Dielectric Permittivity Spectra Research Articles

Terahertz-infrared spectroscopy of Shewanella oneidensis MR-1 extracellular matrix.

Employing optical spectroscopy we have performed a comparative study of the dielectric response of extracellular matrix and filaments of electrogenic bacteria Shewanella oneidensis MR-1, cytochrome c, and bovine serum albumin. Combining infrared transmission measurements on thin layers with data of the terahertz spectra, we obtain the dielectric permittivity and AC conductivity spectra of the materials in a broad frequency band from a few cm-1 up to 7000cm-1 in the temperature range from 5 to 300K. Strong absorption bands are observed in the three materials that cover the range from 10 to 300cm-1 and mainly determine the terahertz absorption. When cooled down to liquid helium temperatures, the bands in Shewanella oneidensis MR-1 and cytochrome c reveal a distinct fine structure. In all three materials, we identify the presence of liquid bound water in the form of librational and translational absorption bands at ≈200 and ≈600cm-1, respectively. The sharp excitations seen above 1000cm-1 are assigned to intramolecular vibrations.

Analysis of Dielectric Spectra of Water with Conductive Impurities in a Wide Frequency Range

Experimental and theoretical studies of the electrophysical characteristics of water with different concentrations of conductive impurity, including the complex dielectric permittivity, complex conductivity, and complex impedance spectra are performed at frequencies in the range from 20 Hz to 40 GHz. It is demonstrated that the complex dielectric permittivity spectrum at frequencies in the range 500 MHz – 40 GHz is well described by the Debye model with a single relaxation time. In the low-frequency range, one more region of dispersion is observed caused by the phenomena occurring on the liquid-electrode interface. The characteristics of this dispersion region depend significantly on the dc electrical conductivity. It is demonstrated that in the examined frequency range, the influence of the interface phenomena on the complex impedance spectra of water with conductive impurity are well described by adding the impedance of an constant phase element. For the examined samples, the electrophysical characteristics and the parameters of the constant phase element are determined. The static dielectric permittivity and the parameters characterizing the double electric layer increase with the electrical conductivity.

A model delineating the dielectric spectra of a relaxor PLZT obtained by impedance analyzer

AbstractThe origin of the dielectric responses of relaxor ferroelectrics, featured by a signal dispersion according to the measurement frequency, were investigated systematically using a canonical relaxor Pb0.92La0.08(Zr0.65Ti0.35)0.98O3 (PLZT 8/65/35) ceramic. By scanning complex dielectric permittivity over a frequency range from 10 mHz to 10 MHz as a function of temperature from 0°C to 100°C, we revealed that the complex dielectric permittivity spectra obtained from an impedance analyzer are a consequence of a convolution of at least three distinct relaxation processes, featured by the unique relaxation time and distribution. The complex dielectric permittivity spectra at each measurement temperature were deconvoluted by the application of a series of Havriliak‐Negami relaxation models, resulting in three distinguished processes; namely, slow, intermediate, and fast process. We identified that the fast process is responsible for the overall magnitude of capacitance with little influence on the dielectric loss, the intermediate mainly for the thermal evolution of the capacitance, and the slow mainly for the thermal evolution of the loss. With this model, we successfully rationalized the characteristics of the relaxor behavior such as the frequency dispersion of the dielectric maxima, the disparity in peak positions of real and imaginary parts, and the unique feature during aging, so‐called a “dip.”

Terahertz spectroscopy of charge transport in films of pristine and doped single-wall carbon nanotubes

Electrical transport mechanisms of 2D carbon nanotube networks are presently under intensive studies. The related experimental data are ambiguous and controversial. We report on terahertz-infrared spectra of optical conductivity and dielectric permittivity of thin transparent films composed of pristine and CuCl- or iodine-doped single-walled carbon nanotubes (SWCNTs) measured in the frequency range from 7 to 25 000 cm−1 and at temperatures from 5 to 300 K. Controversially to the existing results, we have not observed a clear signature of the so-called terahertz conductivity peak. Instead, a typical metallic-like frequency- and temperature-dependent behavior of the conductivity and permittivity has been discovered. It was attributed to the high quality interconnected SWCNT network providing the almost free pathways for charge carriers. Applying Drude conductivity model, we have determined the temperature and doping dependences of effective parameters of the carriers in the films: plasma frequency, scattering rate, mobility, mean-free path. The obtained results demonstrate a great potential of the material in the field of electromagnetic applications at frequencies up to few terahertz.

