Progress in the Foaming of Polymer-based Electromagnetic Interference Shielding Composites by Supercritical CO2

As a critical action plan formulated for peaking carbon dioxide emissions, polymeric electromagnetic interference (EMI) shielding materials based on CO₂ foaming technology have recently been attracting widespread attention in both research and industry, attributable to their efficient use of CO₂, high specific strength, corrosion resistance and low-cost characteristics. In the past decade, the emergence of novel design concepts and preparation techniques for CO₂ foaming technology has led to the development of new high-performance EMI shielding materials in this field. This review summarizes the research progress made to date on the fabrication of EMI shielding composite foams by supercritical carbon dioxide (scCO₂) foaming. We also explore the structure-activity relationships between the component/distribution and EMI shielding properties. Additionally, the application prospects and development challenges of new EMI shielding composite foams are described.     

Recent progress in MXene and graphene based nanocomposites for microwave absorption and electromagnetic interference shielding

There is widespread use of telecommunication and microwave technology in modern society, and raised the electromagnetic interference (EMI) issue to alarming situation due to apprehensive demand and growth of 5G technology undesirably disturbing the human health. The two dimensional (2D) materials including graphene and MXenes are already been used for variety of electronic devices due to their exceptional electrical, mechanical, optical, chemical, and thermal properties. MXene is composed of metal carbides, in which mainly metals are the building blocks for dielectrics, semiconductors, or semimetals. However, the strong interfaces with electromagnetic waves (EM) are variable from terahertz (THz) to gigahertz (GHz) frequency levels and are widely used in EMI and Microwave absorption (MA) for mobile networks and communication technologies. The use of different organic materials with metal, organic, inorganic fillers, polymers nanocomposite and MXene as a novel material has been studied to address the recent advancement and challenges in the microwave absorption mechanism of 2D materials and their nanocomposites. In this concern, various techniques and materials has been reported for the improvement of shielding effectiveness (SE), and theoretical aspects of EMI shielding performance, as well stability of 2D materials particularly MXene, graphene and its nanocomposites. Consequently, various materials including polymers, conducting polymers, and metal–organic frameworks (MOF) have also been discussed by introducing various strategies for improved MA and control of EMI shieling. Here in this comprehensive review, we summarized the recent developments on material synthesis and fabrication of MXene based nanocomposites for EMI shielding and MA. This research work is a comprehensive review majorly focuses on the fundamentals of EMI/MA.  The recent developments and challenges of the MXene and graphene based various structures with different polymeric composites are described in a broader perspective.     

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.     

Ku-band EMI shielding effectiveness and dielectric properties of Polyaniline-Y2O3 composites

Electromagnetic interference (EMI) shielding has become a phenomenon of great concern and there is growing demand towards the synthesis of materials with better EMI shielding effectiveness (EMI SE). This work highlights the preparation of Polyaniline-Yttrium Oxide (PANI-Y₂O₃) composites for EMI shielding applications in the frequency range from 12.4 to 18 GHz (Ku-band). The structure and morphology of the composites were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). EMI SE, microwave absorption and reflection, dielectric properties of the composites are discussed in detail. All the computations were based on microwave scattering parameters measured by transmission line waveguide technique. The observed results show absorption dominant EMI shielding in these composites with EMI SE of ?19 to ?20 dB, which mainly depends on the dielectric loss of the composites. Through the results of our observations, we propose these composites to be potential materials for microwave absorption and EMI shielding applications.     

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.     

Biopolymer-Based Aerogels for Electromagnetic Wave Shielding and Absorbing

The rapid development of communication technology and electronic industry has brought unprecedented serious electromagnetic interference (EMI) and electromagnetic wave (EMW) pollution. Although EMI shields and EMW absorbers based on metal or magnetic materials were used to solve these problems, they have long been criticized for their high price, high density and easy corrosion. In order to achieve low density and efficient dissipation of electromagnetic energy, aerogels stand out among manifold materials. However, constructing aerogels with good EMI shielding or EMW absorption performance and acceptable mechanical properties is not an easy task. Burgeoning biopolymers, such as cellulose, lignin, chitin/chitosan and alginate, breathe new life into aerogels for high-efficiency EMW shielding and absorbing. Here, we reviewed the contributions of biopolymers in the fields of aerogels for EMW shielding and absorbing. At the same time, some challenges and outlook were also pointed out, aiming to promote the advance of aerogel-based EMI shields and EMW absorbers as well as the rational utilization of biopolymers.     

