

The dielectric properties of nematic liquid crystal (4-cyano-4′-n-pentylbiphenyl: 5CB) cells in the ultralow frequency regime was investigated. A dielectric relaxation, whose relaxation time is 160 s, is observed at 303 K, and the dielectric relaxation is found to be independent of applied electric field. It is shown that the dielectric relaxation is caused by the Helmholtz double layer formed by the adsorption of impurity ions in 5CB onto the electrode surfaces of the cells, and hence the thickness of the double layer is comparable to the radius of impurity ions in 5CB. The dielectric relaxation obeys the empirical Cole-Cole circular arc law, indicating that dielectric relaxation times are distributed. The distribution of dielectric relaxation times can be explained in terms of distributed thicknesses of the Helmholtz double layer.

Dielectric Dispersion of the Complex Perovskite Oxide Ba(Fe1/2Nb1/2)O3 at Low Frequencies

Ceramic specimens of the complex perovskite oxide Ba(Fe1/2Nb1/2)O3 were fabricated by conventional solid state sintering. Dielectric constants were measured as a function of temperature as well as of frequency. As a result, dielectric constants showed an unusual temperature dependence. Moreover, a large dielectric dispersion was observed below 1 MHz, and it was represented by the Cole-Cole circular arc law. The present dielectric dispersion was interpreted on the basis of the interfacial polarization at the grain boundary region.

A finite‐difference time‐domain formulation for transient propagation in dispersive media associated with Cole‐Cole's circular ARC law

AbstractThe three‐dimensional time‐domain formulation for dispersive media which obey Cole‐Cole's circular arc law is presented using the finite‐difference‐time‐domain (FD‐TD) technique. The validity of the formulation is verified by comparing the calculated complex dielectric constant to analytical values.

アルミニウムセッケンの物理化学的研究 (第8報)

Dielectric properties of aluminum stearate in benzene solution were studied. It has been shown that the dielectric loss is due both to the direct-current conductivity and to the relaxation phenomena. Both the dielectric constant and loss decreased with the increase of stearate/aluminum ratio and they varied with aging after dissolution. It was found that the Cole-Cole's circular arc law holds for the complex dielectric constants of aluminum soaps. From the Cole-Cole's circular arc law and also, the method of Williams and Ferry, distribution functions of relaxation time were calculated. The mean relaxation time of mono-soap thus obtained was about the same as that of di-soap, and was greater than that of 1.5-soap. On the basis of these results on dielectric properties, it has been concluded that the mono-soap, as well as the di-soap, forms a kind of aggregate in benzene solution, and the aggregate of mono-soap is probably globular in contrast to the aggregate of di-soap which is believed to be linear.

Studies on dielectric properties of polymethylacrylate

The behaviors of the two dielectric absorptions for polymethyl acrylate were measured over a wide range of frequency and temperature. The temperature dependences of the magnitude and the shape of the two absorptions were determined by using the Cole-Cole's circular arc law. While Cole's plots for the Β-absorption lay on the circular arc, the plots for the α-absorption deviated from the arc on the high frequency side. It was found from the result of the superposition of the α-loss curves that the deviation from the arc is caused by the overlapping of the tail of the Β-absorption on the tail of the high frequency side of the α-absorption. The mean apparent activation energy for the α-absorption was 57 Kcal/mole and that for the Β-absorption was 15 Kcal/mole.

Studies on dielectric properties of polyacrylonitrile

The dielectric properties of polyacrylonitrile were measured over frequencies from 100 c/s to 2 Mc/s and temperatures from −70° C to 150° C, where only one dielectric absorption could be identified. In comparison with the result of visco-elastic measurement of polyacrylonitrile, it is concluded that the dielectric absorption will be attributed to the dipolar orientation related to the mierobrownian motion of segment.Cole andCole's circular arc law was satisfactorily applied to the data, andCole's parameter, (e 0−e ∞) and $$\bar \beta $$ were determined at each temperature. (e 0−e ∞) and $$\bar \beta $$ increase with the rise of temperature and reach to asymptotic values.

Studies on dielectric properties of polyvinylidene chloride

The ɛ′ and ɛ″ for polyvinylidene chloride investigated were measured at frequencies from 100 c/s to 2 M c/s, at various fixed temperatures from −60° C to 50° G. In this range of measurement, only one dielectric absorption could be observed. The parameters representing the magnitude and the shape of this dielectric absorption were determined by usingCole-Cole's circular arc law, and the apparent activation energy for this dielectric absorption was calculated from the temperature-dependence of the frequency corresponding to loss maximum. Then the dielectric absorptions of polyvinylidene chloride and polyvinyl chloride were compared in respect to their magnitude, shape and apparent activation energy, where in magnitude the former was smaller than the latter, in shape broader and in apparent activation energy smaller. These fact will be explained by the fact that polyvinylidene chloride has the smaller resultant dipole moment and better crystallizability.