Dielectric study on mixtures of ionic liquids

Ionic liquids are promising candidates for electrolytes in energy-storage systems. We demonstrate that mixing two ionic liquids allows to precisely tune their physical properties, like the dc conductivity. Moreover, these mixtures enable the gradual modification of the fragility parameter, which is believed to be a measure of the complexity of the energy landscape in supercooled liquids. The physical origin of this index is still under debate; therefore, mixing ionic liquids can provide further insights. From the chemical point of view, tuning ionic liquids via mixing is an easy and thus an economic way. For this study, we performed detailed investigations by broadband dielectric spectroscopy and differential scanning calorimetry on two mixing series of ionic liquids. One series combines an imidazole based with a pyridine based ionic liquid and the other two different anions in an imidazole based ionic liquid. The analysis of the glass-transition temperatures and the thorough evaluations of the measured dielectric permittivity and conductivity spectra reveal that the dynamics in mixtures of ionic liquids are well defined by the fractions of their parent compounds.

Structural and dielectric properties of (PEO–PMMA)–SnO2 nanocomposites

Abstract Polymer nanocomposite (PNC) films based on poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend as host polymer matrix dispersed with tin dioxide (SnO 2 ) nanoparticles have been prepared by the solution-cast method. X-ray diffraction measurements confirm that these films are semicrystalline and the degree of crystalline phase reduces with increase of SnO 2 contents in the polymer blend. The scanning electron microscopy reveals that the surface morphology of the PNC films is smooth with homogeneous distribution of the SnO 2 particles. Complex dielectric permittivity, electrical conductivity, electric modulus and impedance spectra of the PNC films have been investigated in the frequency range from 20 Hz to 1 MHz. The real part of the dielectric permittivity of these films has non-linear increase with the increase of SnO 2 nanoparticles contents in the PEO–PMMA blend over the audio frequency range, whereas it is found tunable with nanofiller concentration in the range from 2 to 3 at the radio frequencies. Dielectric loss tangent and the loss part of electric modulus spectra exhibit relaxation peaks which are ascribed to cooperative chain segmental dynamics of the PEO and PMMA macromolecules. It is observed that the polymers chain segmental dynamics becomes much faster when only 1 wt% SnO 2 nanoparticles are dispersed in the polymer blend matrix, which further enhances moderately with the increase of SnO 2 concentration up to 5 wt%. The dielectric relaxation time and electrical conductivity values of the PNC film are found Arrhenius in temperature of activation energies 0.15 eV and 0.43 eV, respectively.

Salinity index determination of porous materials using open-ended probes

The relations among soil water content, bulk electrical conductivity and electrical conductivity of soil solution can be described by a number of theoretical and empirical models. The aim of the paper is to examine the performance of open-ended coaxial probes with and without a short antenna in determination of complex dielectric permittivity spectra, moisture and salinity of porous materials using the salinity index approach. Glass beads of 0.26 and 1.24 mm average diameters moistened to various water contents with distilled water and KCl solutions were used to model the soil material. Due to the larger sensitivity zone, only the probe with the antenna enabled determination of bulk electrical conductivity and salinity index of the samples. The relations between bulk electrical conductivity and dielectric permittivity of the samples were highly linear, which was consistent with the salinity index model. The slope of the relation between salinity index and electrical conductivity of moistening solutions closely matched the value for sand presented in literature.

Glass Transition Dynamics and Crystallization Kinetics in the Smectic Liquid Crystal 4-n-Butyloxybenzylidene-4'-n'-octylaniline (BBOA).

