Effect of oxyfluorination on electromagnetic interference shielding behavior of MWCNT/PVA/PAAc composite microcapsules

Composite microcapsules of poly(vinyl alcohol)/poly(acrylic acid)/multi-walled carbon nanotubes were prepared and the electromagnetic interference shielding behavior was evaluated for the composite microcapsules. The dispersion and adhesion of multi-walled carbon nanotubes in microcapsules were improved by the surface modification through direct oxyfluorination which introduced polar groups on the multi-walled carbon nanotubes. The composite microcapsules containing the oxyfluorinated multi-walled carbon nanotubes showed significant increases in permittivity, permeability, and electromagnetic interference shielding efficiency. The electromagnetic interference shielding efficiency of composite microcapsule increased up to 51 dB mainly base on the absorption mechanism.     

Tough and Conductive Nacre-inspired MXene/Epoxy Layered Bulk Nanocomposites

A long-standing quest in materials science has been the development of tough epoxy resin nanocomposites for use in numerous applications. Inspired by nacre, here we report tough and conductive MXene/epoxy layered bulk nanocomposites. The orientation of MXene lamellar scaffolds is enhanced by annealing treatment. The improved interfacial interactions between MXene lamellar scaffold and epoxy through surface chemical modification resulted in a synergistic effect. Tailoring the interlayer spacing of MXene nanosheets to a critical distance resulted in a fracture toughness about eight times higher than that of pure epoxy, surpassing other epoxy nanocomposites. Our nacre-inspired MXene/epoxy layered bulk nanocomposites also show high electrical conductivity that provides self-monitoring capability for structural integrity and exhibits an excellent electromagnetic interference shielding efficiency. Our proposed strategy provides an avenue for fabricating high-performance epoxy nanocomposites.     

具有隔离结构的聚丙烯/碳纳米管复合材料的制备及电磁屏蔽性能

通过共挤出包覆-热压法制备了具有隔离结构的聚丙烯(PP)/碳纳米管(CNTs)电磁屏蔽复合材料。 其中,CNTs随机分布于PP基体中形成导电相,该导电复合物作为包覆层包敷在纯PP颗粒表面,形成包覆复合粒子,经热压后形成隔离导电网络。 结果表明,所制备的隔离结构复合材料呈现良好的导电性能,可获得较低的导电逾渗值0.28%(体积分数);在CNTs质量分数为5.6%时,该复合材料电磁屏蔽性能达到25.6 dB,同时具有良好的力学性能。 本文结果表明,共挤出包覆-热压法制备隔离结构导电复合材料方法简单可控、绿色环保,对开发高性能电磁屏蔽复合材料具有重要指导意义。     

Improved flame retardant properties of epoxy resin by fluorinated MMT/MWCNT additives

Flame retardant additives of montmorillonite (MMT) and multi-walled carbon nanotube (MWCNT) were embedded in epoxy resin to improve the resin's flame retardant properties. MMT was fluorinated to exfoliate its layers and enhance its dispersion into the epoxy resin. The MWCNT was also fluorinated to create hydrophobic functional groups for improved dispersion into the epoxy resin. The MWCNT reduced the degradation rate of the epoxy resin and increased the char yield. Limiting oxygen index also increased showing first order against char yield. The exfoliated MMT acted as an energy storage medium to hinder thermal transfer within the epoxy resin. The activation energy increased almost two times by fluorinated MMT/MWCNT additives. The fluorination of the additives, MMT and MWCNT significantly improved the flame retardant properties of the epoxy resin.     

Graphene and MnO2 decorated graphene filled composites for electromagnetic shielding applications having excellent dielectric properties

Graphene nanoplatelets (GnP) and α-MnO₂ decorated GnP were integrated into an ethylene vinyl acetate (EVA) matrix using the dual mixing method (solution followed by melt mixing). GnP was added in 1, 3, 5, 8, 10 and 15 phr loadings into an EVA matrix to obtain composites and evaluate their various properties suitable for mechanical and electrical applications. The graphene nanoplatelets were further decorated with α-MnO₂ which was subsequently integrated into EVA at an 8 phr loading to form composites. It was observed in the GnP-EVA composites, that with an increasing GnP content, a substantial increase in the tensile strength (188%) over the neat polymer was observed at a 10 phr loading but reduced thereafter at a 15 phr loading. Dielectric permittivity of the composites were observed to increase with an increasing filler loading, the addition of α-MnO₂ also having a beneficial effect. Conductivity as well as the electromagnetic interference shielding performance were improved with increasing GnP concentrations. A maximum 28 dB of shielding was observed in the 15 phr loaded GnP-EVA composite whereas the α-MnO₂ decorated GnP-EVA composite showed a shielding efficiency of 22 dB at a concentration of 8 phr for a thickness of 2 mm with excellent thermal and mechanical properties. Overall, the composite material will find its application as a flexible EMI shielding material.     

