Study on dielectric properties of oil/water random composites

Considering the electric double layers between oil and water, a new “complex model” of dielectric constant of oil/water composites was built up. Starting from the Maxwell–Garnett theory and Bruggeman theory, the effective dielectric constant of oil/water random composites is presented. The nonlinearity of the theory is obvious. The model is especially suited to study the dielectric properties of oil/water composites of different nature. The model is also suited to study the dielectric properties of two-phase random composites with an interfacial shell. The theoretical results on dielectric properties of different kinds of oil/water composites are in good agreement with experimental data.     

Dielectric properties of electrolytic solutions

The variation in dielectric properties of water with the addition of ionic salts have been measured using automated frequency domain experimental microwave C-band. The dielectric properties, that is dielectric constant (ε′) and dielectric loss (ε″) of two electrolyte solutions for various concentrations have been measured at 5-GHz frequency at room temperature. It has been observed that for concentration between 0.2 to 1.0 mole the dielectric constant of water is smaller and some larger than that of pure water and dielectric loss increases with increasing concentration of these salts. It has been also observed that the variation in dielectric loss is different, though the ionic concentration of the two salts are equal.     

加压水介质耐μs级高电压击穿实验研究

 采用水介质同轴电极实验装置,开展了μs级充电加压水介质击穿实验研究,并对实验结果进行了分析和讨论,结果表明：在水介质正电极击穿类型的实验中,常压下水介质击穿场强与Martin公式吻合。加压水介质击穿场强随静压的增加而增加,其场强增幅与Mirza定性理论场强增幅的相对差别在5%以内。根据实验结果推导出了更为准确的水介质击穿场强随静压变化的关系式。对水介质加压,将压缩电极表面气泡,减少气泡数目,从而可以提高水介质耐高电压击穿能力。     

The effective dielectric constant of a dispersion of clustering spheres

If one measures the dielectric constant of a water in oil microemulsion the large increase of this dielectric constant both as function of the temperature as well as a function of the volume fraction of water suggests that the water droplets will bind together in clusters. In order to analyse this suggestion in more detail we derive a systematic expansion of the Clausius-Mossotti function in terms of integrals over products of excess cluster polarizabilities and correlation functions. It is found that the excess polarizability of a cluster of spherical droplets is zero except when the spheres almost touch each other. Crucial for this property is the fact that the water spheres are conducting or if they are not conducting have a dielectric constant much larger than the dielectric constant of oil. The large increase of the dielectric constant is a consequence of the increase of the number of bound clusters. An explicit formula is given for the resulting temperature and volume fraction dependence of the dielectric constant.Dedicated to Professor Harry Thomas on the occasion of his 60th birthday     

Relations between the association of liquid water molecules and the dielectric and raman spectra of H<Subscript>2</Subscript>O

A two-fraction model that makes it possible to analytically calculate the complex dielectric permittivity of liquid water in wide frequency and temperature ranges is described. The far IR spectrum of water is found as a dielectric response of vibrating H₂O monomers and dimers, while the spectrum of low-frequency (Debye) relaxation is found as a response of collective reorientations of associated water molecules. It is shown that the dielectric spectra of water calculated at ?5.6, 27, and 81.4°C agree well with its experimental spectra. The low-frequency Raman spectrum of water is calculated for the same set of model parameters as the spectrum of the complex dielectric permittivity. These spectra are found to correlate with each other, and the physical nature of the difference between them is clarified. An interpretation of the well-known anomaly of water at a temperature of T = 300 K is presented. It is shown that the number of water molecules that compose an associate at this temperature is minimal.     

Dielectric relaxation spectrum of water studied by the site—site generalized Langevin/modified mode-coupling theory

The dielectric relaxation spectrum of water is calculated from the site-site generalized Langevin/modified mode-coupling theory. The main part of the relaxation follows the Debye-type function, and a small deviation from the Debye relaxation is found on the high-frequency side. This tendency is consistent with recent experiments, although the absolute relaxation time does not agree with the experimental value quantitatively. The time development of the longitudinal polarization function resembles the dielectric part of the memory function, and we consider that this is because the dielectric friction dominates the collective reorientation of the dipole moment of water. We performed calculations with different dielectric constants using the reference interaction-site model integral equation, and found that the large gap between the time scales of the dielectric relaxation and the longitudinal polarization relaxation causes the Debye-type dielectric relaxation in our theory when the dielectric friction is dominant in the friction on the collective reorientation of the dipole moment. Namely, the longitudinal polarization relaxation is fast enough to be considered as a white noise to the dielectric relaxation process, so that the relaxation becomes a Markov process. The large gap between the two relaxation times originates from a large local field correction owing to the large dielectric constant of water. It is also suggested that the deviation from the Debye relaxation at the high-frequency side is the manifestation of the slow memory caused by the long-time part of the longitudinal polarization relaxation in the low-wavenumber region.     

