Novel 1–3 metal nanoparticle/polymer composites induced by hybrid external fields

We reported a novel 1–3 nanocomposite consisting of carbon-coated nickel (Ni@C) nanoparticles and epoxy resin matrix, in which nanoparticles were found one-dimensional-aligned by applying hybrid electric and magnetic fields during the curing of resin. The alignment was explained based on the dipole–dipole interaction between Ni@C nanoparticles under external fields. The dc resistivity, dielectric constant and dielectric loss of composites were tested as the function of the loading content and external fields. The results show the resistivity of aligned composites decreases by 3–4 orders of magnitude than that of random composites in the loading content range of 3–10 wt%, accompanied with an increase in dielectric constant and dielectric loss. Specially, it deserves to note that the synergistic effect of electric field and magnetic field was observed.     

Enhanced thermal conductivity in polymer composites with aligned graphene nanosheets

We developed highly aligned graphene nanosheets (GNSs) in epoxy composites with incorporating magnetic GNS–Fe₃O₄ hybrids under a magnetic field with the aim to take full advantage of the high inplane thermal conductivity of graphene. GNS–Fe₃O₄ hybrids were fabricated by a simple coprecipitation method, and their morphology, chemistry, and structure were characterized. GNS–Fe₃O₄ hybrids were found to be homogenously dispersed and well aligned through the direction of the magnetic field in the epoxy matrix, as confirmed by SEM observation and Raman spectra analysis. The resulting epoxy/GNS–Fe₃O₄ composites possessed high thermal conductivity in a parallel magnetic-alignment direction at low GNS–Fe₃O₄ loadings, which greatly outperformed the composites with randomly dispersed bare GNSs. The obtained results indicated that the magnetic alignment of magnetic-functionalized GNSs is an effective way for greatly improving the thermal conductivity of the graphene-based composites.     

The enhanced microwave absorption property of CoFe(2)O(4) nanoparticles coated with a Co(3)Fe(7)-Co nanoshell by thermal reduction

CoFe(2)O(4) nanoparticles were fabricated by a sol-gel method and then were coated with Co(3)Fe(7)-Co by means of a simple reduction process at different temperatures under 2% H(2) with the protection of argon to generate the dielectric-core/metallic-shell structure. The optimum reflection loss (RL) calculated from permittivity and permeability of the 80 wt% CoFe(2)O(4)/Co(3)Fe(7)-Co and 20 wt% epoxy resin composites reached - 34.4 dB, which was much lower than that of unreduced CoFe(2)O(4) and epoxy resin composites, at 2.4 GHz with a matching thickness of 4.0 mm. Moreover the RL exceeding - 10 dB in the maximum frequency range of 2.2-16 GHz was achieved for a thickness of composites of 1.0-4.5 mm with 600?°C thermal reduction process. The improved microwave absorption properties are a consequence of a proper electromagnetic match and the enhanced magnetic loss besides its dielectric loss due to the existence of the core/shell structure in CoFe(2)O(4) composites. Thus, the reductive CoFe(2)O(4) nanoparticles have great potential for being a highly efficient microwave absorber.     

Electrical and thermophysical properties of epoxy/aluminum nitride nanocomposites: Effects of nanoparticle surface modification

The traditional epoxy resin used for electrical and electronic industry has a poor thermal conductivity and no longer meets the increasingly cooling requirements of electric equipments and electronic devices. Ceramic nanoparticles with high thermal conductivity and low dielectric constant represent good candidates to improve the thermophysical properties of epoxy resin. This paper reports the effects of surface modification of AlN nanoparticles on morphology, glass transition, electrical property and thermal conductivity of the epoxy composites. Gamma-aminopropyl triethoxysilane was used as a silane coupling agent for the surface modification of the AlN nanoparticles. It was found that the surface modification of the nanoparticles not only improved the dispersion of the nanoparticles, but also showed an enhancement in electrical and thermophysical properties of the epoxy composites. The surface modification technology presented a strategy to prepare nanocomposites having high thermal conductivity simultaneously with low dielectric loss.     