Conducting polystyrene/polyaniline blend through template-assisted emulsion polymerization

Electrically conducting polystyrene (PS)/polyaniline blends have been prepared through a one-step “anilinium-surfactant template”-assisted emulsion polymerization at room temperature. The self-assembled cylindrical An⁺PDPSA^? micelle formed inside the PS matrix can act as a structure directing template cum dopant. Morphological observation under scanning electron microscopic studies revealed that during the progress of polymerization, the initially formed nanostructured conducting polyaniline was changed into cubic/hexagonal/lamellar particles and finally transformed into a percolated structure inside the PS matrix. Blend was further characterized by UV-Vis spectroscopy, FTIR spectroscopy, X-ray diffraction, electrical conductivity, thermal stability, dielectric property, rheological property, and electromagnetic shielding efficiency. The key finding of this work is that the conductive blend prepared through micelle-guided polymerization exhibited superior electrical conductivity (9.6 S/m) with low percolation threshold concentration (5 wt%), excellent thermal stability, electromagnetic interference (EMI) SE of 1–10 dB which makes it a promising candidate for EMI shielding and antistatic discharge matrix for the encapsulation of microelectronic devices.     

Polymerization and characterization of high conductivity and good adhension polypyrrole films for electromagnetic interference shielding

<正>Polypyrrole(PPy) shows a favorable application in the electromagnetic interference(EMI) shielding due to its good electrical conductivity and outstanding air stability.Conducting PPy films with high conductivity and good adhesion were successfully polymerized on the surface of insulating epoxy resin substrates using chemical polymerization.The factors affecting the properties of PPy films,such as the surface morphology,adhesion between PPy film and substrate,electrical conductivity,EMI shielding effectiveness(SE),were investigated.The adhesion was improved significantly through a three-step surface pretreatment of epoxy resin substrates including removing impurities,roughening,and surface modification with silane coupling agent.An enhancement in the conductivity of PPy films of about one order of magnitude was achieved by adding dopant in FeCl_3 solution.The higher the conductivity,the better the shielding effectiveness.Taking sodium p-toluenesulfonate doped PPy film as example,EMI SE was in the practically useful range of about 30 dB over a wide frequency range from 30 MHz to 1500 MHz.The PPy film samples were characterized by scanning electron microscopy (SEM),infrared spectra(IR),X-ray photoelectron spectroscopy(XPS) and the flange coaxial transmission device.The fourpoint probe method was used to measure conductivity of PPy films.     

Combined effect of graphene oxide and MWCNTs on microwave absorbing performance of epoxy composites

Currently, carbon nanotube (CNT) ‐based composites have been considered as microwave absorbers because of the fascinating properties of CNTs. In this work, multi‐walled CNTs (MWCNTs) and graphene oxide (GO) ‐based epoxy composites (i.e. MWCNT/EPr and GO‐MWCNT/EPr), with sample thickness of 2 mm, were prepared to study microwave absorbing properties in the frequency band of 8–18 GHz. Uniform dispersion of MWCNTs in the organic solvent and polymer matrix was achieved by preparation of GO. The test for electromagnetic parameters, i.e. complex permittivity and the permeability of the samples, was carried out with vector network analyzer (VNA) using reflection‐transmission waveguides. Results showed that GO‐MWCNT/EPr composites have better absorption capability than MWCNT/EPr composites. The improved reflection loss for the composites with 0.4 wt% and 0.6 wt% of GO (out of total filler loading 6 wt%) were ?14.32 dB and ?14.29 dB, respectively. The improvement in reflection loss and absorption bandwidth for GO‐MWCNTs composites suggested that MA features are synergistically effected by GO and MWCNTs. Further skin depth and shielding effectiveness terms are studied to observe overall mechanism of electromagnetic (EM) shielding which showed that multiple reflections also play a role in EM shielding. Copyright © 2015 John Wiley & Sons, Ltd.     