The molecular dynamics of 4-n-butyloxybenzylidene-4'-n'-octylaniline (BBOA, abbreviated also as 4O.8) was studied by broadband dielectric spectroscopy (BDS) for samples that were exposed to various thermal treatments. Phase transitions between liquid crystalline phases (N, SmA, SmBhex, and SmBCr) were evidenced by abrupt changes in the temperature dependence of the dielectric permittivity spectra and dielectric relaxation times. A particularly complex dynamic behavior was revealed for the highly ordered SmBCr phase that showed clear evidence for cooperative dynamics of a glass-forming liquid as manifested by a Vogel-Fulcher-Tammann (VFT)-type temperature dependence of its structural relaxation time τ(T). At low temperatures, dependence τ(T) again changes from VFT to Arrhenius behavior, a phenomenon commonly observed for supercooled liquids confined to nanometer length scales and occasionally discussed as strong-fragile transition on heating. In this context, our observation supports the idea of partial orientation disorder in a quenched SmBCr phase, where the length scale of cooperative motions is restricted to the nanometer size of glassy domains causing the deviation from "bulk" VFT-type behavior. Finally, the isothermal crystallization kinetics of the metastable SmBCr phase was studied in detail. On the basis of structural information about the SmBhex and SmBCr phases, determined by X-ray diffraction, the subtle relation between molecular order and relaxation behavior is discussed.

Proton-conducting biopolymer electrolytes based on pectin doped with NH4X (X=Cl, Br)

Research has been undertaken to develop polymer electrolytes based on biodegradable natural polymers such as cellulose acetate, starch, gelatin, and chitosan, which are being used as polymer hosts for obtaining new polymer electrolytes for their applications in various electrochemical devices such as batteries, sensors, and electrochromic windows. Pectin is a naturally available material which is extracted from the skin of citrus fruits. Pectins, also known as pectic polysaccharides, are rich in galacturonic acid. The present study focuses on the proton-conducting polymer electrolytes based on the biopolymer pectin doped with ammonium chloride (NH4Cl) and ammonium bromide (NH4Br) prepared by solution casting technique. The prepared membranes are characterized using XRD, FTIR, and AC impedance techniques to study their complexation behavior, amorphous nature, and electrical properties. The conductivity of pure pectin membrane has been found to be 9.41 × 10−7 S cm−1. The polymer systems with 30 mol% NH4Cl-doped pectin and 40 mol% NH4Br-doped pectin have been found to have maximum ionic conductivity of 4.52 × 10−4 and 1.07 × 10−3 S cm−1, respectively. The conductivity value has increased by three orders of magnitude compared to pure pectin membrane. The dielectric behavior of both the systems has been explained using dielectric permittivity and electric modulus spectra.

Relaxation dynamics and thermophysical properties of vegetable oils using time-domain reflectometry

Dielectric relaxation studies of vegetable oils are important for insights into their hydrogen bonding and intermolecular dynamics. The dielectric relaxation and thermo physical properties of triglycerides present in some vegetable oils have been measured over the frequency range of 10MHz to 7GHz in the temperature region 25 to 10°C using a time-domain reflectometry approach. The frequency and temperature dependence of dielectric constants and dielectric loss factors were determined for coconut, peanut, soya bean, sunflower, palm, and olive oils. The dielectric permittivity spectra for each of the studied vegetable oils are explained using the Debye model with their complex dielectric permittivity analyzed using the Havriliak-Negami equation. The dielectric parameters static permittivity (ε 0), high-frequency limiting static permittivity (ε ∞), average relaxation time (τ 0), and thermodynamic parameters such as free energy (∆F τ), enthalpy (∆H τ), and entropy of activation (∆S τ) were also measured. Calculation and analysis of these thermodynamic parameters agrees with the determined dielectric parameters, giving insights into the temperature dependence of the molecular dynamics of these systems.

Impact of water on the charge transport of a glass-forming ionic liquid

Using dielectric spectroscopy and differential scanning calorimetry, we have performed a detailed investigation of the influence of water uptake on the translational and reorientational glassy dynamics in the typical ionic liquid 1-Butyl-3-methyl-imidazolium chloride. From a careful analysis of the measured dielectric permittivity and conductivity spectra, we find a significant acceleration of cation reorientation and a marked increase of the ionic conductivity for higher water contents. The latter effect mainly arises due to a strong impact of water content on the glass temperature, which for the well-dried material is found to be larger than any values reported in literature for this system. The fragility, characterizing the non-Arrhenius glassy dynamics of the ionic subsystem, also changes with varying water content. Decoupling of the ionic motion from the structural dynamics has to be considered to explain the results.

Dielectric properties of 1-methylimidazole at temperatures 298–336 K

ABSTRACT Dielectric permittivity and loss spectra of 1-methylimidazole (MeIm) have been measured over the frequency range from 100 MHz to 20 GHz at 298–336 K using an open-ended coaxial probe technique. Dielectric parameters are described by the Davidson–Cole model. The shape parameter shows temperature-independence. The Kirkwood correlation factor (g), enthalpy, entropy and the activation energy of molecular reorientation of MeIm also have been calculated.

