Stability of new electrostatic discharge protection and electromagnetic wave shielding effectiveness from poly(vinyl chloride)/graphite/nickel nanoconducting composites

Poly(vinyl Chloride)/graphite nanosheet/nickel (PVC/GN) nancomposites are new alternative candidates for electrostatic charge dissipation and electromagnetic interference shielding applications due to their lightweight, ease processing and tunable conductivities. The structures of the nanocomposites were examined by means of scanning electron microscopy (SEM) and X-ray analysis. The mechanical properties such as hardness, modulus of elasticity and elongation at break as a function of GN content were examined. The applicability of the nanocomposites as electrostatic charge dissipation was tested in terms of displaying the variation of decay voltage with time. In addition, the dielectric properties such as real and imaginary permittivity of composites as functions of frequency were investigated. Finally, the electromagnetic properties were measured in the frequency range from 1 to 12 GHz and compared with theoretical modeling. The highest shielding effectiveness at microwave frequency of these nanocomposites was 47 dB which is realistic for defense applications like radar evasion.     

Impedance and electric modulus approaches to investigate four origins of giant dielectric constant in CaCu3Ti4O12 ceramics

The frequency dependence of electric modulus of polycrystalline CaCu₃Ti₄O₁₂ (CCTO) ceramics has been investigated. The experimental data have also been analyzed in the complex plane of impedance and electric modulus, and a suitable equivalent circuit has been proposed to explain the dielectric response. Four dielectric responses are first distinguished in the impedance and modulus spectroscopies. The results are well interpreted in terms of a triple insulating barrier capacitor model. Using this model, these four dielectric relaxations are attributed to the domain, domain-boundary, grain-boundary, and surface layer effects with three Maxwell–Wagner relaxations. Moreover, the values of the resistance and capacitance of bulk CCTO phase, domain-boundary, grain-boundary and surface layer contributions have been calculated directly from the peak characteristics of spectroscopic plots.     

Dielectric behavior of polyaniline synthesized by different techniques

Polyaniline doped with dodecylbenzenesulfonic acid (Pani.DBSA) was synthesized by different procedures: by a dedoping-redoping process, by one step inverted emulsion polymerization and by one step aqueous dispersion polymerization. The effect of these different techniques on the electric properties (dielectric constant, dielectric losses, and complex electric modulus) of the corresponding emeraldine base has been studied by thermal dielectric analyzer (DETA) in the temperature range −130 °C to 200 °C and in frequency range 0.03-10⁵ Hz. It was found that the preparation technique has significant influence on the dielectric properties of Pani. The different synthetic routes give rise to polyaniline with different distribution of electric relaxation process, indicating different chain structure. Emeraldine base from Pani.DBSA prepared by one step aqueous dispersion polymerization exhibits one single relaxation peak with narrow distribution whereas that prepared by inverted emulsion polymerization exhibits two relaxation peaks, indicating two-phase structure as indicated by a bimodal distribution of relaxation process. Emeraldine base from Pani.DBSA prepared by dedoping-redoping process presents an intermediary behavior. Percentage crystallinity of Pani.DBSA samples has also been investigated using wide-angle X-ray diffraction analysis. Pani.DBSA prepared by aqueous dispersion exhibited higher crystallinity degree, which agrees with the higher conductivity.     

Study of dielectric properties of styrene-acrylonitrile graphite sheets composites in low and high frequency region

Conducting polymer composites should have a high dielectric constant and a high dissipation factor in the low and high frequency regions if they are to be used in charge storing devices, decoupling capacitors and electromagnetic interference shielding applications. Currently, extensive research is being carried out to enhance the dielectric constants of graphite-polymer, ceramic powder-polymer, metal powder-polymer and nanotube-polymer composites in the low frequency region. In this paper, we present the dielectric properties of styrene-acrylonitrile (SAN)-graphite sheets (GS) composites in the low and high frequency ranges. SAN-GS composites were prepared by the mixing process and by the hot compression mold technique. The composites showed a high dielectric constant and a high dissipation factor in the low and radio frequency region. Furthermore, the EMI shielding properties of these composites are evaluated in the radio frequency range. The conductivity and the dielectric constant of the SAN/GS composites increased with the addition of GS composites, and followed the power law model of percolation theory. The dielectric constant and the dissipation factor of the composites were analyzed according to the low and high frequency region.     