Microstructure,electrical, and electromagnetic interference shielding properties of carbon nanotube/acrylonitrile–butadiene–styrene nanocomposites

Processing, electrical, and electromagnetic interference (EMI) shielding behaviors of carbon nanotube (CNT)/acrylonitrile–butadiene–styrene (ABS) nanocomposites were studied as function of CNT concentration. The nanocomposites were prepared by melt mixing followed by compression molding. The selective and good level of dispersion of CNT in the styrene–acrylonitrile section of the ABS polymer was found to create conductive networks in the ABS matrix at a nanofiller loading of 0.75 wt %. At this nanofiller loading, the nanocomposite electrical conductivity was 10^?5 S/m. This conductivity makes the nanocomposite suitable for electrostatic discharge protection applications. The EMI shielding effectiveness of the nanocomposites increased with the increase in nanofiller concentration. In the 100–1500 MHz frequency range, 1.1 mm thick plates made of ABS nanocomposite filled with 5 wt % CNT exhibit an EMI shielding effectiveness of 24 dB. At this shielding level, the nanocomposite is suitable for a broad range of applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Electromagnetic interference shielding effectiveness and microwave absorption properties of thermoplastic polyurethane/montmorillonite‐polypyrrole nanocomposites

In this work, thermoplastic polyurethane‐filled montmorillonite‐polypyrrole (TPU/Mt‐PPy) was prepared through melt mixing process for using in electromagnetic shielding applications. The effect of conducting filler content and type, sample thickness, and X‐band frequency range on the electromagnetic interference shielding effectiveness (EMI SE) and EMI attenuation mechanism was investigated. A comparative study of electrical and microwave absorption properties of TPU/Mt‐PPy nanocomposites and TPU/PPy blends was also reported. The total EMI SE average and electrical conductivity of all Mt‐PPy.Cl or Mt‐PPy.DBSA nanocomposites are higher than those found for TPU/PPy.Cl and TPU/PPy.DBSA blends. This behavior was attributed to the higher aspect ratio and better dispersion of the nanostructured Mt‐PPy when compared with neat PPy. Moreover, the presence of Mt‐PPy into TPU matrix increases absorption loss (SE_A) mechanism, contributing to increase EMI SE. The total EMI SE values of nanocomposites containing 30 wt% of Mt‐PPy.DBSA with 2 and 5 mm thickness were approximately 16.6 and approximately 36.5 dB, respectively, corresponding to the total EMI of 98% (75% by absorption) and 99.9% (88% by absorption). These results highlight that the nanocomposites studied are promising materials for electromagnetic shielding applications.     

Synergistic effect of double percolated co‐supportive MWCNT‐CB conductive network for high‐performance EMI shielding application

The recent development in telecommunication technology has led electromagnetic interference (EMI) to a serious threat to both electronic devices and living beings. In this work, we designed a highly efficient EMI shielding material by taking advantage of both carbonaceous hybrid filler and double percolation phenomenon. Here, a flexible, lightweight microwave absorbing conductive polymer composite was fabricated by employing poly (ethylene‐co‐methyl acrylate) and ethylene octene copolymer (EMA/EOC) binary blend as the matrix and multiwall carbon nanotube carbon black (MWCNT/CB) hybrid filler as the conductive moiety. We investigated the effect of MWCNT content in the hybrid composite on mechanical, thermomechanical, electrical, and shielding efficiency. A total EMI shielding efficiency of ?37.4 dB in the X band region was attained with 20 wt% hybrid filler containing 50 wt% MWCNT along with promising mechanical properties.     

Improving Elasticity of Conductive Silicone Rubber by Hollow Carbon Black

Carbon black-based conductive rubber composites have important impacts on electromagnetic interference(EMI) shielding applications. However, an excessive amount of carbon black in the recipes of these conductive rubbers has caused their weak elasticity. Herein, hollow carbon black(HCB) particles were used to tune the elasticity of conductive rubber composites. Unique hollow morphology produced a better compression recovery of HCB than other solid carbon black, such as acetylene black. When the coupling agent was bonded to HCB, their conductive silicone rubber composites were featured by high stretching resilience, a fast compression recovery and excellent conductivity to satisfy the electromagnetic interference shielding requirements. Importantly, the rubber composites with coupling HCB had extremely low variations of mechanical property, conductivity and EMI shielding effectiveness after thermal accelerated aging tests. It is therefore revealed that the elasticity of HCB and its interfacial chemical coupling with rubber chains both play crucial roles in adjusting the elasticity of conductive rubber to sever long-term EMI protection.     