Soil Complex Dielectric Permittivity Spectra Determination Using Electrical Signal Reflections in Probes of Various Lengths

Core Ideas A new complex dielectric permittivity spectra determination method was developed. The method uses Fourier analysis of the reflected signals in two probes of different length. No assumptions on soil dielectric relaxation model are necessary. The complex dielectric permittivity (CDP) of soils is used in moisture and salinity measurements. We have developed a CDP spectra determination method based on Fourier analysis of electrical signals reflected in probes of various lengths. The S11 parameters of the probes placed in samples under test were measured using a vector network analyzer, and the results were transformed into the time domain using transient‐state analysis and a simulated needle pulse. The pulses reflected from the ends of the probes' rods were extracted using a windowing function and transformed into the frequency domain. The CDP was then calculated independently at each frequency using an analytical expression. In contrast to time‐domain spectroscopy techniques, knowledge of the incident signal in the soil sample is not needed. Also, no assumptions on a dielectric relaxation model of the tested materials are necessary. The method was tested on six reference materials and samples of two soils at various water contents. The accuracy of the obtained results was assessed and a rod length combination of 4 and 10 cm was selected for further use. The measurement errors for the tested reference media were determined. The method performed the best in the frequency range 0.2 to 1.0 GHz for the real part of the CDP and 0.20 to 0.85 GHz for the imaginary part. This approach may be adapted for use with a time domain reflectometry needle pulse device.

Evaluating the Correlation Between the Geotechnical Index and the Electromagnetic Properties of Fouled Ballasted Track by a Full-Scale Laboratory Model

To determine the correlation between water content or fouling of a railroad track and ground-penetrating radar (GPR) signals, a full-scale railway track model was designed and constructed at the University of Massachusetts Amherst. A track section was simulated by creating a model consisting of rails and ties placed on a ballast layer on a subballast layer. The model was constructed three times with three fouling percentages. Each model was tested with water-content conditions of dry, field capacity, and two points in between these extremes. Frequency antennae of 450 MHz and 2 GHz were used to evaluate the conditions. The design and construction of the full-scale track in addition to the GPR data analysis and interpretation are presented in this paper. The results show that the dielectric permittivity and frequency spectrum can be used as an indicator of percentage of fouling and water content of a track. In addition, a linear correlation was observed between the percentage of fouling and the water content under field capacity conditions.

Исследование диэлектрических свойств и частотных спектров диэлектрических потерь водного раствора NaCl в заисимости от параметров состояния

The frequency spectra of dielectric permittivity, E1(v), and dielectric loss, E2(v), coefficients for the aqueous solution of sodium chloride and their dependences on the concentration, density, and temperature have been studied. Numerical calculations of those parameters are made for a certain choice of the potential interaction energy Φab(r) and the radial distribution function gab(r). The results obtained are in satisfactory agreement with experimental data.

Dielectric permittivity spectra of oil-water-saturated sandy-clayey rocks of different mineralogical compositions and relaxation properties of water in these rocks

Experimental measurements of the dielectric permittivity and equivalent conductivity of sandy-clayey samples (a mixture of river sand with bentonite or kaolin) saturated with salt-solution-diesel-fuel emulsions were performed in the frequency range from 10 kHz to 1 GHz at temperatures of 25-65 °C. It is shown that when the content of the salt solution in the saturating fluid does not exceed 10%, the dielectric permittivity in the frequency range from 1 MHz to 1 GHz depends little on the mineral composition of the sample and on the concentration of the saturating solution. When the portion of water is 33.3% or higher, increasing the concentration of the salt solution leads to an increase in the equivalent conductivity and the real part of the complex dielectric permittivity. Using the refractive model of the complex dielectric permittivity, we have estimated the dielectric properties of bound water, which depend on temperature and the type of clay (bentonite or kaolin) in the sand-clay mixture but are independent of the water saturation and the amount of clay in the sample.

