氧化剂对聚吡咯复合材料介电性能的影响

为了探究氧化剂对聚吡咯复合材料介电性能的影响,以吡咯为单体,采用原位聚合法制备了聚吡咯涂层复合材料。通过BDS50介电谱仪研究了氧化剂种类和氧化剂物质的量浓度对复合材料介电常数实部、虚部、损耗角正切、表面电阻的影响;采用Quanta200型环境扫描电子显微镜和Instron万能材料试验机研究了聚吡咯涂层复合材料的外观形貌和强度。结果表明:氧化剂种类、氧化剂浓度对聚吡咯涂层复合材料介电常数实部、虚部、损耗角正切、表面电阻影响较大;制备的聚吡咯涂层复合材料既具备良好的介电性能和导电性,又兼具良好的强度.     

聚吡咯涂层织物的介电性能研究

采用原位聚合法以棉机织物、尼龙为基布,以吡咯为单体,制备了具有良好介电性能的柔性聚吡咯涂层棉织物和聚吡咯涂层尼龙织物,探讨了掺杂剂种类、掺杂剂浓度对聚吡咯涂层棉织物、聚吡咯涂层尼龙织物介电性能和表面电阻的影响.结果表明,掺杂剂对聚吡咯复合材料的介电性能和表面电阻的影响较大.所制备的聚吡咯涂层棉织物、聚吡咯涂层尼龙织物均具备良好的介电性能和导电性,为最终开发出较为实用的多功能吸波复合材料奠定了基础.     

Electrorheological and dielectric properties of polypyrrole dispersions

The electrorheological (ER) response and dielectric properties of the polypyrrole (PPy) dispersions in mineral oil were investigated. Various PPy particles were synthesized controlling the amount of oxidant and surfactant to investigate the effect of these variables on the ER response. The ER response increases with the oxidant and surfactant amount, passes through a maximum, and then decreases with the oxidant and surfactant amount. However, the decrease in the ER response at large surfactant amounts is not so significant compared to that at large oxidant amounts. The increase in the ER response with the oxidant and surfactant amount arises from the enhanced particle polarization originated from the increased PPy conductivity. The decrease in the ER response at large oxidant amounts seems to arise from the increased conduction between the PPy particles, while that at large surfactant amounts arises from the decreased particle polarization.     

Large dielectric constant in zirconia polypyrrole hybrid nanocomposites

Zirconia nanoparticles have been synthesized by a novel two-reverse emulsion technique and combined with polypyrrole (PPY) to form ZrO2-PPY nanocomposites. Complex impedance and dielectric permittivity of ZrO2-PPY nanocomposite have been investigated as a function of frequency and temperature for different compositions. The composite samples are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy. The composites reveal ordered semiconducting behaviour. Polypyrrole is the major component in electrical transport process of the samples. A very large dielectric constant of about 12,000 at room temperature has been observed. The colossal dielectric constant is mainly dominated by interfacial polarization due to Maxwell-Wagner relaxation effect. Two completely separate groups of dielectric relaxation have been observed. The low frequency dielectric relaxation arises from surface defect states of zirconia nanoparticles. The broad peak at high frequency is due to Maxwell-Wagner type polarization.     

Effect of conducting polypyrrole on the transport properties of carbon nanotube yarn

Experiments were conducted to measure the electrical conductivity in three types of pristine and carbon nanotube-polypyrrole (CNT-PPy) composite yarns and its dependence on over a wide temperature range. The experimental results fit well with the analytical models developed. The effective energy separation between localized states of the pristine CNT yarn is larger than that for both the electrochemically and chemically prepared CNT-PPy yarns. It was found that all samples are in the critical regime in the insulator-metal transition, or close to the metallic regime at low temperature. The electrical conductivity results are in good agreement with a Three Dimensional Variable Range Hopping model at low temperatures, which provides a strong indication that electron hopping is the main means of current transfer in CNT yarns at T < 100 K. We found that the two shell model accurately describes the electronic properties of CNT and CNT-PPy composite yarns in the temperature range of 5-350 K.     

Effect of water on the dielectric behavior of solder

Journal of Materials Science: Materials in Electronics - The electrical conduction behavior of solder is well-known, but the dielectric behavior has been reported only recently. Water in the...     

High-temperature dielectric response of ferroelectric relaxors

It has long been considered that polar nanoregions in relaxors form at Burns temperature T(d) ≈ 600K. High-temperature dielectric investigations of Pb(Mg(1/3)Nb(2/3)) O(3) (PMN) single crystal, PMN-PbTiO(3) ceramics, and (Pb,La) (Zr,Ti)O(3) ceramics reveal, however, that dielectric dispersion, detected around 600K, is due to the Maxwell-Wagner-type contributions of surface layers. The intrinsic response was analyzed in terms of the universal scaling, taking into account the asymptotic and the correction-to-scaling behavior, and the results imply much higher T(d) or formation of polar nanoregions in a broad temperature range. High values of the dielectric constant indicate, however, that polar order already exists at the highest measured temperatures of 800K. The obtained critical exponents indicate critical behavior associated with universality classes typically found in spin glasses.     

