Highly Conductive Transition Metal Carbide/Carbonitride(MXene)@polystyrene Nanocomposites Fabricated by Electrostatic Assembly for Highly Efficient Electromagnetic Interference Shielding

Highly conductive polymer nanocomposites are greatly desired for electromagnetic interference (EMI) shielding applications. Although transition metal carbide/carbonitride (MXene) has shown its huge potential for producing highly conductive films and bulk materials, it still remains a great challenge to fabricate extremely conductive polymer nanocomposites with outstanding EMI shielding performance at minimal amounts of MXenes. Herein, an electrostatic assembly approach for fabricating highly conductive MXene@polystyrene nanocomposites by electrostatic assembling of negative MXene nanosheets on positive polystyrene microspheres is demonstrated, followed by compression molding. Thanks to the high conductivity of MXenes and their highly efficient conducting network within polystyrene matrix, the resultant nanocomposites exhibit not only a low percolation threshold of 0.26 vol% but also a superb conductivity of 1081 S m^?1 and an outstanding EMI shielding performance of >54 dB over the whole X‐band with a maximum of 62 dB at the low MXene loading of 1.90 vol%, which are among the best performances for electrically conductive polymer nanocomposites by far. Moreover, the same nanocomposite has a highly enhanced storage modulus, 54% and 56% higher than those of neat polystyrene and conventional MXene@polystyrene nanocomposite, respectively. This work provides a novel methodology to produce highly conductive polymer nanocomposites for highly efficient EMI shielding applications.     

Effective electromagnetic shielding of plastic packaging in low-cost optical transceiver modules

A low-cost plastic package of the standard 1 /spl times/ 9 type with effective electromagnetic (EM) shielding ability is developed. Optical transceiver modules with transmission rates of 155 Mb/s and 1.25 Gb/s are tested to evaluate the EM shielding against emitted radiation from the plastic packaging. The results show that the packaged optical transceiver modules exhibit shielding effectiveness (SE) of over 20 dB. The EM shielding properties of plastic materials consisting of nylon66 and liquid crystal polymer (LCP) with carbon fiber reinforced are investigated. The effects of weight percentage of fibers, carbon fiber length, and material thickness on the SE of the plastic composites are studied both from the plane-wave and near-field sources approaches. The packaged plastic optical transceiver modules with their good SE are suitable for use in low-cost and low electromagnetic interference (EMI) Gigabit Ethernet lightwave transmission systems.     

Ultrathin Wood-Derived Conductive Carbon Composite Film for Electromagnetic Shielding and Electric Heating Management

Recently, wood-based composites have absorbed widespread concern in the field of electromagnetic interference (EMI) shielding due to their sustainability and inherent layered porous structure. The channel structure of wood is often used to load highly conductive materials to improve the EMI shielding performance of wood-based composites. However, there is little research on how to use pure wood to prepare ultrathin EMI shielding materials. Herein, ultrathin veneer is obtained by cutting wood in parallel to the annual rings. Then, carbonized wood film (CWF) is prepared by a simple two-step compressing and carbonization. The specific EMI shielding effectiveness (SSE/t) of CWF-1200 with an ultrathin thickness (140 µm) and high electrical conductivity (58 S cm⁻¹) can reach 9861.41 dB cm² g⁻¹, which is much higher than other reported wood-based materials. In addition, the zeolitie imidazolate framework-8 ( ZIF-8) nanocrystals are grown in situ on the surface of the CWF to obtain CWF/ZIF-8. CWF/ZIF-8 exhibits an EMI shielding effectiveness (SE) of up to 46 dB and an ultrahigh SSE/t value of 11 330.04 dB cm² g⁻¹ in X band. In addition, the ultrathin CWF also shows an excellent Joule heating effect. Therefore, the development of ultrathin wood-based film provides a research basis for wood biomass to replace traditional non-renewable and expensive electromagnetic (EM) shielding materials.     