石墨/碳化硅/铁氧体涂层复合材料性能研究

为了开发具备良好介电性能和力学性能的多功能吸波复合材料,以涤纶针织物为基布,以环氧树脂为基体,在基布上进行石墨/碳化硅/铁氧体三层复合涂层整理,制备1.5 mm涂层厚度的柔性纺织涂层复合材料.采用介电谱仪研究了吸波剂的含量对吸波涂层材料介电常数和损耗角正切的影响.鉴于该材料多用于工程领域,采用万能材料实验机测试了该复合材料的拉伸、弯曲、剪切等力学性能.结果表明,该复合材料在低频段具备良好的介电性能,且具备一定的力学性能.     

Polymer matrix,polymer ribbon-reinforced transparent composite materials

Composites of a polymer–matrix reinforced by polymer ribbon monofilaments are investigated as mechanically robust, transparent composite materials. Transparent nylon monofilaments are mechanically worked to form flattened nylon ribbons, which are then combined with index-matched epoxy resin to create transparent composites. A range of optical and mechanical experiments are performed on composites and surrogate systems in order to quantify properties and guide system design. The results show that these polymer–polymer composites provide good transparency over a wide temperature range, and superior ballistic penetration resistance compared to monolithic transparent polymers.     

Dielectric and magnetic response of Fe3O4/epoxy composites

Magnetic and dielectric properties of Fe₃O₄/epoxy resin composites were studied as a function of Fe₃O₄ concentration. The Fe₃O₄ powder was milled using a planetary ball-mill in order to reduce the particle size. B.E.T. area of these particles was determined, and a structural characterization was performed by X-ray diffraction (XRD). Fe₃O₄/epoxy composites were prepared mixing the raw materials and pouring them into suitable moulds. Dielectric measurements were performed at different frequencies and temperatures, while magnetic properties were assessed at different temperatures. It was found that permittivity was strongly dependent on the filler concentration and frequency. Maxwell–Wagner–Sillars interfacial polarization, Intermediate Dipolar Polarization (IDE), and α relaxation process were responsible for the observed behavior. Magnetic measurements revealed the presence of magnetite nanoparticles in the composites, with a blocking temperature close to 170 K.     

Optimum mixing ratio of epoxy for glass fiber reinforced composites with high thermal stability

The optimum condition of glass fiber/epoxy composites was investigated according to mixing ratio of two epoxy matrices. Novolac type epoxy and isocyanate modified epoxy were used as composites matrix. Based on chemical composition of mixing matrix, optimum mixing ratio of epoxy resins was obtained through FT-IR instrument. In order to investigate thermal stability and interface of epoxy resin, glass transition temperature was observed by DSC instrument, and static contact angle was measured by reflecting microscope. Change of IR peak and T_g was conformed according to different epoxy mixing ratios. After fabrication of glass fiber/epoxy composites, tensile, compression, and flexural properties were tested by UTM by room and high temperature. The composites exhibited best mechanical properties when epoxy mixing ratio was 1:1.     

Microwave Absorption of Crystalline Fe/MnO@C Nanocapsules Embedded in Amorphous Carbon

Crystalline Fe/MnO@C core–shell nanocapsules inlaid in porous amorphous carbon matrix(FMCA)was synthesized successfully with a novel confinement strategy.The heterogeneous Fe/MnO nanocrystals are with approximate single-domain size which gives rise to natural resonance in 2–18 GHz.The addition of MnO2 confines degree of graphitization catalyzed by iron and contributes to the formation of amorphous carbon.The heterogeneous materials composed of crystalline–amorphous structures disperse evenly and its density is significantly reduced on account of porous properties.Meanwhile,adjustable dielectric loss is achieved by interrupting Fe core aggregation and stacking graphene conductive network.The dielectric loss synergistically with magnetic loss endows the FMCA enhanced absorption.The optimal reflection loss(RL)is up to−45 dB,and the effective bandwidth(RL<−10 dB)is 5.0 GHz with 2.0 mm thickness.The proposed confinement strategy not only lays the foundation for designing high-performance microwave absorber,but also offers a general duty synthesis method for heterogeneous crystalline–amorphous composites with tunable composition in other fields.     

