Gradient Structure Design of Flexible Waterborne Polyurethane Conductive Films for Ultraefficient Electromagnetic Shielding with Low Reflection Characteristic

Electromagnetic Interference Shielding Films: Structure Design and Prospects

The popularity of portable and wearable flexible electronic devices, coupled with the rapid advancements in military field, requires electromagnetic interference (EMI) shielding materials with lightweight, thin, and flexible characteristics, which are incomparable for traditional EMI shielding materials. The film materials can fulfill the above requirements, making them among the most promising EMI shielding materials for next-generation electronic devices. Meticulously controlling structure of composite film materials while optimizing the electromagnetic parameters of the constructed components can effectively dissipate and transform electromagnetic wave energy. Herein, the review systematically outlines high-performance EMI shielding composite films through structural design strategies, including homogeneous structure, layered structure, and porous structure. The attenuation mechanism of EMI shielding materials and the evaluation (Schelkunoff theory and calculation theory) of EMI shielding performance are introduced in detail. Moreover, the effect of structure attributes and electromagnetic properties of composite films on the EMI shielding performance is analyzed, while summarizing design criteria and elucidating the relevant EMI shielding mechanism. Finally, the future challenges and potential application prospects of EMI shielding composite films are prospected. This review provides crucial guidance for the construction of advanced EMI shielding films tailored for highly customized and personalized electronic devices in the future.

Enhancing EMI Shielding Efficiency of Polyurethane Foam by Incorporating MWCNT-Decorated Hollow Glass Microspheres

This work explores the enhancement of EMI shielding efficiency of polyurethane (PU) foam by loading multiwall carbon nanotube (MWCNTs)-decorated hollow glass microspheres (HGMs). MWCNT was coated onto the HGM surface by a simple solution casting technique. The coated HGM particles were loaded in PU foams, resulting in an even dispersion of MWCNT in the foam struts, thereby forming an interconnected conductive network in the polymer matrix. The synthesized polymeric foam composites were characterized for bulk density, cellular morphology, Fourier transform infrared spectra, compression strength, electrical conductivity, and EMI shielding efficiency. The highest electrical conductivity, i.e., 15.75 × 10-3 S/cm, was achieved at 13 wt % loading, which resulted in the EMI shielding efficiency of -25.03 dB. Finally, we proposed a mechanism exploring the enhancement of EMI shielding of PU foam composite showing that the incident EMI radiations are being absorbed into the material due to the presence of interconnected MWCNTs and successive reflection via hollow glass spheres. The synthesized foam can be used as an EMI shielding material in such applications where flexibility and lightweight are the primary requirements.

Incorporation of polyvinyl alcohol in bacterial cellulose/polypyrrole flexible conductive films to enhance the mechanical and conductive performance

The integration of polypyrrole (PPy) into bacterial cellulose (BC) has provided significant conductivity and cost benefits. However, this combination has led to a reduction in mechanical properties, particularly in terms of elongation at break and tensile strength. This study investigated the enhancement of BC/PPy composite films by incorporating polyvinyl alcohol (PVA). The resulting BC/PPy/PVA films demonstrated improvements in flexibility, tensile strength and thermal stability. Specifically, with 7 % PVA, the flexible films exhibited remarkable enhancements: tensile strength increased from 11.01 MPa (for BC/PPy) to 25.27 MPa and elongation at break rose from 5.81 % to 11.54 %. Additionally, the electrical conductivity of the BC/PPy/PVA films with a resistance of 38.5 Ω, surpassed that of the BC/PPy films. Furthermore, the equilibrium swelling water absorption rates of BC/PPy and BC/PPy/PVA films were 30.6 % and 81.4 %, respectively, with corresponding resistances of 530 Ω and 540 Ω. The variation in resistance between the dry and swollen states of the BC/PPy/PVA flexible conductive film resulted in differences in the brightness of the small light bulb. These findings highlighted the synergistic effects of PVA within the BC/PPy matrix, presenting a promising avenue for developing high-performance conductive materials suitable for flexible electronics and wearable devices.

A review on recent progress in polymer composites for effective electromagnetic interference shielding properties - structures, process, and sustainability approaches

The rapid proliferation and extensive use of electronic devices have resulted in a meteoric increase in electromagnetic interference (EMI), which causes electronic devices to malfunction. The quest for the best shielding material to overcome EMI is boundless. This pursuit has taken different directions, right from materials to structures to process, up to the concept of sustainable materials. The emergence of polymer composites has substituted metal and metal alloy-based EMI shielding materials due to their unique features such as light weight, excellent corrosion resistance, and superior electrical, dielectric, thermal, mechanical, and magnetic properties that are beneficial for suppressing the EMI. Therefore, polymer nanocomposites are an extensively explored EMI shielding materials strategy. This review focuses on recent research developments with a major emphasis on structural aspects and processing for enhancing the EMI shielding effectiveness of polymer nanocomposites with their underlying mechanisms and some glimpses of the sustainability approaches taken in this field.

Multifunctional phase-change composites for green electromagnetic interference shielding and thermal response prepared under the guidance of an impedance matching strategy

With the advent of the information age, electromagnetic hazards are becoming more serious. In view of environmental protection, green electromagnetic interference (EMI) shielding materials with little or no secondary reflection have become the ideal choice. In this paper, by freeze-drying, high-temperature carbonization, coating and impregnation backfilling, we prepared carbonized Ni-MOF/reduced graphene oxide/silver nanowire-polyimide@polyethylene glycol composites (Ni@C/r-GO/AgNW-PI@PEG) with gradient conductivity based on impedance matching. The impedance matching layer Ni@C/r-GO-300 reduces the reflection of electromagnetic waves from the surface of the material, the dissipation layer Ni@C/r-GO-600 provides excellent electromagnetic wave dissipation capability, and the reflection layer AgNW-PI ensures that the electromagnetic waves are reflected back into the material. Meanwhile, the EMI shielding performance value of Ni@C/r-GO/AgNW-PI@PEG reaches 62.3 dB with an ultra-low reflectivity (R) of 0.04. In CST simulations, the intrinsic mechanism of electromagnetic energy loss within the material is revealed by energy loss density cloud maps. In addition, heat from high-temperature objects is transferred through the highly thermally conductive AgNW-PI membrane to the long-channel Ni@C/r-GO backbone. Therefore, the composites prepared on the basis of impedance matching will accelerate the use of EMI shielding materials for the thermal management of portable electronic devices and battery heat dissipation packaging.

