Filler-Free Conducting Polymers as a New Class of Transparent Electromagnetic Interference Shields

Advanced Functional Electromagnetic Shielding Materials: A Review Based on Micro-Nano Structure Interface Control of Biomass Cell Walls

Research efforts on electromagnetic interference (EMI) shielding materials have begun to converge on green and sustainable biomass materials. These materials offer numerous advantages such as being lightweight, porous, and hierarchical. Due to their porous nature, interfacial compatibility, and electrical conductivity, biomass materials hold significant potential as EMI shielding materials. Despite concerted efforts on the EMI shielding of biomass materials have been reported, this research area is still relatively new compared to traditional EMI shielding materials. In particular, a more comprehensive study and summary of the factors influencing biomass EMI shielding materials including the pore structure adjustment, preparation process, and micro-control would be valuable. The preparation methods and characteristics of wood, bamboo, cellulose and lignin in EMI shielding field are critically discussed in this paper, and similar biomass EMI materials are summarized and analyzed. The composite methods and fillers of various biomass materials were reviewed. this paper also highlights the mechanism of EMI shielding as well as existing prospects and challenges for development trends in this field.

Multispectral smart window: Dynamic light modulation and electromagnetic microwave shielding

A novel multispectral smart window has been proposed, which features dynamic modulation of light transmittance and effective shielding against electromagnetic microwave radiation. This design integrates liquid crystal dynamic scattering and dye doping techniques, enabling the dual regulation of transmittance and scattering within a single-layer smart window. Additionally, the precise control of conductive film thickness ensures the attainment of robust microwave signal shielding. We present a theoretical model for ion movement in the presence of an alternating electric field, along with a novel approach to manipulate negative dielectric constant. The proposed model successfully enables a rapid transition between light transparent, absorbing and haze states, with an optimum drive frequency adjustable to approximately 300 Hz. Furthermore, the resistive design of the conductive layer effectively mitigates microwave radiation within the 2-18 GHz range. These findings offer an innovative perspective for future advancements in environmental construction.

An Integrated Approach for Piezo-Electrochemical Nanoenergy Generation, Storage, and Real-Time Electromagnetic Interference Shielding Control

The extensive utilization of high-end wireless electronic equipment in medical, robotics, satellite, and military communications has created a pressing challenge for real-time electromagnetic interference (EMI) control. Herein, a piezo-powered self-chargeable supercapacitor (PPSC) architecture based on an iron-doped graphitic nitride (Fe-g-C3N4: FGN) electrode with a solid piezoelectrolyte is devised, which can provide real-time controlled EMI shielding through piezo-powered self-charging voltage (SCV). This PPSC device along with real-time SCV-controlled EMI shielding also integrates additional features like nanoenergy generation and storing capability. The results demonstrate that the PPSC device is capable of exhibiting a piezo-tuned self-charging ability of up to 669.2 mV under 9.47 N of dynamic pressing for 180 s. The SCV electrostatically modifies the PPSC device that causes destructive interference and governs the absorption of electromagnetic radiation (EMR) and controls the absorption-dominated EMI shielding up to 59.2 dB at 500 mV. Additionally, the SCV-led electrification of the PPSC device also controls a unique functional transition from the EMR reflector to the EMR absorber at ∼90 mV. Hence, this strategy of tailored absorption and reflection adjustments of EMR could also potentially contribute toward the advancement of stealth technology for military armaments with externally controlled stealth capabilities.

Surfactant-Mediated Highly Conductive Cellulosic Inks for High-Resolution 3D Printing of Robust and Structured Electromagnetic Interference Shielding Aerogels

Technological fusion of emerging three-dimensional (3D) printing of aerogels with gel processing enables the fabrication of lightweight and functional materials for diverse applications. However, 3D-printed constructs via direct ink writing for fabricating electrically conductive structured biobased aerogels suffer several limitations, including poor electrical conductivity, inferior mechanical strength, and low printing resolution. This work addresses these limitations via molecular engineering of conductive hydrogels. The hydrogel inks, namely, CNC/PEDOT-DBSA, featured a unique formulation containing well-dispersed cellulose nanocrystal decorated by a poly(3,4-ethylene dioxythiophene) (PEDOT) domain combined with dodecylbenzene sulfonic acid (DBSA). The rheological properties were precisely engineered by manipulating the solid content and the intermolecular interactions among the constituents, resulting in 3D-printed structures with excellent resolution. More importantly, the resultant aerogels following freeze-drying exhibited a high electrical conductivity (110 ± 12 S m-1), outstanding mechanical properties (Young's modulus of 6.98 MPa), and fire-resistance properties. These robust aerogels were employed to address pressing global concerns about electromagnetic pollution with a specific shielding effectiveness of 4983.4 dB cm2 g-1. Importantly, it was shown that the shielding mechanism of the 3D printed aerogels could be manipulated by their geometrical features, unraveling the undeniable role of additive manufacturing in materials design.

