Electromagnetic interference shielding of graphene/epoxy composites

Composites based on graphene-based sheets have been fabricated by incorporating solution-processable functionalized graphene into an epoxy matrix, and their electromagnetic interference (EMI) shielding studies were studied. The composites show a low percolation threshold of 0.52 vol.%. EMI shielding effectiveness was tested over a frequency range of 8.2-12.4 GHz (X-band), and 21 dB shielding efficiency was obtained for 15 wt% (8.8 vol.%) loading, indicating that they may be used as lightweight, effective EMI shielding materials.     

Fluorination effects of carbon black additives for electrical properties and EMI shielding efficiency by improved dispersion and adhesion

Electrospinning and heat treatment were carried out to get nano sized carbon fibers (CFs) as a matrix for shielding the electromagnetic interference (EMI). In order to improve the electrical conductivity and EMI shielding efficiency of electrospun CFs, carbon black (CB) was fluorinated and embedded into the electrospun CFs. Electrospun fiber sheets embedded fluorinated CB were heat-treated at different temperatures to determine the effects on electrical properties. It is demonstrated that fluorination treatment of CB and heat treatment of electrospun sheets at higher temperature lead to higher electrical conductivities and EMI shielding efficiencies, because fluorination significantly improved its dispersion in electrospun CF webs and created good adhesion between the CB and the CFs. The electrical conductivity of carbon composite sheets (webs) reached ∼38 S/cm, and a high EMI shielding efficiency was obtained (∼50 dB).     

Electrical,rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)‐filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator–conductor transition was very sharp and the electrical percolation threshold at room temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, respectively. The EMI SE over the X‐band frequency range (8–12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15 wt% conductive fillers, respectively, were in the range ?22 to ?20 dB, indicating that these composites are promising candidates for shielding applications. © 2013 Society of Chemical Industry     

Effect of MnO2 additive on the dielectric and electromagnetic interference shielding properties of sintered cement-based ceramics

Cement-based ceramic pellets were prepared and their properties were studied for electromagnetic interference (EMI) shielding applications. The shielding materials were made of Portland cement with the addition of different concentrations of manganese oxide (MnO₂) up to 10 wt%. The pellets were sintered at 850 °C for 5 h and then polished prior to characterizations of density, porosity, microstructures, dielectric properties, and EMI shielding effectiveness (SE). Results show that the MnO₂-cement pellets have good dielectric properties, i.e. high dielectric constant (∼300) and low dielectric loss (<0.3). The dielectric constant increased with increasing MnO₂ content in the cement matrix. The SE values of the MnO₂-cements fluctuated between 2 dB and 9 dB in the frequency range of 8-13 GHz. The sample with 10 wt% MnO₂ additive had SE values of up to 9 dB. Most of the samples with high additive concentrations produced SE exceeding 7 dB.     

Enhanced electromagnetic interference shielding performance of geopolymer nanocomposites by incorporating carbon nanotubes with controllable silica shell

The development of construction materials with exceptional electromagnetic interference (EMI) shielding performance is urgently needed to restrict the admittance of electromagnetic (EM) radiation. In this work, silica (SiO₂)-coated carbon nanotubes (S-CNT) with different shell thicknesses (～7, ～10, and ～15 nm) were prepared by a sol-gel method. The effect of SiO₂ shell thickness on the EMI shielding performance of the resulting geopolymer nanocomposites was studied. The coated SiO₂ shell effectively facilitated the dispersion of CNT in the geopolymer matrix due to the chemical reaction between SiO₂ and the geopolymer. The dispersability of modified CNT could be further improved by increasing the thickness of the SiO₂ shell. However, electron delocalization was hindered by the insulating SiO₂ shell. The conductive nature of CNT was restored during geopolymerization when the SiO₂ shell was thin. A high EMI shielding effectiveness (SE) of 24.2 dB was achieved for the geopolymer nanocomposite containing 5 vol% S-CNT with a thin SiO₂ shell. The value achieved was more competitive than reported composites for construction when the sample thickness and filler content were considered.     