Electromagnetic porous lignocellulosic matrix composites: A green electromagnetic shielding material with high absorption efficient electromagnetic interference

Electromagnetic interference (EMI) shielding materials play a vital role in human society, especially in light of the rapid development of electronic communication equipment. Therefore, it is urgent to develop green, high-efficiency EMI shielding materials. Wood, as a renewable raw material, possesses significant structural advantages in studying EMI materials due to its unique 3D pore structure. Herein, we report magnetoelectric lignocellulosic matrix composites derived from the delignified wood for efficient EMI shielding. The composite was fabricated by in-situ polymerization of PEDOT conductive coating and magnetic Fe3O4 in delignified wood. The conductive 3D pore structure of Fe3O4/PEDOT@wood could effectively cause dielectric loss and multiple internal reflections. Combined with the magnetic loss of Fe3O4, the material exhibited excellent EMI shielding effectiveness (SE), which could be attributed to the synergistic effect of dielectric and magnetic losses. The Fe3O4/PEDOT@wood showed excellent conductivity (103 S/m), good magnetism (26.7 emu/g), the EMI SE up to 59.8 dB, and high SEA/SET ratios of∼84.2 % to 95.7 % at 2 mm in X -band. Moreover, the material exhibited a high compressive strength and tensile strength of 100.8 MPa and 18.1 MPa, respectively. Therefore, this work provided a reference for the preparation of high-efficiency EMI shielding materials.

Cellulose-derived carbon scaffolds with bidirectional gradient Fe3O4 distribution: Integration of green EMI shielding and thermal management

Cellulose papers (CPs) possess a pore structure, rendering them ideal precursors for carbon scaffolds because of their renewability. However, achieving a tradeoff between high electromagnetic shielding effectiveness and low reflection coefficient poses a tremendous challenge for CP-based carbon scaffolds. To meet the challenge, leveraging the synergistic effect of gravity and evaporation dynamics, laminar CP-based carbon scaffolds with a bidirectional gradient distribution of Fe3O4 nanoparticles were fabricated via immersion, drying, and carbonization processes. The resulting carbon scaffold, owing to the bidirectional gradient structure of magnetic nanoparticles and unique laminar arrangement, exhibited excellent in-plane electrical conductivity (96.3 S/m), superior electromagnetic shielding efficiency (1805.9 dB/cm2 g), low reflection coefficients (0.23), and a high green index (gs, 3.38), suggesting its green shielding capabilities. Furthermore, the laminar structure conferred upon the resultant carbon scaffold a surprisingly anisotropic thermal conductivity, with an in-plane thermal conductivity of 1.73 W/m K compared to a through-plane value of only 0.07 W/m K, confirming the integration of thermal insulation and thermal management functionalities. These green electromagnetic interference shielding materials, coupled with thermal insulation and thermal management properties, hold promising prospects for applications in sensitive devices.

Design and Analysis of a Textured Cu-Encapsulated Ni Tube for Low-Reflection Electromagnetic Interference Shielding Material

With the frequent increase and update of electromagnetic interference (EMI) shielding materials, a low-resolution material that can absorb most electromagnetic waves, thereby effectively reducing the secondary pollution, is urgently needed. However, the excellent performance, flexibility, and low cost of these methods are usually incompatible with current reports. To address the above dilemma, we reported a facile solution for fabricating a low-reflection and high-performance EMI shielding composite by means of electroless nickel plating (EP-Ni), electroless copper plating (EP-Cu), annealing, and coating with a polydimethylsiloxane (PDMS) polymer with the structure of a Ni@Cu tube encapsulated with PDMS. The results indicate that the active groups on vegetable wool can act as active sites for the absorption of the Pd catalyst, thereby catalyzing the reduction of Ni2+, Cu2+, and the subsequent deposition on the plant fiber surface. Notably, the Ni@Cu-encapsulated plant fibers decreased during annealing at 100 °C. According to the segregated network and synergistic effect of the porous structure, the as-fabricated EMI shielding material demonstrated high absorption and low reflection, in which the power coefficient of the T value was approximately 0.0001, the R value was about 0.1764 (a decrease of 27.5% compared that of EP-Ni cotton), and the A value was approximately 0.8235.

Scaled Production of Functionally Gradient Thin Films Using Slot Die Coating on a Roll-to-Roll System

Polymer thin films with a cross-web gradient structure is a burgeoning area of research, having received more attention in the last two decades, for improvements in the performance and material properties. Such patterned films have been fabricated using several techniques, but in practice these techniques are non-scalable, material-dependent, wasteful, and not highly efficient. Slot die coating, a well-known scalable manufacturing process, is used to fabricate gradient polymer thin films which will be investigated herein. By incorporating slot die with the custom roll-to-roll imaging system, gradient thin films are successfully fabricated by forcing two fluidic materials into the slot die simultaneously and by manipulating the viscous, diffusive, and inertial forces. The materials will be allowed to intermix, with the aim of having approximately a 50% mix along the centerline of any two contiguous stripes. Moreover, several characterizations such as FTIR, UV-vis spectroscopy, and SEM are performed to assess the quality of the gradient polymer thin films. The gradient structure fabricated using functional and nonfunctional materials has successfully improved the functional properties compared to fully blended two materials. This work will provide an understanding of the mechanisms to obtain gradient polymer thin-film structures that exhibit the desired geometric structure and performance.

