屏蔽EMI的金属及炭素填充的高分子复合材料

屏蔽EMI材料是现代电子、电器工业不可缺少的材料之一,尤其是屏蔽EMI高分子材料已经成为绝大多数信息技术设备的壳体材料,它们在现代电子工业中有着举足轻重的地位.本文对屏蔽EMI的方法及高分子复合材料的特性和发展概况等作简要介绍.     

Co-Ni Electromagnetic Coupling in Hollow Mo2C/NC Sphere for Enhancing Electromagnetic Wave Absorbing Performance†

For enhancing the electromagnetic wave (EW) attenuation and adsorption, rational constructing and homogeneously distributing bimetallic electromagnetic coupling units in hollow structure is an effective way, but hard to achieve. Herein, a CoNi-doped hybrid zeolite imidazole framework was synthesized as precursor, which was further converted into a hollow CoNi-bimetallic doped molybdenum carbide sphere (H-CoNi@MoC/NC) through a two-step etching and calcination strategy. At the loading amount of 15 wt%, a strong absorption of minimum reflection loss (RL_min) of –60.05 dB at 7.2 GHz with the thickness of 3.1 mm and a wide effective adsorption bandwidth (EAB) of 3.52 GHz at the thickness of 2.5 mm were achieved, which was far beyond the reported MoC-based metallic hybrids. The crucial synergistic Co-Ni electromagnetic coupling effect in the composite was characterized, not only enhancing the dipolar/interfacial polarization, but also promoting the impedance matching, displaying the optimized EW absorbing performance.      

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.     

Facile Fabrication of PBS/CNTs Nanocomposite Foam for Electromagnetic Interference Shielding

In order to reduce the pollutants of environment and electromagnetic waves, environment friendly polymer foams with outstanding electromagnetic interference shielding are imminently required. In this paper, a kind of electromagnetic shielding, biodegradable nanocomposite foam was fabricated by blending poly (butylene succinate) (PBS) with carbon nanotubes (CNTs) followed by foaming with supercritical CO₂. The crystallization temperature and melting temperature of PBS/CNTs nanocomposites with 4 wt % of CNTs increased remarkably by 6 °C and 3.1 °C compared with that of pure PBS and a double crystal melting peak of various PBS samples appeared in DSC curves. Increasing the CNT content from 0 to 4 wt % leads to an increase of approximately 3 orders of magnitude in storage modulus and nearly 9 orders of magnitude in enhancement of electrical properties. Furthermore, CNTs endowed PBS nanocomposite foam with adjustable electromagnetic interference (EMI) shielding property, giving a specific EMI shielding effectiveness of 28.5 dB cm³/g. This study provides a promising methodology for preparing biodegradable, lightweight PBS/CNTs foam with outstanding electromagnetic shielding properties.     

一种提高有机硅导电橡胶复合材料导电和电磁屏蔽性能的方法

描述了一种利用多元复合导电网络提高有机硅橡胶复合材料导电和电磁屏蔽性能的思想。这种含有多元复合导电网络的复合材料是通过将镀银泡沫、导电填料和有机硅橡胶复合在一起而制备的。利用扫描电子显微镜观察了复合材料的微观结构,采用电阻测试仪、矢量网络分析仪、热失重分析仪分别研究了复合材料的导电性、电磁屏蔽性能及热稳定性,并探讨了补强剂SiO2对这些性能的影响。结果表明,2%碳纳米管/导电泡沫/硅橡胶多元复合体系相比于2%碳纳米管/硅橡胶单一复合体系电阻率降低了6个数量级,平均电磁屏蔽效能由12dB提高到52dB,增大了4倍。当导电填料换为炭黑后,2%炭黑/导电泡沫/硅橡胶多元复合体系相比于2%炭黑/硅橡胶单一复合体系电阻率降低了7个数量级,平均电磁屏蔽效能由10dB提高到50dB,增大了5倍。由于多元复合导电网络,材料的导电性能和电磁屏蔽性能大幅度提升。此外,补强剂的加入增大了复合材料的热稳定性,但降低了其导电和电磁屏蔽性能。     

Carbon Papers from Tall Goldenrod Cellulose Fibers and Carbon Nanotubes for Application as Electromagnetic Interference Shielding Materials

To transform tall goldenrods, which are invasive alien plant that destroy the ecosystem of South Korea, into useful materials, cellulose fibers isolated from tall goldenrods are applied as EMI shielding materials in this study. The obtained cellulose fibers were blended with CNTs, which were used as additives, to improve the electrical conductivity. TGCF/CNT papers prepared using a facile paper manufacturing process with various weight percent ratios and thickness were carbonized at high temperatures and investigated as EMI shielding materials. The increase in the carbonization temperature, thickness, and CNT content enhanced the electrical conductivity and EMI SE of TGCF/CNT carbon papers. TGCF/CNT-15 papers, with approximately 4.5 mm of thickness, carbonized at 1300 °C exhibited the highest electrical conductivity of 6.35 S cm⁻¹, indicating an EMI SE of approximately 62 dB at 1.6 GHz of the low frequency band. Additionally, the obtained TGCF/CNT carbon papers were flexible and could be bent and wound without breaking.     

