Modulation of electromagnetic absorption and shielding properties of geopolymer nanocomposites by designing core–shell structure of carbon nanotubes

In this work, an electromagnetic (EM) protective building material was developed by combining silica (SiO₂)-grafted carbon nanotubes (S@CNTs) with geopolymer (GeoP). The EM absorption and shielding properties of the GeoP nanocomposites were modulated by tailoring the SiO₂ shell thickness. With the increase in shell thickness, the attenuation coefficient decreased, while the impedance matching degree, which acted as a prerequisite for evaluating EM absorption performance, improved. As a result, the minimum reflection loss (RL_min) reached ?38.4 dB at 11.1 GHz and the effective absorption bandwidth of 3.4 GHz with a thickness of 2.9 mm was obtained. Practically, the electron transport capability was promoted with a thinner SiO₂ shell, leading to an improvement in electrical conductivity. As the conductivity increased, the EM interference shielding effectiveness (SE) increased to 11.0 dB, while the RL_min also increased to ?8.7 dB. Based on the underlying mechanism analysis, the strategy for modulating EM performance can be extended to other building materials.     

Multifunctional bioceramic-based composites reinforced with silica-coated carbon nanotube core-shell structures

Carbon nanotube (CNT) possesses eminent mechanical properties and has been widely utilized to toughen bioceramics. Major challenges associated with CNT-reinforced bioceramics include the inhomogeneous dispersion of CNTs and the insufficient interfacial strength between the two phases. To address such issues, this research describes the first use of silica-coated CNT (S-CNT) core-shell structures to reinforce bioceramics using hydroxyapatite (HA) as a representative matrix. HA-based composites with 0.1–2 wt% S-CNT are sintered by spark plasma sintering to investigate their mechanical and biological properties. It is found that when 1 wt% raw CNT (R-CNT) is added, very limited increases in fracture toughness (K_IC) is observed. By contrast, the incorporation of 1 wt% S-CNT increased the K_IC of HA by 101.7%. This is attributed to more homogeneously dispersed fillers and stronger interfacial strengths. MG63 cells cultured on the 1 wt% S-CNT/HA pellets are found to proliferate faster and possess significantly higher alkaline phosphatase activities than those grown on the HA compacts reinforced with 1 wt% R-CNT, probably by virtue of the released Si ions from the SiO2 shell. Therefore, the S-CNT core-shell structures can improve both mechanical and biological properties of HA more effectively than the conventionally used R-CNTs. The current study also presents a novel and effective approach to the enhancement of many other biomedical and structural materials through S-CNT incorporation.     

Roll-to-roll processable MXene-rGO-PVA composite films with enhanced mechanical properties and environmental stability for electromagnetic interference shielding

MXene films promise potential electromagnetic interference (EMI) shielding materials, but poor scalable processability, environmental instability, and weak mechanical properties severely restrict their applications. Herein, we engineer the large-area, high-performance, and compact nacre-like MXene-based composite films through cooperative co-assembly of Ti₃C₂T_X MXene and reduced graphene oxide (rGO) in the presence of polyvinyl alcohol (PVA). The resulting MXene-rGO-PVA composite films benefit from enhanced bonding strength and extra chain bridging effect of linear PVA molecules enriched with hydroxyl groups. Therefore, the composite film achieves high tensile strength (～238 MPa) and toughness (～1.72 MJ m^?3) while having high conductivity of ～32 S cm^?1. A significant EMI shielding effectiveness (41.35 dB) is also demonstrated, with an excellent absolute shielding effectiveness of ～20,200 dB cm² g^?1 at only 12-μm thickness. Moreover, due to the synergistic effect of multiple components, the composite films maintain a stable EMI shielding performance in harsh environments (sonication, hot/cold annealing, and acid solution) with mechanical properties that fluctuate only within 10% compared to the original film. More importantly, commercial polyethylene terephthalate release liner can be applied for the film coating, facilitating continuous roll-to-roll production of large-area films and future applications.     

