Electric Fields In Frequency Range Research Articles

Metal-ligand Lability and Ligand Mobility Enables Framework Transformation via Ligand Release in a Family of Crystalline 2D Coordination Polymers.

A family of seven silver(I)‐perfluorocarboxylate‐quinoxaline coordination polymers, [Ag4(O2CRF)4(quin)4] 1–5 (RF=(CF2)n‐1CF3)4, n=1 to 5); [Ag4(O2C(CF2)2CO2)2(quin)4] 6; [Ag4(O2CC6F5)4(quin)4] 7 (quin=quinoxaline), denoted by composition as 4 : 4 : 4 phases, was synthesised from reaction of the corresponding silver(I) perfluorocarboxylate with excess quinoxaline. Compounds 1–7 adopt a common 2D layered structure in which 1D silver‐perfluorcarboxylate chains are crosslinked by ditopic quinoxaline ligands. Solid‐state reaction upon heating, involving loss of one equivalent of quinoxaline, yielding new crystalline 4 : 4 : 3 phases [Ag4(O2C(CF2)n‐1CF3)4(quin)3]n (8–10, n=1 to 3), was followed in situ by PXRD and TGA studies. Crystal structures were confirmed by direct syntheses and structure determination. The solid‐state reaction converting 4 : 4 : 4 to 4 : 4 : 3 phase materials involves cleavage and formation of Ag−N and Ag−O bonds to enable the structural rearrangement. One of the 4 : 4 : 3 phase coordination polymers (10) shows the remarkably high dielectric constant in the low electric field frequency range.

Analysis of the temperature-frequency effect on dielectric losses in a grain medium

The aim of the study is to determine the influence of the thermal effect on dielectric losses in grain mass subject to bruising during drying and storage on the example of wheat across a wide external electric field frequency range. The study of the electrophysical characteristics of a dispersed medium comprising mechanically activated wheat grains takes into account the effect of the degree of breakage on the dielectric parameters of the studied medium. The studies were carried out on experimental samples having different degrees of mechanical activation of particles, which ranged in size from from 50 to 1000 μm. Variations in the dielectric loss tangent were studied using the dielectric method across a wide temperature-frequency range. Studies of variations in dielectric properties were carried out for wheat sam-ples subjected to grinding according to the mechanical activation method at temperatures varying from 20°C to 255°C with a constant heating rate of 0.7 deg / min. During the course of the experiment, the frequency of the external electric field was varied from 25 Hz to 1∙106 Hz. Dielectric constant and dielectric loss tangent calculations were carried out using data on electrical capacity and conductivity obtained using an E7-20 immittance meter and a measuring cell in the form of a flat capacitor. An analysis of variations in these dielectric characteristics was also performed. The obtained stable correlation of the dielectric loss tangent with the frequency of external electric impact and the degree of heating of the samples was most pronounced for finely dispersed samples (particle size 50 μm). Variations in dielectric characteristics are most significant when the frequency decreases to 100 Hz and below. The study of variations in the main dielectric parameters can be used to prevent self-heating and ignition of the grain mass during storage, as well as for selecting the most efficient energy-saving drying mode.

MOLECULAR MECHANISMS OF HIGHLY POLAR LIQUID CRYSTAL DIELECTRIC POLARIZATION

This article studies the dielectric constants of the nematic ε, ε, and isotropic εis phases of a highly polar liquid crystal of 4-cyanophenyl ether of 4′-n-octyloxybenzoic acid in the megahertz range of electric field frequencies (105-108) Hz, as well as the anisotropy of the dielectric constant Δε = ε − ε. The authors have revealed the relaxation processes and mechanisms responsible for them. In addition, they calculated the relaxation times, dipole polarization activation energy, and deceleration parameters in the nematic phase. The design of a measuring cell is presented, which allows studying the dielectric constant of the liquid crystal at various orientations of the director (provided by the magnetic field) relative to an alternating electric field with small volumes of matter. The results show that the dispersion of the dielectric constant in the investigated frequency range of the electric field is characterized by two relaxation processes with τ ~3 ∙ 10−8 s and (τ)в ~ 1,5 ∙ 10−9 s. The dispersion mechanisms are due to the rotation of polar molecules about their short and long axes respectively. The dispersion of the dielectric constant corresponds to the spectrum of relaxation times. The dispersion mechanisms are associated with two relaxation processes: the precession of molecules along a cone within the spatial angle allowed by the value of the order parameter of the liquid crystal S < 1, and the rotation of molecules around the longitudinal axes. The relaxation times corresponding to these mechanisms are commensurate with each other. The dispersion of the dielectric constant in the isotropic phase is characterized by a relaxation process with τis ~ 6 ∙ 10−9 s. The dispersion mechanism is due to the rotation of molecules around short axes.