Porous Gradient Composite with Dependable Superhydrophobic Protection for Multifunctional Electromagnetic Interference Shielding

Simultaneously realizing high electromagnetic interference (EMI) shielding and superhydrophobic properties of materials to ensure long-term stability in harsh environments is a very challenging task. In this work, an efficient superhydrophobic EMI shielding composite with a gradient conductivity and porous structure was prepared by chemical plating, in situ polymerization, and spraying processes. Benefiting from the structural characteristics of porous multilayers and the rational distribution of electromagnetic two-component fillers in the composite, as well as the synergistic effect of various electromagnetic loss mechanisms, a perfect unification of high EMI shielding effectiveness of 62 dB and high absorption coefficient (A) of 0.77 was achieved. Meanwhile, a thin layer with further enhanced impedance matching was constructed on the surface of the composite using double-sized mixed particles of Fe3O4 and graphite particles (GP) in conjunction with the spraying process. The rough surface microstructure of the thin layer bestows the composite superhydrophobicity, and even after long-term immersion in acidic and alkali solutions or repetitive bending, the water contact angle still remains at a high level. Additionally, the sprayed materials also endow the composite with outstanding photothermal conversion properties that enhance the ability to adapt to environmental changes, significantly raising the practical application value.

Incorporating Loss Factor Modular Design for Full Ku-Band Microwave Attenuation in Double-Layered Graphene Aerogels

The fabrication of absorption-dominant electromagnetic interference (EMI) shielding materials is a pressing priority to prevent secondary electromagnetic pollution in miniaturized electronic devices and communication systems. Meeting this goal has remained a tough challenge to keep pace with the rapid evolution of electronics due to the complex compositional and structural design and narrow operating bands. This work articulates a sound and simple strategy to precisely modulate the electrical conductivity of reduced graphene oxide (rGO), as the building block in lightweight double-layered rGO-film/rGO-aerogel/polyvinyl-alcohol (PVA) composites, for efficient microwave absorption over the entire Ku-band frequency range. These constructs reasonably comprised a porous absorption structure built from parallel rGO sheets aligned and prepared via freeze casting followed by freeze drying. The electrical conductivity and impedance of this layer were tuned by varying the annealing temperature from 400 to 800 °C, thereby adjusting the degree of reduction and the absorption characteristic. This layer was backed by a highly conductive rGO film reduced at a high temperature of 1000 °C, with a reflectivity of 97.5%. The incorporation of this film ensured high EMI shielding effectiveness of the double-layered structure through the absorption-reflection-reabsorption mechanism, consistent with the predicted values based on calculated loss factors and the input impedance of the structure. Accordingly, at an average EMI shielding effectiveness of 57.59 dB, the reflection shielding effectiveness (SER) and reflectivity (R) of the assembled composites were optimized to be as low as 0.22 dB and 0.049, respectively. This equates to approximately 99.999% shielding (SET) and ∼95% absorptivity (A) of the incident wave. This study opens new avenues for the development of lightweight (with a density as low as 15 mg/cm3) absorption-dominant EMI shielding composite materials with promising EMI shielding efficiency and potential applications in modern electronics.

Research Progress on Intrinsically Conductive Polymers and Conductive Polymer-Based Composites for Electromagnetic Shielding

Electromagnetic shielding materials are special materials that can effectively absorb and shield electromagnetic waves and protect electronic devices and electronic circuits from interference and damage by electromagnetic radiation. This paper presents the research progress of intrinsically conductive polymer materials and conductive polymer-based composites for electromagnetic shielding as well as an introduction to lightweight polymer composites with multicomponent systems. These materials have excellent electromagnetic interference shielding properties and have the advantages of electromagnetic wave absorption and higher electromagnetic shielding effectiveness compared with conventional electromagnetic shielding materials, but these materials still have their own shortcomings. Finally, the paper also discusses the future opportunities and challenges of intrinsically conductive polymers and composites containing a conductive polymer matrix for electromagnetic shielding applications.

Rapid Fabrication of Flexible Cu@Ag Flake/SAE Composites with Exceptional EMIS and Joule Heating Performance

High electromagnetic interference shielding (EMIS) effectiveness and good thermal management properties are both required to meet the rapid development of integrated electronic components. However, it remains challenging to obtain environmentally friendly and flexible films with high EMIS and thermal management performance in an efficient and scalable way. In this paper, an environmentally friendly strategy is proposed to synthesize multifunctional waterborne Cu@Ag flake conductive films using water as the solvent and silicone-acrylic emulsion (SAE) as a matrix. The obtained films show high electrical conductivity and exceptional EMI SE and electrothermal conversion properties. The EMI SE in the X-band is higher than 76.31 dB at a thickness of 60 μm owing to the ultrahigh electrical conductivity of 1073.61 S cm-1. The film warms up quickly to 102.1 °C within 10 s under a low voltage of 2.0 V. In addition, the shielding coating is sufficiently flexible to retain a conductivity of 93.4% after 2000 bending-release cycles with a bending radius of 3 mm. This work presents an alternative strategy to produce high EMIS effectiveness and Joule heating films for highly integrated and flexible electronic components in a green, scalable, and highly efficient way.

