Highly Flexible Fabrics/Epoxy Composites with Hybrid Carbon Nanofillers for Absorption-Dominated Electromagnetic Interference Shielding

Water immersion behavior of CNF/GNP reinforced green epoxy hybrid nanocomposites

Environmental challenges have prompted the development of sustainable materials such as nanocomposites. However, these composites exhibit inadequate water resistance, leading to suboptimal performance. This study investigates the impact of water absorption on the properties of green epoxy nanocomposites reinforced with low loading of cellulose nanofibrils (CNF) and graphene nanoplatelets (GNP) at (0.1, 0.25, and 0.5) wt%. After 15 days of water immersion, contact angle tests showed that CNF increased hydrophilicity 80.26°, while GNP improved water resistance 90.04°. The presence of nanoparticles was confirmed by XRD and Raman spectra. Micrographs from FESEM confirmed the role of CNF in making nanocomposite hydrophilic due to water molecule penetration through capillary flow due to hydrolytic breakdown. Mechanical tests indicated a 46.6 % increase in hardness for water-absorbed hybrid nanocomposites, with GNP enhancing impact resistance, tensile strength ranging from 400 to 600 MPa and flexural strength between 600 and 800 MPa. Thermally, the composites offer conductivity values of 10-30 W/m·K, supporting efficient heat dissipation, and maintain structural integrity at temperatures up to 300 °C due to the synergistic effects of CNF and GNP. The GNP enhances interfacial bonding with the epoxy matrix through π-π stacking and van der Waals forces. Its high aspect ratio and 2D structure improve stress transfer, load distribution, and crack resistance. Additionally, GNP forms continuous thermal pathways, boosting thermal conductivity and heat dissipation. This study emphasizes that filler dispersion and component interaction play vital roles in defining density performance and water absorption and highlights the role of filler type and dispersion in controlling moisture behavior, offering the potential for moisture-resistant composites in electronics applications.

Mechanical and electromagnetic shielding properties of carbon fabric with graphene nanoplatelets reinforced epoxy composites

In this work, carbon fabric-reinforced epoxy (CF/E) and carbon fabric/graphene nanoplatelets (1 wt%, 2 wt% and 3 wt%) reinforced epoxy (CF/GNP/E) laminates (one-layer, two-layer, and four-layer) were prepared using the hand layup method. Further, according to ASTM standards, the test samples were machined using abrasive waterjet machining, and tensile properties and hardness were studied. It was found that tensile strength modulus and strain-to-failure improved due to the addition of GNPs into the epoxy matrix in the composite; the CF/1GNP/E composite showed the highest tensile strength modulus and strain-to-failure. Further addition of GNPs of more than 2 wt% deteriorates the mechanical properties due to agglomeration. The electromagnetic interference shielding effectiveness by absorption and reflection of all the samples was investigated using the measured S-parameters in an X-band frequency range. The effectiveness of electromagnetic interference shielding increased with the addition of GNPs, and the multi-layer structure in the composites showed absorption-dominated electromagnetic shielding. The CF/3GNP/E 4-layer composite showed the highest (32.4dB) shielding effectiveness and was recommended for commercial application in the X-band frequency range.

Electrically Insulating yet Excellent EMI Shielding FeSiAl/CNF Composite Film with Thermal Conductivity for Electronic Packaging Applications

Electrical conductivity is typically prioritized when designing and fabricating high-performance electromagnetic interference (EMI) shielding materials. Achieving electrically insulating yet high-performance EMI shielding presents a significant challenge in the field of advanced electronic packaging due to the essence of the conflict between electric insulation and EMI shielding. Herein, we innovatively design and propose a flaky FeSiAl/cellulose nanofiber composite film (FFSA/CNF) with a markedly aligned structure, which achieves an insulation resistivity of up to 109 Ω·cm while providing broadband EMI shielding efficiency of 60 dB with a thickness of 220 μm. The mechanism of electrically insulating EMI shielding is systematically investigated based on the contact resistance between FFSA, localized eddy current losses, and strong magnetic loss of FFSA. Moreover, the FFSA/CNF film with densely stacked and oriented FFSA possesses a high thermal conductivity of 4.74 W/m·K. Interestingly, it exhibits a tunable and intelligent characteristic for EM attenuation by varying the aqueous FFSA/CNF composite film. In addition, the outstanding near-field shielding performance of FFSA/CNF is demonstrated in simulated electronic chips, which have the potential to be applied in the electronic packaging field. This study provides insights for design and development in both electrically insulating and high-performance EMI shielding materials.