Features of frequency dependence of electrical conductivity and dielectric properties in lignins from conifers and deciduous trees

Abstract Lignins are among the most common plant polymers and demonstrate pronounced electrical conductivity properties due to their conjugated polymolecular aromatic structure and polyfunctional nature. Electrical conductivity and dielectric properties of lignins from conifers and deciduous trees in the range of electric field frequencies from 10−2 to 107 Hz were investigated by means of dielectric spectroscopy. Characteristic parameters of static and high frequency electrical conductivity were calculated. To study the influence of the lignins functional nature on their electrophysical properties, the study determined three types of relaxators (separate charges or charge systems in the structure of a substance changing their position in space when exposed to an external alternating electric field) in the structure of the lignin macromolecule. Low-frequency relaxators are associated with oscillations of methoxyl groups. Mid-frequency relaxators correspond predominantly to phenolic hydroxyl groups and to hydroxyl groups of adsorbed water. High-frequency relaxators correspond to the hopping of π-electrons along the chain of conjugated bonds of a benzene ring. Differences in the structure and functional nature of lignins from conifers and deciduous trees cause different contributions of low-frequency relaxators. As a result, these features form differences in the electrophysical properties of lignins from conifers and deciduous trees.

Some features of the dielectric relaxation of nitroglycerin

This paper presents the results of an experimental study of the dielectric relaxation of nitroglycerin in the temperature range of the liquid–solid phase transition. Measurements were performed in the electric field frequency range of 1–1264 MHz. It is shown that the dielectric relaxation of nitroglycerin includes at least two relaxation process. Possible factors that determine the temperature and frequency dependences of the complex dielectric permittivity of nitroglycerin are discussed.

Oscillating electric-field effects on adsorbed-water at rutile- and anatase-TiO2 surfaces.

We have performed non-equilibrium molecular dynamics simulations of various TiO2/water interfaces at ambient temperature in presence of oscillating electric fields in frequency range 20-100 GHz and RMS intensities 0.05-0.25 V/Å. Although the externally applied fields are by one order of magnitude lower than the intrinsic electric field present on the interfaces (∼1.5-4.5 V/Å), significant non-thermal coupling of rotational and translational motion of water molecules was clearly observed. Enhancement of the motion, manifested by increase of diffusivity, was detected in the first hydration layer, which is known to be heavily confined by adsorption to the TiO2 surface. Interestingly, the diffusivity increases more rapidly on anatase than on rutile facets where the adsorbed water was found to be more organized and restrained. We observed that the applied oscillating field reduces number of hydrogen bonds on the interface. The remaining H-bonds are weaker than those detected under zero-field conditions; however, their lifetime increases on most of the surfaces when the low-frequency fields are applied. Reduction of adsorption interaction was observed also in IR spectra of interfacial water where the directional patterns are smeared as the intensities of applied fields increase.

Quantifying the Effect of Electric Fields in the Frequency Range of 100-500 khz on Mitotic Spindle Structures