Studies of structural,dielectric relaxor and electrical characteristics of lead-free double Perovskite:Gd2NiMnO6

In the current communication, structural, microstructural, dielectric, relaxor, impedance, AC conductivity, and electrical modulus characteristics of double perovskite Gd₂NiMnO₆ (synthesized by a solid state reaction route) as a function of temperature (25–125 °C) and frequency (1 kHz–1MHz) have mainly been reported. From preliminary X-ray structural analysis, it is found that the crystal structure of the material is monoclinic. In temperature dependence of dielectric constant analysis, relaxor behaviour of the material was observed. Such type of behaviour is described by modified Curie–Weiss law and a Vogel–Fulcher law. From Nyquist plots, the existence of grain and grain boundary effect in the material is observed. The non–Debye type of relaxation is confirmed from the complex impedance spectroscopy. From the impedance data, the determined grain resistance reduces with increment of temperature showing negative temperature co-efficient of resistance (NTCR)-type nature of the material which also confirmed from conductivity analysis. Again, non-Debye type of relaxation phenomena is observed from the analysis of modulus spectroscopy which is also proved by complex impedance plot. From these result it may be concluded that this material may be used for different high temperature applications.     

Dielectric and conducting behaviors in quasi-amorphous hybrid poly(diallyldimethylammonium phosphomolybdate)

A quasi-amorphous inorganic-organic hybrid solid, which is comprised of poly(diallyldimethylammonium) polyelectrolyte cations with phosphomolybdates and denoted as PDDA/PMA, was prepared and characterized using elemental analysis, powder x-ray diffraction, IR spectrum, thermal and energy dispersive X-ray analyses. The PDDA/PMA exhibits multistep dielectric anomalies and dielectric relaxations. The dielectric anomaly around 353 K arises partially from the water trapped in the PDDA/PMA network releasing. The PDDA/PMA was further dried under vacuum at 373 K to give water-free sample PDDA/PMA-1. With water being removed, the broad anomaly peak around 353 K in the ε′-T plot of PDDA/PMA changes into a platform in that of PDDA/PMA-1, indicating that the dielectric anomalies result from not only losing water but also the network disorder in PDDA/PMA-1. In addition, the platform strongly depends on the AC frequency in PDDA/PMA-1; the electric modulus and ion conductance analyses demonstrated that the dielectric relaxations at elevated temperature are related to the PMA ions displacing motion.     

Conductivity measurement and dielectric,impedance and modulus spectroscopic studies on bis (P-nitrophenol) melaminium monohydrate

The present work is aimed to study the dielectric and electrical characteristics of bis (P-nitrophenol) melaminium monohydrate (BNPM) over the temperature and frequency ranges of 333–453 K and 50 Hz–5 MHz, respectively. The dielectric properties such as dielectric constant (ε′), dielectric loss (ε″), ac-conductivity (σ_ac), real (M′) and imaginary part (M″) of dielectric modulus were investigated as a function of temperature and frequency. The impedance analysis has been carried out using Cole-Cole plots to elucidate the electrical conduction mechanism. Further, observations indicated that the grain boundaries are more resistive and capacitive than the grains, inducing inhomogeneity in the material, which, in turn, causes broad frequency-dependent dielectric anomalies. The observed frequency-dependence of the AC conductivity validated the Jonscher power law. Further, an asymmetric dispersion peak in the imaginary part of the electrical modulus (M”) was noticed, indicating that the fabricated material exhibits non-Debye relaxation behavior.     

Dielectric properties and frequency response of self-assembled monolayers of alkanethiols

This paper presents dielectric properties of alkanethiol self-assembled monolayers (SAMs) under an ac electric field. Using a Hg-SAM/SAM-Hg junction, we measured the ac impedance of alkanethiol SAMs using a sinusoidal perturbation of 30 mV (peak-to-peak) with frequency ranging from 1 Hz to 1 MHz at zero bias. Semicircles at higher frequencies and at middle frequencies along with Warburg lines at lower frequencies were observed in complex plane impedance plots, that is, Nyquist plots. The frequency response of SAMs was analyzed by modeling the junction using an equivalent circuit and fitting the Nyquist plots. The semicircles at higher frequencies are attributed to the effect of the SAM/SAM interfaces, and the ones at middle frequencies are attributed to the effect of alkanethiol SAMs. The comparison in the plots of the imaginary part of the impedance Z against frequency for the bare Hg electrodes (in pure ethanal) and the SAM-covered Hg electrodes (in alkanethiol solution) supports the analysis. The Warburg lines are attributed to a certain ionic impurity. The dielectric loss spectra are further analyzed. Chain-length-dependent peaks, which correspond to different relaxation mechanisms, at higher frequencies and middle frequencies were observed in the spectra of the dissipation factor (tan delta vs frequency). The peaks move to small frequency with the increase of chain length of alkanethiols. Using a correlation of peak position with the chain length, we then derived active energies of 39-99 meV for alkanethiol SAMs of C7-C18 under an ac electric field.     