Lightweight and Anisotropic Porous MWCNT/WPU Composites for Ultrahigh Performance Electromagnetic Interference Shielding

Lightweight, flexible and anisotropic porous multiwalled carbon nanotube (MWCNT)/water‐borne polyurethane (WPU) composites are assembled by a facile freeze‐drying method. The composites contain extremely wide range of MWCNT mass ratios and show giant electromagnetic interference (EMI) shielding effectiveness (SE) which exceeds 50 or 20 dB in the X‐band while the density is merely 126 or 20 mg cm^?3, respectively. The relevant specific SE is up to 1148 dB cm³ g^?1, greater than those of other shielding materials ever reported. The ultrahigh EMI shielding performance is attributed to the conductivity of the cell walls caused by MWCNT content, the anisotropic porous structures, and the polarization between MWCNT and WPU matrix. In addition to the enhanced electrical properties, the composites also indicate enhanced mechanical properties compared with porous WPU and CNT architectures.     

Electromagnetic Response and Energy Conversion for Functions and Devices in Low‐Dimensional Materials

Low‐dimensional materials have been long sought after for their particular electromagnetic (EM) functions, with promising applications in EM wave absorbing and shielding, communicating and imaging, sensing and detecting, driving and actuating, etc. Herein, across the whole EM spectrum, low‐dimensional EM functional materials and devices are highly focused on. The crystal engineering and function‐guiding features addressed relate to crystal and electronic structures, EM responses and properties, energy conversion, as well as EM wave absorbing and shielding. Moreover, insight is given into this rapidly broadening field, the main challenges are proposed and future directions are predicted.     

Structured Reduced Graphene Oxide/Polymer Composites for Ultra‐Efficient Electromagnetic Interference Shielding

A high‐performance electromagnetic interference shielding composite based on reduced graphene oxide (rGO) and polystyrene (PS) is realized via high‐pressure solid‐phase compression molding. Superior shielding effectiveness of 45.1 dB, the highest value among rGO based polymer composite, is achieved with only 3.47 vol% rGO loading owning to multi‐facet segregated architecture with rGO selectively located on the boundaries among PS multi‐facets. This special architecture not only provides many interfaces to absorb the electromagnetic waves, but also dramatically reduces the loading of rGO by confining the rGO at the interfaces. Moreover, the mechanical strength of the segregated composite is dramatically enhanced using high pressure at 350 MPa, overcoming the major disadvantage of the composite made by conventional‐pressure (5 MPa). The composite prepared by the higher pressure shows 94% and 40% increment in compressive strength and compressive modulus, respectively. These results demonstrate a promising method to fabricate an economical, robust, and highly efficient EMI shielding material.     

碳基纳米吸波材料制备的研究进展

为探索民用电磁屏蔽和军用隐形碳基高性能吸波材料的制备,研究了碳纳米管和磁性金属复合,碳纳〖JP2〗米管和铁氧体复合,碳纳米管/聚合物复合,碳、石墨基复合等碳基吸波材料的不同复合和制备方法,比较了其反射损耗等不同的特点、影响因素和性能特点及其相关应用。结果表明,多元复合、低维化、工艺优化是其制备的有效途径。     

螺旋形碳纤维结构吸波材料的制备及性能研究

用基板法以乙炔为碳源,镍板为催化剂,PCI,为助催化剂,通过化学气相沉积制备了螺旋形碳纤维手性吸收剂,并研究了其在2～18GHz的微波电磁特性：具有较高的介电损耗,电磁参数随频率的增大有减小的趋势,有利于实现宽频吸波。以螺旋形碳纤维作为吸收剂制备了Nomex蜂窝夹芯结构吸波材料,复合材料的厚度为9．5mm时,在3．76～18GHz反射率R小于-10dB,反射率小于-10dB的频宽为14．24GHz;最大吸收峰在10．4GHz,反射率R为-21．62dB。探讨了螺旋形碳纤维的吸波机理,螺旋形碳纤维是一种非常有发展前景的手性吸收剂和吸波材料。     

镀镍中间相沥青基碳纤维的吸波性能

为了改善中间相沥青基碳纤维的磁性能和吸波性能,通过化学镀工艺在中间相沥青基碳纤维表面均匀包覆了金属镍,研究了镀镍中间相沥青基碳纤维的磁性能和微波吸收性能。以镀镍中间相沥青基碳纤维作为吸收剂,环氧树脂为基体制备了单层吸波涂层,涂层的厚度为1.02 mm时,吸波涂层在15.4~18 GHz反射率R小于-10 dB,最大吸收峰在18 GHz,反射率R为-20.74 dB。探讨了镀镍中间相沥青基碳纤维的吸收机理,在含镀镍中间相沥青基碳纤维的吸波涂层中,镀镍中间相沥青基碳纤维作为偶极子在电磁场的作用下,会产生耗散电流,在周围基体作用下,耗散电流被衰减,从而电磁波能量转换为其它形式的能量,主要为热能,这是镀镍中间相沥青基碳纤维偶极子吸波涂层的主要吸波机理。     