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.     

Hydrothermal synthesis of micro-flower like morphology aluminum-doped MoS2/rGO nanohybrids for high efficient electromagnetic wave shielding materials

In this study, a three-dimensional (3D) micro-flower like morphology aluminum-doped molybdenum disulfide/reduced graphene oxide (Al@MoS₂/rGO) nanohybrids have been developed using a simple and sensitive hydrothermal approach. Their electromagnetic (EM) parameters (permittivity, permeability) and microwave shielding parameters (S₁₁, S₁₂) have been analyzed and reported for the first time in the microwave frequency range of 8.0–12.0 GHz. It is interesting to note that the electrical conductivity of the nanohybrids increases with the doping concentration of Al-ions, whereas skin-depth has a reverse trend. The 12% Al@MoS₂/rGO nanohybrid shows a higher total electromagnetic interference shielding effectiveness (EMI SE) value about SE_T ~33.38 dB, whereas undoped MoS₂/rGO nanohybrid exhibits a lower value around ~17.07 dB at the same thin thickness. The higher doping concentration of Al-ion creates lattice distortion and crystal defects with high charge carrier mobility between multiple interfaces and at defective sites. Hence, the Al-doping into MoS₂ lattice supported on the rGO surface can greatly enhance EM wave absorption and EMI SE value. The present work suggests that the 12% Al@MoS₂/rGO nanohybrid can be treated as a good microwave absorbing and shielding material and useful in various techno-commercial devices.     

Electromagnetic interference shielding effectiveness of carbon-based materials prepared by screen printing

Screen printing, as a simple and efficient method, is used to fabricate a carbon-based film for electromagnetic interference (EMI) shielding applications. The results show that carbon nanotube (CNT) sheets are more effective in providing EMI shielding compared to graphite and carbon black sheets in abroad-band frequency range due to better electron transmission. A thin printed 150 μm 15 wt% CNT film exhibits similar shielding performance to a thicker 1.5 mm 15 wt% CNT epoxy composites, illustrating that screen printing could be a promising approach to fabricate thin EMI shielding films for commercial applications.     

Electromagnetic interference shielding and dielectric properties of SiCf/SiC composites containing pyrolytic carbon interphase

The SiC_f/SiC composites containing various thickness of pyrolytic carbon (PyC) interphase were prepared and their properties were investigated for electromagnetic interference (EMI) shielding applications in the frequency of 8.2–12.4 GHz. The composites containing 310 nm thickness (3.3 vol%) PyC interphase show an about 25 dB shielding effectiveness in the whole frequency band. Interestingly, the contribution of reflection to the EMI shielding effectiveness increases and the contribution of absorption decreases as the PyC interphase thickness increases.     

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).     

Core@shell and sandwich-like Ti3C2Tx@Ni particles with enhanced electromagnetic interference shielding performance

Novel and highly effective electromagnetic interference (EMI) shielding materials are desirable to attenuate unwanted electromagnetic radiation or interference produced by electrical communication devices. Here, functional Ti₃C₂T_x@Ni particles with a core@shell and sandwich like structure were fabricated using the facile electroless plating technique. The core@shell structured Ti₃C₂T_x@Ni consists of a Ti₃C₂T_x core and a Ni shell. In the core, thin Ni layers are sandwiched in between Ti₃C₂T_x flakes. EMI shielding effectiveness (SE) values of Ti₃C₂T_x@Ni/wax composites increased with increasing Ti₃C₂T_x@Ni content. The average EMI SE value of 60 wt% Ti₃C₂T_x@Ni/wax composite was 43.12 dB, increased by 73% as compared with 24.93 dB for the same content of pristine Ti₃C₂T_x in wax in the frequency range 2–18 GHz. An average EMI SE of 74.14 dB was achieved in the 80 wt% Ti₃C₂T_x@Ni/wax. The enhanced EMI shielding performance should be ascribed to the synergic effect of the absorption loss of the Ti₃C₂T_x core and the magnetic loss of the Ni shell and the inner Ni layers.     