Functional and Structural Facts of Effective Electromagnetic Interference Shielding Materials: A Review

Electromagnetic interference (EMI) shielding effectiveness (SE) systems have received immense attention from researchers owing to the rapid development in electronics and telecommunications, which is an alarming matter in our modern society. This radiation can damage the performance of EM devices and may harmfully affect animal/human health. The harmonious utilization of magnetic alloys and conducting but nonmagnetic materials (such as carbon/graphene) is a practical approach toward EMI SE. This review is not exhaustive, although it is comprehensive and aimed at all materials for EMI SE especially graphene-based polymeric composites. It encompasses multifunctional and functional structural EMI shields. These materials comprise polymers, carbons, ceramics, metals, cement composites/nanocomposites, and hybrids. The accessibility of abundant categories of carbon-based materials in their microscale, nanoscale, and quantum forms as EMI shields as polymer-carbon, cement-carbon, ceramic-carbon, metal-carbon, and their hybrids, makes them receive much attention, as a result of their unique amalgamation of electrical, magnetic, dielectric, thermal, and/or mechanical properties. Herewith, we have discussed the principles of EMI shields along with their design and state of the art basis and material architecture along with the drawbacks in research on EMI shields.

Investigation of the Conditions for the Synthesis of Poly(3,4-ethylenedioxythiophene) ATRP Macroinitiator

One of the most widely used conductive polymers in the growing conductive polymer industry is poly(3,4-ethylenedioxythiophene) (PEDOT), whose main advantages are good thermal and chemical stability, a conjugated backbone, and ease of functionalization. The main drawback of PEDOT for use as wearable electronics is the lack of stretchable and self-healing properties. This can be overcome by grafting PEDOT with flexible side branches. As pure PEDOT is highly stable and grafting would not be possible, a new bromine-functionalized thiophene derivative, 2-(tiophen-3-yl) ethyl 2-bromo-2-methylpropanoate (ThBr), was synthesized and copolymerized with EDOT for the synthesis of a poly(EDOT-co-ThBr) ATRP macroinitiator. After the synthesis of the macroinitiator, flexible polymers could be introduced as side branches by atom-transfer radical polymerization (ATRP) to modify mechanical properties. Before this last synthesis step, the conditions for the synthesis of the ATRP macroinitiator should be investigated, as only functionalized units can function as grafting sites. In this study, nine new copolymers with different monomer ratios were synthesized to investigate the reactivity of each monomer. The ratios used in the different syntheses were ThBr:EDOT = 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1, 0.8:1, 0.6:1, 0.4:1, and 0.2:1. In order to determine the effect of reaction time on the final properties of the polymer, macroinitiator synthesis at a 1:1 ratio was carried out at different time periods: 8 h, 16 h, 24 h, and 48 h. The obtained products were characterized by different techniques, and it was found that polymerizations longer than 24 h yielded practically insoluble macroinitiators, thus limiting its further application. Reactivity ratios of both monomers were found to be similar and close to 1, making the copolymerization reaction symmetrical and the obtained macroinitiators almost random copolymers.

Enhanced Microwave-Absorbing Property of Honeycomb Sandwich Structure with a Significant Interface Effect

Honeycomb sandwich structures (HSSs) are excellent candidates for light and efficient microwave-absorbing materials. In this work, we design an HSS using SiO₂ fiber-reinforced epoxy resin (SiO_2f/ER) composites as both the top and bottom layers to improve the impedance matching with free space. Target dielectric properties of the honeycomb and coated lossy material of the HSS were calculated based on the multilayer transmission line theory, metal backplane model, and homogenization theory. In addition, the interface effect between the SiO_2f/ER and honeycomb of the HSS was discussed theoretically, experimentally, and numerically, indicating a 1-4% contribution of microwave absorption resulting from the interface. By analyzing the equivalent resistance, equivalent capacitance, as well as equivalent inductance, the enhanced microwave absorption of HSS is attributed to the formation of the interfacial transition zone, which benefits both impedance matching and electromagnetic loss.

