Dielectric spectroscopy of some heteronuclear amino alcohol complexes

The temperature dependent dielectric spectroscopic properties of two heteronuclear complexes of monoethanolamine (MEA) at a wide temperature range (303-413 K) were investigated by impedance spectroscopy, in the frequency range from 100 Hz to 100 kHz. The frequency dependence of the impedance spectra plotted in the complex plane shows semi-circles. The Cole-Cole diagrams have been used to determine the molecular relaxation time, tau. The temperature dependence of tau is expressed by thermally activated process. Relaxation frequencies corresponding to the rotation of the molecules about their long axes are expected to lie above 10 MHz and exhibit Arrhenius behavior, where a single slope is observed with activation energy values equal to 0.67 and 0.78 eV. The ac conductivity sigma(ac) (omega) is found to vary as omega(s) with the index s相似文献   

Relative permittivities of binary mixtures of 1-butanol + n-alkane AT 298.15 k

A previous study on the physical properties of 1-alkanol + n-alkane has establised a correlation between dielectric permittivity at 1 GHz and excess molar volumes for all binary systems that were studied. In order to determine whether this behaviour is similar at lower frequencies, relative permittivity was measured at 100 kHz. The refractive index was measured to explore the effects at higher frequencies. Mixtures under study are in particular the systems (1-butanol + n-hexane, or n-octane, or n-decane) at the temperature of 298.15 K and atmospheric pressure, over the entire composition range. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dielectric properties of a protein-water system in selected animal tissues

Dielectric spectroscopy has been applied to study aspects of the organization of water in selected animal tissues (tendon, bone and horn). The measurements of the relative permittivity epsilon' and the dielectric loss epsilon' were carried over the frequency range of 10-100 kHz and at temperatures from 22 to 240 degrees C. The water content was 10% for bone and horn, and 22% for tendon by mass at room temperature at a relative humidity of 70%. The temperature dependencies of epsilon' and epsilon' reveal distinctively the temperature ranges corresponding to the release of water in temperatures up to about 200 degrees C for all tissues and the melting of the crystalline structure only for tendon and horn, above this temperature. The frequency dependencies of epsilon' and epsilon' show a remarkable dispersion in the low-frequency at selected temperatures up to 200 degrees C for all tissues due to the release of the loosely and strongly bound water. The results were discussed in terms of the interfacial (Maxwell-Wagner) polarization and polarization mechanism involving hopping charge carriers interacting with the bound water molecules. The information on the effect of temperature, water content and frequency of the electromagnetic field on the dielectric behaviour of the tissues studied is of importance in the design and construction of medical diagnostic or therapeutic instruments based on the use of electric signals.     

Novel frequency dependence of dielectric biaxiality of surface stabilized ferroelectric liquid crystals

The frequency dependence of the dielectric biaxiality of surface stabilized ferroelectric liquid crystals (SSFLCs) was studied. The principal values of the dielectric tensor ε₁, ε₂ and ε₃ were measured by the MOM (molecular orientational model) method. Three dielectric permittivities were measured for each of two samples. These were the permittivity of the homeotropic cell and the permittivity of the planar homogeneous cell with and without the DC bias. Then the dielectric tensor components were calculated based on the molecular orientational models. We present the theory and experimental procedure of the MOM method. Measurements have been performed on Merck FLC compound SCE-8. The following novel dielectric behaviour was observed, as the DC bias voltage was increased the dielectric permittivity of the planar homogeneous cell decreased at the low frequencies (∼ 1 kHz) while increased at the high frequencies (10kHz ∼). The sign of the dielectric biaxiality ∂εε (= ε₂ - ε₁) inverted around 1 kHz, being negative at low frequencies and positive at high frequencies. The roles of the biaxiality on the dielectric behaviour of SSFLC cells are discussed.     

Preliminary communication Low frequency dielectric relaxation in the smectic C* phase of a ferroelectric liquid crystal

Dielectric measurements were made on the ferroelectric liquid crystal Felix 018/100 manufactured by Hoechst, Germany, over the temperature range 30 to 65degreeC (smectic C* phase), frequency range 0.1Hz to 100kHz, with bias voltages of 0, 1, 3 and 10 V, and in a dielectric cell with a spacing of 4 times the helical pitch. Plots of the dielectric loss versus log (frequency) show the usual monotonic increase in the loss with decreasing frequency, as well as the usual loss peak at approximately 1kHz. Plots of the log (dielectric loss) against log (frequency) at low frequencies, have slopes varying from -0.75 to -0.89 when the temperature increases from 30 to 65degreeC. Following the suggestion of Scaife, transforming the complex permittivity data to the complex polarizability of a sphere of unit radius in a vacuum, and plotting the loss polarizability against log (frequency), shows two distinct and separate loss peaks. The sums of the two loss peaks appear to be independent of temperature and bias voltage, even though both depend on these variables.     