Efficient fabrication of carbon/silicon carbide composite for electromagnetic interference shielding applications

Ceramic matrix composites are typically prepared by a costly, time-consuming process under severe conditions. Herein, a cost-effective C/SiC composite was fabricated from a silicon gel-derived source by Joule heating. The β-SiC phase was generated via carbothermal reduction, and the carbon fabric showed a well-developed graphitic structure, promoting its thermal and anti-oxidation stabilities. Owing to the excellent dielectric loss in carbon fabric, SiC and SiO₂ as well as the micropore structure of the ceramic matrix, the absolute electromagnetic interference shielding (EMI) effectiveness (SSE/t) reached 948.18 dB?cm²?g^-1 in the X-band, exhibiting an excellent EMI SE. After oxidation at 1000 °C for 10 h in the air, the SSE/t of the composite was only reduced to 846.02 dB?cm²?g^-1. The C/SiC composite promises the efficient fabrication of high-temperature resistant materials for electromagnetic shielding applications.     

Ti3C2Tx-coated diatom frustules-derived porous SiO2 composites with high EMI shielding and mechanical properties

Effective electromagnetic interference (EMI) shielding materials have garnered substantial interest for their efficacy in attenuating electromagnetic wave energy, ensuring data confidentiality, ensuring the operational stability of fragile electronic systems. To begin, artificially cultured diatom frustules (DF)-derived porous silica (DFPS) skeletons were constructed as templates in this study. Porous ceramics hot-pressed at 800 °C displayed a high compressive strength with a high specific surface area due to their three-dimensional (3D) multilayered and porous structures. Then, mechanically robust Ti₃C₂T_x/DFPS composites with exceptional EMI shielding performance were fabricated by immersing porous DF-based ceramics into Ti₃C₂T_x solutions and annealing in an argon environment to increase the materials’ shielding efficiency (SE). The EMI SE of composites hot-pressed at 800 °C achieved the maximum EMI SE of 43.2 dB in the X-band and a compressive strength of 67.5 MPa, establishing a hitherto unreported balance of mechanical characteristics and shielding performance. Prolonged transmission paths, multiple dissipation, scattering and reflection of electromagnetic energy were achieved using a well-maintained hierarchical porous silica framework decorated with MXene, with adsorption caused by surface MXene serving as the primary shielding mechanism for the composites. Due to their superior overall performance, MXene/DFPS EMI shielding composites have a bright future in the aircraft sector as delicate electronic device components.     

Fine-grained and electrically conductive NdB6/SiO2: A promising electromagnetic interference shielding material with good thermal and mechanical properties

Searching for thermal conductive materials with high electromagnetic interference (EMI) shielding effectiveness (SE) is the key to protect electronic equipment against electromagnetic pollution and excess heat emission. Herein, NdB₆/SiO₂ bulks with high EMI SE and thermal conductivity which also exhibit good mechanical properties were prepared by liquid phase sintering (LPS). The NdB₆/SiO₂ bulk prepared by LPS at 1550 °C has fine grain-size, which is beneficial to improving mechanical property and EMI shielding performance. It exhibits high conductivity of 1.47 × 10⁴ S/cm, high EMI SE of 55.1 dB in K band, and high thermal conductivity of 37.9 W/m K. It also possesses flexural strength of 266 MPa and Vickers hardness of 14.8 GPa. Thus, NdB₆/SiO₂ composite ceramics are promising candidates for EMI shielding with good heat dissipation and mechanical load-bearing capabilities.     