Ionic Conductivity and Dielectric Properties of CMC Doped NH<sub>4</sub>SCN Solid Biopolymer Electrolytes

In this work, solid biopolymer electrolytes (SBE) containing carboxymethyl cellulose (CMC) doped with ammonium thiocyanate (NH4SCN) were prepared via solution casting method. The ionic conductivity and dielectric properties of CMC-NH4SCN system were investigated by electrical impedance spectroscopy in the temperature range of 303-353 K. The dc conductivity shows that the highest ionic conductivity of 6.48 x 10-5 Scm-1 at ambient temperature was obtained when 25 wt.% of NH4SCN was incorporated. The temperature dependence of ionic conductivity revealed that CMC-NH4SCN system was discovered to obey Arrhenius law where the regression value is almost unity (R2≈1). Activation energy of CMC-NH4SCN system was found to decrease with the increment of NH4SCN concentration. The dielectric behaviour of the CMC-NH4SCN system have been analyzed using dielectric permittivity (ε*) and electrical modulus (M*) spectra. Results from dielectric studies showed a non-Debye behaviour of CMC-NH4SCN system.

Quantum Effects Under Migratory Polarization in Nanometer Layers of Proton Semiconductors and Dielectrics at Ultralow Temperatures

Quantum mechanism of interlayer polarization in condensed media in an alternating electric field at low and ultralow temperatures is studied. The nonstationary Liouville equation is solved jointly with the stationary Schrodinger equation and operator Poisson equation without taking into account the proton-proton and proton-phonon interaction. The nonequilibrium density matrix is calculated for an ensemble of non-interacting protons moving in a one-dimensional multi-well potential relief of rectangular shape in an alternating polarizing field. With the help of the non-stationary density matrix, anomalous effects associated with the displacement of the low-temperature maximum of the angle of tangent of dielectric loss in the layered crystals to the temperature of liquid helium are investigated. The results of quantum-mechanical calculations of the complex dielectric permittivity spectra (SCDP) can be used to study the tunneling mechanism of spontaneous polarization in ferroelectrics (KDP, DKDP).

Microwave and millimeter wave dielectric permittivity and magnetic permeability of epsilon-gallium-iron-oxide nano-powders

In millimeter wave frequency range, hexagonal ferrites with high uniaxial anisotropic magnetic fields are used as absorbers. These ferrites include M-type barium ferrite (BaFe12O19) and strontium ferrite (SrFe12O19), which have natural ferromagnetic resonant frequency range from 40 GHz to 60 GHz. However, the higher frequency range lacks suitable materials that support the higher frequency ferromagnetic resonance. A series of gallium-substituted ε-iron oxides (ε-GaxFe2−xO3) are synthesized, which have ferromagnetic resonant frequencies appearing over the frequency range of 30 GHz to 150 GHz. The ε-GaxFe2−xO3 is synthesized by the sol-gel method. The particle sizes are observed to be smaller than 100 nm. In this paper, in-waveguide transmission and reflection method and the free space magneto-optical approach have been employed to study these newly developed ε-GaxFe2−xO3 particles in millimeter waves. These techniques enable to obtain precise transmission spectra to determine the dielectric and magnetic properties of both isotropic and anisotropic ferrites in the microwave and millimeter wave frequency range from single set of direct measurements. The complex dielectric permittivity and magnetic permeability spectra of ε-GaxFe2−xO3 are shown in this paper. Strong ferromagnetic resonances at different frequencies determined by the x parameter are found.

Dielectric relaxation studies of aqueous solution of polyethylene glycol 200 (PEG200), using time-domain reflectometry

Using time-domain reflectometry measurement technique, the dielectric complex permittivity spectra over the frequency range 10 MHz to 30 GHz have been studied for series of various compositions, at various temperatures, for the aqueous solution of polyethylene glycol 200 (PEG200). The relaxation in these mixtures can be described by a single relaxation time using the Cole–Cole model.[1] The values of static dielectric constant, dielectric relaxation time, excess dielectric permittivity, Bruggeman factor and Kirkwood correlation factor are determined for the series of various compositions. Using above parameters, intermolecular interaction of molecules at molecular level are predicated. The negative values of excess dielectric permittivity suggest reduction in dipole moment, and the values of Kirkwood correlation factor, which are found to be greater than unity, show the parallel orientation of electric dipoles. The study confirms that the intermolecular homogeneous and heterogeneous hydrogen bonding varies significantly with the increase in the concentration of PEG200 in water.