Electromagnetic shielding of nylon-66 composites applied to laser modules

Electromagnetic shielding of nylon-66 composites applied to laser modules was studied experimentally and theoretically. The effects of conductive carbon fiber length and weight percentage upon the shielding effectiveness (SE) of nylon composites were investigated. The SE of long carbon fiber filled nylon-66 composites was found to be higher than short carbon fiber composites under the same weight percentage of carbon fibers. In addition, higher electromagnetic shielding was obtained for the composite with higher carbon fibers contents at the same length. The SE of conductive carbon fiber filled nylon-66 composites was measured to be 42 dB at a low frequency of 30 MHz and 50 dB at a high frequency of 1 GHz. The SE predicted by theoretical models and measured by experiments were in good agreement for filled nylon-66 composites with different length fiber.     

Reversible Crumpling of 2D Titanium Carbide (MXene) Nanocoatings for Stretchable Electromagnetic Shielding and Wearable Wireless Communication

In the emerging Internet of Things, stretchable antennas can facilitate wireless communication between wearable and mobile electronic devices around the body. The proliferation of wireless devices transmitting near the human body also raises interference and safety concerns that demand stretchable materials capable of shielding electromagnetic interference (EMI). Here, an ultrastretchable conductor is fabricated by depositing a crumple‐textured coating composed of 2D Ti₃C₂T_x nanosheets (MXene) and single‐walled carbon nanotubes (SWNTs) onto latex, which can be fashioned into high‐performance wearable antennas and EMI shields. The resulting MXene‐SWNT (S‐MXene)/latex devices are able to sustain up to an 800% areal strain and exhibit strain‐insensitive resistance profiles during a 500‐cycle fatigue test. A single layer of stretchable S‐MXene conductors demonstrate a strain‐invariant EMI shielding performance of ≈30 dB up to 800% areal strain, and the shielding performance is further improved to ≈47 and ≈52 dB by stacking 5 and 10 layers of S‐MXene conductors, respectively. Additionally, a stretchable S‐MXene dipole antenna is fabricated, which can be uniaxially stretched to 150% with unaffected reflected power <0.1%. By integrating S‐MXene EMI shields with stretchable S‐MXene antennas, a wearable wireless system is finally demonstrated that provides mechanically stable wireless transmission while attenuating EM absorption by the human body.     

Low-cost and low-electromagnetic-interference packaging of optical transceiver modules

The low-cost and low-electromagnetic-interference (EMI) packaging of optical transceiver modules employing housings of plastic composites are developed and fabricated. Optical transceiver modules fabricated by the plastic composites with transmission rates of 1.25 and 2.5 Gb/s are tested to evaluate the electromagnetic (EM) shielding against emitted radiation from the plastic packaging. The results show that these packaged optical transceiver modules with their high shielding effectiveness (SE) are suitable for use in low-cost and low-EMI Gigabit Ethernet lightwave transmission systems. By comparison of cost, weight, and shielding performance for optical transceiver modules fabricated by the housings of nylon and liquid-crystal polymer with carbon fiber filler composites, woven continuous carbon fiber (WCCF), and nanoscale hollow carbon nanocapulses (HCNCs) epoxy composites, the WCCF composite shows lower cost, lighter weight, and higher EM shielding than the other types of composites. Future studies may develop the low-cost and low-EMI optical transceiver modules using nanoscale HCNCs that have the combination of excellent physical and mechanical properties, light weight, and thinness compared with the conventional fabrication techniques.     