Dielectric constant of solvents at nano to bulk regimes: linear response theory and statistical mechanics-based approaches

Statistical mechanics and generalised linear response theory based approaches are employed to derive the analytical expressions for size-dependent dielectric constant and normalised orientation polarisation of solvents. As an illustrative example, water is considered and the dielectric constants for the same are calculated over the entire range of water clusters. Our results reveal that the dielectric constant and normalised orientation polarisation are monotonically increasing with the increase in the number of solvent molecules and converge to the respective bulk values in the thermodynamic limit. More importantly, the dielectric constant of water is found to be independent of the nature, geometry and microscopic charges of the non-spherical ions. This finding offers a new platform for calculating the hydration energy and orientation polarisation based on linear response theory for different kinds of ions in the solvent medium.     

The Evaluation of Dielectric Resonators Containing H2O or D2O as RF Coils for High-Field MR Imaging and Spectroscopy

Electromagnetic resonators consisting of low-loss dielectric material and/or metallic boundaries are widely used in microwave technologies. These dielectric resonators usually have high Q factors and well-defined field distributions. Magnetic resonance imaging was shown as a way of visualizing the magnetic field distribution of the resonant modes of these resonators, if the dielectric body contains NMR sensitive nuclei. Dielectric resonators have also been proposed as RF coils for magnetic resonance experiments. The feasibility of this idea in high-field MR is discussed here. Specifically, the dielectric resonances of cylindrical water columns were characterized at 170.7 MHz (4 T¹H Larmor frequency), and evaluated as NMR transmit and receive coils. The dielectric resonance of a cylindrical volume of D₂O was used to image a hand at 170.7 MHz. This study demonstrated that MRI is an effective way of visualizing the magnetic field in dielectric structures such as a water cylinder, and can potentially be generalized to solid-state dielectric devices. The possible applications of dielectric resonators other than simple cylindrical volumes in MRI and MR solution spectroscopy at high field strengths are also discussed.     

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.     

Anomalous dielectric behavior of water in ionic newton black films

The electrostatics of two charged surfactant layers in aqueous media (surfactant/water/surfactant films) is investigated using molecular dynamics simulations. In the films studied (with a surfactant-surfactant distance from approximately 35 A to contact) we observe an anomalous dielectric response of water. The electrostatic potential phi(z) inside the aqueous core of the films (containing bulk water with rho=1 g/cm(3)) is completely different from that expected for a film containing a dielectric medium with the dielectric constant of water. In addition, our results are not consistent with a local relation between the water polarization P(z)(z) and the electric field E(z)(z). The polarization P(z)(z) is maximum at the interfaces (due to solvent molecules forming part of the structure of the surfactant layers) and decays from the interfaces inside the aqueous core with a decay length of order of approximately 10 A.     

Dielectric half-disk resonator with whispering-gallery modes for measurements of the electric properties of water

We study experimentally the possibility of measuring the dielectric properties of water in the millimeter wavelength range using dielectric resonators excited at the whispering-gallery modes. The influence of various conditions for excitation of such resonators by a local source on the sensitivity and resolution of the performed measurements is shown. Electrodynamic characteristics of the dielectric resonator as a cell for measurements of the electric properties of water are studied. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 9, pp. 769–776, September 2008.     

Experimental evidence of the ferroelectric nature of the λ-point transition in liquid water

We studied the dielectric properties of nano-sized liquid water samples confined in polymerized silicates MCM-41 characterized by pore sizes 3–10 nm. Freezing temperature suppression in nanopores helps keep the water samples in liquid form at temperatures well below 0°C and thus effectively study the properties of supercooled liquid water. We report the first direct measurements of the dielectric constant by the dielectric spectroscopy method and demonstrate very clear signatures of the second-order phase transition of ferroelectric nature at temperatures next to the λ-point in the supercooled bulk water in full agreement with the recently developed model of the polar liquid.     