External field-assisted techniques for polymer matrix composites with electromagnetic interference shielding

The rapid development of mobile devices has greatly improved the lives of people, but they have also caused problems with electromagnetic interference (EMI) and information security. Therefore, there is an urgent need to develop high performance EMI shielding materials to suppress electromagnetic radiation and prevent information leakage. Some reports point out that the self-orientation behavior of fillers under external forces contributes to the improvement of EMI shielding performance. So how to construct an effective filler orientation structure in the polymer matrix is becoming a hot topic in the research of EMI shielding materials. In view of the fact that there are few reports on the preparation of polymer matrix EMI shielding composites by external field induction, from this perspective, we first highly focus on strategies for the construction of conductive networks within composites based on external field induction. Subsequently, the research progress on the preparation of polymer matrix EMI shielding composites by inducing the orientation of inorganic fillers through external fields, including temperature, electrostatic, gravity, mechanical force and magnetic fields, is organized and sorted out in detail. Notably, the particular response relationship between the unique composite structures prepared by external field induction and the incident electromagnetic waves is further dissected. Finally, the key scientific problems that need to be solved in the preparation of polymer matrix EMI shielding composites assisted by external fields are proposed. The approach discussed and the strategies proposed are expected to provide some guidance for the innovative design of high-performance polymer matrix EMI shielding composites.

Flexible Nanocomposite Conductors for Electromagnetic Interference Shielding

HIGHLIGHTS

Convincing candidates of flexible (stretchable/compressible) electromagnetic interference shielding nanocomposites are discussed in detail from the views of fabrication, mechanical elasticity and shielding performance. Detailed summary of the relationship between deformation of materials and electromagnetic shielding performance. The future directions and challenges in developing flexible (particularly elastic) shielding nanocomposites are highlighted. With the extensive use of electronic communication technology in integrated circuit systems and wearable devices, electromagnetic interference (EMI) has increased dramatically. The shortcomings of conventional rigid EMI shielding materials include high brittleness, poor comfort, and unsuitability for conforming and deformable applications. Hitherto, flexible (particularly elastic) nanocomposites have attracted enormous interest due to their excellent deformability. However, the current flexible shielding nanocomposites present low mechanical stability and resilience, relatively poor EMI shielding performance, and limited multifunctionality. Herein, the advances in low-dimensional EMI shielding nanomaterials-based elastomers are outlined and a selection of the most remarkable examples is discussed. And the corresponding modification strategies and deformability performance are summarized. Finally, expectations for this quickly increasing sector are discussed, as well as future challenges.

Transparent and Flexible Composite Films with Excellent Electromagnetic Interference Shielding and Thermal Insulating Performance

As the working environment becomes more complex, the visualization of windows in electronic devices increasingly requires transparent and flexible electromagnetic interference (EMI) shielding films. There is a need for materials with EMI shielding properties, while maintaining excellent high light transmission and good thermal insulation. However, the preparation of such multifunctional materials remains challenging due to the respective mechanisms of action of the different properties. Herein, a multilayer structure strategy is proposed to fabricate transparent and flexible indium tin oxide (ITO)/silver nanowire (AgNW) composite films, achieving a multifunctional integration of high light transmission, strong EMI shielding, and good thermal insulation properties of the composite films. Simultaneously, the layered structure was designed and the potential optimization mechanism of the EMI shielding performance of the composite film was analyzed, providing great flexibility for the preparation of transparent composite films. The combination of excellent EMI shielding performance, outstanding near-infrared shielding performance, and high light transmittance makes the ITO/AgNW (IA) composite films promising for abundant potential applications.

Multi-hierarchically Structural Polycaprolactone Composites with Tunable Electromagnetic Gradients for Absorption-Dominated Electromagnetic Interference Shielding

Achieving absorption-dominated electromagnetic interference (EMI) shielding composites with high shielding effectiveness (SE) remains a great challenge due to their minimization of secondary EM radiation pollution, which is highly desired for next-generation electronic devices. Herein, an ingenious approach is proposed to develop asymmetric hierarchical polycaprolactone (PCL) composites composed of an impedance matching layer and a conductive layer through the combination of alternate casting and electroless plating methods, while the polarization loss caused by the difference in conductivity between the two layers would further attenuate the EM waves. The gradient distribution of the shielding fillers creates a positive conductive gradient and a negative magnetic gradient; the higher the gradient, the more it induces magnetic and dielectric losses, which results in an enhanced absorption mechanism that could overcome the restrictions of the nonadjustable reflective properties. The obtained Fe₃O₄@rGO/Ni/Ag/PCL composite possesses a remarkable EMI SE of 47.6 dB, while the power coefficient of reflectivity (R) could be significantly reduced to 0.27. This research provides a feasible strategy for developing absorption-dominated shielding materials with tunable EM performance that are appropriate for the next generation of electronic devices.

Study of a Novel Fluorine-Containing Polyether Waterborne Polyurethane with POSS as a Cross-Linking Agent

Waterborne polyurethane are more eco-friendly materials due to lower volatile organic compounds (VOCs, mainly isocyanates) content than the alternative materials. However, these rich hydrophilic groups polymers have not yet reached good mechanical properties, durability and hydrophobicity behaviors. Therefore, hydrophobic waterborne polyurethane has become a research hotspot, attracting significant attention. In this work, firstly, a novel fluorine-containing polyether P(FPO/THF) was synthesized by cationic ring-opening polymerization of 2-(2,2,3,3-tetrafluoro-propoxymethyl)-oxirane (FPO) and tetrahydrofuran (THF). Secondly, fluorinated polymer P(FPO/THF), isophorone diisocyanate (IPDI) and hydroxy-terminated polyhedral oligomeric silsesquioxane (POSS-(OH)₈) were used to prepare a new fluorinated waterborne polyurethane (FWPU). Hydroxy-terminated POSS-(OH)₈ was used as a cross-linking agent, while dimethylolpropionic acid (DMPA) and triethylamine (TEA) were used as a catalyst. Four kinds of waterborne polyurethanes (FWPU0, FWPU1, FWPU3, FWPU5) were obtained by adding different contents of POSS-(OH)₈ (0%, 1%, 3%, 5%). The structures of the monomers and polymers were verified by ¹H NMR and FT-IR, and the thermal stabilities of various waterborne polyurethanes were analyzed by thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC). As the results, the thermal analysis showed that the FWPU performed the good thermal stability and the glass transition temperature could reach at about -50 °C. The FWPU1 film exhibited that the elongation at break was 594.4 ± 3.6% and the tensile strength at break was 13.4 ± 0.7 MPa, elucidating that the FWPU1 film developed the excellent mechanical properties relative to the alternative FWPUs. Further, the FWPU5 film performed the promising properties, including the higher surface roughness of FWPU5 film (8.41 nm) obtained by the atomic force microscope (AFM) analysis, and the higher value of water contact angle (WCA) at 104.3 ± 2.7°. Those results illustrated that the novel POSS-based waterborne polyurethane FWPU containing a fluorine element could develop the excellent hydrophobicity and mechanical properties.