The influence of single-walled carbon nanotube structure on the electromagnetic interference shielding efficiency of its epoxy composites

Three types of single-walled carbon nanotube (SWCNT) homogeneous epoxy composites with different SWCNT loadings (0.01-15%) have been evaluated for electromagnetic interference (EMI) shielding effectiveness (SE) in the X-band range (8.2-12.4 GHz). The effect of the SWCNT structure including both the SWCNT aspect ratio and wall integrity, on the EMI SE have been studied and are found to correlate well with the conductivity and percolation results for these composites. The composites show very low conductivity thresholds (e.g. 0.062%). A 20-30 dB EMI SE has been obtained in the X-band range for 15% SWCNT loading, indicating that the composites can be used as effective lightweight EMI shielding materials. Furthermore, their EMI performance to radio frequencies is found to correspond well with their permittivity data.     

Electromagnetic interference shielding properties of polymer-grafted carbon nanotube composites with high electrical resistance

Poly(methyl methacrylate) (PMMA)-grafted multiwalled CNTs were prepared, and then dispersed into additional PMMA matrix, yielding highly insulated PMMA–CNT composites. The volume resistivity of PMMA–CNT was as high as 1.3 × 10¹⁵ Ω cm even at 7.3 wt% of the CNT. The individual CNTs electrically-isolated by the grafted PMMA chains in PMMA–CNT transmitted electromagnetic (EM) waves in the frequency range of 0.001–1 GHz, whereas the percolated CNTs in a conventional composite prepared by blending PMMA with the pristine CNTs strongly shielded the EM waves. This result suggests that the intrinsic conductivity of the CNT itself in PMMA–CNT does not contribute to the EM interference (EMI) shielding in the frequency range of 0.001–1 GHz. On the other hand, PMMA–CNT exhibited EMI shielding at the higher frequency range than 1 GHz because the dielectric loss of the CNT itself was rapidly increased over 1 GHz. At 110 GHz, PMMA–CNT with 7.3 wt% of the CNT had EMI SE of as high as 29 dB (0.57 mm thickness), though is slightly lower than that of the percolated conventional composite (35 dB). Thus, it is demonstrated that the highly insulated PMMA–CNT has the good EMI shielding at extremely high frequency range (30–300 GHz).     

A parametric study of carbon nanotubes production from tetrachloroethylene using a supersonic thermal plasma jet

In this study we produce carbon nanotubes (CNT) using a DC non-transferred plasma torch operated at a power of 30 kW in argon and producing a supersonic jet. Tetrachloroethylene (TCE) is used as the carbon raw material. As an initial demonstration of the supersonic plasma jet approach and in an attempt to simplify the flow/nucleation fields of metal catalyst nanoparticles, the erosion of the torch tungsten electrodes is used as a source of metal vapours nucleating in situ into catalytic nanoparticles within the plasma jet. CNT mass yield values are based on thermogravimetry analysis correlated using electron microscopy and Raman spectroscopy. A parametric study is made to evaluate the influence of the different operating parameters on the yields of carbon nanotubes. The rapid quench generated by the supersonic jet, the high vapour pressures of carbon and a control of the temperature profile within the torch nozzle enable the rapid growth of CNT. Decreasing the reactor pressure from 0.66 to 0.26 atm leads to a CNT yield increase by 22%. High vapour pressure of carbon is obtained by increasing the TCE feed rate. From 0.05 to 0.15 mol/min, the yield of CNT is improved from 38.6 to 53.7 wt%. Beyond 0.15 mol TCE/min, the yield of CNT levels to around 50 wt%. In the start-up phase, the time of operation controls the temperature profile, which in turn drastically increases the yield of CNT from 0 to 8.2 wt% between the 3rd and the 4th minute of operation and to 53.7 wt% after the 5th minute.     