It is well established that electric fields can influence cells: Low frequency electric fields (f 1 MHz) cause tissue heating. More recently, it was shown that exposing dividing cells to low intensity (∼1 V/cm) electric fields in the frequency range of 100 - 500 kHz leads to disruption of the mitotic process, and ultimately cell death. This discovery motivated the development of Tumor Treating Fields (TTFields) therapy: a non-invasive treatment that utilizes electric fields in the intermediate frequency range to treat solid tumors. TTFields have been approved by the US Food and Drug Administration for the treatment of recurrent glioblastoma multiforme since 2011.It is thought that TTFields exert their effect on cells by inhibiting tubulin polymerization through interactions of the electric fields with the highly polarized tubulin dimers. However, only few studies have been performed that quantify the intracellular intensity of electric fields, in the frequency range of 100-500 kHz, and how these fields disrupt tubulin polymerization. Here we present the results of computational simulations and in-vitro studies that address these issues. The simulations show that the frequency range of 100-500 kHz marks a transition region in which the magnitude of the electric field inside cells increases significantly, and that the threshold at which this increase occurs depends on the dielectric properties of the cell's membrane and cytoplasm. The experiments show that exposure of cell cultures to TTFields leads to a 10-20% increase in the amount of unpolymerized tubulin dimers within the cells, suggesting that TTFields influence tubulin polymerization dynamics. These studies provide new insight into the biophysical mechanisms that underlie TTFields therapy.

Metal-assisted chemical etching of silicon 3D nanostructure using direct-alternating electric field

Metal-assisted chemical etching (MaCE) of silicon (Si) is a well-used method for the fabrication of Si nanostructures. To simplify the control etching for the fabrication of Si 3D nanostructures, we developed a new method using direct-alternating electric field to control the etching direction. We examined the MaCE process in the electric field, and evaluated the effect of different electric field frequencies and ultrasonic ion bubbles on the production of Si nanostructures. The results demonstrate that electric fields can effectively control etching direction and can be used to fabricate Si 3D nanostructures. Optimization of the electric current density and electric field frequency range has been performed.

Effect of low concentrations of carbon nanotubes on electric dipole relaxation in a polyurethane elastomer

The effect of small (up to 0.018 wt %) additions of single-walled carbon nanotubes (SWNTs) on the complex electric modulus M*= M′ - jM″ and the spectrum of the relaxation times G(τ) of a cross-linked polyurethane elastomer containing ∼10 vol % of polyamide-6 dispersed in the polyurethane matrix and incompatible with it was studied. The measurements were conducted in the range of electric field frequencies 10−3–105 Hz at temperatures from 133 to 413 K. Based on the shape analysis of the M″(M′) diagrams, the contributions of electric conductivity and dielectric relaxation to complex dielectric permittivity ɛ* = ɛ′ - jɛ″ were separated and the effect of additions on α and β relaxation for both polyurethane and polyamide phases was analyzed in accordance with the peculiarities of phase-separated systems. The introduction of SWNTs in the composite affected the dielectric properties of the material; the maximum effect was observed at concentrations of 0.002–0.008 wt %; at higher SWNT concentrations, the scatter of data increased and did not allow us to evaluate the effect. The effect of SWNTs on G(τ) in the main phase was opposite to that in the polyamide phase. In the temperature range of α relaxation of the polyurethane phase, the relaxation times increased after the introduction of SWNTs evidently because of the decrease in the free volume that determines the α relaxation times of polyurethane. In contrast, for the polyamide phase in the range of α relaxation, the relaxation times decreased after the introduction of SWNTs. The results agree with the literature data on the effect of ultrasmall SWNT concentrations on the physicomechanical characteristics of the polyurethane elastomer and its electric conductivity.

Rapid assembly of gold nanoparticle-based microstructures using optically-induced electrokinetics

This paper presents a rapid approach for assembling gold nano-particles (AuNPs)-based microstructures using optically-induced electrokinetics. Results showed that number of AuNPs in the assembled microstructures could be controlled by adjusting the input optically-induced electrokinetics parameters. The formation conditions were experimentally investigated by varying several key electrokinetics parameters, and the results were compared to a numerical simulation of the electrokinetic forces. The experimental results were also analyzed by counting the number of deposited AuNPs in a microstructure using an image processing algorithm. We will show that the optimal parameters for this optoelectronic AuNPs assembly method are electric field frequency range from 9 to 11 kHz with a voltage range of 18-20 Vpp, and an optical exposure time of ~120 s.

