Broadband Dielectric Spectrometer Research Articles

Electrical and Dielectric Properties of Stitched Non-woven Engineered Fabrics Containing Activated Carbon Fiber

Smart textile is considered to be a new trend that can revolutionize the functionality of clothing. One of the most promising fields of smart textiles is in energy storage devices. Recently, many research efforts focus on supercapacitor as an energy storage device that can overlap the gap between conventional batteries and traditional capacitors. Activated carbon fiber (ACF) is one of the important candidate for this application. Different groups of non-woven polyester fabrics were prepared with and without adding the activated carbons. The effect of structure of the samples on the permittivity, dielectric loss as well as the ac-conductivity is investigated and interpreted. The mechanism of the storage of the charge carriers is given by two different capacities. The first one is the capacity of the electric double layer at the interface between the electrode and the dielectric material. The second is the capacity due to the redox or what is called pseudo capacity. In this work, the broadband dielectric spectrometer, BDS, is employed to study the effect of frequency in the range of 1mHz – 10 MHz and sometimes temperature (20 – 60 oC). The non-woven samples prepared with ACF showed the best results among the prepared nonwoven samples without activated carbon fibers and even nonwoven samples with carbon granules. This is due to the good electrical conductivity of activated carbon fiber used in the nonwoven samples.

Effect of Supercritical Carbon Dioxide Conditions on PVDF/PVP Microcellular Foams

Supercritical carbon dioxide (ScCO2) was used as a physical foaming agent to prepare poly(vinylidene f luoride)/poly(N-vinyl pyrrolidone) (PVDF/PVP) microstructure material. The effects of foaming conditions including saturation pressure, foaming temperature and foaming time on PVDF/PVP foams morphology, thermal and electrical behavior were systematically investigated by scanning electron microscope, differential scanning calorimeter and broadband dielectric spectrometer. Small cell and low cell density were achieved at low pressure of 12 MPa, as increasing saturation pressure, the average cell size increased first, and then decreased. The competition between the cell growth and cell nucleation played an important role in average cell size, which was directly related to ScCO2 processing conditions. With increasing foaming temperature, cell size was increased and cell density was decreased, in a nearly linear manner. The variation of foaming time was considered to be closely related to the time for cells to grow. Thus, the results revealed that the average cell size enhanced with extending foaming time. The thermal properties of PVDF/PVP composites are slightly inf luenced by foaming parameters, and the dielectric constant of PVDF/PVP composite foams decreased with increasing volume expansion ratio.

A Planar Layered Two-Phase System Model of Frequency Response of Insulation System for Estimating Moisture in IOCT

In the estimation of moisture content of the inverted-type oil-immersed current transformer (IOCT) insulation system, the interfacial polarization between oil-immersed insulation paper and semi-conductive paper should be considered. The classical model functions of frequency-domain dielectric spectroscopy (FDS) are no longer applicable. Therefore, the planar layered two-phase system model is applied in this paper. First, the FDS of oil-immersed paper and semi-conductive paper with certain moisture content is measured using Alpha-A broadband dielectric spectrometer. Then, the FDS of oil-immersed insulation paper is explained using the Havriliak–Negami (H–N) model function and the amendatory H–N model function considering that the dc conductance is used to explain the FDS of semi-conductive paper. The two functions are substituted into the planar layered two-phase system model. The model parameters are fit by means of least-squares technique. Finally, the numerical relationship between the chosen characteristic parameter and the moisture content of the IOCT insulation system is obtained by least-squares technique. In engineering, one can use the results considering the influence of interfacial polarization to estimate the moisture content of the IOCT insulation system.

High damping epoxized natural rubber/diallyl adiallyl phthalate prepolymer (ENR/DAP‐A) blends engineered by interphase crosslinking

ABSTRACTWhile a great diversity of rubber/plastic damping blends have been reported, the damping trough resulted from phase incompatibility, which usually exists between the glass transition temperatures (Tg) of each component, remains an unsolved problem by separating the effective temperature range of damping blends. Herein, we reported a new and facile way of preparing rubber/plastic binary blends with high damping property by eliminating the inherent damping trough. Specifically, we envisaged that peroxides can trigger free radical reactions both within and between epoxidized natural rubber/diallyl phthalate prepolymer moieties, which serve as the co‐vulcanizer to generate interphase reactions thus enhancing phase compatibility. Accordingly, apart from the resulting high damping epoxidized natural rubber40/diallyl phthalate prepolymer binary blends with an effective (tan δmin > 0.35) temperature range of 178 °C from −33 to 145 °C, the proposal has also been demonstrated via the support of broadband dielectric spectrometer testing, dynamic mechanical analysis, and differential scanning calorimetry. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46300.