Synthesis of ionic liquid modified 1-D nanomaterial and its strategical distribution into the biodegradable binary polymer matrix to get reduced electrical percolation threshold and electromagnetic interference shielding effectiveness

Ionic liquid is increasingly being used as a chemical modulator of multi-walled carbon nanotubes (MWCNT). Here, we report the practical method for producing biodegradable electromagnetic interference (EMI) shield films made of thermoplastic polyurethane (TPU), polybutylene adipate-co-terephthalate (PBAT), and 1-(2-aminoethyl)-3-methyl-1H-imidazol-3-ium modified MWCNT (MIL). The field emission scanning electron microscopy study of cryo-fractured 50:50 PBAT/TPU blend giving co-continuous morphology and subsequent polymer EMI shield nanocomposite material had shown the co-continuous nanofiller distribution. The nanoparticles were chosen to be distributed in the PBAT portion, according to subsequent research employing HRTEM and DMA. The electrical percolation threshold (EPT) is determined to be situated within 1–3 wt% of nanoparticles loading as the remarkable shift in total EMI shielding efficiency from −14.6 dB (for 1 wt%) to −28.6 dB (for 3 wt%) of nanoparticle-loaded film at 10 GHz (in X-band region) for a 0.8 mm thick film reveals that the EPT is approximately at 2 wt% of nanoparticle loading. The effective EMI shielding of −37.3 dB was achieved by 10 wt% of MIL loading.     

A Unique Double Percolated Polymer Composite for Highly Efficient Electromagnetic Interference Shielding

This study has developed a carbon nanotube (CNT)/ethylene vinyl acetate (EVA)/ultrahigh molecular weight polyethylene (UHMWPE) composite with a unique double percolated conductive structure, in which only 20 wt% of CNT enriched EVA is needed to form a continuous conductive network. Compared with conventional double percolated conductive polymer composites (CPCs) which require filler‐enriched polymer content up to 50 wt%, the low CNT/EVA content gives rise to an unprecedentedly increased effective CNT concentration in the CNT/EVA/UHMWPE composite. The double percolated composite exhibits electrical conductivity comparable to that obtained in CNT‐loaded single EVA composite with five times of CNT content. Only 7.0 wt% CNT gives the composite an electromagnetic interference (EMI) shielding effectiveness of 57.4 dB, much higher than that of mostly reported CNT and graphene based CPCs. Absorption is demonstrated to be the primary shielding mechanism due to the numerous interfaces between UHMWPE domains and CNT/EVA layers facilitating multiple reflection, scattering, and absorption of the incident microwaves. The construction of unique double percolated structure in this work provides a promising strategy for developing cost‐effective and high‐performance CPCs for use as efficient EMI shielding materials.

     

Excellent electromagnetic interference shielding and mechanical properties accomplished in a manganese dioxide decorated graphene/polymer composite

In this work, we have incorporated pristine graphene and graphene sheets decorated with α and δ forms of manganese dioxide in a hydrogenated nitrile butadiene rubber matrix to obtain high-performance composites. The dual mixing technique was adopted to fabricate the composites having enhanced tensile, dielectric, and electromagnetic interference (EMI) shielding properties. The pristine graphene was introduced at various loadings, however, the α and δ manganese dioxide doped graphene was integrated at a single 8 phr concentration onto the rubber matrix. At an optimized concentration of 8 phr graphene in the matrix, a 101% increase in the tensile strength was observed compared to the unfilled rubber. An excellent improvement in the dielectric properties and a high EMI shielding value of 24.5 dB was observed for the15 phr loaded composite having a thickness of 2 mm. The composites should principally find applications as a robust and lightweight EMI shielding material.     