3D Printed Carbon Nanotube/Phenolic Composites for Thermal Dissipation and Electromagnetic Interference Shielding

Here we demonstrate direct ink write (DIW) additive manufacturing of carbon nanotube (CNT)/phenolic composites with heat dissipation and excellent electromagnetic interference (EMI) shielding capabilities without curing-induced deformation. Such polymer composites are valuable for protecting electronic devices from overheating and electromagnetic interference. CNTs were used as a multifunctional nanofiller to improve electrical and thermal conductivity, printability, stability during curing, and EMI shielding performance of CNT/phenolic composites. Different CNT loadings, curing conditions, substrate types, and sample sizes were explored to minimize the negative effects of the byproducts released from the cross-linking reactions of phenolic on the printed shape integrity. At a CNT loading of 10 wt %, a slow curing cycle enables us to cure printed thin-walled CNT/phenolic composites with highly dense structures; such structures are impossible without a filler. Moreover, the electrical conductivity of the printed 10 wt % CNT/phenolic composites increased by orders of magnitude due to CNT percolation, while an improvement of 92% in thermal conductivity was achieved over the neat phenolic. EMI shielding effectiveness of the printed CNT/phenolic composites reaches 41.6 dB at the same CNT loading, offering a shielding efficiency of 99.99%. The results indicate that high CNT loading, a slow curing cycle, flexible substrates, and one thin sample dimension are the key factors to produce high-performance 3D-printed CNT/phenolic composites to address the overheating and EMI issues of modern electronic devices.

Preparation and Microwave-Absorbing Properties of FeCo Alloys by Condensation Reflux Method

Five groups of FeCo alloy samples with different atomic ratios of Fe/Co (3:7, 4:6, 5:5, 6:4, 7:3) were prepared using the condensation reflux method. The results indicate that varying the atomic ratios of Fe/Co has a significant impact on the microstructure, electromagnetic parameters, and microwave absorption properties of FeCo alloys. As the Fe atom content increases, the morphology of the FeCo alloys transitions from irregular flower-shaped to uniformly spherical and eventually to lamellar. The attenuation of electromagnetic waves in the five groups of alloys is primarily due to magnetic loss. Among them, Fe6Co4 exhibits the best absorption performance, with a minimum reflection loss (RL) value of -35.56 dB at a frequency of 10.40 GHz when the matching thickness is 7.90 mm. Additionally, at a matching thickness of 5.11 mm, the maximum effective absorption bandwidth (EAB) reached 2.56 GHz (15.44-18 GHz).

Facile synthesis of a GO-g-C3N4/BaTiO3 ternary nanocomposites for visible-light-driven photocatalytic degradation of rhodamine B

Photogenerated charge carriers can undergo rapid recombination in conventional photocatalyst systems, reducing their photocatalytic efficiency. To address this bottleneck, a g-C3N4/BaTiO3 (CNB) heterojunction composite was decorated with different mass ratios of graphene oxide (GO) to form a novel visible-light responsive ternary GO-g-C3N4/BaTiO3 (GOCNB) nanocomposite using a facile fabrication method. The GOCNB photocatalyst exhibited significantly higher light absorption and greater charge transfer than CNB, g-C3N4, or BaTiO3. The photodegradation performance of GOCNB was optimized with a 2% mass loading of GO, and it achieved a degradation rate constant of 14.9 × 10-3 min-1 for rhodamine B with an efficiency of 94% within 180 min. The rate constant was 8-fold and 6-fold higher than that of bare BaTiO3 and CNB, respectively. The stronger photocatalytic activity was attributed to the synergistic effect of GO, g-C3N4, and BaTiO3, with g-C3N4 and BaTiO3 promoting charge transfer within a wider visible light range and GO promoting electron mobility and the photocatalyst's adsorption capacity. In particular, the proposed system maintained the spatial separation of photogenerated electron-hole pairs, which is vital for high photocatalytic activity. This study provides new insights into semiconductor-based photocatalytic systems and suggests a route for more environmentally sustainable technologies.