Synthesis and characterization of polyaniline/tosylcellulose stearate composites as promising semiconducting materials

Tosylcellulose stearate (TCSt) as a thermoplastic polymer has been prepared starting from microcrystalline cellulose (MCC) which was converted into a more reactive and solvent soluble tosylcellulose (TC) with degree of substitution = 0.45 under homogenous conditions. Then, tosylcellulose underwent esterification reaction through its reaction with stearic anhydride in DMF/DCM to afford tosylcellulose stearate. FT-IR, 13C NMR, and elemental analyses confirmed the chemical structure of both tosylcellulose and tosylcellulose stearate. TCSt fibers were used as matrix for polyaniline (PANI) which had been prepared via in situ oxidative polymerization of aniline hydrochloride using hydrochloric acid as dopant and ammonium persulfate as an oxidizing agent. PANI/TCSt composites with loading ratios of 75:25, 50:50, and 25:75 wt/wt were fabricated. The thermal stability, degree of crystallinity, and surface morphology of the prepared composites were characterized. The presence of PANI improved the thermal stability of the PANI/TCSt composites with (50:50 wt:wt). The electrical conductivity for PANI/TCSt composites was measured by Broadband Dielectric Spectrometer, and the conductivity values of PANI/TCSt composite prepared at weight ratio 75:25 wt% was coincided with those of PANI alone. Increasing the temperature from −40 to +50 °C increased the conductivity of the composites by about two orders of magnitudes for all investigated samples. The films prepared from TCSt and PANI/TCSt composite (50:50 wt:wt) displayed improved mechanical properties when compared with the films prepared from cellulose acetate (CA) and CA/PANI composite (50:50 wt:wt).

Dielectric relaxation and carrier transport in epoxy resin and its microcomposite

Epoxy resin and its microcomposite are widely used as electrical insulation in electrical equipment. Surface flashover and breakdown properties of these materials can be influenced by dielectric relaxation process and charge carrier behavior. The charge transport characteristics and dielectric relaxation process for neat EP and its microcomposites were studied by means of dielectric relaxation spectroscopy. The glass transition temperatures Tg of the two kinds of samples were investigated with differential scanning calorimetry measurement, which were approximately 105 °C and 120 °C, respectively. Both the two kinds of samples were sputtered with gold electrodes on two sides, and electrodes' diameter was 30 mm. The properties of dielectric relaxation was measured by Concept 80 Novocontrol broadband dielectric spectrometer at various temperatures from 100 °C to 180 °C. There is a relaxation peak which labeled α in the range of high frequencies on account of the molecular chain movement or motion of segmental chains when the temperature is above Tg. At the same time, the dc conductivity attributed by the charge carrier transport occurs in the range of low frequencies. Besides, there are different relaxation times for molecular chains with different length scales. Moreover, there is a broad distribution of relaxation time for both neat EP and its microcomposites and the relaxation time distribution at different temperatures was calculated. In addition, it was found that the relation between peak frequency of relaxation process and temperature follow the Vogel-Fulcher-Tammann (VFT) law, and temperature dependences of dc conductivity also obey the VFT equation. The Vogel temperatures of dielectric relaxation process and charge carrier transport were calculated by fitting the results of permittivity and conductivity. The glass transition temperatures for neat EP and its microcomposite were estimated to be 102 °C and 117 °C through Vogel temperatures, which are in consistence with DSC measurement results. It represents that free volume in the two kinds of samples increases with the increase of temperature, thus enhancing molecular chain movement and charge carrier transport process.

Fabrication of low specific resistance ceramic carbon composites by colloidal processing using glucose as soluble carbon source

Ceramic carbon composites were fabricated by colloidal processing using glucose as soluble carbon source. Glucose is converted into conducting carbon at high temperature treatment. Ceramic carbon composites were sintered in flowing argon at \(1400{^{\circ }}\hbox {C}\) showing resistor behaviour even at low carbon content (1 wt%). In this work, ceramic carbon composites were fabricated using alumina–clay slurries with addition of glucose as a soluble carbon source. Morphology of the sintered samples was characterized by field emission gun (FEG) electron microscopy. Phase analysis was done by X-ray diffraction (XRD). Electrical properties of ceramic carbon composites were measured by broad band dielectric spectrometer. Carbon produced from glucose at high temperature was characterized independently by BET surface area, dynamic light scattering, field emission gun scanning electron microscopy, field emission gun transmission electron microscopy, XRD and Raman spectroscopy.