Carbon nanotube imprinting on a polymer surface

Imprinting of multi-walled carbon nanotubes (CNTs) on the surface of a polymer sheet was demonstrated using interphase CNT transfer from one polymer to another. A pure polycarbonate (PC) sheet was placed on top of a sheet of a polypropylene (PP)/CNT composite and annealed at either 200 or 300 °C. It was found that CNTs move from the PP/CNT composite to the PC during annealing. The sheets of PP/CNT and PC were easily separated because of the large interfacial tension between PP and PC. The formation of a thin CNT-rich layer on the surface of the separated PC sheet produces electrical conductivity. Consequently, a conductive sheet is obtained with 2 wt.% of CNTs only in the thin surface layer. Since the CNT transfer is attributed to Brownian motion, the annealing conditions such as temperature and time are responsible for the diffusion. The polymer species decides the ability of the CNTs to transfer.     

Probing the engineered sandwich network of vertically aligned carbon nanotube–reduced graphene oxide composites for high performance electromagnetic interference shielding applications

Herein, we developed a strategy for fabrication of iron oxide infiltrated vertically aligned multiwalled carbon nanotubes (MWCNT forest) sandwiched with reduced graphene oxide (rGO) sheets network for high performance electromagnetic interference (EMI) shielding application which offers a new avenue in this area. Such engineered sandwiched network exhibits enhanced shielding effectiveness compared to conventional EMI shielding materials. This network of exotic carbons demonstrates the shielding effectiveness value more than 37 dB (>99.98% attenuation) in Ku-band (12.4–18 GHz), which is greater than the recommended limit (∼30 dB) for techno-commercial applications.     

Electrical conductivity and electromagnetic interference shielding effectiveness of nano-structured carbon assisted poly(methyl methacrylate) nanocomposites

Nanostructured carbon-based polymeric nanocomposites are gaining research interest because of their cost-effectiveness, lightweight, and robust electromagnetic interference (EMI) shielding performance. Till now, it is a great challenge to design and fabricate highly scalable, cost-effective nanocomposites with superior EMI shielding performance. Herein, highly scalable EMI shielding material with tunable absorbing behaviors comprising of low-budget ketjen black (K-CB) reinforced poly(methyl methacrylate) (PMMA) nanocomposites have been prepared using simple solvent assisted solution mixing technique followed by hot compression technique. The morphological investigation revealed the homogeneous distribution of K-CB and strong interfacial interaction in PMMA matrix, which validated the strong reinforcement and other intriguing properties of the nanocomposites. The PMMA nanocomposites showed a low percolation threshold (2.79 wt%) and excellent electrical conductivity due to the formation of 3D conductive network like architecture within the polymer matrix. Specifically, the 10 wt% K-CB nanocomposite possessed a superior EMI shielding performance of about 28 dB for X-band frequency range. Further, a huge change in EMI shielding performance of PMMA nanocomposites is observed with varying thickness. The brand new K-CB decorated PMMA nanocomposites are expected to open the door for next-generation cost-effective EMI shielding materials for academic and industrial applications.     

Design of artificial nacre-like hybrid films as shielding to mitigate electromagnetic pollution

Multifunctional designs of biomimetic layered materials are in great demand for broadening their applications. Artificial hybrid films are fabricated using a simple evaporation-induced assembly method, using nacre as the structural model, two-dimensional reduced graphene oxide (RGO) and magnetic graphene (MG) as inorganic building blocks and poly(vinyl alcohol) (PVA) as glue. The nacre-like films exhibit good mechanical performance, such as high stiffness, strength and toughness. The biomimetic materials possess the shielding properties of electromagnetic pollution. MG based nacre-like films present more significant electromagnetic interference (EMI) shielding performance than RGO film, because of a synergism between dielectric loss of graphene and magnetic loss of magnetic nanoparticles. Average EMI shielding effectiveness (SE) reaches ∼20.3 dB over the frequency range of 8.2–12.4 GHz (X band) for MG hybrid film only 0.36 mm thick. The lightweight, flexible and thin MG artificial hybrid films possess good potential for EMI shielding applications.     