Electromagnetic interference shielding effectiveness of hybrid multifunctional Fe3O4/carbon nanofiber composite

Electromagnetic interference shielding effectiveness (EMI SE) of multifunctional Fe₃O₄/carbon nanofiber composites in the X-band region (8.2–12.4 GHz) is studied. Here, we examine the contributing effects of various parameters such as Fe₃O₄ content, carbonization temperature and thickness on total shielding efficiency (SE_total) of different samples. The maximum EMI SE of 67.9 dB is obtained for composite of 5 wt.% Fe₃O₄ (0.7 mm thick) with the dominant shielding by absorption (SE_A) of electromagnetic radiation. The enhanced electromagnetic shielding performance of Fe₃O₄/carbon nanofiber composites is attributed to the increment of both magnetic and dielectric losses due to the incorporation of magnetite nanofiller (Fe₃O₄) in electrically conducting carbon nanofiber matrix as well as the specific nanofibrous structure of carbon nanofiber mats, which forms a higher aspect ratio structure with randomly aligned nanofibers. Furthermore, we prove that the addition of elastomeric polydimethylsiloxane (PDMS) as a coating for carbon nanofiber composite strengthens the composite structure without interfering with its electromagnetic shielding efficiency.     

Enhanced electromagnetic shielding property of cf/mullite composites fabricated by spark plasma sintering

Aiming to prepare high-performance electromagnetic interference (EMI) shielding materials, chopped carbon fibers were incorporated into mullite ceramic matrix via rapid prototyping process of spark plasma sintering (SPS). Results indicate that C_f/mullite composites with only 1 wt% of carbon fibers exhibit highest shielding effectiveness (SE_T) over 40 dB at a small thickness of 2.0 mm, showing great advantages both in terms of performance and thickness compared with many mature carbon/ceramic composites. The high EMI shielding properties mainly depend on two mechanisms of absorption and reflection in this present work. The enhanced absorption and reflection of electromagnetic wave are ascribed to the promotional electrical conductivity arising from the formation of conductive network by introduction of carbon fibers. Regarding enhanced electrical conductivity, notable intensified interfacial polarization on a large number of interfaces between mullite matrix and carbon fibers is also the key factor to the improved absorption, which makes absorption play a dominant role in the significant improvement of EMI SE_T. The C_f/mullite composites with excellent EMI shielding properties and thin thickness show great potential application as EMI materials.     

Promoting the electromagnetic interference shielding of Ti3C2Tx flakes by loading Fe3O4 nanoparticles: Insights into the performance of oligo-layers exposed to microwave interferences

This study aims to provide insights into the absorption and shielding performances of Fe₃O₄ modified oligo-layered Ti₃C₂T_x towards microwave electromagnetic interference. Oligo-layered Ti₃C₂T_x was modified by Fe₃O₄ nanoparticles (60 nm) via a facile electrostatic assembly approach at different loading rates. This composite was shown to have high dielectric constant and high permeability compared with oligo-layered Ti₃C₂T_x. The microwave electromagnetic absorbing and shielding performances were monitored through a vector network instrument with focuses on the EMI performance. The sample Ti₃C₂T_x/Fe₃O₄ with a 5:1 mass ratio of Ti₃C₂T_x to Fe₃O₄ displayed the optimized EMI shielding performance. The average SE value was 62.19 dB, and the maximum value was 68.72 dB at 18 GHz with a 2.6 mm thickness. The EMI shielding mechanism was understood based on the conductive loss, magnetic loss, dipole polarization, and multiple scattering. Results suggests that Ti₃C₂T_x/Fe₃O₄ composites are expected to be superior EMI shielding material.     

Multiwalled carbon nanotubes–BaTiO3/silica composites with high complex permittivity and improved electromagnetic interference shielding at elevated temperature

Composites with silica matrix and mixed filler of multiwalled carbon nanotubes (MWCNTs) and BaTiO₃ powder were fabricated. Excellent uniform dispersion of MWCNTs can be obtained using a two-step mixing method. Both of the real and imaginary parts of complex permittivity increased with increasing MWCNT content and measured temperature. The electromagnetic interference (EMI) shielding results showed that the absorption mechanism is the main contribution to the total EMI shielding effectiveness (SE). Compared with the EMI SE resulting from reflection, the absorption showed more dependence on the MWCNT content, measured temperature and frequency. The total EMI SE is greater than 20 dB at 25 °C and 50 dB at 600 °C in the whole frequency range of 12.4–18 GHz with a 1.5 mm composite thickness, which suggests that the MWCNT–BaTiO₃/silica composites could be good candidates for the EMI shielding materials in the measured frequency and temperature region.     