Optical, electrical and ferromagnetic studies of ZnO:Fe diluted magnetic semiconductor nanoparticles for spintronic applications

In the present investigation, diluted magnetic semiconductor (Zn1−xFexO) nanoparticles with different doping concentrations (x=0, 0.02, 0.04, 0.06, and 0.08) were successfully synthesized by sol-gel auto-combustion method. The crystal structure, morphology, optical, electrical and magnetic properties of the prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis using x-rays (EDAX), ultraviolet–visible spectrophotometer, fluorescence spectroscope (FS), vibrating sample magnetometer (VSM) and broad band dielectric spectrometer (BDS). XRD results reveal that all the samples possess hexagonal wurtzite crystal structure with good crystalline quality. The absence of impurity phases divulge that Fe ions are well incorporated into the ZnO crystal lattice. The substitutional incorporation of Fe3+ at Zn sites is reflected in optical absorption spectra of the samples. Flouorescence spectra of the samples show a strong near-band edge related UV emission as well as defect related visible emissions. The semiconducting behavior of the samples has been confirmed through electrical conductivity measurements. Magnetic measurements indicated that all the samples possess ferromagnetism at room temperature.

Electrospinning preparation and properties of Tb (TTA)3(TPPO)2/PANI/PVP electrical-luminescence bifunctional nanofibers

Tb(TTA)3(TPPO)2/PANI/PVP conductive-luminescence composite nanofibers have been successfully fabricated by the electrospinning technique. The morphologies and properties of the final nanofibers were investigated in detail by scanning electron microscopy (SEM), fluorescence spectroscopy (FL) and broadband dielectric spectrometer measurement. The results show that the bifunctional composite nanofibers possess both good electrical conductivity properties and excellent luminescent properties. The luminescence and electrical conductivity of the composite nanofibers can be tuned by adjusting the amount of Tb complex and PANI.

Electrical conductivity of polyazomethine/fullerene C60 nanocomposites

We prepared the polyazomethine/fullerene C60 nanocomposites varying in C60 loading. With a broadband dielectric relaxation spectrometer, we measured their electrical conductivity σm being a sum of dc conductivity σdc and ac conductivity σac. A small C60 content (0.25 and 0.5 wt.%) was shown to decrease σdc, whereas a larger amount of C60 (2.5 wt.%) was found to increase σdc of the nanocomposite. The temperature dependences of σac were described with the Arrhenius equation, while the frequency dependences of σac were characterized with a power function. The correlated barrier hopping was accepted as the most suitable mechanism to explain the σac behavior of the nanocomposites.

Dielectric and energy storage properties of Mn-doped Ba0.3Sr0.475 La0.12Ce0.03TiO3 dielectric ceramics

Microstructure, temperature and frequency dependent dielectric and energy storage properties of Ba0.3Sr0.475La0.12Ce0.03Ti1−xMnxO3(x=0−0.005) have been investigated with X-ray diffractometer, and scanning electron microscope, broad band dielectric spectrometer and ferroelectric analyzer. The doping of Mn substantially decreased the dielectric loss, but made some of Ce3+ be oxidized to Ce4+ entering into B-site, which resulted in the formation secondary phases. For the Mn-doped composition, extremely low dielectric loss (10−5 order of magnitude at 10kHz) could be obtained at room temperature. The relaxation mechanism at low temperature is of the dipole type for the undoped composition and that at high temperature (>500K) is governed by the trap controlled ac conduction, respectively. The energy storage properties were improved by the doping with Mn due to the increase of insulation. Maximum energy density of 0.953J/cm3 could be obtained for x=0.003 composition with the BDS of 247kV/cm and efficiency of 93%.

Dielectric relaxation dynamics of Al/epoxy micro-composites

The dynamic dielectric properties of the Al/epoxy composites were investigated by means of broadband dielectric spectroscopy spectrometer with the frequency range 1–107 Hz at the temperature of −20–200 °C. Three relaxation processes are detected in the dielectric spectra as a function of temperature and frequency: (1) Maxwell interfacial polarization (IP) at low frequencies and high temperatures; (2) a primary α-relaxation process near Tg at the middle frequencies; and (3) Intermediate dipolar effect (IDE) relaxation at high frequencies above −20 °C. The dynamics of all the recorded processes include contributions from both polymer and the inorganic reinforcing phases. The analyses of loss tangent and electric modulus spectrum of the composites indicate that the chain segmental dynamics of the polymer are accompanied by the absorption of energy given to the system. Finally, the alternating current (AC) conductivity spectra support the hopping type of conduction in the composites and the ionic conduction relaxation processes are observed also.