A review on carbon/magnetic metal composites for microwave absorption

At present,developing high-efficiency microwave absorption materials with properties including light-weight,thin thickness,strong absorbing intensity and broad bandwidth is an urgent demand to solve the electromagnetic pollution issues.An ideal microwave absorber should have excellent dielectric and magnetic loss capabilities,thereby inducing attenuation and absorption of incident electromagnetic radiation.Recently,various carbon/magnetic metal composites have been developed and expected to become promising candidates for high-performance microwave absorbers.In this review,we introduce the mechanisms of microwave absorption and summarize the recent advances in carbon/magnetic metal composites.Preparation methods and microwave absorption properties of carbon/magnetic metal com-posites with different components,morphologies and microstructures are discussed in detail.Finally,the challenges and future prospects of carbon/magnetic metal absorbing materials are also proposed,which will be useful to develop high-performance microwave absorption materials.     

磁功能化石墨烯改性环氧树脂及其复合材料的性能

先以氧化石墨烯和三氯化铁为原料并用高温水热法制备还原氧化石墨烯/ Fe₃O₄(rGO/Fe₃O₄)复合物,再用其改性环氧树脂制备出rGO/Fe₃O₄/环氧树脂复合材料,研究了(rGO/Fe₃O₄)复合物的添加对其性能的影响。结果表明,(rGO/Fe₃O₄)复合物的添加量为30%的复合材料其冲击强度达到27 kJ/m²,比纯环氧树脂的冲击强度提高了58.8%。在环氧树脂中添加rGO/Fe₃O₄复合物,使其吸波性能显著提高。rGO/Fe₃O₄复合物的添加量为20%的复合材料,其反射率在小于-10 dB的频率范围为7.7~12.3 GHz,有效吸收频宽达4.6 GHz,覆盖了整个X波段。随着石墨烯含量的提高rGO/Fe₃O₄/环氧树脂复合材料达到最小反射率的位置向低频位置移动,控制rGO和Fe₃O₄的相对含量可调控这种复合材料的吸波性能。     

The influence of heat treatment and finishing on the mechanical and dielectric properties of glass fabric-epoxy resin laminar composites

The aim of this investigation was to define the optimum conditions of obtaining glass fabric-epoxy resin laminar composites with mechanical and dielectric properties that satisfy the quality needed for production of printed circuit boards for microelectronics. Commercial materials: glass woven fabric, different types of silane finish and epoxy resin were the starting materials in obtaining composites. The conditions needed for the thermal removal of the original size from glass fabric were investigated. The optimal heat treatment should be performed at temperatures less than 550 °C, while cooling rates should be as low as possible. In this manner, the fabric has less than 0.1% of residual size, and the mechanical properties remain satisfactory. Different types of adhesion promoters based on silanes were applied on heat-treated glass fabric as finishes. The quality of the composite material made of thermally and chemically treated glass fabric and epoxy resin was controled by measuring the tensile and dielectric strength of the composite. Depending on which properties of composite are of primary concern, mechanical or dielectric, a finish with an amino functional group and lower heat-treatment temperature or epoxy-modified coatings and higher heat-treatment temperature should be used for obtaining glass-fabric epoxy resin laminar composites.     