Fabrication and Investigation of the Microwave Absorption of Nonwovens Modified by Carbon Nanotubes and Graphene Flakes

This study aims to investigate the influences of carbon nanotubes (CNTs) and graphene flakes (GFs) on the microwave absorption performance of nonwovens. Nonwovens were modified with CNTs and GFs through an impregnation method, creating a series of absorption samples with different carbon nanomaterial contents. Then the absorption performance of the samples was tested on both sides in the X-band (8.2~12.4 GHz) and the Ku-band (12~18 GHz) using the arch method. The experimental results showed that the absorption performance of GF-impregnated nonwovens was superior to that of CNT-impregnated nonwovens, and the overall absorption performance in the Ku-band was better than in the X-band. At a CNT content of 5 wt.%, the reflection loss of the impregnated nonwovens on the backside reached a minimum of -14.06 dB and remained below -10 dB in the 17.42~17.88 GHz frequency range. The sample fabricated with 4 wt.% GFs in the impregnation solution exhibited the best absorption performance, with minimum reflection losses of -15.33 dB and -33.18 GHz in the X-band and Ku-band, respectively. When the GFs were at 3 wt.%, the absorption bandwidth below -10 dB reached 4.16 GHz. In contrast to CNT-impregnated nonwovens, the frontside of GF-impregnated nonwovens demonstrated better absorption performance in the Ku-band. The results of this work provide experimental data support for the fabrication and application of microwave absorption materials.

A Review on Interface Engineering of MXenes for Perovskite Solar Cells

With an excellent power conversion efficiency of 25.7%, closer to the Shockley-Queisser limit, perovskite solar cells (PSCs) have become a strong candidate for a next-generation energy harvester. However, the lack of stability and reliability in PSCs remained challenging for commercialization. Strategies, such as interfacial and structural engineering, have a more critical influence on enhanced performance. MXenes, two-dimensional materials, have emerged as promising materials in solar cell applications due to their metallic electrical conductivity, high carrier mobility, excellent optical transparency, wide tunable work function, and superior mechanical properties. Owing to different choices of transition elements and surface-terminating functional groups, MXenes possess the feature of tuning the work function, which is an essential metric for band energy alignment between the absorber layer and the charge transport layers for charge carrier extraction and collection in PSCs. Furthermore, adopting MXenes to their respective components helps reduce the interfacial recombination resistance and provides smooth charge transfer paths, leading to enhanced conductivity and operational stability of PSCs. This review paper aims to provide an overview of the applications of MXenes as components, classified according to their roles as additives (into the perovskite absorber layer, charge transport layers, and electrodes) and themselves alone or as interfacial layers, and their significant importance in PSCs in terms of device performance and stability. Lastly, we discuss the present research status and future directions toward its use in PSCs.

Absorption-Dominant mmWave EMI Shielding Films with Ultralow Reflection using Ferromagnetic Resonance Frequency Tunable M-Type Ferrites

Although there is a high demand for absorption-dominant electromagnetic interference (EMI) shielding materials for 5G millimeter-wave (mmWave) frequencies, most current shielding materials are based on reflection-dominant conductive materials. While there are few absorption-dominant shielding materials proposed with magnetic materials, their working frequencies are usually limited to under 30 GHz. In this study, a novel multi-band absorption-dominant EMI shielding film with M-type strontium ferrites and a conductive grid is proposed. This film shows ultralow EMI reflection of less than 5% in multiple mmWave frequency bands with sub-millimeter thicknesses, while shielding more than 99.9% of EMI. The ultralow reflection frequency bands are controllable by tuning the ferromagnetic resonance frequency of M-type strontium ferrites and composite layer geometries. Two examples of shielding films with ultralow reflection frequencies, one for 39 and 52 GHz 5G telecommunication bands and the other for 60 and 77 GHz autonomous radar bands, are presented. The remarkably low reflectance and thinness of the proposed films provide an important advancement toward the commercialization of EMI shielding materials for 5G mmWave applications.