Study on the Controllable Preparation of Nd3+ Doped in Fe3O4 Nanoparticles for Magnetic Protective Fabrics

Magnetic protective fabrics with fine wearability and great protective properties are highly desirable for aerospace, national defense, and wearable protective applications. The study of the controllable preparation method of Nd3+ doped in Fe3O4 nanoparticles with supposed magnetic properties remains a challenge. The characterization of the microstructure, elemental composition, and magnetic properties of NdFe2O4 nanoparticles was verified. Then, the surface of NdFe2O4 was treated with glyceric acid to provide sufficient –OH. Subsequently, the connection of the nanoparticle by the succinimide group was studied and then grafted onto cotton fabrics as its bridging effect. The optimal loading rate of the functional fabrics with nanoparticles of an average size of 230 nm was 1.37% after a 25% alkali pretreatment. The color fatness to rubbing results showed better stability after washing and drying. The corresponding hysteresis loop indicated that the functional fabrics exhibited typical magnetism behavior with a closed “S” shape and a magnetic saturation value of 17.61 emu.g−1 with a particle size of 230 nm. However, the magnetic saturation value of the cotton fabric of 90 nm was just 4.89 emu.g−1, exhibiting controllable preparation for the aimed electromagnetic properties and great potential in radiation protective fields. The electrochemical properties of the functional fabrics exhibited extremely weak electrical conductivity caused by the movement of the magnetic dipole derived from the NdFe2O4 nanoparticles.

Controlled Distributed Ti3 C2 Tx Hollow Microspheres on Thermally Conductive Polyimide Composite Films for Excellent Electromagnetic Interference Shielding

Flexible multifunctional polymer-based electromagnetic interference (EMI) shielding composite films have important applications in the fields of 5G communication technology, wearable electronic devices, and artificial intelligence. Based on the design of a porous/multilayered structure and using polyimide (PI) as the matrix and polymethyl methacrylate (PMMA) microspheres as the template, flexible (Fe₃ O₄ /PI)-Ti₃ C₂ T_x -(Fe₃ O₄ /PI) composite films with controllable pore sizes and distribution of Ti₃ C₂ T_x hollow microspheres are successfully prepared by sacrificial template method. Owing to the porous/multilayered structure, when the pore size of the Ti₃ C₂ T_x hollow microspheres is 10 µm and the mass ratio of PMMA/Ti₃ C₂ T_x is 2:1, the (Fe₃ O₄ /PI)-Ti₃ C₂ T_x -(Fe₃ O₄ /PI) composite film has the most excellent EMI shielding performance, with EMI shielding effectiveness (EMI SE) of 85 dB. It is further verified by finite element simulation that the composite film has an excellent shielding effect on electromagnetic waves. In addition, the composite film has good thermal conductivity (thermal conductivity coefficient of 3.49 W (m·K)^-1 ) and mechanical properties (tensile strength of 65.3 MPa). This flexible (Fe₃ O₄ /PI)-Ti₃ C₂ T_x -(Fe₃ O₄ /PI) composite film with excellent EMI shielding performance, thermal conductivity, and mechanical properties has demonstrated great potential for applications in EMI shielding protection for high-power, portable, and wearable flexible electronic devices.

Engineering of the Core-Shell Boron Nitride@Nitrogen-Doped Carbon Heterogeneous Interface for Efficient Heat Dissipation and Electromagnetic Wave Absorption

The effective integration of multiple functions into electromagnetic wave-absorbing (EWA) materials is the future development direction but remains a huge challenge. A rational selection of components and the design of structures can make the material have excellent EWA performance and heat dissipation. Herein, the core-shell structured boron nitride@nitrogen-doped carbon (BN@NC) is prepared by using waterborne polyurethane (WPU) as the carbon source via a facile pyrolysis treatment process, where NC is used as the conductive loss shell, and BN serves as an impedance matching core and dominant heat transfer media. As a result, the BN@NC-900 filled with paraffin wax yields a minimum reflection loss of -42.2 dB at 2.2 mm and an effective absorbing bandwidth of 4.48 GHz at 1.8 mm, and its thermal conductivity reaches up to 0.92 W/m·K in epoxy resin. Most importantly, flexible BN@NC/WPU films are prepared and simultaneously achieve the dual-functional capability of efficiently dissipating heat and electromagnetic waves (-50.0 dB). Besides, an attractive multiband absorption feature (>99%) from C to Ku bands is realized and a strong absorbing over -27.0 dB at the S band (2.88 GHz) is even achieved. This study may pave a new route for the rational design of multifunctional EWA materials.