Measurement of the microwave conductivity of a polymeric materialwith potential applications in absorbers and shielding

The microwave conductivity of a new material, the polymer poly-p-phenylene-benzobis-thiazole (PBT) made conductive by ion-implantation doping with iodine, is measured at 9.89 GHz as a function of temperature using the cavity perturbation technique applicable to thin films of arbitrary shape. The DC and microwave conductivities of PBT are seen to approach asymptotically the low-temperature limit predicted by Mott's energy-dependent hopping model. The potential utilization of conductive polymers in microwave absorbers and electromagnetic interference (EMI) shielding is examined using layered media EM theory     

The influence of fiber orientation on electromagnetic shielding in liquid-crystal polymers

The influence of conductive carbon-fiber orientation and weight percentage on the electromagnetic (EM) shielding effectiveness (SE) in liquid-crystal polymer (LCP) composites was investigated experimentally and theoretically. The experimental results show that the SE of LCP composites with longitudinal fiber orientation is higher than random fiber orientation under the same weight percentage of carbon fibers filled. This is because longitudinal fiber orientation is parallel to the electric field of the incident EM wave, and most of the energy of the incident wave is reflected by the longitudinal fiber. In comparison with nylon66 composites, the SEs of LCP composites with longitudinal fiber orientation are also higher than nylon66 composites with the same content of carbon fibers. Furthermore, the SE of 20% conductive carbon-fiber-filled LCP composites was measured to be 50 dB at a frequency of 0.3 GHz and 53 dB at 1 GHz, which is at least 10 dB higher than that of nylon66 composites. The SE predicted by theoretical models and measured by experiments was in good agreement for carbon-fiber-filled LCP composites of longitudinal and random fiber orientations.     

Flexible and Multifunctional Silk Textiles with Biomimetic Leaf‐Like MXene/Silver Nanowire Nanostructures for Electromagnetic Interference Shielding,Humidity Monitoring,and Self‐Derived Hydrophobicity

Although flexible and multifunctional textiles are promising for wearable electronics and portable device applications, the main issue is to endow textiles with multifunctionalities while maintaining their innate flexible and porous features. Herein, a vacuum‐assisted layer‐by‐layer assembly technique is demonstrated to conformally deposit electrically conductive substances on textiles for developing multifunctional and flexible textiles with superb electromagnetic interference (EMI) shielding performances, superhydrophobicity, and highly sensitive humidity response. The formed leaf‐like nanostructure is composed of silver nanowires (AgNWs) as the highly conductive skeleton (vein) and transition metal carbide/carbonitride (MXene) nanosheets as the lamina. The presence of MXene protects AgNWs from oxidation and enhances the combination of AgNWs with the fabric substrate, and the transformation of its functional groups leads to self‐derived hydrophobicity. The flexible and multifunctional textile exhibits a low sheet resistance of 0.8 Ω sq^?1, outstanding EMI shielding efficiency of 54 dB in the X‐band at a small thickness of 120 µm, and highly sensitive humidity responses, while retaining its satisfactory porosity and permeability. The self‐derived hydrophobicity with a large contact angle of >140° is achieved by aging the hydrophilic MXene coated silk. The wearable multifunctional textiles are highly promising for applications in intelligent garments, humidity sensors, actuators, and EMI shielding.     

不同形状特征的碳基复合材料吸波性能分析

基于短切碳纤维、碳纳米纤维、石墨烯及炭黑,分析研究碳基复合材料中吸收剂形状比对电磁特性,尤其是吸波性能的影响。采用矢量网络分析仪测试基于不同形状比吸收剂形成碳基复合材料的电磁参数,并且计算出样品理论反射损耗。结果发现,随着频率的增加,碳基复合材料的介电常数逐渐减小;碳纳米纤维样品厚度为2 mm,在8 GHz时反射损耗达到-8 d B;炭黑与石墨烯质量比为1∶1时,在0. 5~12. 8 GHz频段内损耗角正切tanδ随频率的增大而增大且样品厚度为2mm时,其在12~16. 2 GHz反射损耗小于-10 d B,且在12. 8 GHz时反射损耗达到-22. 5 d B。通过对不同形状比吸收剂形成碳基复合材料的电磁参数分析,发现具有一定长径比或较大比表面积的吸收剂复合有利于提升碳基复合材料的吸波性能。     

Shielding Effectiveness Data on Commercial Thermoplastic Materials

Ten different commercially available conductive thermoplastic materials have been tested for near- and far-field shielding effectiveness (SE). Far-field SE was tested using a modified standard measurement technique to provide results comparable with the company-provided data. Further, housings of different thermoplastic materials were constructed and equipped with an electromagnetic interference (EMI) source to model a realistic near-field SE situation. The SE data up to 1 GHz is presented. Conductive thermoplastic materials with fillings of stainless steel fibers and nickel-coated carbon fibers were the two materials that offer the best far-field shielding performance. For the near-field shielding, two materials with filling of stainless steel fibers were the best performing ones. A thermoplastic with polycarbonate (PC) base and stainless steel content of 1.5 vol% showed the best combined far- and near-field shielding results     

