Preparation of Porous Silver Nanowires-Melamine Formaldehyde Hybrid Composite Materials and Their Electromagnetic Shielding and Flame-Retardant Properties

Along with the booming development of communication technology and electronic equipment, higher requirements of flame-retardant and EMI shielding performances for electromagnetic interference (EMI) shielding materials are put forward. Herein, the ultralight and porous silver nanowires (AgNWs)-melamine formaldehyde (MF) hybrid composite with unique micro-/nanostructure is developed by a facile dip-coating method, which uses the AgNWs as 1D conductive coating and MF foam (MF foam) as 3D skeleton template. Benefiting from the unique porous micro-/nanostructure, the resultant hybrid composite displays low density, excellent EMI shielding performances, and superior flame-retardant property. The EMI shielding effectiveness (SE) and specific EMI SE (SSEt) of the hybrid composite in X-band (8.2–12.4 GHz) can be up to 77 dB and 26971.4 dB cm⁻² g⁻¹, respectively. At the same time, the hybrid composite also passes the vertical burning test and shows an increased LOI value of 40.6%. The combination of flame-retardant and EMI shielding performances for EMI shielding materials makes the AgNWs-MF hybrid composite great application potential in civil and military fields. This work provides a new guide for the design of multifunctional high-performance EMI shielding materials.     

Carbon Nanotube–Multilayered Graphene Edge Plane Core–Shell Hybrid Foams for Ultrahigh‐Performance Electromagnetic‐Interference Shielding

Materials with an ultralow density and ultrahigh electromagnetic‐interference (EMI)‐shielding performance are highly desirable in fields of aerospace, portable electronics, and so on. Theoretical work predicts that 3D carbon nanotube (CNT)/graphene hybrids are one of the most promising lightweight EMI shielding materials, owing to their unique nanostructures and extraordinary electronic properties. Herein, for the first time, a lightweight, flexible, and conductive CNT–multilayered graphene edge plane (MLGEP) core–shell hybrid foam is fabricated using chemical vapor deposition. MLGEPs are seamlessly grown on the CNTs, and the hybrid foam exhibits excellent EMI shielding effectiveness which exceeds 38.4 or 47.5 dB in X‐band at 1.6 mm, while the density is merely 0.0058 or 0.0089 g cm^?3, respectively, which far surpasses the best values of reported carbon‐based composite materials. The grafted MLGEPs on CNTs can obviously enhance the penetration losses of microwaves in foams, leading to a greatly improved EMI shielding performance. In addition, the CNT–MLGEP hybrids also exhibit a great potential as nano‐reinforcements for fabricating high‐strength polymer‐based composites. The results provide an alternative approach to fully explore the potentials of CNT and graphene, for developing advanced multifunctional materials.     

孔隙率对三维针刺C/C复合材料电磁屏蔽性能的影响

通过多次重复先驱体浸渍裂解(PIP)工艺过程,改变材料的孔隙率和体密度,制备不同孔隙率的三维针刺碳/碳(C/C)复合材料,并研究了在8.2~12.4GHz频率范围内(X波段)不同孔隙率C/C复合材料的电磁屏蔽效能。结果表明:适当降低孔隙率有利于提高C/C复合材料的总电磁屏蔽效能和电磁吸收屏蔽效能,当开气孔率为33.4%时,C/C复合材料具有最大的电磁屏蔽效能(40dB),且电磁吸收屏蔽效能(30dB)远大于电磁反射屏蔽效能(12dB),是极具潜力的高吸收低反射电磁屏蔽材料。     

Hydrophobic,Flexible, and Lightweight MXene Foams for High‐Performance Electromagnetic‐Interference Shielding

Ultrathin, lightweight, and flexible electromagnetic‐interference (EMI) shielding materials are urgently required to manage increasingly serious radiation pollution. 2D transition‐metal carbides (MXenes) are considered promising alternatives to graphene for providing excellent EMI‐shielding performance due to their outstanding metallic electrical conductivity. However, the hydrophilicity of MXene films may affect their stability and reliability when applied in moist or wet environments. Herein, for the first time, an efficient and facile approach is reported to fabricate freestanding, flexible, and hydrophobic MXene foam with reasonable strength by assembling MXene sheets into films followed by a hydrazine‐induced foaming process. In striking contrast to well‐known hydrophilic MXene materials, the MXene foams surprisingly exhibit hydrophobic surfaces and outstanding water resistance and durability. More interestingly, a much enhanced EMI‐shielding effectiveness of ≈70 dB is achieved for the lightweight MXene foam as compared to its unfoamed film counterpart (53 dB) due to the highly efficient wave attenuation in the favorable porous structure. Therefore, the hydrophobic, flexible, and lightweight MXene foam with an excellent EMI‐shielding performance is highly promising for applications in aerospace and portable and wearable smart electronics.     