Dielectric and impedance properties of Sr(Sm0.5Nb0.5)O3 ceramics

Perovskite types Sr(Sm_0.5Nb_0.5)O₃, (SSN) ceramics have been prepared through solid state reaction route. The scanning electron microscopy provides information on the quality of the samples and uniform grain distribution over the surface of the samples. The field dependence of the dielectric response was measured in a frequency range from 50 Hz to 1 MHz and in a temperature range from 60 °C to 420 °C indicates polydispersive nature of the materials. An analysis of the dielectric constant (?′) and tangent loss (tanδ) with frequency is performed assuming a distribution of relaxation times as confirmed by the scaling behavior of electric modulus spectra. The frequency dependence of the electric modulus peak is found to obey Arrhenius law with activation energy of ∼0.026 eV. The complex plane impedance plot shows the grain boundary contribution for higher value of dielectric constant in the law frequency region. The frequency dependence of electrical data is also analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behavior of imaginary part of electric modulus M″ suggests that the relaxation describes the same mechanism at various temperatures in SSN.     

Study of electrical and dielectric properties of styrene-acrylonitrile/graphite sheets composites

This paper reports the structural, electrical, dielectric and mechanical properties of the Styrene-acrylonitrile (SAN)/graphite sheets (GS) composites. The composites were prepared by in situ polymerization. The variation of electrical conductivity, dielectric constant and ac conductivity as a function of volume fraction of GS was found to follow the power law model. The dielectric constant and dissipation factor of SAN/GS composites increased significantly near the percolation. The frequency dependence of dielectric constant, dissipation factor and ac conductivity was also analyzed. Nearly ohmic behavior of current density with electric field was observed above the percolation threshold. The composite was found to possess the hardness of pure polymer at the threshold value of GS.     

Dielectric properties of FeNbO4 ceramics prepared by the sol-gel method

In this work, FeNbO₄ powders were prepared using the sol-gel method. The fine powder particles were pressed into pellets and sintered at temperatures between 500 and 1200 °C. The powder was studied by X-ray diffraction and Raman spectroscopy. The morphology of the grains was investigated by scanning electron microscopy. Heat-treatment of the particles results in higher crystallinity, larger grains, and a decrease in the porosity of the material.The dielectric properties were measured in the frequency range of 10²–10⁶ Hz, in function of temperature (200–370 K). In all samples the real (ε′) and imaginary (ε″) parts of the complex permittivity increase with increasing annealing temperature. The sample heat treated at 1200 °C shows the highest ε′, > 10⁴ at 300 K. All samples show a dielectric relaxation phenomenon, analysed using the modulus formalism. The evolution of the ac conduction activation energy and of the activation energy associated with the relaxation mechanism, is directly related with the changes promoted by the heat treatment in the structure and in the morphology of the base powders.     

Chloride Assisted Growth of Aluminum Nitride Nanobelts and Their Enhanced Dielectric Responses

Aluminum nitride (AlN) nanobelts were successfully synthesized in high yield through a chloride assisted vapor-solid process. X-ray diffraction, transmission electron microscopy, and selected area electronic diffraction demonstrate that the as-prepared nanobelts are pure, structurally uniform and single crystalline, and can be indexed to hexagonal wurtzite structure. The micro observations show that there exist no defects in the obtained nanobelts. The growth direction of the nanobelts is along 0001. The frequency spectra of the relative dielectric constant and of the dielectric loss were measured in the frequency range of 50 Hz to 5 MHz. Analysis of these spectra indicates that the interface in samples has great influence on the dielectric behavior of samples. As compared with AlN micropowders, AlN nanobelts have much higher relative dielectric constant, especially at low frequencies at room temperature.     

