Contribution a L'etude de melanges susceptibles de former des microemulsions selon leurs compositions,par la definition de leurs comportements dielectriques a 9,455 GHz

The dielectric studies of four components mixtures are rarely made on a great deal of concentrations. The authors propose a dielectric behavior study of mixtures made with toluene-water-butanol-SDS, from specific mappings of permittivities which are plotted on pseudo ternary diagrams at 9.455 GHz. They draw different conclusions to know how at 9.455 GHz the variations of real and imaginary parts of permittivity involve the concentration of each component and the structure of the mixture.These conclusions will be perfected by studies made at other frequencies and by spectral analysis of each mixture.     

Reconstruction of spectral function from effective permittivity of a composite material using rational function approximations

The paper deals with the problem of reconstruction of microstructural information from known effective complex permittivity of a composite material. A numerical method for recovering geometric information from measurements of frequency dependent effective complex permittivity is developed based on Stieltjes analytic representation of the effective permittivity tensor of a two-component mixture. We derive the Stieltjes representation for the effective permittivity of the medium using the eigenfunction expansion of the solution of a boundary-value problem. The spectral function in this representation contains all information about the microgeometry of the mixture. A discrete approximation of the spectral measure is derived from a rational (Padé) approximation followed by its partial fractions decomposition. The approach is based on the least squares minimization with regularization constraints provided by the spectral properties of the operator. The method is applied to calculation of volume fractions of the components in a mixture of two materials in a Bruggeman effective medium analytic model which has a continuous spectral density and to analytical models of two-phase composites with coated cylindrical and ellipsoidal inclusions. The numerical results of reconstruction of spectral measure for a mixture of silver and silicon dioxide and a composite of magnesium and magnesium fluoride show good agreement between theoretical and predicted values. The approach is applicable to geological materials, biocomposites, porous media, etc.     

Dielectric properties of moist disperse materials in the microwave range

The behavior of the dielectric permittivity of a mixture of disperse materials is investigated for a change in the volume content of the component with a high value of the dielectric permittivity. An analysis is performed from the viewpoint of computing the dielectric permittivity of such mixtures. A formula is proposed for computation of the dielectric permittivity of mixtures of disperse materials with water.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 74–78, July, 1981.     

The dielectric relaxation study of 2(2-alkoxyethoxy)ethanol-water mixtures using time domain reflectometry

Complex permittivity spectra of 2(2-alkoxyethoxy)ethanol-water mixtures for the entire concentration range and at 25 °C have been measured using time domain reflectometry technique up to 30 GHz. The relaxation processes have been obtained by fitting the complex permittivity spectra of the binary mixtures in 2-Debye equation. In glycol ether-water mixtures except for pure water and its rich region the double relaxation times, primary process (τ₁) and secondary process (τ₂) have been observed. The primary relaxation process (τ₁) may be due to cooperative relaxation of the H-bond network of mixture constituents and the secondary relaxation process (τ₂) may be due to its flexible parts attached to the carbon chain. The intra and intermolecular hydrogen bonding of 2(2-alkoxyethoxy)ethanol in pure form as well as in binary mixtures of water have been discussed using Kirkwood correlation factor, Excess dielectric properties and the Bruggeman factor.     

On the application of homogenization formalisms to active dielectric composite materials

The Maxwell Garnett and Bruggeman formalisms were applied to estimate the effective permittivity dyadic of active dielectric composite materials. The active nature of the homogenized composite materials (HCMs) arises from one of the component materials which takes the form of InAs/GaAs quantum dots. Provided that the real parts of the permittivities of the component materials have the same sign, the Maxwell Garnett and Bruggeman formalisms give physically plausible estimates of the HCM permittivity dyadic that are in close agreement. However, if the real parts of the permittivities of the component materials have different signs then there are substantial differences between the Bruggeman and Maxwell Garnett estimates. These differences are slightly less pronounced if the relative permittivity of the metallic component material is described by the extended version of the Drude formula appropriate to very small particles. However, these differences become enormous - with the Bruggeman estimate being physically implausible - as the imaginary parts of the permittivities of the component materials tend to zero.     

Structural study of aqueous solutions of tetrahydrofuran and acetone mixtures using dielectric relaxation technique

The complex permittivity, static dielectric constant and relaxation time for tetrahydrofuran-water and acetone-water mixtures have been determined at 0°, 10°, 25° and 35°C using time domain reflectometry technique (TDR). The behaviour of relaxation time of the mixture shows a maxima for the mixture with 30% of water by volume. This suggests that the tendency to form cluster between water and solute molecule is maximum for this mixture. The excess permittivity for both tetrahydrofuran-water mixture and acetone-water mixtures, are found to be negative. The Kirkwood correlation factor has been determined at various concentrations of water. Static dielectric constant for the mixtures have been fitted well with the modified Bruggeman model. The values of the Bruggeman parametera for tetrahydrofuran is found to be more than the corresponding value for acetone.     