Electromagnetic Interference Shielding Polymers and Nanocomposites - A Review

Intrinsically conducting polymers (ICP) and conductive fillers incorporated conductive polymer-based composites (CPC) greatly facilitate the research in electromagnetic interference (EMI) shielding because they not only provide excellent EMI shielding but also have advantages of electromagnetic wave absorption rather than reflection. In this review, the latest developments in ICP and CPC based EMI shielding materials are highlighted. In particular, existing methods for adjusting the morphological structure, electric and magnetic properties of EMI shielding materials are discussed along with the future opportunities and challenges in developing ICP and CPC for EMI shielding applications.     

双功能聚二甲基硅氧烷/铜纳米线复合薄膜的制备与性能

通过环境友好的葡萄糖模板法和改进的湿化学还原法制备了聚二甲基硅氧烷/铜纳米线(PDMS/CuNWs)复合薄膜, 其采用的“类夹心结构”有效解决了铜在空气中易氧化进而导致电导率大幅度下降的问题, 同时获得了具有优异电磁屏蔽和光热转化性能的双功能轻质柔性复合薄膜. CuNWs面密度为1.6 g/cm²的复合薄膜在重复弯折1000次后性能保持率最高可达99.07％; CuNWs面密度为2.4 g/cm²的复合薄膜在X波段下总电磁屏蔽效能达到30.1 dB, 屏蔽效率达到99.9％; 同时, 在2 W/cm²的近红外光照射下, 复合薄膜在仅加热15 s后其表面温度高达211.2 ℃, 具有十分快速的光热响应和转化效率.     

Multi-layered graphene-Fe3O4/poly (vinylidene fluoride) hybrid composite films for high-efficient electromagnetic shielding

A flexible and multi-layered graphene nanosheets (GNSs)-Fe₃O₄/poly (vinylidene fluoride) hybrid composite film with high-efficient electromagnetic interference (EMI) shielding was fabricated via a facile layer-by-layer coating. The well-designed multi-layered and hybrid electromagnetic fillers endow the prepared film with good surface impedance matching and prominent internal multiple absorption, which forms “absorb-reflect-reabsorb” electromagnetic transmission pattern and results in highly efficient electromagnetic shielding effectiveness (EMI SE). The resultant composite film exhibits an exceptional EMI SE of 52.0 dB at a thickness of 0.3 mm. What is more important is that the prepared film exhibits excellent flexibility and EMI stability, and the retention rate of efficient EMI SE is high as 91.9% after 1000 bending-release cycles. This study provides a feasible strategy for designing high-efficient EMI shielding film with excellent flexibility and ultra-thin thickness that suitable for next-generation intelligent protection devices.     

Effect of oxyfluorination on electromagnetic interference shielding of polyaniline-coated multi-walled carbon nanotubes

Highly conducting polyaniline (PANi)-coated multi-walled carbon nanotubes (MWCNTs) were prepared by in situ polymerization method for electromagnetic interference shielding. The thickness of the PANi coatings was controlled by the oxyfluorination treatment on the multi-walled carbon nanotubes and analyzed with both SEM and TEM. The oxyfluorination with higher oxygen content produced more hydrophilic functional groups on the surface of multi-walled carbon nanotubes. The functional groups led to the well distribution and coating of PANi on the multi-walled carbon nanotubes resulting in the higher interfacial affinity between them. The uniform coating of PANi on MWCNTs by controlling the oxyfluorination conditions also played a crucial role in increasing the electrical conductivity of nanocomposites. The improved interfacial affinity resulted in the higher electromagnetic interference (EMI) SE of 47.03?dB based on the synergistic combination of the conductive components. The EMI shielding mechanism of PANi on MWCNTs suggested that EMI was mainly shielded by adsorption to avoid secondary EMI.     