Ultrathin,flexible,and high-strength Ni/Cu/metallic glass/Cu/Ni composite with alternate magneto-electric structures for electromagnetic shielding

Electromagnetic interference (EMI) shielding materials with ultrathin,flexible,superior mechanical and thermal management properties are highly desirable for smart and wearable electronics.Here,ultrathin and flexible Ni/Cu/metallic glass/Cu/Ni (Ni/Cu/MG) multilayer composite with alternate magnetic and electrical structures was designed via facial electroless plating of Cu and Ni on an Fe-based metallic glass.The resultant 0.02 mm-thick Ni/Cu/MG composite displays a superior EMI shielding effectiveness (EMISE)of 35 dB and a great EMISE/t of 1750 dB/mm,which is greater than those of composites with monotonous multilayer or homogeneous structures.The improved EMI SE originates from the massive ohmic losses,the enhanced internal reflection/absorption,and the abundant interfacial polarization loss.Particularly,Ni/Cu/MG exhibits a high tensile strength of up to 1.2 GPa and outstanding mechanical stability,enabling the EMI SE remains unchanged after 10,000 times of bending.Moreover,Ni/Cu/MG has excellent Joule heating characteristics and thermal stability,which is very suitable for heating components of wearable hyperthermia devices.     

Electromagnetic interference (EMI) shielding of single-walled carbon nanotube epoxy composites

Single-walled carbon nanotube (SWNT)-polymer composites have been fabricated to evaluate the electromagnetic interference (EMI) shielding effectiveness (SE) of SWNTs. Our results indicate that SWNTs can be used as effective lightweight EMI shielding materials. Composites with greater than 20 dB shielding efficiency were obtained easily. EMI SE was tested in the frequency range of 10 MHz to 1.5 GHz, and the highest EMI shielding efficiency (SE) was obtained for 15 wt % SWNT, reaching 49 dB at 10 MHz and exhibiting 15-20 dB in the 500 MHz to 1.5 GHz range. The EMI SE was found to correlate with the dc conductivity, and this frequency range is found to be dominated by reflection. The effects of SWNT wall defects and aspect ratio on the EMI SE were also studied.     

Highly Stretchable Polymer Composite with Strain-Enhanced Electromagnetic Interference Shielding Effectiveness

Polymer composites with electrically conductive fillers have been developed as mechanically flexible, easily processable electromagnetic interference (EMI) shielding materials. Although there are a few elastomeric composites with nanostructured silvers and carbon nanotubes showing moderate stretchability, their EMI shielding effectiveness (SE) deteriorates consistently with stretching. Here, a highly stretchable polymer composite embedded with a three-dimensional (3D) liquid-metal (LM) network exhibiting substantial increases of EMI SE when stretched is reported, which matches the EMI SE of metallic plates over an exceptionally broad frequency range of 2.65–40 GHz. The electrical conductivities achieved in the 3D LM composite are among the state-of-the-art in stretchable conductors under large mechanical deformations. With skin-like elastic compliance and toughness, the material provides a route to meet the demands for emerging soft and human-friendly electronics.     

Effect of carbon nanofiber reinforcement on electromagnetic interference shielding effectiveness of syntactic foam

A novel carbon nanofiber (CNF)-reinforced syntactic foam (CNFRSF) was fabricated. The electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) of CNFRSF with various volume fraction of CNFs (0–2.0 vol%) were evaluated experimentally. The measurement of EMI SE was carried out in a frequency range of 30 MHz to 1.2 GHz. The experimental results showed that the SE of CNFRSF increases with increase of CNFs content and CNF is more effective in providing EMI shielding compared to chopped carbon fiber and long carbon fiber due to the larger aspect ratio. The CNFRSF having 2.0 vol% CNFs has a SE of 25 dB, which is good enough for most practical applications. Compared to CNFs composites, the EMI SE of CNFRSF has been enhanced by the presence of hollow carbon microspheres. The underlying mechanism is discussed in detail.     