Colossal dielectric constant in PrFeO3 semiconductor ceramics

The perovskite PrFeO₃ ceramics were synthesized via sol–gel method. The dielectric properties and impedance spectroscopy (IS) of these ceramics were studied in the frequency range from 100 Hz to 1000 kHz in the temperature range from 80 K to 300 K. These materials exhibited colossal dielectric constant value of ∼10⁴ at room temperature. The response is similar to that observed for relaxorferroelectrics. IS data analysis indicates the ceramics to be electrically heterogeneous semiconductor consisting of semiconducting grains with dielectric constant 30 and more resistive grain boundaries with effective dielectric constant ∼10⁴. We conclude, therefore that grain boundary effect is the primary source for the high effective permittivity in PrFeO₃ ceramics.     

Dielectric analysis of sheep erythrocyte ghost. Examination of applicability of dielectric mixture equations

The purpose of this study is to confirm the applicability of dielectric mixture equations in dielectric analysis of biological cell suspensions. Two dielectric mixture equations, the Pauly-Schwan (P-S) equation and the Hanai-Asami-Koizumi (H-A-K) equation were tested using sheep erythrocyte ghosts whose internal solution is identical with the external solution. Dielectric measurements were carried out for the ghost suspensions over a frequency range 10 kHz to 100 MHz; a single dielectric relaxation was found between 100 kHz and 10 MHz. From the dielectric relaxation, the conductivity and permittivity of the ghost interior and the capacitance of the cell membrane were calculated following the P-S and H-A-K equations. When the H-A-K equation was employed (and as expected from the property of the ghosts), the estimated internal conductivity was in good agreement with the external conductivity at volume fractions up to about 0.7. With the P-S equation, on the other hand, the same results as above were obtained but only at low volume fractions below about 0.3. In addition, the H-A-K equation provided a better simulation for the observed relaxation curves than did the P-S equation, especially at high volume fractions. It is, therefore, concluded that the H-A-K equation is applicable to a wider range of volume fraction than is the P-S equation.     

Dielectric properties of microvillous cells simulated by the three-dimensional finite-element method

Most of biological cells have microvilli on their surfaces, which significantly influence their dielectric properties. The complex permittivity of a cubical system containing a spherical cell model with cylindrical projections was calculated over a frequency range of 10 kHz to 100 MHz using the three-dimensional finite-element method. The spectra of the complex permittivity consisted of low- and high-frequency relaxation processes which were respectively attributed to the polarization of the membranes covering the projections and the spherical body. Conventional analysis based on the spherical shell model was applied to the simulated spectra to discuss the effects of cell surface morphology on the electric parameters estimated for the plasma membrane and the cytoplasm.     

Dielectric behavior of some ferrofluids in low-frequency fields

The dielectric behavior of a ferrofluid with magnetite particles dispersed in kerosene was analyzed taking into account the Schwarz model, concerning the low-frequency dielectric behavior in systems consisting of colloidal particles suspended in electrolytes. For this reason, the complex dielectric permittivity and dielectric loss factor, in the frequency range of 10 Hz-500 kHz, at different temperatures between 20 degrees C and 100 degrees C were measured. Based on these experimental results, the experimental dependencies on both temperature of the relaxation time and activation energy of the relaxation process were analyzed. The obtained results show that the Schwarz model can be applied, in order to explain the low-frequency dielectric behavior of a ferrofluid with magnetite particles in kerosene, if the change of counterion concentration at the surface of colloidal particles is taken into account. Consequently, it is shown that the dielectric spectroscopy can be used in order to analyze the presence of particle agglomerations within ferrofluids.     