Comparison of theoretical predictions and experimental values of the dielectric constant of epoxy/BaTiO<Subscript>3</Subscript> composite embedded capacitor films

Polymer/ceramic composites are the most promising embedded capacitor material for organic substrates application. Predicting the effective dielectric constant of polymer/ceramic composites is very important for design of composite materials. In this paper, we measured the dielectric constant of epoxy/BaTiO₃ composite embedded capacitor films with various BaTiO₃ particles loading for 5 different sizes BaTiO₃ powders. Experimental data were fitted to several theoretical equations to find the equation useful for the prediction of the effective dielectric constant of polymer/ceramic composites and also to estimate the dielectric constant of BaTiO₃ powders. The Lichtenecker equation and the Jayasundere-Smith equation were useful for the prediction of the effective dielectric constant of epoxy/BaTiO₃ composites. And calculated dielectric constants of the BaTiO₃ powders were in the range of 100 to 600, which were lower than the dielectric constant of BaTiO₃ bulk ceramics probably due to the presence of voids or pores.     

碳纳米管的偶联剂修饰及其在环氧树脂复合材料中的应用

为了在环氧树脂( EP) 复合材料中改善碳纳米管(CNTs) 的分散性和获得优良的界面特性, 利用Fenton 试剂对CNTs 进行了羟基化处理, 然后分别利用硅烷偶联剂KH550、KH560、KH570 和钛酸酯偶联剂NDZ201对羟基化CNTs 进行表面修饰, 通过SEM、TGA、DSC 和阻抗分析仪研究偶联剂修饰对CNTs/ EP 复合材料性能的影响。实验结果表明: Fenton 试剂和4 种偶联剂修饰都能显著改善CNTs 在复合材料中的分散性, 提高EP的玻璃化温度(T_g) 和热稳定性, 其中偶联剂修饰比Fenton 试剂处理更有效; 然而这些改性却大幅度降低了复合材料的导电性能、介电常数以及介电损耗。4 种偶联剂中, KH560 对应的复合材料的T_g最高, 热稳定性和导电性能最好, 同时具有较高的介电常数和较低的介电损耗。      

Flexural and interlaminar shear strength properties of carbon fibre/epoxy composites cured thermally and with microwave radiation

The ease of heating an epoxy resin with microwaves depends, among other factors, on the dielectric properties of its components at the frequency of the radiation used. The majority of the papers published on the microwave curing of reinforced epoxy resin composites have used widely available DGEBA type resins and amine hardeners such as 4,4′-diaminodiphenylsulphone (DDS). This paper investigates the use of two epoxy systems where the choice of resin and hardener was based on their measured dielectric loss factors. System 1 contained a resin and hardener with higher loss factors than those used in System 2. The two systems are formulated with polyetherimide (PEI) as a toughening agent. Unidirectional carbon fibre prepregs were prepared from both systems. Composites were laid up from these prepregs, which were then cured in three different ways: autoclave curing, partial autoclave curing followed by microwave post-curing, and microwave curing. System 1 composites had greater flexural properties and interlaminar shear strengths than System 2 composites when autoclave cured. Flexural properties and interlaminar shear strengths were greater for System 2 in the microwave post-cured composites. When fully microwave-cured the properties were similar. In the microwave-cured composites the flexural and interlaminar shear properties were influenced by the structure of the phase separated PEI and the void content.     

Three-phase polymer–ceramic–metal composite for embedded capacitor applications

This paper addresses the materials and processes for printed wiring board compatible embedded capacitor using ceramic, polymer and metal. The Ca[(Li_1/3Nb_2/3)_0.8Ti_0.2]O_3?δ (CLNT)–epoxy–silver, three-phase composites were prepared by two step mixing and thermosetting technique. The dielectric properties of the three-phase composites were investigated in terms of volume fraction of silver, temperature and frequency. The dielectric properties of epoxy–CLNT composites were compared with theoretical predictions. The relative permittivity of the three-phase composites increased with silver loading. Addition of 0.28 volume fraction of silver increases the relative permittivity of epoxy–CLNT composites from 8 to 142 at 1 MHz. This composite is flexible and can be fabricated into various shapes with low processing temperature.     