Electrical conductivity and shielding effectiveness of poly(trimethylene terephthalate)/multiwalled carbon nanotube composites

Poly(trimethylene terephthalate) (PTT)/multiwalled carbon nanotube (MWCNT) composites have been fabricated to evaluate the potential of PTT composites as electromagnetic interference (EMI) shielding material. The room temperature electrical conductivity, complex permittivity, and shielding effectiveness (SE) of PTT/MWCNT composites were studied in the frequency range of 8.2–12.4 GHz (X-band). The dc conductivity (σ) of composites increased with increasing MWCNT loading and a typical percolation behavior was observed at 0.48 vol% MWCNT loading. The highest EMI SE of PTT/MWCNT composites was ~23 decibel (dB) at 4.76 vol% MWCNT loading which suggest that these composites can be used as light weight EMI shielding materials. The correlation among the SE, complex permittivity, and electrical conductivity was also studied. The EMI shielding mechanism of PTT/MWCNT composites was studied by resolving the total EMI SE into absorption and reflection loss.     

Anticorrosive,Ultralight, and Flexible Carbon‐Wrapped Metallic Nanowire Hybrid Sponges for Highly Efficient Electromagnetic Interference Shielding

Metal‐based materials with exceptional intrinsic conductivity own excellent electromagnetic interference (EMI) shielding performance. However, high density, corrosion susceptibility, and poor flexibility of the metal severely restrict their further applications in the areas of aircraft/aerospace, portable and wearable smart electronics. Herein, a lightweight, flexible, and anticorrosive silver nanowire wrapped carbon hybrid sponge (Ag@C) is fabricated and employed as ultrahigh efficiency EMI shielding material. The interconnected Ag@C hybrid sponges provide an effective way for electron transport, leading to a remarkable conductivity of 363.1 S m^?1 and superb EMI shielding effectiveness of around 70.1 dB in the frequency range of 8.2–18 GHz, while the density is as low as 0.00382 g cm^?3, which are among the best performances for electrically conductive sponges/aerogels/foams by far. More importantly, the Ag@C sponge surprisingly exhibits super‐hydrophobicity and strong corrosion resistance. In addition, the hybrid sponges possess excellent mechanical resilience even with a large strain (90% reversible compressibility) and an outstanding cycling stability, which is far better than the bare metallic aerogels, such as silver nanowire aerogels and copper nanowire foams. This strategy provides a facile methodology to fabricate lightweight, flexible, and anticorrosive metal‐based sponge for highly efficient EMI shielding applications.     

Flexible and Ultrathin Waterproof Cellular Membranes Based on High-Conjunction Metal-Wrapped Polymer Nanofibers for Electromagnetic Interference Shielding

Ultrathin, lightweight, and flexible electromagnetic interference (EMI) shielding materials are urgently demanded to address EM radiation pollution. Efficient design to utilize the shields' microstructures is crucial yet remains highly challenging for maximum EMI shielding effectiveness (SE) while minimizing material consumption. Herein, novel cellular membranes are designed based on a facile polydopamine-assisted metal (copper or silver) deposition on electrospun polymer nanofibers. The membranes can efficiently exploit the high-conjunction cellular structures of metal and polymer nanofibers, and their interactions for excellent electrical conductivity, mechanical flexibility, and ultrahigh EMI shielding performance. EMI SE reaches more than 53 dB in an ultra-broadband frequency range at a membrane thickness of merely 2.5 µm and a density of 1.6 g cm⁻³, and an SE of 44.7 dB is accomplished at the lowest thickness of 1.2 µm. The normalized specific SE is up to 232 860 dB cm² g⁻¹, significantly surpassing that of other shielding materials ever reported. More, integrated functionalities are discovered in the membrane, such as antibacterial, waterproof properties, excellent air permeability, high resistance to mechanical deformations and low-voltage uniform heating performance, offering strong potential for applications in aerospace and portable and wearable smart electronics.     

三维碳化硅纳米线增强碳化硅陶瓷基复合材料的电磁屏蔽性能

碳化硅纳米线具有优异的电磁吸收性能, 三维网络结构可以更好地使电磁波在空间内被多次反射和吸收。通过抽滤的方法制备得到体积分数20%交错排列的碳化硅纳米线网络预制体。然后采用化学气相渗透工艺制备热解炭界面和碳化硅基体, 并通过化学气相渗透和前驱体浸渍热解工艺得到致密的SiCNWs/SiC陶瓷基复合材料。甲烷和三氯甲基硅烷分别是热解炭和碳化硅的前驱体, 随着热解碳质量分数从21.3%增加到29.5%, 多孔SiCNWs预制体电磁屏蔽效率均值在8~12 GHz (X)波段从9.2 dB增加到64.1 dB。质量增重13%的热解碳界面修饰的SiCNWs/SiC陶瓷基复合材料在X波段平均电磁屏蔽效率达到37.8 dB电磁屏蔽性能。结果显示, SiCNWs/SiC陶瓷基复合材料在新一代军事电磁屏蔽材料中具有潜在应用前景。     