Effect of small additions of carbon nanotubes on the electrical conductivity of polyurethane elastomer

The effect of small (0.002–0.018 wt %) additions of single-walled carbon nanotubes on the dielectric properties and electrical conductivity of crosslinked polyurethane elastomer is studied in the temperature range of 133–453 K and the 10−3 to 105 Hz range of electric field frequencies. It is shown that the dependence of direct current conductivity σdc on temperature deviates significantly from the Arrhenius dependence and is described by the Vogel-Fulcher-Tamman equation σdc = σdc0exp{−DT0/(T − T0)}, where T0 is the Vogel temperature and D is the strength parameter. A correlation is found between the nonmonotonic dependences of the glass transition temperature (Tg), D parameter, and σdc and the concentration of nanotubes with earlier results for their effects on the physicomechanical characteristics (strength and Young’s modulus) of these systems.

Dielectric properties of perovskite ferroelectrics at the nonequilibrium concentrations of point defects

Dielectric properties of ceramic barium titanate modified by the addition of aluminum oxide are studied via impedance spectroscopy in weak electric fields in frequency range of 0.3–103 kHz. For better separation of the properties of the inner regions of crystallites and the boundary regions by quenching, an excess concentration of point defects is created, leading to the formation of bulk charge. The experimental results are performed using the Maxwell-Wagner capacitor model and the Schottky barrier model.

Pb(Tab)2(4,4′-bipy)](PF6)2: two-step ambient temperature quantitative solid-state synthesis, structure and dielectric properties

Ambient temperature solid-state reaction of Pb(OAc)2 with TabHPF6 afforded an intermediate product [Pb(Tab)2]2(PF6)4, which further reacted with 4,4'-bipy in the solid state to generate a unique 2D cationic coordination polymer [Pb(Tab)2(4,4'-bipy)](PF6)2 in quantitative yield. Both complexes possess a low dielectric constant and low dielectric loss in the high electric field frequency range.

Impedance spectroscopy of composites based on waste polymeric materials for electrical engineering purposes

We have developed a high-sensitivity capacitance transducer and a method for measuring the complex of elec- trical indices of composites based on waste polymeric materials in the frequency range from 100 Hz to 1 MHz. The electrical properties of composites depending on the electric field frequency and the content and type of the filler have been investigated. Introduction. The development of effective methods for controlling and diagnosing the electrical properties of electrical-engineering composites based on waste polymeric materials is dictated by the necessity of their testing for the compliance of the complex of their electrical indices (relative permittivity, bulk electrical resistivity, dielectric loss tangent) with the norms regulated by the corresponding standards (1-3). The urgency of the problem is due to the fact that composites based on waste polymeric materials can find various applications in electrical engineering. For exam- ple, composites containing finely dispersed quartz sand or lignin as fillers can be used as electrical insulating materials, and composites based on powdery carbon fibers, powdery electrolytic copper, or rubber crumbs obtained from used tires can be used as current-conducting materials for a wide range of technical and household objects. In this connection, the purpose of the present work is to develop effective methods for controlling and diag- nosing composites based on waste polymeric materials with the aim of investigating their electrical properties depend- ing on the content and type of the filler in the electric field frequency range from 100 Hz to 1 MHz. Materials and Methods of Investigation. The technology of obtaining composites based on waste polymeric materials containing powdery carbon fiber (PCF), sand (S), PGRS powder, or powdery electrolytic copper (PEC) is as follows. Waste polyethylene film was ground with the help of a knife grinder. A certain quantity of fractured particles was placed on microrollers heated to a temperature of 115-120 o C, and the necessary quantity of powdery carbon fiber predried at a temperature of 150-200 o C was added to it portionwise; then the mixture was stirred for 5-7 min until a homogeneous mass was obtained. From the rolled sheet, composite plates with given sizes were formed by the method of hot pressing for 15-20 min at a temperature of 160-170 o C. To investigate the electrical properties of composites based on waste polymeric materials, we created a meas- uring facility incorporating a high-sensitivity capacitive transducer (sensor) and a small-sized digital immitance meter in which there is an interface for current control data output to the monitor of the personal computer screen. The de- sign of the high-sensitivity capacitive transducer is shown in Fig. 1. The capacitive transducer designed by us has the following advantages over the existing analogs: a) it permits obtaining information on the complex of electrical indices of composites based on waste poly- meric materials in the electric field frequency range between 100 Hz and 1 MHz; b) it permits determining the thickness of the composite plate by means of a micrometric device in the 0.1-6 mm range with an accuracy of 0.005 mm;

Design and Application of Natural Audio Electric Field Frequency Selecting Instrument