On the Bergman-Milton bounds for the homogenization of dielectric composite materials

The Bergman-Milton bounds provide limits on the effective permittivity of a composite material comprising two isotropic dielectric materials. These provide tight bounds for composites arising from many conventional materials. We reconsider the Bergman-Milton bounds in light of the recent emergence of metamaterials, in which unconventional parameter regimes for relative permittivities are encountered. Specifically, it is demonstrated that: (a) for nondissipative materials the bounds may be unlimited if the constituent materials have relative permittivities of opposite signs; (b) for weakly dissipative materials characterized by relative permittivities with real parts of opposite signs, the bounds may be exceedingly large.     

Dielectric relaxation and hydrogen bonding studies of 1,3-propanediol–dioxane mixtures using time domain reflectometry technique

The complex permittivity, static dielectric constant and relaxation time for 1,3-propanediol, 1,4-dioxane and their mixtures have been studied using time domain reflectometry (TDR). The excess permittivity, excess inverse relaxation time and Kirkwood correlation factor have also been determined at various concentrations of dioxane. Hydrogen bonded theory was applied to compute the correlation terms for the mixtures. The Bruggeman model for the nonlinear case has been fitted to the dielectric data for mixtures.     

Study of heterogeneous interaction in binary mixtures of 2-methoxyethanol-water using dielectric relaxation spectroscopy

The dielectric relaxation measurements on binary mixtures of 2-methoxyethanol with water have been carried out over entire concentrations and at temperature range of 0 °C to 25 °C using a picosecond time domain reflectometry technique. The complex dielectric permittivity spectra of 2-methoxyethanol/water mixtures were fitted using Havriliak-Negami equation. The static dielectric constant and relaxation time for all concentrations were obtained using least square fit method. The principal relaxation time is small if compared to that of corresponding alcohol/water mixtures this may be due to the hydrogen bonding ether oxygen in the 2-ME-water system. Excess dielectric properties, Kirkwood correlation factor, thermodynamic properties and Bruggeman factor are also determined and the results are interpreted in terms of heterogeneous interactions among the unlike molecules due to hydrogen bonding.     

Dependence of dielectric permittivity of moist disperse materials on the temperature

The behavior of the dielectric permittivity of a mixture of disperse materials with change in volume content of the component with high dielectric permittivity (water) and temperature is investigated. An analysis of the results is presented. A formula is given for the calculation of the dielectric permittivity of moist disperse materials as a function of the temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 65–68, January, 1982.     

Dielectric permittivity, density, viscosity and refractive index of binary mixtures of anisole with methanol and 1-propanol at different temperatures

Static dielectric permittivity, density, viscosity, and refractive index of anisole (AN), methanol (MeOH), 1-propanol (1-PrOH) and binary mixtures of AN with MeOH and 1-PrOH at nine different concentrations, were measured at 303, 313 and 323 K temperatures. Measured properties of pure AN, MeOH and 1-PrOH were compared with literature values and they were found in good agreement. The investigation of binary mixtures showed a systematic change in static dielectric permittivity, density and viscosity with change in concentration of anisole in the mixture. Measured properties of liquid samples were used to calculate Kirkwood correlation factor and excess parameters such as excess dielectric permittivity, excess molar volume and excess viscosity. Determined parameters have been interpreted in terms of molecular interaction among the molecular species of the binary mixtures.     

Dielectric relaxation studies of aqueous sucrose in ethanol mixtures using time domain reflectometry

Time domain reflectometry method has been used in the frequency range of 10 MHz to 10 GHz to determine dielectric properties of aqueous sucrose in ethanol. The dielectric parameters, i.e., static dielectric constant and relaxation time were obtained from the complex permittivity spectra using the non-linear least squares fit method. The Luzar theory is applied to compute the cross-correlation terms for the mixtures. It adequately reproduces the experimental values of static dielectric constants. The Bruggeman model for the non-linear case has been fitted to the dielectric data for mixtures.     

Frequency and temperature dependence of the dielectric parameters of wide temperature range TGBA and TGBC* phases of unsymmetrical liquid crystal dimers

In the present work we have carried out frequency and temperature dependent dielectric studies of an optically active dimeric compound, 4-n-undecyloxy-4′-(cholesteryloxycarbonyl-1-butyloxy)chalcone which shows wide temperature range twist grain boundary (TGB) phases namely TGBA and TGBC*. Dielectric permittivities and DC conductivities have been determined along and normal to the TGB helix axes. Two weak collective modes of dielectric relaxations have been detected for the planar oriented sample where permittivity is measured normal to the long axes of the molecules (but along the TGB helix axis). One mode, which exists in the MHz region, has behavior similar to those of the soft mode due to the amplitude fluctuation. The second one exists in the low frequency region (～100 Hz) and appears due to phase fluctuation as happens in the case of Goldstone mode. Sample confined between electrodes treated for the homeotropic alignment (permittivity measured normal to the helix axis) does not show any mode of relaxation in the frequency range of 1 Hz to 1 MHz. Measured permittivities suggest negative dielectric anisotropy for the system.     