Low Cost Embedded Copper Mesh Based on Cracked Template for Highly Durability Transparent EMI Shielding Films

Embedded copper mesh coatings with low sheet resistance and high transparency were formed using a low-cost Cu seed mesh obtained with a magnetron sputtering on a cracked template, and subsequent operations electroplating and embedding in a photocurable resin layer. The influence of the mesh size on the optoelectric characteristics and the electromagnetic shielding efficiency in a wide frequency range is considered. In optimizing the coating properties, a shielding efficiency of 49.38 dB at a frequency of 1 GHz, with integral optical transparency in the visible range of 84.3%, was obtained. Embedded Cu meshes have been shown to be highly bending stable and have excellent adhesion strength. The combination of properties and economic costs for the formation of coatings indicates their high prospects for practical use in shielding transparent objects, such as windows and computer monitors.

Hydrophobic, flexible electromagnetic interference shielding films derived from hydrolysate of waste leather scraps

With the rapid development of wireless telecommunication technologies, it is of fundamental and technological significance to design and engineer high-performance shielding materials against electromagnetic interference (EMI). Herein, a three-step procedure is developed to produce hydrophobic, flexible nanofiber films for EMI shielding and pressure sensing based on hydrolysate of waste leather scraps (HWLS): (i) electrospinning preparation of HWLS/polyacrylonitrile (PAN) nanofiber films, (ii) adsorption of silver nanowires (AgNWs) onto HWLS/PAN nanofiber films, and (iii) coating of HWLS/PAN/AgNWs nanofiber films with polydimethylsiloxane (PDMS). Scanning electron microscopy studies show that AgNWs are interweaved with HWLS/PAN nanofibers to form a conductive network, exhibiting an electrical conductivity of 10⁵ S m^-1 and shielding efficiency of 65 dB for a 150 μm-thick HWLS/PAN/AgNWs film. The HWLS/PAN/AgNWs/PDMS film displays an even better electromagnetic shielding efficiency of 80 dB and a water contact angle of 132.5°. Results from this study highlight the unique potential of leather solid wastes for the production of high-performance, environmentally friendly, and low-cost EMI shielding materials.

Near-Infrared Laser Direct Writing of Conductive Patterns on the Surface of Carbon Nanotube Polymer Nanocomposites

Near-infrared (NIR) laser annealing is used to write conductive patterns on the surface of polypropylene/multi-walled carbon nanotube nanocomposite (PP/MWCNT) plates. Before irradiation, the surface of the nanocomposite is not conductive due to the partial alignment of the MWCNT, which occurs during injection molding. We observe a significant decrease in the surface sheet resistance using NIR laser irradiation, which we explain by a randomization of the orientation of MWCNTs in the PP matrix melt by NIR laser irradiation. After only 5 s of irradiation, the sheet resistance of PP/MWCNTs, annealed with a laser at a power density of 7 W/cm², decreases by more than 4 decades from ∼100 MΩ/sq to ∼1 kΩ/sq. Polarized Raman, TEM, and SEM are used to investigate the changes in the sheet resistance and confirm the physico-chemical processes involved. This allows direct writing of conductive patterns using a NIR laser on the surface of nanocomposite polymer substrates, with the advantages of a fast, easy, and low-energy consumption process.

Freestanding "core-shell" AgNWs/metallic hybrid mesh electrodes for a highly efficient transparent electromagnetic interference shielding film

We fabricated the freestanding "core-shell" AgNWs/ Ni mesh electrodes by employing AgNWs solution onto the freestanding Ni-mesh. The combination of AgNWs and Ni mesh resulted in higher electrical conductivity, thereby enhancing the electromagnetic interference (EMI) shielding effectiveness (SE). The hybrid freestanding electrode created highly effective transparent and flexible EMI shielding films, featuring an ultrathin thickness (3 µm), the high optical transparency of 93% at 550 nm, and a SE of 41.5 dB in the X-band, which exceeds that of 30 dB for a freestanding Ni-mesh (94%). We showed that the hybrid freestanding AgNWs/Ni-mesh film is a promising high-performance transparent and flexible EMI shielding material that satisfies the requirements for optoelectronic devices.

Chemically Room Temperature Crosslinked Polyvinyl Alcohol (PVA) with Anomalous Microwave Absorption Characteristics

Polyvinyl alcohol (PVA) is a great interest polymer due to its excellent film-forming, emulsifying, microwave dielectrics and adhesive properties. However, PVA is a water-soluble synthetic polymer making it susceptible to environmental factors. In this work, PVA is crosslinked at room temperature using divinyl sulfone (DVS) as a crosslinker, and the obtained crosslinked PVA (XPVA) is water-insoluble. Crosslinking mechanism is proposed, thermal and microwave dielectric properties of X-PVA are studied. The studies revealed that X-PVA has better thermal stability and microwave absorption properties. The obtained minimum reflection loss (RL) of X-PVA is -23 dB (filler-free) with entire X-band (8.2-12.4 GHz) absorption bandwidth (RL ≤ -10 dB), indicating excellent microwave absorption properties. Artificial neural network (ANN) predicted RL of X-PVA also matched well with the experimental data. Electromagnetic power simulation suggests that the microwave power absorption density due to the dielectric loss is intrinsically predominant in X-PVA compared to the pristine PVA. Further, the ratio of electromagnetic energy to heat energy conversion power (absorption) of X-PVA is much higher than pristine PVA, indicating the suitability for self-powered devices. X-PVA also fulfils many commercial requirements such as bulk level facile synthesis, large area fabrications, ultralight, and inexpensive.