Electromagnetic interference shielding characteristics of carbon nanofiber-polymer composites

Electromagnetic interference (EMI) shielding characteristics of carbon nanofiber-polystyrene composites were investigated in the frequency range of 12.4-18 GHz (Ku-band). It was observed that the shielding effectiveness of such composites was frequency independent, and increased with increasing carbon nanofiber loading within Ku-band. The experimental data exhibited that the shielding effectiveness of the polymer composite containing 20 wt% carbon nanofibers could reach more than 36 dB in the measured frequency region, indicating such composites can be applied to the potential EMI shielding materials. In addition, the results showed that the contribution of reflection to the EMI shielding effectiveness was much larger than that of absorption, implying the primary EMI shielding mechanism of such composites was reflection of electromagnetic radiation within Ku-band.     

Porous composites coated with hybrid nano carbon materials perform excellent electromagnetic interference shielding

This work reported preparation of porous composites using a simple dip-coating method, and the fabricated composites containing hybrid carbon nanomaterials performed excellent electromagnetic interference (EMI) shielding properties. A commercial sponge was coated with silver nanoparticles before being dip-coated with graphene (GP)/ink, multi-wall carbon nanotubes (MWCNTs)/ink, or hybrid GP/MWCNTs/ink to form Ag/carbon nanomaterial hybrid composites, and then the composites were subjected to EMI measurements in the frequency range of 0.45–1.5 GHz. For comparison, the sponges without Ag nanoparticle coating were also prepared. Herein, we found an insignificant difference in EMI SE among the porous composites without Ag nanoparticle coating, and the maximum values of approximately 14.4 dB was attained. Interestingly, the hybrid composites with Ag nanoparticle coating exhibited maximum EMI shielding of 24.33 dB. Due to their porous structure, the EMI SE measurements showed that reflection dominates the EMI SE for all the sponge composites studied in this work.     

Novel carbon nanotube-polystyrene foam composites for electromagnetic interference shielding

A novel carbon nanotube-polystyrene foam composite has been fabricated successfully. The electromagnetic interference (EMI) shielding effectiveness measurements indicated that such foam composites can be used as very effective, lightweight shielding materials. The correlation between the shielding effectiveness and electrical conductivity and the EMI shielding mechanism of such foam composites are also discussed.     

Electromagnetic interference shielding of composites consisting of a polyester matrix and carbon nanotube-coated fiber reinforcement

We investigated the electromagnetic interference shielding effectiveness (EMI SE) of composites consisting of an unsaturated polyester matrix containing woven glass or carbon fibers that had been coated with multiwalled carbon nanotubes (MWCNTs). Composite panels consisting of fiber fabrics with various combinations of fabric type and stacking sequence were fabricated. Their EMI SE was measured in the frequency range of 30 MHz–1.5 GHz. The underlying physics governing the EMI shielding mechanisms of the materials, namely, absorption, reflection, and multiple reflections, was investigated and used in analytical models to predict the EMI SE. Simulation and experimental results showed that the contributions of reflection and absorption to EMI shielding is enhanced by sufficient impedance mismatching, while multiple reflections have a negative effect. For a given amount of MWCNTs in the glass-fiber–reinforced composite, coating the outermost, instead of intermediate, glass fiber plies with MWCNTs was found to maximize the conductivity and SE.     

A mechanistic study on electromagnetic shielding effectiveness of polysulfone/carbon nanofibers nanocomposites

The present study aims to produce a light weight electromagnetic interference (EMI) shielding material from carbon nanofibers (CNFs)-based polysulfone (PSU) nanocomposites. EMI shielding effectiveness (EMI SE) was studied by analyzing the electromagnetic wave transmission, reflection, and absorption characteristics of nanocomposites. The electrical conductivity and EMI SE of the nanocomposite with different weight percentage of CNFs (3–10 wt%) were investigated at room temperature and the measurement of EMI SE was carried out in a frequency range of 8.2–12.4 GHz (X-band). The mechanism of EMI shielding of PSU/CNFs nanocomposite has been well explained by comparing the contribution of reflection and absorption to the total EMI SE. The state of dispersion of CNFs and PSU–CNFs interaction was studied by high resolution transmission electron microscopy and scanning electron microscopy. The thermal stability of nanocomposite studied from thermogravimetric analysis was increased after addition of CNFs to PSU matrix. Electrical conductivity of nanocomposite followed power law model of percolation theory having a percolation threshold Φ_c = 0.0079 vol% (0.9 wt%) and exponent t = 1.73. The EMI SE of nanocomposites with thickness of 1 mm was 19–45 decibel (dB) at 3–10 wt% CNFs loading. This high thermal stability and high EMI SE suggest the potential use of PSU/CNFs nanocomposite as effective lightweight EMI shielding material in different electronic applications.     