电活性超支化聚合物的合成与性质

通过分子设计, 利用A2+B3反应合成了一种新型电活性超支化聚合物材料. 该材料在保持聚苯胺的电活性基础上, 还具有超支化聚合物特有的低黏度(其特性黏度为0.33 dL/g)、低结晶性及良好的溶解性. 利用紫外-可见光谱对聚合物的氧化过程进行了监测. 热失重分析显示, 该材料具有较好的热稳定性, 失重10%时的温度高达517 ℃. 该材料具有较高的介电常数, 有望成为一种具有实际应用价值的高介电材料.     

Recent advance in electromagnetic shielding of MXenes

As a new type of two-dimensional material,MXene's unique layered structure,outstanding electrical conductivity,low density,tunable surface chemistry,and solution processability make it receive extensive attention in various fields,especially for the lightweight shielding mate rials since the report on electromagnetic interference(EMI) shielding of 2D Ti_3 C_2 T_x in 2016.In this review,the progress on the MXe nes material including their synthetic strategies,prope rties and EMI application is highlighted.First,the recent advance on the different synthesis methods and properties of MXene is summarized.According to their intrinsic characteristics,the application of MXene in EMI fields is then discussed.Finally,the challenges and perspective on the future development of MXene in low-cost preparation and practical application are proposed.     

Eco-friendly non-acid intercalation and exfoliation of graphite to graphene nanosheets in the binary-peroxidant system for EMI shielding

The development of the preparation strategy for high-quality and large-size graphene via eco-friendly routes is still a challenging issue. Herein, we have successfully developed a novel route to chemically exfoliate natural graphite into high-quality and large-size graphene in a binary-peroxidant system. This system is composed of urea peroxide (CO(NH₂)₂⋅H₂O₂) and hydrogen peroxide (H₂O₂), where CO(NH₂)₂⋅H₂O₂ is used in preparing graphene for the first time. Benefiting from the complete decomposition of CO(NH₂)₂⋅H₂O₂ and H₂O₂ into gaseous species under microwave (MW) irradiation, no water-washing and effluent-treatment are needed in this chemical exfoliation procedure, thus the preparation of graphene in an eco-friendly way is realized. The resultant graphene behaves a large-size, high-quality and few-layer feature with a yield of ~100%. Then 4 µm-thick ultrathin graphene paper fabricated from the as-exfoliated graphene is used as an electromagnetic interference (EMI) shielding material. And its absolute effectiveness of EMI shielding (SSE/t) is up to 34,176.9 dB cm²/g, which is, to the best of our knowledge, among the highest values so far reported for typical EMI shielding materials. The EMI shielding performance demonstrates a great application potential of graphene paper in meeting the ever-increasingly EMI shielding demands in miniaturized electronic devices.     

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.     

Current trends in spinel based modified polymer composite materials for electromagnetic shielding

The present article deals with current trends in spinel based modified polymer composite materials for applications in the field of electromagnetic shielding. The interaction between the various spinel based materials and polymers is an emerging field of studies among various researchers. The thermal stability, electrical conductivity, the bonding between the metal ferrites and the polymer plays an important role in the interaction of electromagnetic radiation. These properties also effect the mechanism of the EM waves for the shielding applications. Considering these all properties, polyaniline appears to be an suitable polymer for electromagnetic shielding applications. Polyaniline composites not only reinforced the properties of spinel materials but also enhanced the dielectric properties of the composite material. When carbon based materials such as graphene, graphene oxide and CNT was added along with spinel material in polyaniline based composite, they accelerate the electrical properties and enhances the shielding applications. In this paper the various synthesis methods, fabrication methods of polyaniline, and the properties of polyaniline based composites have been discussed. In addition, the various salient features and futuristic challenges of polyaniline based composite materials for EMI shielding applications were attempted to make a well equipped material for radar absorption.     