Boosting transparent electromagnetic interference shielding by multi-cavity resonances

We propose a multi-cavity resonant architecture that is established by employing two opposing ultrathin silver-based films to form a Fabry-Pérot (F-P) cavity and inserting one or two metallic mesh layers in between. Compared with the single F-P cavity, the multi-cavity architecture with one metallic mesh layer experimentally exhibits a ∼37% improvement in the average shielding effectiveness and maintains a transmittance over 80% at 550 nm. A more significant improvement of ∼108% in shielding effectiveness (SE) can be achieved by inserting two metallic mesh layers. The proposed multi-cavity architecture provides a strategy for removal of the hindrance to transparent electromagnetic interference shielding.

Leather Solid Waste/Poly(vinyl alcohol)/Polyaniline Aerogel with Mechanical Robustness, Flame Retardancy, and Enhanced Electromagnetic Interference Shielding

Renewable biobased aerogels display a promising potential to fulfill the surging demand in various industrial sectors. However, its inherent low mechanical robustness, flammability, and lack of functionality are still huge obstacles in its practical application. Herein, a novel integrated leather solid waste (LSW)/poly(vinyl alcohol) (PVA)/polyaniline (PANI) aerogel with high mechanical robustness, flame retardancy, and electromagnetic interference (EMI) shielding performance was successfully prepared. Amino carboxyl groups in LSW could be effectively exposed by solid-state shear milling (S³ M) technology to form strong hydrogen-bond interactions with the PVA molecular chains. This led to a change in the compressive strength and the temperature of the initial dimensional change to 15.6 MPa and 112.7 °C at a thickness of 2.5 cm, respectively. Moreover, LSW contains a large number of N elements, which ensures a nitrogen-based flame-retardant mechanism and increase in the limit oxygen index value of LSW/PVA aerogel to 32.0% at a thickness of 2.5 mm. Notably, by the cyclic coating method, a conductive PANI layer could be polymerized on the surface of LSW/PVA aerogel, which led to the construction of a sandwich structure with impressive EMI shielding capability. The EMI shielding effectiveness (SE) reached more than 40 dB, and the specific shielding effectiveness (SSE) reached 73.0 dB cm³ g^-1. The inherent dipoles in collagen fibers and the conductive PANI synergistically produced an internal multiple reflection and absorption mechanism. The comprehensive performance of LSW/PVA/PANI aerogel not only demonstrates a new strategy to recycle LSW in a more value-added way but also sheds some more light on the development of biomass aerogels with high-performance, environmentally friendly, and cost-effective properties.

Continuous and Patterned Conducting Polymer Coatings on Diverse Substrates: Rapid Fabrication by Oxidant-Intermediated Surface Polymerization and Application in Flexible Devices

Conducting polymer coatings and patterns are the most important forms of these materials for many practical applications, but a simple and efficient approach to these forms remains challenging. Herein, we report a universal oxidant-intermediated surface polymerization (OISP) for the fabrication of conducting polymer coatings and patterns on various substrates. A coating or pattern composed of densely packed colloidal V₂O₅·nH₂O nanowires is deposited on the substrate via spin coating, dip coating, or printing, which is converted into a conducting polymer one after in situ oxidation polymerization. The polymerization occurs selectively on the V₂O₅·nH₂O coatings, and high-quality polypyrrole, polyaniline, and poly(3,4-ethylenedioxythiophene) coatings and patterns on planar and curved polymeric, metallic, and ceramic substrates are obtained in a fast reaction rate similar to the electrochemical polymerization. The mechanistic study reveals that the method relies on the excellent processability and formability of V₂O₅·nH₂O nanowires, which is further explained by their large aspect ratio and surface activity. A flexible gas sensor array comprising three individual sensors made of different conducting polymers is fabricated using oxidant-intermediated surface polymerization, and it is successfully used to distinguish various analyte vapors. The method developed here will provide a powerful tool for the fabrication of conducting polymer-based devices.