Enhanced corrosion protection performance with MWCNT dispersed epoxy coating prepared under supercritical CO2 assistance

The corrosion protection performance of epoxy coatings could be enhanced by incorporation of nanofillers such as MWCNT. However, a homogeneous dispersion of MWCNT in epoxy polymer is still a teasing challenge. Herein, we report an environmentally benign single‐step supercritical CO₂ processing method to improve the dispersion of MWCNT in epoxy matrix in order to achieve an effective anticorrosive coating. The executed approach provides a cluster‐free uniform distribution of MWCNT in epoxy matrix as characterized with UV‐visible spectroscopy, Fourier transforms infrared spectroscopy, X‐ray diffraction, and surface analysis. The anticorrosive characteristics of MWCNT/epoxy coating were studied in NaCl as well as in photodegraded dye medium through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. We observed the remarkable corrosion of model metal substrate in photodegraded dye medium besides NaCl medium. In both mediums, the protection efficacy of MWCNT/epoxy coating was deduced from the stable impedance arcs in Nyquist plot and increased impedance modulus. The electrochemical impedance spectra were best fitted with equivalent circuits showing the higher values of pore resistance. Also, the MWCNT/epoxy coating exhibited a positive shift of corrosion potential and possessed a lower corrosion rate as compared with neat epoxy coating. More direct evidence of the excellent barrier properties for MWCNT/epoxy coating was visualized in SEM images. The obtained results implied that the superior dispersion of MWCNT into epoxy matrix significantly reduces the porosity of coating and inhibits the permeability of corrosive ions. We expect supercritical CO₂ assisted dispersion method can offer an efficient, cost‐effective, and industrially viable route to develop high performance protective coatings for varied commercialized applications.     

Thermally reversible light scattering films based on the melting/crystallization of organic crystals dispersed in an epoxy matrix

Films that can be reversibly switched from opaque to transparent states by varying temperature (TRLS films), have potential applications in thermal sensors, optical devices, recording media, etc. A dispersion of organic crystals in a thermoset may be used for these purposes provided that at temperatures higher than the melting point there is a matching of refractive indices of both phases. A model system consisting on a dispersion of diphenyl (DP) crystals in an epoxy matrix based on diglycidyl ether of bisphenol A and m-xylylenediamine, was analyzed as a possible TRLS film encapsulated between transparent covers to avoid sublimation of DP. To obtain a uniform dispersion of DP-rich domains in the epoxy matrix by polymerization-induced phase separation, it was necessary to add 5 wt% of polystyrene (PS) to the initial formulation. Phase separation induced by polymerization at 80 °C led to a dispersion of PS/DP domains in the epoxy matrix due to the low compatibility of PS with the epoxy and its high compatibility with DP. Crystallization and melting processes were confined to the interior of dispersed domains leading to an excellent reproducibility of the optical properties of TRLS films in the course of successive heating-cooling cycles.     

Mechanically robust conductive carbon clusters confined ethylene methyl acrylate–based flexible composites for superior shielding effectiveness

Arresting of conducting carbon black into polymeric matrix to develop flexible and light weight composite has been a widely practiced platform. Extensive development of telecommunication creates a major vexations regarding radiation pollution. Thereafter, we have been motivated to develop low‐cost, flexible composites of specialty carbon black VXC (Vulcan XC 72)–filled ethylene methyl acrylate (EMA) by mechanical mixing technique. Developed composite has significant conductivity (6.67 × 10⁻⁴ S cm⁻¹) with promising mechanical and thermal properties. Dispersion of high‐structured carbon blacks in EMA was investigated by small angle X‐ray scattering to reflect the dependency of conducting mesh formation on dispersion. Interconnected filler network development has been visualized by field emission scanning electron microscope and high‐resolution transmission electron microscope. Electromagnetic interference shielding value in the X band has calculated to be 30.8 dB. Such features can make this EVXC (EMA‐Vulcan XC 72) composite a useful alternate for flexible electromagnetic interference shielding material.     

电磁屏蔽材料的研究进展

介绍了电磁屏蔽材料在军用和民用领域的重要性;简要阐述了电磁屏蔽的机理;综述了4种不同电磁屏蔽材料的优缺点以及研究现状,分别为金属型、表面导电型、填充复合型和本征型导电聚合物电磁屏蔽材料;分析并提出了3种提高电磁屏蔽效能的方式,分别为多孔结构设计、多层结构设计、复合填料优化.