Investigation of MWS polarization and dc conductivity in polyamide 610 using dielectric relaxation spectroscopy

Dielectric relaxation spectroscopy technique was employed to study the Maxwell–Wagner–Sillars (MWS) polarization and dc conductivity in polyamide 610. The experimental dielectric data were analyzed within the formalisms of complex permittivity and electric modulus. The results were discussed in terms of ac conductivity, MWS polarization, electrode polarization and dc conductivity. In the frequency spectra of polyamide 610, charge carriers movement resulted in high values of the dielectric permittivity. The results revealed that the motion of the polymer chains governs the charge carrier transport. Two different mechanisms for charge carrier movement showed a transition temperature located between 110 and 120 °C. The change of charge carrier movement mechanisms was resulted from the onset of the polymeric chains in the interphase between amorphous and crystalline phases.     

Dielectric relaxation processes and ionic conduction behaviour in poly(ethylene oxide)–montmorillonite clay nanocomposite aqueous colloidal suspensions

The relative complex dielectric function, electric modulus, alternating current (ac) electrical conductivity and complex impedance spectra of poly(ethylene oxide) (PEO)–montmorillonite (MMT) clay aqueous colloidal suspension (hydrocolloids) were investigated over the frequency range 20 Hz to 1 MHz at 27 °C. The relaxation time corresponding to electrode polarisation and Maxwell–Wagner polarisation processes (ionic conduction) were determined from these plots. The direct current (dc) electrical conductivity is evaluated from the fitting of real part ac conductivity data to the Jonscher power law. A correlation of increase in dc conductivity and decrease of ionic conduction relaxation time with increase of clay concentration is discussed considering intercalation of PEO chains and its dynamics and exfoliation of MMT clay nanoplatelets in these complex fluids. The formation of PEO–MMT clay supramolecular lamellar nanostructures with increase in continuity of lamellae arrangements were explored for the structural conformation of these nanocomposite novel materials.     

Facile Fabrication of PBS/CNTs Nanocomposite Foam for Electromagnetic Interference Shielding

In order to reduce the pollutants of environment and electromagnetic waves, environment friendly polymer foams with outstanding electromagnetic interference shielding are imminently required. In this paper, a kind of electromagnetic shielding, biodegradable nanocomposite foam was fabricated by blending poly (butylene succinate) (PBS) with carbon nanotubes (CNTs) followed by foaming with supercritical CO₂. The crystallization temperature and melting temperature of PBS/CNTs nanocomposites with 4 wt % of CNTs increased remarkably by 6 °C and 3.1 °C compared with that of pure PBS and a double crystal melting peak of various PBS samples appeared in DSC curves. Increasing the CNT content from 0 to 4 wt % leads to an increase of approximately 3 orders of magnitude in storage modulus and nearly 9 orders of magnitude in enhancement of electrical properties. Furthermore, CNTs endowed PBS nanocomposite foam with adjustable electromagnetic interference (EMI) shielding property, giving a specific EMI shielding effectiveness of 28.5 dB cm³/g. This study provides a promising methodology for preparing biodegradable, lightweight PBS/CNTs foam with outstanding electromagnetic shielding properties.     

锰掺杂Ba0.6Sr0.4TiO3-MgTiO3复相陶瓷的制备和介电性能

以分析纯的Ba(NO3)2、Sr(NO3)2、草酸和钛酸丁酯为原料, 采用草酸盐共沉淀法制备了钛酸锶钡（Ba0.6Sr0.4TiO3, BST）纳米粉体. XRD和SEM分析结果表明, 该方法制备出立方相的Ba0.6Sr0.4TiO3粉体, 平均粒径小于100 nm, 具有较高的烧结活性. 用传统固相法制备了锰掺杂钛酸锶钡-钛酸镁(Ba0.6Sr0.4TiO3-MgTiO3, BST-MT)复相陶瓷, 系统研究了掺杂0.1%-2.0%(x, 摩尔分数, 下同)锰对钛酸锶钡-钛酸镁复相陶瓷微观形貌和介电性能的影响机理. 结果表明, 当锰的掺杂量小于1.5%时, Mn作为受主掺杂取代占据钙钛矿ABO3的B位, 因此导致居里点略微向高温偏移和相变扩散的发生, 锰的掺杂导致晶格畸变, 促进了晶粒生长, 使晶界相比例下降, 因此介电损耗随着锰掺杂量的增大而减小; 当锰的掺杂量为1.5%时, 介电损耗达到最小值, 继续增大掺杂量, 介电常数下降, 介电损耗上升.     