Universal power law behavior of the AC conductivity versus frequency of agglomerate morphologies in conductive carbon nanotube‐reinforced epoxy networks

ABSTRACTThe Jonscher universal power law for ac conductivity versus frequency (f = ω/2π) in the dispersion region was tested for a multiwall carbon nanotube/epoxy nanocomposite. The effect of changes in agglomerate morphology on the fitting parameters A and n in the equation σac = Aωn was investigated. Changing nanotube agglomerate morphology was tracked by optical microscopy through curing. Evolving morphology was compared alongside ac conductivity obtained via a broadband dielectric spectrometer to elucidate possible physical meaning of the universal power law in the context of this system. The −logA/n was unaffected by changes in agglomerate morphology affected during cure, yet connected with each other in their dependence on temperature. For this system, the relationship between the fitting parameters in the universal dynamic response equation remains empirical at this stage with regard to biphasic “texture” or morphology within such a network. Electrical conductivity σ versus frequency ω for a composite consisting of agglomerated multiwalled carbon nanotubes dispersed throughout a cured epoxy matrix was discovered to follow the empirical universal dynamic response equation of Jonscher. The frequency behavior of the exponent n is discussed in terms of underlying morphology throughout which charge carriers migrate. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1918–1923

Dielectric spectroscopy characterization of relaxation process in Ni/epoxy composites

Nickel (Ni)/epoxy composites with different Ni filler additions were prepared, and the dynamic dielectric properties of the composites were investigated using broadband dielectric spectroscopy spectrometer with the frequency range 1–107 Hz at the temperature of −20 to 200 °C. The dielectric properties as a function of temperature and frequency show three relaxation processes: (1) Maxwell interfacial polarization at low frequencies; (2) a primary α-relaxation process at near glass transition temperature (Tg); and (3) ionic conduction relaxation at the middle frequencies between 100 °C and 200 °C. Detailed studies of modulus spectrum suggest non-Debye type of relaxation mechanism for the composites. The Cole-Cole plots exhibit the contribution of filler concentration effect in the modulus characteristics of the Ni/epoxy composites. Alternating current (AC) conductivity and electric modulus studies support the hopping type of conduction in the composites, and frequency dependent AC conductivity data obey Jonscher’s power law.

Monodispersed fabrication and dielectric studies on ethylenediamine passivated α-manganese dioxide nanorods

In this present work, pure α-MnO2 nanorods were fabricated by the reduction of 0.2m/L of KMnO4 with 0.2m/L of Na2S2O3·5H2O and by passivating with the organic ligand Ethylenediamine (EDA). The structural, functional, morphological and chemical composition of the nanorods were investigated by X-Ray Diffractometer (XRD), Fourier Transform Infrared Spectrometer (FTIR), High Resolution Scanning Electron Microscope (HR-SEM) and Energy Dispersive X-Ray Spectrometry (EDX). The XRD analysis indicated high crystalline nature of the product and FTIR confirmed the contribution of the organic ligand in surface passivation. HR-SEM image revealed the morphology of the α-MnO2 nanorods with an average size of about 40×200nm. EDX confirmed the presence of Mn and O in the material. UV–visible spectrophotometery was used to determine the absorption behavior of the nanorods and an indirect band gap of 1.37eV was acquired by Taucplot. Dielectric studies were carried out using Broadband Dielectric Spectrometer(BDS) and the resistivity was found to be around the semiconductor range (ρ=1.46 to 5.76×103Ωcm).

Experimental study on frequency-dependent properties of soil electrical parameters

In the value calculation of the impulse characteristics of a grounding device, the suitability of the key parameters of the control equation, namely, soil resistivity and dielectric constant, has a considerable effect on the accuracy of the calculation results. The values of these two soil electrical parameters differ at various current frequencies. Thus, rules on the changes of soil electrical parameters with the current frequency into the ground have to be studied. Limited research has been conducted on the change in the rules of the soil electrical parameters in the lightning current band. This paper reports on the use of the broadband dielectric impedance spectrometer to conduct frequency sweep measurement of soil samples at various moisture content levels, discusses the change rules of soil resistivity and relative dielectric constant with current frequency from 50Hz to 106Hz, and details the conduct of rational analysis and value fitting. Results show that change is rapid when the soil resistivity and relative dielectric constant are at low frequency (below 100kHz), and the change slows down when the frequency increases. In the low-frequency band (below 100kHz), the soil moisture content has a significant effect on the frequency-dependent properties of the resistivity and relative dielectric constant, and the effect is minimal in the high-frequency band. The soil resistivity and relative dielectric constant as well as the current frequency meet the power function relation.