Electrochemical characterization of sodium and potassium doped lanthanum–titanium mixed oxides prepared by sol–gel method

Varying amounts of Na and K doped lanthanum–titanium oxides were synthesized by gel entrapment technique. These ceramics were characterized by X-ray diffraction. Microstructural investigations revealed grain growth in the doped material compared to undoped sample. Dielectric relaxations of these compounds were investigated in the temperature range 250–900 °C. A high degree of dispersion of the permittivity of un-doped lanthanum–titanium oxide and K and Na doped lanthanum–titanium oxide was observed in the frequency range <100 kHz which was attributed to oxygen vacancies. An increase in the permittivity values were observed with 1 % Na and K doped samples. The permittivity values further deteriorated with the dopant concentration. Using the Cole–Cole model, an analysis of the dielectric loss with frequency was performed, assuming a distribution of relaxation time. The dielectric loss was found to decrease by doping K in lanthanum–titanium oxide matrix. The dc conductivity studies showed that a temperature dependent hopping type mechanism is responsible for electrical conduction in the system.     

Dielectric imaging of biological cells

A dielectric technique that can image local permittivity and conductivity has been applied to living biological cells in an aqueous environment. The local permittivity and conductivity were measured between 10 kHz and 10 MHz with a fine probe electrode, which was laterally scanned over cells on a plate electrode. The dielectric images of the cells depended on frequency, indicating dielectric relaxation that is due to interfacial polarization. The low-frequency image (at 10 KHz) in which the cells have high permittivity and low conductivity compared with the medium results from the presence of the plasma membrane with high resistivity. The dielectric image of the cell interior is obtainable at high frequencies (10 MHz), where the plasma membrane is short-circuited.     

Dielectric spectroscopy of monatomic alcohols

The frequency dependences of permittivity ?(f) and dielectric loss tanδ(f) of monatomic alcohols are measured in range of frequencies f from 0.025 to 1000 kHz. Dielectric relaxation is observed in the investigated frequency range. Empirical correlation equations describing the relationships between the dielectric characteristics and physicochemical properties of monatomic alcohols are obtained.     

Electrical Properties of Polymethylmethacrylate Polymer Dispersed Liquid Crystals*

The effect on the electrical properties of polymethylmethacrylate polymer containing liquid crystal as dispersed molecules is investigated in the temperature range 30-100°C and the frequency ange from 100 Hz to 10 kHz. It is found that increasing the liquid crystal content enhances the ac-impedance, decreases the ac-loss conductivity and decreases the value of the dielectric constant. The decrease in the ac-impedance with increasing frequency is associated with a dramatic increase in the ac-loss conductivity at frequencies higher than 1 kHz. The decrease in the ac-conductivity with increasing the dispersed liquid crystal phase is attributed to the reduction of the mobility of the charge carriers. Thus, the dielectric property of the system improves.     

High dielectric hyperbranched polyaniline materials

New organic materials for the purpose of high speed capacitor applications are discussed. The effect of the microcrystalline size dependence of different polyaniline polymeric systems on the dielectric constant is investigated. Two different methods are described for the preparation of the polyaniline dielectric materials. By sonication polymerization, the prepared polyaniline with a suggested hyperbranched structure showed much larger microcrystalline domains in comparison to the conventional linear polyaniline. Investigations of the dielectric constant and capacitance at a relatively high frequency (>100 kHz) suggested that the system with the larger microcrystalline domains (hyperbranched) gives rise to a larger dielectric constant. The mechanism of the increased dielectric response at higher frequencies is investigated by EPR spectroscopy, and these results suggest that delocalized polarons may provide a way to enhance the dielectric response at high frequency.     

Tunable dielectric thin films by aqueous, inorganic solution-based processing

Sub-micron, nanolaminated, dielectric thin films comprised of amorphous aluminum oxide phosphate (AlPO) and hafnium oxide sulfate (HafSOx) layers were fabricated in open-air conditions from aqueous inorganic precursors by spin coating with minimal thermal processing. These nanolaminated thin film insulators display an averaging effect of effective dielectric permittivity in devices with controlled AlPO:HafSOx thickness ratios, enabling tunable dielectric properties. X-ray reflectivity measurements were used to characterize film thickness, smoothness, and uniformity. Scanning electron microscopy was used to analyze final nanolaminated devices. Electrical characterization of metal-insulator-insulator-metal capacitors revealed tunable relative dielectric constants ranging from approximately 5–10 with loss tangents less than 2% at 10 kHz in devices with approximately 300 nm total dielectric thickness. The results suggest a simple, inexpensive processing approach for fabricating devices that require insulating layers with specific dielectric properties.     