Highly Porous Carbon Aerogels for High-Performance Supercapacitor Electrodes

In recent years, porous carbon materials with high specific surface area and porosity have been developed to meet the commercial demands of supercapacitor applications. Carbon aerogels (CAs) with three-dimensional porous networks are promising materials for electrochemical energy storage applications. Physical activation using gaseous reagents provides controllable and eco-friendly processes due to homogeneous gas phase reaction and removal of unnecessary residue, whereas chemical activation produced wastes. In this work, we have prepared porous CAs activated by gaseous carbon dioxide, with efficient collisions between the carbon surface and the activating agent. Prepared CAs display botryoidal shapes resulting from aggregation of spherical carbon particles, whereas activated CAs (ACAs) display hollow space and irregular particles from activation reactions. ACAs have high specific surface areas (2503 m² g^-1) and large total pore volumes (1.604 cm³ g^-1), which are key factors for achieving a high electrical double-layer capacitance. The present ACAs achieved a specific gravimetric capacitance of up to 89.1 F g^-1 at a current density of 1 A g^-1, along with a high capacitance retention of 93.2% after 3000 cycles.

Development of Electromagnetic-Wave-Shielding Polyvinylidene Fluoride-Ti3C2Tx MXene-Carbon Nanotube Composites by Improving Impedance Matching and Conductivity

Absorption-dominated electromagnetic interference (EMI) shielding is attained by improving impedance matching and conductivity through structural design. Polyvinylidene fluoride (PVDF)-Ti₃C₂T_x MXene-single-walled carbon nanotubes (SWCNTs) composites with layered heterogeneous conductive fillers and segregated structures were prepared through electrostatic flocculation and hot pressing of the PVDF composite microsphere-coated MXene and SWCNTs in a layer-by-layer fashion. Results suggest that the heterogeneous fillers improve impedance matching and layered coating, and hot compression allows the MXene and SWCNTs to form a continuous conducting network at the PVDF interface, thereby conferring excellent conductivity to the composite. The PVDF-MXene-SWCNTs composite showed a conductivity of 2.75 S cm^-1 at 2.5% MXene and 1% SWCNTs. The EMI shielding efficiency (SE) and contribution from absorption loss to the total EMI SE of PVDF-MXene-SWCNTs were 46.1 dB and 85.7%, respectively. Furthermore, the PVDF-MXene-SWCNTs composite exhibited excellent dielectric losses and impedance matching. Therefore, the layered heteroconductive fillers in a segregated structure optimize impedance matching, provide excellent conductivity, and improve absorption-dominated electromagnetic shielding.

Flexible Polydimethylsiloxane Composite with Multi-Scale Conductive Network for Ultra-Strong Electromagnetic Interference Protection

Highlights

A multi-scale conductive network was constructed in flexible PDMS/Ag@PLASF/CNT composite with micro-size Ag@PLASF and nano-size CNT. The PDMS/Ag@PLASF/CNT composite showed outstanding electrical conductivity of 440 S m-1 and superior electromagnetic interference shielding effectiveness of up to 113 dB. The PDMS/Ag@PLASF/CNT composites owned good retention (> 90%) of electromagnetic interference shielding performance even after subjected to a simulated aging strategy or 10,000 bending-releasing cycles.

Abstract

Highly conductive polymer composites (CPCs) with excellent mechanical flexibility are ideal materials for designing excellent electromagnetic interference (EMI) shielding materials, which can be used for the electromagnetic interference protection of flexible electronic devices. It is extremely urgent to fabricate ultra-strong EMI shielding CPCs with efficient conductive networks. In this paper, a novel silver-plated polylactide short fiber (Ag@PLASF, AAF) was fabricated and was integrated with carbon nanotubes (CNT) to construct a multi-scale conductive network in polydimethylsiloxane (PDMS) matrix. The multi-scale conductive network endowed the flexible PDMS/AAF/CNT composite with excellent electrical conductivity of 440 S m−1 and ultra-strong EMI shielding effectiveness (EMI SE) of up to 113 dB, containing only 5.0 vol% of AAF and 3.0 vol% of CNT (11.1wt% conductive filler content). Due to its excellent flexibility, the composite still showed 94% and 90% retention rates of EMI SE even after subjected to a simulated aging strategy (60 °C for 7 days) and 10,000 bending-releasing cycles. This strategy provides an important guidance for designing excellent EMI shielding materials to protect the workspace, environment and sensitive circuits against radiation for flexible electronic devices.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40820-022-00990-7.