Electromagnetic interference shielding Ti_3C_2T_x-bonded carbon black films with enhanced absorption performance

The demand for flexible and freestanding electromagnetic interference(EMI) shielding materials are more and more urgent to combat with serious electromagnetic(EM) radiation pollution.Twodimensional Ti_3C_2T_x is considered as promising EMI shielding material to graphenes because of the low cost and high electrical conductivity.However,the shielding performance still needs to be optimized to decrease the reflection effectiveness(SE_R) and increase absorption effectiveness(SEA).Herein,we prepared Ti_3C_2T_x-bonded carbon black films with a porous structure.The SE_R decreased from 20 dB to12 dB and the SEA increased from 31 dB to 47 dB.The best EMI shielding effectiveness can be as high as60 dB with SE_A of 15 dB and SE_R of45 dB.Their calculated specific shielding effectiveness can be as high as8718 dB cm~2/g.These results indicate that the porous structure can enhance the absorption of the EMI shielding films,resulting from the enhanced scattering and reflectio n.Conseque ntly,this work provides a promising MXene-based EMI shielding film with lightweight and flexibility.     

Effects of sodium laurylsulfate on crystal structure of calcite formed from mixed solutions

This paper presents a solvent-based, mild method to prepare superhydrophobic, carbon nanofiber/PTFE-filled polymer composite coatings with high electrical conductivity and reports the first data on the effectiveness of such coatings as electromagnetic interference (EMI) shielding materials. The coatings are fabricated by spraying dispersions of carbon nanofibers and sub-micron PTFE particles in a polymer blend solution of poly(vinyledene fluoride) and poly(methyl methacrylate) on cellulosic substrates. Upon drying, coatings display static water contact angles as high as 158° (superhydrophobic) and droplet roll-off angles of 10° indicating self-cleaning ability along with high electrical conductivities (up to 309 S/m). 100 μm-thick coatings are characterized in terms of their EMI shielding effectiveness in the X-band (8.2-12.4 GHz). Results show up to 25 dB of shielding effectiveness, which changed little with frequency at a fixed composition, thus indicating the potential of these coatings for EMI shielding applications and other technologies requiring both extreme liquid repellency and high electrical conductivity.     

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.     

Segregated reduced graphene oxide polymer composite as a high performance electromagnetic interference shield

Herein, we report the synthesis of a graphene/polymer composite via a facile and straightforward approach for electromagnetic interference (EMI) shielding applications. Polystyrene (PS) beads were added in graphene oxide (GO)/water solution followed by the addition of hydroiodic acid (HI) for in situ reduction of GO. The composite solution (rGO/PS) was filtered, hot compressed and tested for EMI shielding and dielectric measurements. A 2-mm thick segregated rGO/PS sample with 10 wt% filler loading delivered a high EMI shielding effectiveness (SE) of 29.7 dB and an AC electrical conductivity of 21.8 S m^?1, which is well above the commercial requirement for EMI shielding applications. For comparison with the segregated rGO/PS composite, a control polymer composite sample utilizing a thermally reduced graphene oxide was synthesized by following a conventional coagulation approach. The as-synthesized conventional rGO/PS yield an EMI SE of 14.2 dB and electrical conductivity of 12.5 S m^?1. The high EMI shielding of segregated rGO/PS is attributed to the better filler-to-filler contact among graphene layers surrounded by PS beads and also to the better reduction and preservation of graphene structure during reduction process that makes the low temperature chemically reduced segregated rGO/PS approach a viable route compared to high temperature thermally reduced conventional rGO/PS approach.     

Multifunctional waterproof MXene-coated wood with high electromagnetic shielding performance

Increasing electromagnetic pollution calls for electromagnetic interference (EMI) shielding materials, especially sustainable, lightweight, and environmentally stable, biomass-based materials. MXene-coated wood (M/wood) is prepared by simply spraying MXene sheets on the wood surface. Varying this spray coating manipulates the shielding performance and its application to different wood species. The M/wood exhibits high electrical conductivity (sheet resistance is only 0.65 Ω/sq) with an excellent EMI shielding effectiveness of 31.1 dB at 8.2?~?12.4 GHz and is also fire retardant. Furthermore, waterborne acrylic resin (WA) is coated on M/wood to enhance environmental stability. The WA coating improves EMI shielding performance stability after water-soaking and drying testing and prevents the peeling of MXene from wood. These satisfactory properties of WA-M/wood and the facile manufacturing approach promote the feasibility of wood-based EMI shielding materials.