High-strength,flexible and superhydrophobic graphene/aramid nanofiber nanocomposite films for electromagnetic interference shielding application

Electromagnetic interference (EMI) shielding composite materials exhibit many amazing characteristics, including low density, excellent flexibility and corrosion resistance, compared with metals. However, it is a long-standing challenge for EMI shielding materials to overcome inferior mechanical properties and limited hydrophobic characteristics. In this work, the high-strength, flexible and superhydrophobic graphene nanosheet/aramid nanofiber (GNS/ANF) nanocomposite films with layered microstructure were prepared by the sol-gel transformation and spray coating process. The resultant film exhibits excellent mechanical properties with a high tensile strength (131.17 ± 2.77 MPa), large fracture strain (9.58 ± 0.58%), and favorable toughness (8.84 ± 0.74 MJ m^?3), which are 26.2 times, 7.5 times and 221.0 times higher than those of pure GNS films. These results are attributed to synergistic effect between intensive stretching of three dimensional (3D) nanofiber network and extensive sliding of GNS produced effective energy dissipation. Moreover, the film with content of 70 wt% GNS has EMI shielding effectiveness of 31.3 dB, and its reflection coefficient is more than 0.89, revealing a reflection-dominant shielding mechanism. Meanwhile, the film possesses superhydrophobic property (158.7° ± 1.1°) and flame retardancy. The multilayered nanocomposite films have excellent potential for high-performance EMI shielding applications under some outdoor conditions.     

Nitrate removal from water using functionalized carbon nanotube sheets

Carbon nanotube (CNT) sheets were synthesized via chemical vapor deposition of cyclohexanol and ferrocene in nitrogen atmosphere at 750 °C, functionalized using concentrated nitric acid and liquid ammonia and employed as adsorbents to study their nitrate adsorption characteristics. The results demonstrated that functionalization with nitrogen-containing groups improves nitrate adsorption capacity of the oxidized CNT sheets, significantly. Various isotherms and kinetic models were applied to fit the experimental data. Effects of contact time, initial nitrate concentration and adsorbent dosage were also investigated. Regeneration performance for the first time was also studied. For comparison, a similar study was performed with commercial activated carbon (AC). It was found out that the functionalized CNT sheets with higher nitrate adsorption capacity, shorter equilibrium time and better regeneration performance than AC, can be considered as potential adsorbents for nitrate removal from water in domestic applications.     

Flexible poly(styrene-b-(ethylene-co-butylene)-b-styrene) nanocomposites for electromagnetic interference shielding

In this report, multiwalled carbon nanotubes (CNT) embedded poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) microspheres (CNT/SEBS) were prepared by solvent evaporation method. Reduced graphene oxide (rGO) nanosheets were used to cover the surface of CNT/SEBS microspheres. The CNT/SEBS/rGO nanocomposites with special segregated conductive network were fabricated by hot pressing these as-prepared complex microspheres. The morphology, electrical percolation threshold, electrical conductivity, and electromagnetic interference (EMI) shielding effectiveness (SE) of CNT/SEBS/rGO composites were characterized. The shielding mechanisms were discussed in detail. Analysis of electrical conductive performance shows that the electrical percolation threshold of rGO is 0.22 vol %. Results of EMI shielding test confirmed the synergistic effect between CNT and rGO. The EMI SE of the composite filled by 2.1 vol % CNT and 3.35 vol % rGO can achieve 26 dB in 8.2− 12.4 GHz (X band), which exceeds the basic requirement for commercial application (20 dB). Its reflectance coefficient (19–41%) indicates that the most part of incident electromagnetic (EM) wave energy is attenuated through absorption mechanism. This kind of absorptive EMI shielding material can be applied without serious secondary EM radiation pollution problems. The effects of filler content, molding temperature on EMI SE, and shielding mechanism were also investigated. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48542.     