基于小波变换的时域介电谱分析及其应用

应用小波变换改进时域介电谱的分析法扩宽其应用范围.实验结果表明,通过分析油水混合物的弛豫过程,基于小波变换的时域介电谱分析不但可得反映物性的整体频谱信息,还能得出反映各组成成分不同时域和频域信息.因此,该方法可应用于分析复杂多相混合物. 关键词： 时域介电谱 小波变换 油水混合物     

Dielectric relaxation study of pyridine-alcohol mixtures using time domain reflectometry

Time domain reflectometry is applied to dielectric relaxation measurements on pyridine-alcohol (methanol, ethanol, propan- 1-o1 and butan-1 -o1) mixtures over the entire concentration range and over the frequency range 10MHz-10GHz at 5, 15, 25 and 35°C. From the data, static permittivity and the dielectric relaxation time are extracted using a bilinear calibration method and a nonlinear least-squares fit method. These mixtures exhibit a principal dispersion of the Debye type at microwave frequencies. The Kirkwood correlation factor, which contains information regarding solute-solvent interaction and corresponding structural information, was obtained for these systems, and the excess inverse relaxation time and molar energy of activation for all these systems were determined. The values of the static permittivity, the relaxation time and the Kirkwood correlation factor decrease with increased pyridine concentration in alcohol. The static permittivity of the mixtures fits the modified Brugemann model well.     

Maxwell-Wagner characterization of dielectric relaxation in Ni0.8Zn0.2Fe2O4/Sr0.5Ba0.5Nb2O6 composite

Dense composites were prepared through incorporating the dispersed Ni_0.8Zn_0.2Fe₂O₄ ferromagnetic particles into Sr_0.5Ba_0.5Nb₂O₆ ferroelectric matrix. Extrinsic dielectric relaxation and associated high permittivities of the materials are reported in the composites. We used an ideal equivalent circuit to explain electrical responses in impedance formalism. A Debye-like relaxation in the permittivity formalism was also found. Interestingly, real permittivity (ε′) of the sample containing 30% Ni_0.8Zn_0.2Fe₂O₄ shows obvious independence of the temperature at 100 kHz. Dielectric relaxation and high-ε′ properties of the composites are explained in terms of the Maxwell-Wagner (MW) polarization model.     

Specific features of the approximation of the dielectric spectra of alkylcyanobiphenyl liquid crystals

The frequency dependences of the longitudinal and transverse permittivities of oriented nematic liquid crystals belonging to the alkylcyanobiphenyl group nCB (n=5–8) are measured in the relaxation region in the meter and decimeter wavelength ranges. It is established that the dispersion of the longitudinal permittivity is well approximated by the sum of two Debye processes with different relaxation times. The frequency dependence of the transverse permittivity is represented by the dispersion relation with a continuous distribution of relaxation times in a specified time range. It is demonstrated that, in the high-frequency range (f>200 MHz), in which the dielectric spectra exhibit a number of weakly pronounced dispersion features, the total dispersion of the permittivity is adequately described by the sum of relaxation and resonance processes.     

Dielectric properties of liquid crystals of the cyano derivative compounds with different fragments in the molecular core

This paper reports on the results of investigations into the influence of variations in the chemical composition of the aromatic core of cyano-containing molecules of liquid crystals on their dielectric properties in the frequency range 1–2000 MHz. It is shown that the dispersion of the longitudinal permittivity is adequately described by the sum of two Debye processes with different weighting factors and relaxation times. The frequency dependence of the transverse permittivity is well approximated by the Debye process with a continuous distribution of relaxation times in a specified range. It is established that the replacement of one benzene ring in the biphenyl core of the 5CB liquid-crystal molecule by a cyclohexane (or bicyclooctane) fragment leads to a considerable decrease in both relaxation times for the longitudinal permittivity, a change in the low-frequency limit of the relaxation time range for the transverse permittivity, and the evolution of the frequency dependence of the dielectric anisotropy.     

Dielectric relaxation and hydrogen bond interaction study of diol-water mixtures

Complex dielectric permittivity measurements in the frequency range 10MHz-20GHz have been carried out in diol-water mixtures over the entire concentration range using a time domain reflectometry (TDR) method at 25°C. A hydrogen bonded theory is applied to compute the dielectric constant for the mixtures. It adequately reproduces the experimental values of static dielectric constants for the diol-water mixtures. The dielectric parameters confirm that the intermolecular homogeneous and heterogeneous hydrogen bonding vary significantly with the increase in concentration of the constituents of the diol-water mixtures.     

Exploring interaction effects in two-component gas mixtures using orthogonal signal correction of ultrasound pulses

Within Sweden and the EU, an increased use of biogas gas and natural gas is encouraged to decrease emission of carbon dioxide. To support more effective manufacturing, distribution, and consumption of energy gases, new methods for the measurement of the calorimetric value or the gas composition are needed. This paper presents a method to extract and visualize variations in ultrasound pulse shape, caused by interaction effects between the constituents of a two-component gas mixture. The method is based on a combination of principal component analysis and orthogonal signal correction. Pulse-echo ultrasound experiments on mixtures of oxygen and ethane in the concentration range from 20% to 80% ethane show that the extracted information could be correlated with the molar fraction of ethane in the mixture.