The Preparation of Compressible and Fire‐Resistant Sponge‐Supported Reduced Graphene Oxide Aerogel for Electromagnetic Interference Shielding

We here report a facile method to fabricate a sponge‐supported reduced graphene oxide aerogel (S‐RGOA) using a commercial melamine sponge and graphene oxide (GO). Firstly, GO sheets were self‐assembled within the melamine sponge by the assistance of a chemical cross‐linking agent; and then, freeze‐drying and thermal treatment were adopted to prepare S‐RGOA, in which continuous porous reduced graphene oxide (RGO) network formed between the skeleton. The resulting S‐RGOA exhibited a high electromagnetic interference shielding effectiveness (EMI SE) of 20.4‐27.3 dB in 8–12 GHz and the specific EMI SE could reach 1437 dB?cm³g^?1. The mechanical test suggests that the lightweight S‐RGOA is compressible and possesses low energy dissipation. Burning and TGA measurements indicate that S‐RGOA is fire‐resistant and has excellent thermal stability. Our work provides an economical and environmentally‐friendly method to fabricate RGO aerogels for using as electromagnetic interference materials.     

The Role of Phase Migration of Carbon Nanotubes in Melt-Mixed PVDF/PE Polymer Blends for High Conductivity and EMI Shielding Applications

In this work, the effects of blend ratio and mixing time on the migration of multi-walled carbon nanotubes (MWCNTs) within poly(vinylidene fluoride) (PVDF)/polyethylene (PE) blends are studied. A novel two-step mixing approach was used to pre-localize MWCNTs within the PE phase, and subsequently allow them to migrate into the thermodynamically favored PVDF phase. Light microscopy images confirm that MWCNTs migrate from PE to PVDF, and transmission electron microscopy (TEM) images show individual MWCNTs migrating fully into PVDF, while agglomerates remained trapped at the PVDF/PE interface. PVDF:PE 50:50 and 20:80 polymer blend nanocomposites with 2 vol% MWCNTs exhibit exceptional electromagnetic interference shielding effectiveness (EMI SE) at 10 min of mixing (13 and 16 dB, respectively-at a thickness of 0.45 mm), when compared to 30 s of mixing (11 and 12 dB, respectively), suggesting the formation of more interconnected MWCNT networks over time. TEM images show that these improved microstructures are concentrated on the PE side of the PVDF/PE interface. A modified version of the “Slim-Fast-Mechanism” is proposed to explain the migration behavior of MWCNTs within the PVDF/PE blend. In this theory, MWCNTs approaching perpendicular to the interface penetrate the PVDF/PE interface, while those approaching in parallel or as MWCNT agglomerates remain trapped. Trapped MWCNTs act as barriers to additional MWCNTs, regardless of geometry. This mechanism is verified via TEM and scanning electron microscopy and suggests the feasibility of localizing MWCNTs at the interface of PVDF/PE blends.     

EMI shielding and dynamic mechanical analysis of graphene oxide-carbon nanotube-acrylonitrile butadiene styrene hybrid composites

Carbon nanomaterials such as carbon nanotubes (CNTs), graphene and their hybrid have been studied extensively. Despite having excellent properties of CNTs and graphene have not yet been fully realized in the polymer composites. During fabrication agglomeration of CNTs and restacking of graphene is a serious concern that results in the degradation of properties of nanomaterials into the final composites. To improve the dispersion of CNTs and restacking graphene, in the present research work, we focused on the hybridization of graphene oxide and CNTs. Multiwalled carbon nanotubes (MWCNTs), functionalized carbon nanotubes (FCNTs), and graphene oxide-carbon nanotubes (GCNTs) reinforced acrylonitrile butadiene styrene (ABS) composites were prepared separately by vacuum filtration followed by hot compression molding. Further, dynamic mechanical analysis (DMA), and electromagnetic interference (EMI) shielding properties of ABS composites reinforced carbon nanofillers were investigated. The dynamic mechanical properties of polymers strongly depend on the adhesion of fillers and polymer, entanglement density of polymer chains in the presence of carbon fillers. The dynamic mechanical characteristics such as storage, loss modulus, and damping factor of prepared composites were significantly affected by the incorporation of MWCNTs, FCNTs, and GCNTs. Maximum EMI shielding effectiveness of −49.6 dB was achieved for GCNT-ABS composites which were highest compared to MWCNTs-ABS composites (−38.6 dB) and FCNTs-ABS composites (−36.7 dB) in the Ku band (12.4–18 GHz). These results depict the great potential of GCNTs-ABS composites to be used in various applications of efficient heat dissipative EMI shielding materials for electronic devices.     

Characterisation of morphology of self-assembled PEG monolayers: a comparison of mixed and pure coatings optimised for biosensor applications

For detection of low concentrations of analytes in complex biological matrices using optical biosensors, a high surface loading with capture molecules and a low nonspecific binding of nonrelevant matrix molecules are essential. To tailor biosensor surfaces in such a manner, poly(ethylene glycols) (PEG) in varying lengths were immobilised covalently onto glass-type surfaces in different mixing ratios and concentrations, and were subsequently modified with three different kinds of receptors. The nonspecific binding of a model protein (ovalbumin, OVA) and the maximum loading of the respective analytes to these prepared surfaces were monitored using label-free and time-resolved reflectometric interference spectroscopy (RIfS). The three different analytes used varied in size: 150 kDa for the anti-atrazine antibody, 60 kDa for streptavidin and 5 kDa for the 15-bp oligonucleotide. We investigated if the mixing of PEG in different lengths could increase the surface loadings of analyte mimicking a three-dimensional matrix as was found using dextrans as sensor coatings. In addition, the effect on the surface loading was investigated with regard to the size of the analyte molecule using such mixed PEGs on the sensor surface. For further characterisation of the surface coatings, polarisation modulation infrared reflection absorption spectroscopy, atomic force microscopy, and ellipsometry were applied. All authors contributed equally to this work.     

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.