New glass fiber/bismaleimide composites with significantly improved flame retardancy,higher mechanical strength and lower dielectric loss

Novel glass fiber (GF)/bismaleimide composites with significantly improved flame retardancy, higher mechanical strength and lower dielectric loss were developed, of which the resin matrix is a new flame retarding resin system (BDDP) based on 4,4′-bismaleimidodiphenyl methane (BDM), 2,2′-diallyl bisphenol A (DBA) and [(6-oxido-6H-dibenz [c,e] [1,2] oxaphosphorin-6-yl)-methyl]-butanedioic acid (DDP). The influence of the loading of DDP in the matrix on the integrated performances of composites was intensively studied. Results show that GF/BDDP composites not only have significantly improved mechanical and dielectric properties, but also possess excellent flame retardancy. The main flame retarding mechanism of GF/BDDP composites is the condensed phase mechanism. The introduction of DDP significantly strengthens the interfacial adhesion between GF and the resin matrix, this is responsible for the attractive performances of GF/BDDP composites.     

Infrared and microwave absorbing properties of BaTiO3/polyaniline and BaFe12O19/polyaniline composites

BaTiO₃/polyaniline and BaFe₁₂O₁₉/polyaniline composites were synthesized by in situ polymerization and introduced into epoxy resin and polyethylene to be microwave and infrared absorber. The spectroscopic characterizations of the formation processes of BaTiO₃/polyaniline and BaFe₁₂O₁₉/polyaniline composites were examined using Fourier transform infrared, ultraviolet–visible spectrophotometer, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron spin resonance. Microwave absorbing properties were investigated by measuring reflection loss in the 2–18 and 18–40 GHz microwave frequency range using the free space method. The thermal extinction measurements in the 3–5 and 8–12 μm were done to evaluate the shielding affectivity of infrared. The results showed that the BaTiO₃/polyaniline and BaFe₁₂O₁₉/polyaniline composites have good compatible dielectric and magnetic properties and hence the microwave absorbency show broad frequencies absorbing properties. Moreover, the infrared thermal image testing that the detecting ability of infrared thermal imaging was decreased when the BaFe₁₂O₁₉ and BaTiO₃ was coating with polyaniline.     

纳米Al2O3/聚醚砜-环氧树脂复合材料的介电性能及热稳定性能

本实验制备了纳米Al_2O_3/聚醚砜-环氧树脂复合材料,考察了不同纳米氧化铝和聚醚砜的用量对复合体系力学和介电性能的影响,并对其热稳定性能进行了研究。结果表明:当添加1phr纳米氧化铝(Nano-Al_2O_3)和5phr聚醚砜(PES)时,三元复合材料EP/5PES/1Al_2O_3的拉伸强度提高到58 MPa,断裂伸长率达到13%,冲击强度达到16.2kJ/m~2,相比纯环氧树脂分别提高了61.1%、20.3%和8.0%。而且在100Hz的室温测试条件下,EP/5PES/1Al_2O_3材料的介电常数和介电损耗分别达到7.6和0.016,较纯环氧树脂均有一定幅度的增加。热重分析(TG)结果表明,EP/5PES/1Al_2O_3复合材料的初始分解温度为358℃,比纯环氧树脂提高了14℃,说明热稳定性有较大幅度的提高。     

Microwave–material interaction phenomena: Heating mechanisms,challenges and opportunities in material processing

Efforts to use microwaves in material processing are gradually increasing. However, the phenomena associated with the processing are less understood; popular mechanisms such as dipolar heating and conduction heating have been mostly explored. The current paper reviews most of the significant phenomena that cause heating during microwave–material interaction and heat transfer during microwave energy absorption in materials. Mechanisms involved during interaction of microwave with characteristically different materials – metals, non-metals and composites (metal matrix composites, ceramic matrix composites and polymer matrix composites) have been discussed using suitable illustrations. It was observed that while microwave heating of metal based materials is due to the magnetic field based loss effects, dipolar loss and conduction loss are the phenomena associated with the electric field effects in microwave heating of non-metals. Challenges in processing of advanced materials, particularly composites have been identified from the available literature; further research directions with possible benefits have been highlighted.