Modeling for the electromagnetic properties and EMI shielding of Cf/mullite composites in the gigahertz range

The electromagnetic properties and EMI shielding effectiveness of C_f/mullite composites via the spark plasma sintering were intensively investigated in the gigahertz range (8.2–12.4 GHz). Experimental results have revealed excellent electromagnetic properties and a high value of EMI shielding effectiveness (nearly 40 dB) for C_f/mullite composites with 1.65 vol% carbon fillers at thickness of 2 mm. We quantitatively characterize the contributions of microstructural features to overall EMI shielding effectiveness using a micromechanics-based homogenization model. The EMI shielding effectiveness enhances with respect to the C_f volume concentration before the threshold. The increasing trend of EMI shielding effectiveness with respect to AC (alternating current) frequency can be attributed to enhanced conductivity at high gigahertz range. It is demonstrated that filler and frequency dependent interface effects are essential to obtain excellent electromagnetic properties of C_f/mullite composite. The present research can provide guidances for the design of ceramic-based composites applied in high-temperature EMI shielding devices.     

Highly conductive and flexible bilayered MXene/cellulose paper sheet for efficient electromagnetic interference shielding applications

In this work, a robust and flexible bilayered MXene/cellulose paper sheet with superhigh electrical conductivity was prepared via vacuum-assisted filtration and a subsequent hot-pressing process for electromagnetic interference (EMI) shielding applications. By tightly assembling few-layered MXene (f-Ti₃C₂T_x) on the cellulose substrate via hydrogen bonds, an effective and interconnected conductive network was constructed in the paper sheet, resulting in a high electrical conductivity of 774.6–5935.4 S m^?1 at various f-Ti₃C₂T_x loadings. The highly conductive MXene layer can promptly reflect a great amount of incident EM waves, a process which preceded the transmission of EM waves in the cellulose matrix. Owing to the highly efficient reflection-dominated EMI shielding mechanism, the resultant bilayered MXene/cellulose paper sheets exhibit excellent EMI shielding effectiveness of 34.9–60.1 dB and specific EMI shielding efficiency of 290.6–600.7 dB mm^?1. Moreover, the MXene/cellulose paper sheets demonstrated improved mechanical strength (up to 25.7 MPa) and flexibility due to the mechanical frame effect acted by the cellulose substrate. Consequently, the robust and flexible bilayered MXene/cellulose paper sheet is a promising candidate for application in next-generation electric devices.     

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.     

Electrically conductive and corrosion resistant MAX phases with superior electromagnetic wave shielding performance

MAX phases have emerged as promising corrosion-resistant electromagnetic interference (EMI) shielding materials. Herein, four MAX phases: Ti₃SiC₂, Ti₃AlC₂, V_0.5Cr_1.5AlC, and Nb₄AlC₃, were synthesized via solid–liquid reactions. The electrical conductivities of Ti₃SiC₂, Ti₃AlC₂, V_0.5Cr_1.5AlC, and Nb₄AlC₃ are 14.7 × 10³, 15.5 × 10³, 5.1 × 10³, 8.0 × 10³ S/cm, respectively, and the corresponding average EMI shielding effectiveness values in the frequency of 18–26.5 GHz are 53.9, 69.2, 19.4, and 29.0 dB, respectively. Most importantly, these MAX phases are highly corrosion resistant under acidic conditions. Despite the exposure to the acidic environment and a slight decrease in the electrical conductivity, the corroded MAX phases exhibited excellent EMI shielding properties compared to the pristine MAX phases. Additional analysis showed that reflection was the primary EMI blocking mechanism. The study offers a guide for designing MAX phase ceramics that exhibit high EMI shielding performance in corrosive environments.