Toward Architected Nanocomposites: MXenes and Beyond

Achieving excellent electromagnetic interference (EMI) shielding combined with mechanical flexibility, optical transparency, and environmental stability is vital for the future of coatings, electrostatic discharge, electronic displays, and wearable and portable electronic devices. Unfortunately, it is challenging to engineer materials with all of these desired properties due to a lack of understanding of the underlying materials physics and structure-property relationships. Nature has provided numerous examples of a combination of properties through precision engineering of hierarchical structures at multiple length scales with selectively chosen ingredients. This inspiration is reflected in a wide range of synthetic architected nanocomposites. In this Perspective, we provide a brief overview of recent advances in the role of hierarchical architectures in MXene-based thin-film nanocomposites in the quest to achieve multiple functionalities, especially focusing on a combination of excellent EMI shielding, transparency, and mechanical robustness. We also discuss key opportunities, challenges, and prospects.

Scalable manufacturing of flexible and highly conductive Ti3C2Tx/PEDOT:PSS thin films for electromagnetic interference shielding

A micrometer-thick film of Ti3C2Tx/PEDOT:PSS with exceptional electrical conductivity and EMI shielding was prepared via a simple casting approach and transferred onto various geometries.

Multilayer polymeric nanocomposites for electromagnetic interference shielding: fabrication, mechanisms, and prospects

Fabrication of multilayer EMI shield opens a creative avenue for designing and constructing flexible nanocomposite films simultaneously featuring excellent EMI shielding performance, fascinating heat removal ability, and robust mechanical properties.

From Waste to Wealth: A Lightweight and Flexible Leather Solid Waste/Polyvinyl Alcohol/Silver Paper for Highly Efficient Electromagnetic Interference Shielding

With the popularization of 5G communications and the internet of things, electromagnetic wave (EW) radiation pollution has aroused much concern from the public, and the search for new materials and technologies for preparing electromagnetic shielding materials still continues all around the world. However, the contradiction among high shielding performance, economic applicability, and flexibility is still not well balanced. Herein, we fabricated a novel foldable leather solid waste (LSW)/polyvinyl alcohol (PVA)/silver (Ag) paper with excellent electromagnetic interference (EMI)-shielding ability using a facile but sustainable electroless plating (ELP) method with LSW as the resource. Taking PVA as a cross-linker, debundled leather fibers (LFs) generated by solid-state shearing milling could generate a flexible LSW/PVA substrate with a high specific surface area, and eventually the deposited Ag layer served as a protective layer not only to significantly improve the mechanical and thermal robustness, but also to endow the LSW/PVA/Ag paper with good hydrophobicity, which could protect from potential moisture damage. In addition to the reflection effect of metallic Ag on EW, the hierarchical structure of collagen fibers played an important role in superior high EMI-shielding effectiveness (∼55-∼90 dB) by an absorption-dominant EMI-shielding mechanism. Furthermore, a multilayer LSW/PVA/Ag paper was also prepared with enhanced EMI-shielding effectiveness of 111.3 dB benefited by constructing multiple reflection-absorption interfaces. The high-performance, environmentally friendly, and low-cost EMI-shielding materials not only offered a new avenue toward recycling LSW in a more value-added way, but also displayed promising potential for application in flexible shielding materials or wearable clothing.

(Gold nanorod core)/(poly(3,4-ethylene-dioxythiophene) shell) nanostructures and their monolayer arrays for plasmonic switching

(Gold nanorod core)/(poly(3,4-ethylene-dioxythiophene) (PEDOT) shell) nanostructures are prepared by the surfactant-assisted oxidative polymerization of 3,4-ethylene-dioxythiophene on the surface of gold nanorods (NRs). The PEDOT shell exhibits distinct dielectric properties at doped and undoped states, which allows the manipulation of plasmonic responses of the Au nanorod core. The shift in plasmon resonance induced by the dedoping of PEDOT is found to be associated with the overlap between the plasmon resonance band of the core/shell nanostructure and the spectral region where the largest refractive index variation of PEDOT occurs, as well as with the type of the dedopant. Macroscopic two-dimensional (2D) monolayer arrays of core/shell nanostructures with controlled particle number densities are fabricated on indium tin oxide (ITO)-coated glass substrates by electrophoretic deposition. A reversible plasmonic shift of about 70 nm is obtained on the core/shell nanostructure monolayer array with a number density of around 18 particles per μm2. Our design of colloidal (Au nanorod core)/(PEDOT shell) nanostructures and their 2D monolayer arrays paves the way for the fabrication of high-performance plasmonic switches in large-scale practical usages as well as for the preparation of advanced, programmable chromic materials for a broad range of applications, such as smart windows, anti-counterfeiting tags, and medical and environmental sensors.