Industrially scalable process to separate catalyst substrate materials from MWNTs synthesised by fluidised-bed CVD on iron/alumina catalysts

A multi-step purification process to separate metal catalysts and their support materials from mixtures of straight and spiral multi-walled carbon nanotubes (MWNTs), synthesised via fluidised-bed chemical vapour deposition (CVD) is described. The process involves: (i) refluxing as-synthesised bed materials (iron and non-porous alumina supports coated with carbon nanotubes (CNTs) and amorphous carbon) in either HNO₃, HNO₃/H₂SO₄ (v/v=1:3) or H₂SO₄ at each mixture's boiling point for 3, 6 or 12 h, (ii) filtering these samples using a two-stage (2.7 and 0.5 μm) filtration system, (iii) air drying and (iv) temperature selective, gas-phase oxidation in air to remove amorphous carbon. Both low and high purity as-synthesised bed materials (1.7 and 26.3 wt% CNTs, respectively) were used to investigate the process efficiency. Collectively these four steps were successful in removing amorphous carbon, metal catalysts and their alumina supports from the CNTs, improving the CNT purity from 1.7 wt% in the low purity as-synthesised samples to a maximum of 40.0 wt% and from 26.3 wt% in the higher purity feedstocks to 92.9 wt%. In both cases the remaining impurity was unseparated alumina, which remained bound to the CNTs even after treatment with concentrated acids for 12 h. The process has two potential advantages related to the development of large-scale CNT technologies: (i) the use of hydrofluoric acid, which is expensive and unsafe to use in large quantities has been avoided and (ii) the process is inherently scaleable and uses standard process engineering equipment suitable for large-scale CNT purification.     

High performance EMI shielding applications of Co0.5Ni0.5CexSmyFe2-x-yO4 nanocomposite thin films

The fast development in the compact and wearable opto-electronics devices need a high-performance electromagnetic (EM) shielding materials that are shows a unique feature like lightweight and flexible in characteristics that increase the problems of electromagnetic pollution. At present technological aspects, the absorption predominant microwave shielding materials are gain the huge demand for preventing the major problems of electromagnetic interference over the modern electronic devices as well as environment. In the report we presents synthesis of multifunctional composite thin film material that adequately includes the exceptional EMI shielding, mechanical flexibility and magnetic properties of composite thin film for portable and wearable electronic devices which could be operated at GHz frequencies. The Co_0.5Ni_0.5Ce_xSm_yFe_2-x-yO₄ (denoted as CNCSF) its scanning electron microscopy (SEM) micrographs revel the fact that the samples highly agglomerated characteristics features of the prepared thin film samples, this agglomerated structure of the composite film will enhance the EMI shielding performances and strain sensing responses. Further, the prepared thin films were subjected to characterized XRD and Raman spectroscopic techniques to analyse the crystallinity and different functional groups present in the prepared thin films. By doping of samarium and cesium nanoparticles into the Co_0.5Ni_0.5Fe_2-x-yO₄ forms the superior conducting islands and enhances the dielectric and magnetic properties of the composite thin films. Owing to the improved dielectric and magnetic properties this x,y = 0.02 ferrites based thin film nanocomposite with the 0.4 mm thickness exhibit the absorption predominated outstanding electromagnetic shielding responses in the order of ?23 dB which is almost equal to 99.67% of shielding efficiency in broad band microwave frequencies. Furthermore, these material-based nanocomposite shields show exceptional stability in EMI shielding efficiency under the different mechanical stretching strains. In addition to superior excellent shielding material, this material-based nanocomposite thin film shows an exceptional strain sensing behaviour, which evident that multifunctional applications of this ferrites based thin material. Owing to the all-unique properties like light weight, flexibility, outstanding EMI-SE and excellent strain sensing behaviour, these ferrites-based material thin film could be employed in flexible and fortable electronic devices as crafty jacket on shield.