Dielectric spectroscopy of aminoalcohols and polyethylenepolyamines

Dependences of dielectric permittivity ?(f) and dielectric loss tangents tansδ(f) of aminoalcohols (AAs), polyethylenepolyamines (PEPAs), water, and aqueous solutions of AAs and PEPAs with water concentrations of 1 wt % are investigated in the frequency range of 0.025–1000 kHz. The dielectric relaxation of the liquids under study is investigated. An interrelation between the dielectric parameters and physicochemical properties of AAs and PEPAs is established. Empirical equations that describe this interrelation with a high degree of accuracy of approximation validity are derived. The effect of water on the dielectric characteristics of AAs and PEPAs is shown. It is suggested that we evaluate the energy of affinity of AAs and PEPAs for water using the coefficient of dielectric losses ?″.     

Dielectric spectroscopy as a condition monitoring technique for cable insulation based on crosslinked polyethylene

Dielectric spectroscopy was evaluated as a condition monitoring technique for aged polyethylene electrical insulation in nuclear power plants. Bare core insulations of crosslinked polyethylene were aged at 55 and 85 °C under exposure to ⁶⁰Co γ-radiation at different dose rates (0.42, 0.76 and 1.06 kGy h⁻¹) to different total doses. The samples were studied by dielectric spectroscopy and tensile testing, and the crystallinity, mass fraction of soluble component and density were determined. The oxidation profiles along the depth of the insulations were assessed by infrared microscopy. The aged samples showed an increase in both the real and imaginary parts of the dielectric permittivity over the whole frequency range studied, an increase in the mass fraction of soluble component and in the material density, and a decrease in the strain-at-break. The imaginary part of the dielectric permittivity at 100 kHz increased in a linear fashion with increasing material density, the latter being strictly related to the extent of oxidation of the material according to infrared spectroscopy and differential scanning calorimetry. The generic relationship between the imaginary part of the permittivity and the density included all the data obtained under different ageing conditions. The results suggest that dielectric spectroscopy can be used for in-situ measurements of the degree of oxidation of polyethylene cables, in order to obtain information about the condition of the cable insulation to enable the remaining lifetime to be predicted.     

Mesure en laboratoire de la permittivité diélectrique moyenne fréquence de végétaux à 430 kHz à l'aide d'un capacimètre. Relation entre permittivité apparente d'un ensemble d'épis de blé et leur contenu en eau

The laboratory measurements presented here are additional measurements to those performed on a wheat crop by an electrostatic quadrupole at 430 kHz. They give a first calibration for the correlation between water content and apparent dielectric permittivity of ears. These measurements are performed by means of a capacimeter or a plane condenser of which the apparent permittivity is determined. Wheat ears are placed within the condenser and their permittivity is correlated to their water content. A theoretical approach (method of moments) presents the response of the condenser, containing ears similated to a 3D parallelepipedic body in an electromagnetic field.     

DIELECTRIC PROPERTIES OF 1, 2-POLYBUTADIENES

The dielectric permittivity and loss tangent of 1,2-polybutadienes with different chain structures were determined as a function of temperature from-180℃ to 100℃ at different frequencies, and the frequency and structure dependence of the dielectric propertie of 1,2-polybutadienes have been investigated. It is found that a maximum of the permittivity occurs in the glass-transition region. The width of the glasstransition peak increases with increasing frequency while its height has little change. With a rise in the content of 1,2-units, the permittivity decreases and the height of the glass-transition peak slightly grows. A maximum of the width of the glass-transition peak appears when the content of 1,2-units is about 45%. Both the permittivity and dielectric loss drop down as the growth of the content of syndiotactic 1,2-units.     

Dilectric and thermal properties of PEO doped with cadimium chloride salt

The main aim of this research is to investigate the effect of salt concentration on the dielectric properties(AC (σ_AC),permittivity（ε′）,dielectric loss（ε″）,and dielectric relaxation process) and melting behavior of polyethylene oxide （PEO）/CdCl₂ complexes.The dielectric study was carried out over a frequency range 10-335 kHz and a temperature range 25-45℃.The AC conductivity,permittivity and dielectric loss of the PEO/CdCl₂ complexes increase with increasing salt concentration and temperature.Also,it was found that the addition of CdCl₂ salt to PEO host reduced the melting temperature of PEO host.Dielectric results reveal that the relaxation process of these complexes is due to viscoelastic relaxation or non-Debye relaxation at room temperature.Additionally,it was found that relaxation behavior remained viscoelastic at different temperatures and salt concentrations.