3D Printed Integrated Gradient-Conductive MXene/CNT/Polyimide Aerogel Frames for Electromagnetic Interference Shielding with Ultra-Low Reflection

Construction of advanced electromagnetic interference (EMI) shielding materials with miniaturized, programmable structure and low reflection are promising but challenging. Herein, an integrated transition-metal carbides/carbon nanotube/polyimide (gradient-conductive MXene/CNT/PI, GCMCP) aerogel frame with hierarchical porous structure and gradient-conductivity has been constructed to achieve EMI shielding with ultra-low reflection. The gradient-conductive structures are obtained by continuous 3D printing of MXene/CNT/poly (amic acid) inks with different CNT contents, where the slightly conductive top layer serves as EM absorption layer and the highly conductive bottom layer as reflection layer. In addition, the hierarchical porous structure could extend the EM dissipation path and dissipate EM by multiple reflections. Consequently, the GCMCP aerogel frames exhibit an excellent average EMI shielding efficiency (68.2 dB) and low reflection (R = 0.23). Furthermore, the GCMCP aerogel frames with miniaturized and programmable structures can be used as EMI shielding gaskets and effectively block wireless power transmission, which shows a prosperous application prospect in defense industry and aerospace.

Hollow Gradient-Structured Iron-Anchored Carbon Nanospheres for Enhanced Electromagnetic Wave Absorption

Highlights

Microwave absorber with nanoscale gradient structure was proposed for enhancing the electromagnetic absorption performance. Outstanding reflection loss value (−62.7 dB), broadband wave absorption (6.4 dB with only 2.1 mm thickness) in combination with flexible adjustment abilities were acquired, which is superior to other relative graded distribution structures. This strategy initiates a new method for designing and controlling wave absorber with excellent impedance matching property in practical applications.

Abstract

In the present paper, a microwave absorber with nanoscale gradient structure was proposed for enhancing the electromagnetic absorption performance. The inorganic–organic competitive coating strategy was employed, which can effectively adjust the thermodynamic and kinetic reactions of iron ions during the solvothermal process. As a result, Fe nanoparticles can be gradually decreased from the inner side to the surface across the hollow carbon shell. The results reveal that it offers an outstanding reflection loss value in combination with broadband wave absorption and flexible adjustment ability, which is superior to other relative graded distribution structures and satisfied with the requirements of lightweight equipment. In addition, this work elucidates the intrinsic microwave regulation mechanism of the multiscale hybrid electromagnetic wave absorber. The excellent impedance matching and moderate dielectric parameters are exhibited to be the dominative factors for the promotion of microwave absorption performance of the optimized materials. This strategy to prepare gradient-distributed microwave absorbing materials initiates a new way for designing and fabricating wave absorber with excellent impedance matching property in practical applications.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40820-022-00963-w.

Absorption Dominated Directional Electromagnetic Interference Shielding through Asymmetry in a Multilayered Construct with an Exceptionally High Green Index

Fabricating green electromagnetic interference (EMI) shields is the need of the hour because strong secondary reflections in the vicinity of the shield adversely affect the environment and the reliability of the neighboring devices. To this end, the present work aims to maximize the absorption-based EMI shielding through a multilayered construct comprising a porous structure (pore size less than λ/5), a highly conducting entity, and a layer to match the impedance. The elements of this construct were positioned so that the incoming electromagnetic (EM) radiation interacts with the other layers of the construct before the conducting entity. This positioning of the layers in the construct offers a high green shielding index (g_s) and low reflection coefficient (R ∼ 0.1) with an exceptionally high percent absorption (up to 99%). Polyurethane (PU) foams were fabricated using the salt-leaching technique and strategically positioned with carbon nanotube (CNT) papers and polycarbonate (PC)-based films to obtain symmetric and asymmetric constructs. These structures were then employed to gain mechanistic insight into the directional dependency of shielding performance, g_s, and heat dissipation ability. Interestingly, maximum total shielding effectiveness (SE_T) of -52 dB (88% absorption @8.2 GHz) and specific shielding effectiveness/thickness (SSE_t) of -373 dB/cm²g were achieved for a symmetric construct whereas, for the asymmetric construct, the SE_T and SSE_t were -37 dB and -280 dB/cm²g, respectively, with an exceptionally high g_s of 8.6, the highest reported so far. The asymmetricity in the construct led to directional dependence of the absorption component (% SE_A, shielding effectiveness due to absorption) and heat dissipation, primarily governed by the electrical and thermal conductivity gradient, respectively. This study opens new avenues in this field and reports constructs with an exceptionally high green index.

Generation of Abundant Defects in Ferrite Carbon Magnetic Nanomaterials for Eliminating Electromagnetic Interference in Communication

A series of novel ferrite carbon nanomaterials are considered to obtain the potential advantages in elimination of the electromagnetic interference effects. Herein, the iron nanoparticles coated on amorphous carbon were prepared by facile agar-gel synthesis. Meanwhile, the synergy between carbon supporting and ferrite nanomaterials could be proved to promote the absorption properties. Among all samples, the iron nanoparticles coated on amorphous carbon show the highest microwave absorption properties, achieving the maximum reflection loss (RL) of -14.3 dB at 6 GHz (5.5-milimeter thickness), and the bandwidths over -10 dB (90% absorption) was 2.5 GHz. Combining analysis results, it is confirmed that the as-prepared iron nanoparticles have the highest surface area, homogeneous distribution, abundant defect, and well-defined pore structure, which could significantly affect the absorption properties at 6 GHz. Furthermore, the abundant defects derived from the interface were the essential reason for the improved absorption properties. Overall, it provided a new strategy to design an effective method to absorb nanomaterials for the elimination of electromagnetic interference, especially the coordination of metal species and carbon supporting.