Broadband electromagnetic shielding and dielectric properties of polyaniline-stannous oxide composites

Conducting polyaniline-stannous oxide (PAni-SnO) composites were synthesized by the in situ polymerization of aniline in the presence of SnO. The composites formed were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As there is a greater need for materials with electromagnetic interference (EMI) shielding properties over a large operating frequency band, the present study highlights the dielectric and EMI shielding response of PAni-SnO composites in the microwave frequency range from 8 to 18 GHz (X and Ku bands). All the computations were based on microwave scattering parameters measured by transmission line waveguide technique. The EMI shielding effectiveness (EMI SE), return loss, microwave absorption and dielectric properties of the PAni-SnO composites were evaluated for various wt% of SnO (10, 20, 30, 40 and 50 wt%) in PAni. In X-band, the composites exhibits EMI SE in the range ?18 to ?23 dB, with microwave absorbance of 70–83 % and in the Ku-band, the composites exhibits EMI SE values of ?17.5 to ?22.5 dB with 67–85 % absorbance. Our investigations reveal that the PAni-SnO composites are potential candidates for EMI shielding applications for both the X and Ku bands.     

Lightweight multi-walled carbon nanotube buckypaper/glass fiber–epoxy composites for strong electromagnetic interference shielding and efficient microwave absorption

Multi-walled carbon nanotube buckypaper (BP) reinforced glass fiber–epoxy (GF/EP) composites were selected to fabricate electromagnetic interference (EMI) shielding and microwave absorbing materials. Six different composite configurations with 3.0 mm thick have been conceived and tested over the X-band (8.2–12.4 GHz). Flexible and low-density (0.29 g/cm³) BP provided a high specific EMI SE of 76 dB with controlled electrical conductivity. GF/EP/BP₁₁₁ and GF/EP/BP₁₀₁ composites possess EMI SE as high as of 50–60 dB, which can be attributed to the number of BP inserted and variation in the wave-transmitting layer of the laminates. Furthermore, the shielding mechanism was discussed and suggested that the absorption was the dominant contribution to EMI SE. GF/EP/BP₁₁₀ laminate demonstrated suitable EMI performance (~?20 dB), whereas GF/EP/BP₀₁₁ composite revealed excellent microwave performance, achieving an effective ? 10 dB bandwidth of 3.04 GHz and minimum reflection loss (RL) value of ? 21.16 dB at 10.37 GHz. On the basis of these results, GF/EP/BP composites prepared in this work have potential applications as both EMI shielding and microwave absorber materials given their facile preparation and lightweight use.

     

石墨烯/聚苯胺复合材料的电磁屏蔽性能

采用直流电弧放电法制备高结晶性石墨烯, 利用乙醇助溶分散法得到石墨烯/聚苯胺电磁屏蔽复合材料, 研究不同掺杂比例的石墨烯/聚苯胺复合材料的电磁屏蔽性能。拉曼光谱分析表明: 由于石墨烯与聚苯胺之间的相互作用, 复合材料中聚苯胺特征峰比纯聚苯胺特征峰稍弱或向低频方向移动。复合物的电导率随石墨烯掺杂量的增加而增大, 当掺杂质量分数为25%时, 其电导率达到19.4 S/cm, 接近纯石墨烯电导率(20.1 S/cm)。频率为2~18 GHz时, 复合材料的电磁屏蔽效能随着石墨烯掺杂量和频率的增大而增强; 当石墨烯掺杂质量分数为25%时, 总屏蔽效能在2~18 GHz范围内由19.8 dB增至34.2 dB, 增加了约42%, 其中吸收部分占总屏蔽效能的比例为66%~81%, 这表明石墨烯/聚苯胺复合材料的电磁屏蔽性质是以电磁波吸收为主; 同时也说明了拥有特殊结构与特性的石墨烯是一种较好的聚苯胺填料, 在微波屏蔽与微波吸收领域将会有广阔的应用前景。