锰掺杂Ba0.6Sr0．4TiO3-MgTiO3复相陶瓷的制备和介电性能

以分析纯的Ba(NO3)2、Sr(NO3)2、草酸和钛酸丁酯为原料,采用草酸盐共沉淀法制备了钛酸锶钡(Ba0.6Sr0.4tiO3,BST)纳米粉体.XRD和SEM分析结果表明,该方法制备出立方相的Ba0.6Sr0.4TiO3粉体,平均粒径小于100 nm,具有较高的烧结活性.用传统固相法制备了锰掺杂钛酸锶钡.钛酸镁(Ba0.6Sr0.4TiO3-MgTiO3,BST-MT)复相陶瓷,系统研究了掺杂0.1%-2.0%(x,摩尔分数,下同)锰对钛酸锶钡-钛酸镁复相陶瓷微观形貌和介电性能的影响机理.结果表明,当锰的掺杂量小于1.5%时,Mn作为受主掺杂取代占据钙钛矿ABO3的B位,因此导致居里点略微向高温偏移和相变扩散的发生,锰的掺杂导致晶格畸变,促进了晶粒生长,使晶界相比例下降,因此介电损耗随着锰掺杂量的增大而减小;当锰的掺杂量为1.5%时,介电损耗达到最小值,继续增大掺杂量,介电常数下降,介电损耗上升.     

Preparation and Electromagnetic Properties of Composites of Hollow Glass Microspheres Coated with NiFe2O4 Nanoparticles

"The composites of hollow glass microspheres coated with NiFe2O4 nanoparticles were prepared using polyacrylamide gel method. The structural characteristics, morphology and electromagnetic properties of the composite powders with different weight percent of glass microspheres (15%, 40%, and 65%) were obtained by X-ray diffraction, scanning electron microscope, infrared spectroscopy and HP8510 network analyzer. The results indicated that the phase structure of composite powders was the mixtures of nickel ferrite, quartz, and mullite. The peak intensity for nickel ferrite decreased rapidly and for mullite increased remarkably with the increasing amount of microspheres. A pure spinel structure of NiFe2O4 formed on the glass microspheres at 600 oC. A uniform and continuous NiFe2O4-coating was obtained when the content of microspheres was 40%. A great amount of NiFe2O4 particle size is less than 80 nm. The composite with a content of 40% microspheres exhibits better dielectric and magnetic loss properties which are useful to absorb more electromagnetic wave. It can be a kind of good and light electromagnetic wave absorbing material in the X-band."     

离子交换树脂悬浊液的介电弛豫谱研究

研究了D354阴离子交换树脂分散在不同浓度KCl溶液中的悬浊液的频率域介电谱,发现在测量频率为106～107 Hz处出现了显著的介电弛豫现象,得出了介电常数、电导率以及弛豫时间随KCl溶液浓度的特异的变化关系,理论分析表明,该弛豫是一个以界面极化为主的非单一极化机制的弛豫过程,进而利用Maxwell-Wagner界面极化理论和双电层性质解释了该体系的特异介电行为,得到了树脂悬浊液在外加交变电场下的离子迁移和聚集信息,并确定了该树脂在静态平衡下双电层中对离子的相对离子强度.     

Hydrothermal Synthesis and Dielectric Characterization of a Double Perovskite Ba2FeSbO6

A double perovskite oxide Ba₂FeSbO₆ was hydrothermally synthesized and structurally characterized by X-ray diffraction. This solid compound shows a single phase and has a trigonal structure with space group R m and cell parameters of a=0.57261 nm and c=1.40244 nm. The dielectric constant and loss tangent of the solid measured in a frequency range from 100 Hz to 1 MHz at temperatures from 313 K to 513 K reveal a relaxation process of frequency dependence of the real part(ε') of dielectric constant and dielectric loss tand. The frequency dependence of electrical property led to the framework of conductivity and electric modulus formalisms. The scaling behavior of imaginary part of electric modulus suggests that the relaxation describes the single mechanism at various temperatures. The variation tendency of the alternating current impedance indicates the thermally activated conduction process follows Jonsche’s power law.