Graphical abstract

     

Intrinsically conducting polymers for electromagnetic interference shielding

This paper summarizes and reviews the research on electromagnetic interference (EMI) shielding with intrinsically conducting polymers (ICPs), mainly polyaniline (PANI) and polypyrrole (PPY), and their composites in various frequency ranges. ICPs are new alternative candidates for EMI shielding applications due to their lightweight, corrosion resistance, ease of processing, and tunable conductivities as compared with typical metals. More importantly, the dominant shielding characteristic of absorption other than that of reflection for metals render ICPs more promising materials in applications requiring not only high EMI shielding effectiveness but also shielding by absorption, such as in stealth technology. Copyright © 2005 John Wiley & Sons, Ltd.     

Electromagnetic interference shielding by using conductive polypyrrole and metal compound coated on fabrics

Electromagnetic interference (EMI) shielding materials of complex type of conductive polypyrrole (PPy) as an intrinsically conducting polymer and silver‐palladium (AgPd) metal compound coated on woven or non‐woven fabrics are synthesized. From dc conductivity and SEM photographs of PPy/fabric complexes, we discuss charge transport mechanism and the homogeneity of coating on the fabrics. The EMI shielding efficiency of PPy/fabric and AgPd/fabric complexes is in the range of 8 ～ 80 dB depending on the conductivity and the additional Ag vacuum evaporation. The highest EMI shielding efficiency of PPy/fabric complexes vacuum‐evaporated by Ag is ～80 dB, indicating potential materials for military uses. We propose that PPy/fabrics are excellent RF and microwave absorber because of the relatively high absorbance and low reflectance of the materials. Copyright © 2002 John Wiley & Sons, Ltd.     

Fe-Ni/C复合纳米纤维的原位制备与微波吸收性能

采用静电纺丝技术结合稳定化和碳化处理原位制备了Fe-Ni/C复合纳米纤维, 其平均直径约为215 nm, 所生成的Fe-Ni合金纳米颗粒较均匀地分布在碳基纳米纤维的内部和表面, 且被石墨化碳层所包覆. 以Fe-Ni/C复合纳米纤维为吸收剂、 硅橡胶为基质制备成吸波涂层, 研究了碳化温度对电磁特性和微波吸收性能的影响. 结果表明, 涂层厚度为1.2~2.0 mm、 Fe-Ni/C复合纳米纤维质量分数为5%的吸波涂层表现出优良的微波吸收性能, 在7.4~18 GHz频率范围内的反射损耗均低于-20 dB; 随着复合纳米纤维的碳化温度由800 ℃升高到1200 ℃, 由于阻抗匹配特性的改善, 吸波涂层的微波吸收能力逐步加强, 其最小反射损耗由-22.6 dB降低到-63.0 dB.     

EMI shielding and microwave absorption behavior of Au‐MWCNT/polyaniline nanocomposites

Electrically conducting Au‐multiwalled carbon nanotube/polyaniline (Au‐MWCNT/PANi) nanocomposites were synthesized by two different ways: (1) by direct mixing of MWCNT/PANi and Au nanoparticles (Au‐MWCNT/PANi‐1) and (2) by in situ polymerization of aniline in the presence of both MWCNTs and Au nanoparticles (Au‐MWCNT/PANi‐2). The higher electrical conductivity of Au‐MWCNT/PANi‐2 compared with the other samples (PANi, MWCNT/PANi, Au‐MWCNT/PANi‐1) is supported by the red shifts of the UV‐vis bands (polaron/bipolaron), the high value of the –NH+= stretch peak (Fourier transform infrared spectroscopy studies), the high % crystallinity (X‐ray diffraction analysis) and more uniform dispersion of the Au NPs in the material. The performance of the samples in electromagnetic interference (EMI) shielding and microwave absorption was studied in the X‐band (8–12 GHz). For all the samples, absorption was the dominant factor contributing toward the EMI shielding. Au‐MWCNT/PANi‐2 showed the best performance with a total shielding effectiveness of ?16 dB [averaged over the X‐band (GHz)] and a minimum reflection loss of ?56.5 dB. The higher dielectric properties resulting from the heterogeneities because of the presence of nanofillers and the high electrical conductivity lead to the increased EMI shielding and microwave absorption. The results show the significance of both Au nanoparticles and method of synthesis on the EMI shielding performance of MWCNT/PANi composites. Copyright © 2016 John Wiley & Sons, Ltd.