Pulse response functions of dielectric susceptibility

As dielectric response in the time domain is becoming increasingly of experimental relevance and as such responses for quite a number of well-established susceptibility formulae are still unknown, we examine in this paper how pulse response functions may be calculated from susceptibility by use of various integral transform methods. We need to specialize some parameters in many cases to keep the mathematics sufficiently tractable. The asymptotic behaviour of pulse responses are then classified. Finally we comment on the adequacy of the Shin-Yeung response in the time domain.     

Effect of protein additive on properties of mortar

Test results presented in the article describe the impact of a protein additive (powdered red blood cells) on selected physical properties of cement paste, fresh mortar and physical and mechanical properties of hardened mortar. The protein additive is achieved as a result of industrial processing of animal blood. The research was made in the laboratory of the Institute of Structural Engineering of Poznan University of Technology.The analysis of the test results achieved showed that the protein included in the preparation added to the mortar leads to intensive air entraining, which has a significant effect on the most basic of physical properties both of the fresh mortar (consistence, plasticity, volumetric density) and hardened mortar (bending strength, shrinkage, volumetric density and frost resistance). The intensity of this influence, calculated in relation to the mass of the protein preparation added to the mortar, for most of the tested properties, is much higher than in the case of currently used air entraining agents [Chatterji S. Freezing of air-entrained cement-based materials and specific actions of air-entraining agents. Cem Concr Compos 2003;25:759–65, Du Lianxiang, Folliard KJ. Mechanisms of air entrainment in concrete. Cem Concr Res 2005;35:1463–71, Neville AM. Properties of concrete. 4th and final ed. London: Longman Group Limited, 1995. p. 844].     

The effect of air humidity on the dielectric response of poly-p-xylylene-titania nanocomposites

The dependence of the dielectric relaxation parameters of poly-p-xylylene-titania nanocomposites on relative air humidity is studied. A model of the existence of three different mechanisms of dielectric response in the studied systems is proposed. It is shown that the synthesized nanocomposites can be used for preparation of humidity sensors.     

Microwave transmission,reflection and dielectric properties of conducting and semiconducting polypyrrole films and powders

Microwave transmission, reflection and some dielectric properties of the conducting polymer, polypyrrole, are presented. Methods are discussed for determining microwave transmission and reflection of electrochemically synthesized and doped polypyrrole films with conductivities ranging from 0.1–5000 S m⁻¹. Polypyrrole films were placed between waveguides and irradiated with microwaves centred at frequencies 2.45 and 10 GHz with 0.1 GHz span. The results indicate that the conductivity of doped polypyrrole films has a significant effect on both transmission and reflection. Microwave opacity of polypyrrole varied with the synthesis conditions of the polymer. Samples with low conductivity exhibited high transmission whereas low transmission readings were observed with highly conducting films. Dielectric properties are also presented for frequencies from 100 to 10⁶ Hz in a temperature range of 90–280 K and at microwave frequencies of 2.45 and 10 GHz. These measurements indicate that the real and imaginary parts of the dielectric constant increase in magnitude with increasing doping level.     

The structural,dielectric and magnetic study of cobalt based spinel ferrites and polypyrrole composites

The CoFe₂O₄ was prepared via co-precipitation route, and in situ polymerization was used to prepare the polypyrrole, for the fabrication of nanocomposite. Two-point probe techniques, X-ray diffraction (XRD), as well as vibrating sample magnetometer (VSM) were used to investigate the electrical, magnetic, and structural characteristics of all the synthesized samples. In nanocomposites with higher ferrite concentrations, XRD peaks became more intense, and their widths becomes narrowed. The ferrite content enhanced the dc resistivity as well activation energy of the materials. The hysteresis loop identified the ferromagnetic property. The super paramagnetic behavior has been observed in samples PF1 (with 25% ferrites) and PF2 (having 50% ferrite ratio). These two samples might be employed in hyperthermia, which is a cancer therapy approach.

     

Experimental investigation on performance of additive mixed dielectric during micro-electric discharge drilling on 316L stainless steel

This study investigates the impact of machining factors on the performance of additive mixed micro-electric discharge drilling of 316L stainless steel. The effects of three kinds of powder, powder concentration, voltage, capacitance, feed rate, and speed on tool wear rate, material removal rate, taper angle, and overcut (OC) were also investigated. The experimental results show that adding additives to the dielectric enhanced rate of material removal and reduced rate of tool wear significantly. Mixing powder with dielectric increased the length of the sparking, resulting in significant OC, and process performance also improved with the increase in amount of powder added. Further, scanning electron microscopy analysis was carried out to examine the surface characteristics and material migration properties, which confirmed that the properties of the machined surface are indeed significantly improved.     

The dielectric response of doped semiconducting glasses

Measurements are reported of the dielectric properties of two semiconducting glasses of composition SiO₂ · Na₂O with admixtures of Sb_{2O 5} and SnO₂, covering a wide range of temperatures and a range of six decades of frequency 10^–2 to 10⁴ Hz. Both glasses show a gradual evolution of growing low frequency dispersion (LFD) with increasing temperature, with both the real and imaginary components of the complex susceptibility following a power law of the type ^n–1, with n 1 at the lowest frequencies. There are also clear indications of reversible phase transitions taking place which manifest themselves by changes in the spectral shape of the dielectric response.