Preparation and Preliminary Dielectric Characterization of Structured C60-Thiol-Ene Polymer Nanocomposites Assembled Using the Thiol-Ene Click Reaction.

Fullerene-containing materials have the ability to store and release electrical energy. Therefore, fullerenes may ultimately find use in high-voltage equipment devices or as super capacitors for high electric energy storage due to this ease of manipulating their excellent dielectric properties and their high volume resistivity. A series of structured fullerene (C60) polymer nanocomposites were assembled using the thiol-ene click reaction, between alkyl thiols and allyl functionalized C60 derivatives. The resulting high-density C60-urethane-thiol-ene (C60-Thiol-Ene) networks possessed excellent mechanical properties. These novel networks were characterized using standard techniques, including infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermal gravimetric analysis (TGA). The dielectric spectra for the prepared samples were determined over a broad frequency range at room temperature using a broadband dielectric spectrometer and a semiconductor characterization system. The changes in thermo-mechanical and electrical properties of these novel fullerene-thiol-ene composite films were measured as a function of the C60 content, and samples characterized by high dielectric permittivity and low dielectric loss were produced. In this process, variations in chemical composition of the networks were correlated to performance characteristics.

Synthesis and characterization of low density polyethylene with multiferroic bismuth ferrite nanocomposite

A novel low density polyethylene (LDPE) with multiferroic bismuth ferrite (BiFeO3) nano-dielectric was successfully prepared via a solution-melt blending method. The structure, thermal, magnetic, as well as dielectric properties of the nano-dielectric were examined. The microstructures of LDPE/BiFeO3 were characterized by Fourier transform infrared, X-ray diffraction, and scanning electron microscopy. Microstructural analysis indicated that BiFeO3 nanoparticles were well dispersed in the LDPE matrix and the structure of LDPE was unchanged even after doping with BiFeO3 nanoparticles. The differential scanning calorimetry data of the thermal properties revealed that melting temperature has decreased and crystallinity has increased. The reason was that amount of nucleation agents was increased and crystal propagation rate was changed. The corresponding magnetic and dielectric properties were measured using vibrating sample magnetometer and broadband dielectric spectrometer. The results showed that the magnetization behaviour of diamagnetic LDPE was transformed due to the antiferromagnetism of BiFeO3. In addition, the dielectric permittivity and loss of LDPE/BiFeO3 increased with increasing BiFeO3 filler concentrations in the LDPE matrix due to different response mechanisms.

Electrical investigations of polyaniline/sulfonated polystyrene composites using broadband dielectric spectroscopy

Composites of polyaniline (PAni)/polystyrene sulfonic acid were prepared in different ratios using in-situ polymerization method. Characterization of the formed composites’ structures was performed using FTIR, XRD, UV–vis also their thermal stability was investigated. Extensive study for the dynamic relaxation and charge transport mechanisms of the prepared composites was carried out by broadband dielectric spectrometer (BDS). Dielectric measurements illustrate the effect of annealing on the conductivity mechanism of the composites. The moisture enhances the conductivity abruptly when the atmosphere is ambient air. The unusual behavior was explained as an effect of the water molecules in the composites that behaves like bridges. On the other hand, the parameter playing the main role in the charge transport (conductivity) was found to be the mobility rather than the charge carrier’s density. The obtained results indicate the possibility of commercial utility of the prepared composites as anti-static packaging, anticorrosion shielding or as semi-conductors.

Synthesis and Characteristic of Borazine-Silicon-Containing Arylacetylene Resin

Borazine-silicon-containing arylacetylene (PBZSA) resin was a novel organic inorganic hybrid polymer and prepared through condensation reaction among B,B’,B’’-trichloroborazine, dichlorosilane and arylacetylene Grignard reagent. The chemical structure of PBZSA resin was characterized by FT-IR and 1H NMR. The thermal stability and dielectric properties of cured PBZSA were investigated by TGA and broadband dielectric spectrometer. The results indicated that cured PBZSA showed high thermal stability with char yield up to 87.1% at 1000°C and at decompose temperature (Td5) 580°C, and low dielectric constant (2.8-2.9) and dielectric loss (<0.005).