Multifunctional CoFe2O4@MXene-AgNWs/Cellulose Nanofiber Composite Films with Asymmetric Layered Architecture for High-Efficiency Electromagnetic Interference Shielding and Remarkable Thermal Management Capability

Developing high-efficiency electromagnetic interference (EMI) shielding composite films with outstanding flexibility and excellent thermal management capability is vital but challenging for modern integrated electronic devices. Herein, a facile two-step vacuum filtration method was used to fabricate ultrathin, flexible, and multifunctional cellulose nanofiber (CNF)-based composite films with an asymmetric layered architecture. The asymmetric layered structure is composed of a low-conductivity CoFe₂O₄@MXene/CNF layer and a highly conductive silver nanowires (AgNWs)/CNF layer. Benefiting from the rational placement of the impedance matching layer and shielding layer, as well as the synergistic effect of electric and magnetic losses, the resultant composite film exhibits an extremely high EMI shielding effectiveness (SE) of 73.3 dB and an average EMI SE of 70.9 dB with low reflected efficiency of 4.9 dB at only 0.1 mm thickness. Sufficiently reliable EMI SE (over 95% reservation) is attained even after suffering from continuous physical deformations and long-term chemical attacks. Moreover, the prepared films exhibit extraordinary flexibility, strong mechanical properties, and satisfactory thermal management capability. This work offers a viable strategy for exploiting high performance EMI shielding films with attractive thermal management capacity, and the resultant films present extensive application potential in aerospace, artificial intelligence, advanced electronics, stealth technology, and the national defense industry, even under harsh environments.

Sandwich-Structured Surface Coating of a Silver-Decorated Electrospun Thermoplastic Polyurethane Fibrous Film for Excellent Electromagnetic Interference Shielding with Low Reflectivity and Favorable Durability

Nowadays, high efficiency and low reflection electromagnetic interference (EMI) shielding materials have a wide potential application of electronic fields. However, it is still challenging to achieve long-term durability under external mechanical deformations or other harsh conditions. Herein, sandwich-structured surface coatings with a mixture of polydimethylsiloxane (PDMS)/carboxylated multiwalled carbon nanotube and magnetic ferriferous oxide nanoparticle hybrid fillers (MWCNTs-COOH/Fe₃O₄, MFs) are introduced onto a silver-decorated electrospun thermoplastic polyurethane (TPU) fibrous film to achieve both outstanding low reflective EMI shielding and favorable durability. The surface coatings not only act as an effective absorbing layer but also provide a micro-nano hierarchical superhydrophobic surface. The resultant film shows a remarkable conductivity (361.0 S/cm), an excellent EMI shielding effectiveness (SE) approaching 85.4 dB, and a low reflection coefficient value of 0.61. Interestingly, the obtained film still maintains an excellent EMI SE even after mechanical deformations or being immersed in strong acidic solution, alkaline solution, and organic solvents for 6 h. This work opens a new avenue for the design of low reflective EMI shielding films under harsh environments.

Wood-Based Composites with High Electromagnetic Interference Shielding Effectiveness and Ultra-Low Reflection

With the aggravation of electromagnetic radiation pollution, it is urgent to develop green, lightweight, ultra-thin and high-performance electromagnetic interference shielding materials to eliminate unnecessary electromagnetic interference; however, the construction of wood-based high-performance electromagnetic shielding materials by simple methods remains a challenge. Based on the layer-by-layer assembly strategy, a lightweight Ni/Wood/Ni composite (NWNC) with an interlayer structure was constructed by a simple electroless plating method using natural wood as a substrate for electromagnetic interference shielding. The synthesized NWNC has a smooth surface, and its minimum surface roughness is only 8.34 μm. After 15 min of electroless nickel plating, the contact angle (CA) of NWNC with an ultra-thin nickel layer (65 μm) was 118.3°. When the thickness of the nickel layer is only 0.102 mm, the conductivity can reach 1659.59 S/cm when the three electroless nickel plating time is 15 min. In the L-band, the electromagnetic shielding effectiveness can reach 94.1 dB after three times electroless nickel plating for 20 min. This is due to the conductive loss, magnetic loss and interface polarization loss generated by the electromagnetic network constructed by the nickel layer, which makes the composite material produce an electromagnetic shielding mechanism dominated by absorption. The L-band absorption efficiency can reach 39.01 dB, and due to the porous structure of the original wood, the multiple reflection and absorption inside the wood further lose the electromagnetic wave. This study provides a low-cost and simple method for the design of light, ultra-thin and efficient controllable wood-based electromagnetic shielding materials and has broad application prospects in the fields of construction and aerospace.

Recent Advances in Polymer Nanocomposites for Electromagnetic Interference Shielding: A Review

The mushrooming utilization of electronic devices in the current era produces electromagnetic interference (EMI) capable of disabling commercial and military electronic appliances on a level like never before. Due to this, the development of advanced materials for effectively shielding electromagnetic radiation has now become a pressing priority for the scientific world. This paper reviews the current research status of polymer nanocomposite-based EMI shielding materials, with a special focus on those with hybrid fillers and MXenes. A discussion on the theory of EMI shielding followed by a brief account of the most popular synthesis methods of EMI shielding polymer nanocomposites is included in this review. Emphasis is given to unravelling the connection between microstructures of the composites, their physical properties, filler type, and EMI shielding efficiency (EMI SE). Along with EMI shielding efficiency and conductivity, mechanical properties reported for EMI shielding polymer nanocomposites are also reviewed. An elaborate discussion on the gap areas in various fields where EMI shielding materials have potential applications is reported, and future directions of research are proposed to overcome the existing technological obstacles.