Hybridization of oxidized MWNT and silver powder in polyurethane matrix for electromagnetic interference shielding application

Multiwalled carbon nanotubes (MWNTs) are chemically modified with respect to various different oxidative conditions, including the acid concentration, treatment time, and temperature. The conductivity of polyurethane (PU) composites filled with the MWNTs oxidized under optimal condition is measured as a function of frequency with the content of MWNTs and analyzed using percolation theory. Because the PU composites filled only with the MWNTs cannot satisfy the requirements for materials providing shielding against electromagnetic waves, conductive polymer composites are fabricated by the hybridization of MWNTs with Ag flakes. It is observed that a small amount of the MWNTs remarkably enhances the conductivity and shielding effectiveness of the MWNT/Ag flake/PU composites, by bridging the gap between the flaky Ag clusters. The electromagnetic interference shielding effectiveness of the composites can be controlled from about 60 dB to more than 80 dB at an extremely low loading level of both the MWNTs and the Ag flakes in the frequency range from 10 to 1000 MHz.     

Absorption-Dominant Electromagnetic Interference Shielding through Electrical Polarization and Triboelectrification in Surface-Patterned Ferroelectric Poly[(vinylidenefluoride-co-trifluoroethylene)-MXene] Composite

Extensive utilization of electronic devices and wireless equipment require human to take affirmative measures to weaken unwanted electromagnetic wave radiations. Herein, a ferroelectric poly[(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)-MXene]-poly(3,4-ethylenedioxythiophene) (PEDOT) multilayered film is developed that can increase electromagnetic interference (EMI) shielding performance through electrical polarization. The MXene is encapsulated by a P(VDF-TrFE) matrix, which inhibits oxidation, and a highly conductive MXene is created conductive network resulting in enhancement EMI shielding effectiveness (EMI SE). Furthermore, the surface pattern inducing multiple scattering and PEDOT layer contributes to the increasing absorption due to the electrically conductive PEDOT. Thanks to the electrically polarized and negatively charged P(VDF-TrFE)-MXene, the composite film demonstrates superior EMI SE and absolute EMI SE (SSE_t) are exhibited remarkable ≈61 dB and 15230 dB cm²g⁻¹ with high absorptivity (0.87) at thickness of 120 µm in X-band. Additionally, P(VDF-TrFE)-MXene composite film is applicable to motion and thermo-resistive sensor due to the negatively charged P(VDF-TrFE) and thermo-resistive property of PEDOT, respectively, for multifunctionality. This work provides a feasible avenue for flexible absorption dominant EMI shielding materials via electrical polarization with remarkable EMI shielding performance.     

Preparation of High‐Performance Conductive Polymer Fibers through Morphological Control of Networks Formed by Nanofillers

A general method is described to prepare high‐performance conductive polymer fibers or tapes. In this method, bicomponent tapes/fibers containing two layers of conductive polymer composites (CPCs) filled with multiwall carbon nanotubes (MWNT) or carbon black (CB) based on a lower‐melting‐temperature polymer and an unfilled polymer core with higher melting temperature are fabricated by a melt‐based process. Morphological control of the conductive network formed by nanofillers is realized by solid‐state drawing and annealing. Information on the morphological and electrical change of the highly oriented conductive nanofiller network in CPC bicomponent tapes during relaxation, melting, and crystallization of the polymer matrix is reported for the first time. The conductivity of these polypropylene tapes can be as high as 275 S m^?1 with tensile strengths of around 500 MPa. To the best of the authors' knowledge, it is the most conductive, high‐strength polymer fiber produced by melt‐processing reported in literature, despite the fact that only ～5 wt.% of MWNTs are used in the outer layers of the tape and the overall MWNT content in the bicomponent tape can be much lower (typically ～0.5 wt.%). Their applications could include sensing, smart textiles, electrodes for flexible solar cells, and electromagnetic interference (EMI) shielding. Furthermore, a modeling approach was used to study the relaxation process of highly oriented conductive networks formed by carbon nanofillers.