结合有效介质理论的乳状液太赫兹光谱分析

原油乳状液对原油的长距离输运具有重要影响,乳状液的油、水状态及相互作用机制还需新理论和新方法获得新认识,基于有效介质理论,本文研究了原油乳状液太赫兹光谱响应特征.通过太赫兹时域光谱系统测试得到了含水率为0～28％的原油乳状液的太赫兹时域光谱,结合傅里叶变换计算了吸收系数和介电常数等光学参数,同一频率下吸收系数等光学参数...     

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.     

Residual stresses and white layer in electric discharge machining (EDM)

The effect of dielectric liquid and electrode type on white layer structure in electric discharge machined surfaces has been studied in terms of retained austenite and residual stresses using X-ray diffraction method. The machining tests were conducted by using two different tool electrodes (copper and graphite) and dielectric liquid (kerosene and de-ionized water) under same operational conditions. The present work suggests that the surface is saturated with carbon irrespective of the tool electrode material when machining with kerosene dielectric liquid. But, retained austenite is formed on the surface due to carbon uptake from graphite tool electrode when machining with de-ionized water dielectric liquid. On the other hand, even though surface residual stresses increase with structural non-homogeneities in the white layer, no clear consequences have been observed in residual stress distribution beneath the white layer.     

Water flows induced by microwave electric fields in microsystems

AC electric fields are of increasing importance for the generation of fluid flows in microsystems. We analyse numerically the use of AC electric fields at microwave frequencies for electro-thermal actuation of water in microdevices. Water is heated because of its significant dielectric loss at microwave frequencies. Buoyancy and dielectric forces actuate in the liquid bulk, and the relative importance between them is studied. The microwave liquid actuation can be used for pure water as well as for water saline solutions, such as bio-fluids. Therefore, it is of interest for the Lab-on-a-Chip technology.     

The effect of air plasma on barrier dielectric surface in dielectric barrier discharge

Barrier dielectric is an important part of atmospheric pressure dielectric barrier discharge (AP-DBD), which partly affects discharge characteristics. Conversely, discharge plasma also has influence on dielectric surface properties. To investigate this influence, some experiments were carried out on a home-built AP-DBD system with glass plate as barrier dielectric. Surface wettability was evaluated by water contact angles on a drop shape analysis system. The morphologies and chemical compositions of the glass sample surfaces were observed by field-emission scanning electron microscope (FESEM) and energy dispersive X-ray spectroscopy (EDS) attached to FESEM. The results show that water contact angles decrease as discharge energy increases, micro-discharge etching zones are formed into glass surface and different from the control glass in surface micro-structure and chemical compositions.     

电极表面光滑程度对水介质高电压击穿的影响

 采用水介质同轴实验装置,改变电极表面的光滑程度,在μs级充电时进行水介质击穿实验,并对实验结果进行了分析和解释。结果表明：抛光电极表面可有效提高水介质耐高电压击穿能力;表面粗糙度为0.4～0.8 μm的抛光电极表面的击穿场强比表面粗糙度为1.6～3.2 μm的粗糙抛光电极表面,更符合Martin公式。电极表面光滑程度的改善,使阴极场致发射电流减弱进而击穿延迟时间变长,气泡也更难以附着在光滑的电极表面,从而可以提高水介质耐高电压击穿能力。     

Investigation of dielectric spectra from moist soils during freezing-thawing processes

A frequency spectrum of the complex dielectric permittivity of soils is measured in the range of frequencies from 0.5 to 15.0 GHz in the course of frost penetration and thawing. The phase transitions taking place during frost penetration and thawing are analyzed within the concept of the generalized refractive mixing dielectric model (GRMDM). Two types of water concurrently present in the soil are identified: bound and free water. Temperature dependences of the Debye model parameters for each type of water are given, and parameters of a dielectric spectroscopic model of frozen and thawed soils are found. The hysteresis phenomenon during the phase transition of the soil moisture is investigated. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 24–28, September, 2008.     

水介质同轴线型方波脉冲延时线

 介绍了水介质同轴型方波脉冲延时线的基本原理和基本特性参数,并对延时线传输脉冲的脉冲损耗和脉冲畸变的主要影响因素进行了理论分析。在理论分析的基础上,设计、建立了一套延迟500 ns、阻抗为12 Ω的水介质同轴线型方波脉冲延时线,并进行了初步的实验研究。实验结果表明:该延时线输入方波脉冲前沿为18 ns,输出方波脉冲前沿增加到26 ns;方波脉冲幅度损耗率为9.6%;延迟时间为476 ns。