An observation scheme, which is designed several frequencies suited over the natural audio electric field frequency range, is used to qualitatively understand the electrical structure of underground geological body. Weak signal detection technology has been used to amplify and filter the weak natural electric field signal, and read out them after selecting corresponding frequencies and integrating. This instrument can observe eight natural electric field signal at frequency of 8Hz, 16Hz, 32Hz, 64Hz, 128Hz, 256Hz, 512Hz, 1024Hz. Several reliable technologies have been used in the hardware design and software development to improve both the anti-interferences capability and system stability. Compared with field work instance, we conclude that natural audio electric field frequency selecting instrument can get the underground geological information within a certain depth, and therefore it can be used for fast survey in geology and mineral resources, and in engineering geophysical and water resources.

Dielectric anisotropy of the single crystal of isopropylviologen copper(i) triiodide

Solvothermal reactions of CuI with isopropanol, 4,4'-bipyridine, I(2) and a small amount of water in MeCN produced one coordination compound [isopropylviologen][CuI(3)] (isopropylviologen = N,N'-diisopropyl-4,4'-bipyridinium) (1). The dielectric constants of the single crystal of 1 along the three crystal axes are different with the largest diversity ratio of ∼3.3, showing dielctric anisotropic behavior. Under low temperature (<273 K) or medium electric field frequency range (1 KHz-1 MHz), the dielectric constant of the title compound is nearly unchanged, exhibiting a temperature/frequency-independent characteristics. The crystalline powder of 1 has a low dielectric constant and low dielectric loss in the medium electric field frequency range, which is comparable to the traditional low-k material SiO(2).

Dielectric properties of liquid-crystalline copolymers with side cyanobiphenyl groups and acrylic acid units

Dielectric properties of a number of liquid-cry stalline comb-shaped copolymers with different ratios of side-chain mesogenic cyanobiphenyl groups and acrylic acid units are studied. In the electric-field frequency range 300 Hz-100 MHz, temperature dependences of dielectric permittivity are obtained for nematic and isotropic phases. The times of relaxation and the energies of activation for processes responsible for dielectric-permittivity dispersion are measured. The quantitative relationship between the dielectric characteristics and the content of acrylic acid units in the copolymer is established.

Solar Wind Electric Fields in the Ion Cyclotron Frequency Range

Measurements of fluctuations of electric fields in the frequency range from a fraction of one Hz to 12.5 Hz are presented, and corrected for the Lorentz transformation of magnetic fluctuations to give the electric fields in the plasma frame. The electric fields are large enough to provide the dominant force on the ions of the solar wind in the region near the ion cyclotron frequency of protons, larger than the force due to magnetic fluctuations. They provide sufficient velocity space diffusion or heating to counteract conservation of magnetic moment in the expanding solar wind to maintain nearly isotropic velocity distributions.

Dielectric relaxation of dendronized polystyrene in solutions

The molecular properties of polystyrene modified by Frechet-type dendrons of the first–fourth generation containing polar CONH groups, were studied by means of the dielectric spectroscopy method in dilute solutions. The dispersion of the dielectric permittivity of dendronized polystyrene was found in benzene, chloroform and THF solutions in the electric field frequency range 0.2 kHz–10 MHz. It was established that the increase of dendron generation number leads to the growth of the relaxation times of dielectric polarization. It was found that the dipole moment of the monomer unit of the polystyrene molecules modified by first generation dendrons coincides with the dipole moment of CONH group.

Electric properties of non-irradiated and gamma-irradiated bone

Dielectric spectroscopy has been applied to study the effect of water and γ-irradiation on bone. Measurements were performed in the electric field frequency range of 10 1–10 5 Hz and at temperatures from 22 to 240 °C. The bone samples contained about 3% water by mass at room temperature. The doses of γ-irradiation were 5, 50, 100, 300 and 1000 kGy. The influence of water and γ-irradiation on the permittivity and conductivity of bone is significant at temperatures above 100 °C. Results of this paper would suggest that γ-irradiation initiates two important processes: cross-linking for doses 5 and 50 kGy and main-chain degradation for higher doses. Analysis of polarisation and conduction mechanisms for bone was interpreted on the basis of proton transport.