Computational Optimizing the Electromagnetic Wave Reflectivity of Double-Layered Polymer Nanocomposites

Double-layered absorption-dominated electromagnetic interference (EMI) shielding composites are highly desirable to prevent secondary electromagnetic wave pollution. However, it is a tremendous challenge to optimize the shielding performance via the trial-and-error method due to the low efficiency. Herein, a novel approach of computation-aided experimental design is proposed to efficiently optimize the reflectivity of the double-layered composites. A normalized input impedance (NII) method is presented to calculate the electromagnetic wave reflectivity of multilayered EMI shielding composites. The calculated results are a good match with the experimental results. Then, the NII method is utilized to design polyvinylidene difluoride/MXene/carbon nanotube (PVDF/MXene/CNT) composites. According to the optimization of the NII method, the prepared PVDF/MXene/CNT composite has an ultralow reflectivity of 0.000057, which outperforms that reported in current work and satisfies the requirement of electromagnetic wave absorbing material. Additionally, its average EMI shielding effectiveness is 30 dB, demonstrating that PVDF/MXene/CNT composite simultaneously achieves shielding and absorption. The ultralow reflection mechanism can be ascribed to the ideal impedance match. Both the PVDF/MXene and the PVDF/CNT layers can attenuate electromagnetic energy, which subverts the traditional cognition of double-layered absorption-dominated EMI shielding composites. The NII method opens a way for the practical fabrication of double-layered absorption-dominated EMI shielding composites.

A Perspective for Developing Polymer-Based Electromagnetic Interference Shielding Composites

The rapid development of aerospace weapons and equipment, wireless base stations and 5G communication technologies has put forward newer and higher requirements for the comprehensive performances of polymer-based electromagnetic interference (EMI) shielding composites. However, most of currently prepared polymer-based EMI shielding composites are still difficult to combine high performance and multi-functionality. In response to this, based on the research works of relevant researchers as well as our research group, three possible directions to break through the above bottlenecks are proposed, including construction of efficient conductive networks, optimization of multi-interfaces for lightweight and multifunction compatibility design. The future development trends in three directions are prospected, and it is hoped to provide certain theoretical basis and technical guidance for the preparation, research and development of polymer-based EMI shielding composites.

Integration of efficient microwave absorption and shielding in a multistage composite foam with progressive conductivity modular design

Ultra-efficient electromagnetic interference (EMI) shielding composites with excellent microwave absorbing properties are the most desirable solution for eliminating microwave pollution. However, integrating absorbing and electromagnetic shielding materials is a difficult challenge because they have different design strategies. In this work, the compatibility of high absorption and shielding capability based on progressive conductivity modular design was realized. Reduced graphene oxide@ferroferric oxide/carbon nanotube/tetraneedle-like ZnO whisker@silver/waterborne polyurethane (rGO@Fe₃O₄/CNT/T-ZnO@Ag/WPU) multistage composite foams with aligned porous structures were fabricated, which exhibited an excellent average EMI SE > 92.3 dB and remarkable microwave absorption performance with reflection loss < -10 dB in the frequency range of 8.2-18.0 GHz. The average shielding effectiveness of reflection (SE_R) and reflectivity (R) are as low as 0.065 dB and 0.015, respectively. Besides, the correlations between the morphology and structure of the composite foam and the electromagnetic wave attenuation mechanism were established via electromagnetic simulation. Significantly, the integration of efficient absorbing and shielding materials was realized for the first time. Such composite foams with electromagnetic wave absorption and shielding characteristics are light weight and structurally designable with an adjustable shielding mechanism, and exhibit low filler consumption and high performance. They display promising applications in demanding electromagnetic environments. Our work provides a new strategy to design ultra-efficient EMI shielding materials with reliable absorption-dominated features.

MXene-Coated Wrinkled Fabrics for Stretchable and Multifunctional Electromagnetic Interference Shielding and Electro/Photo-Thermal Conversion Applications

Stretchability and multifunctional heating abilities are highly desired for wearable electromagnetic interference (EMI) shielding fabrics to tackle the growing electromagnetic pollution for special crowd, such as pregnant women. Herein, we fabricated stretchable MXene-coated thermoplastic polyurethane (TPU) fabrics by simple uniaxial prestretching and spraying methods. The obtained unique wrinkled structure endowed the film with effective strain-invariant electrical conductivity and EMI shielding properties. Specifically, the prepared stretchable film with an extremely low MXene loading (0.417 mg cm^-2) exhibited a stable EMI shielding effectiveness of approximately 30 dB under 50% tensile strain and durability during stretching and bending cycles. More importantly, owing to the high electrical conductivity and localized surface plasmon resonance (LSPR) effect of the MXene layer, the stretchable fabrics exhibited excellent Joule heating (up to 104 °C at a voltage of 5 V) and superior photothermal conversion abilities. Moreover, the unique wrinkled MXene-coating layer not only endows the fabrics with stretchable heat abilities but also enhances the photothermal conversion performance by increasing the light absorption area and travel path. We believe that this study offers a novel strategy for the versatile design of stretchable and multifunctional wearable shielding fabrics.

Biomass-Derived, Highly Conductive Aqueous Inks for Superior Electromagnetic Interference Shielding, Joule Heating, and Strain Sensing

Conductive composite inks are widely used in various applications such as flexible electronics. However, grand challenges still remain associated with their relatively low electrical conductivity and require heavy use of organic solvents, which may limit their high performance in broad applications and cause environmental concerns. Here, we report a generalized and eco-friendly strategy to fabricate highly conductive aqueous inks using silver nanowires (AgNWs) and biomass-derived organic salts, including succinic acid-chitosan (SA-chitosan) and sebacic acid-chitosan. SA-chitosan/AgNW composite coatings can be prepared by directly casting conductive aqueous inks on various substrates, followed by subsequently heating for cross-linking. The composite coatings exhibit an ultrahigh electrical conductivity up to 1.4 × 10⁴ S/cm, which are stable after being treated with various organic solvents and/or kept at a high temperature of 150 °C, indicating their high chemical and thermal resistance. The flexibility and performance durability of these composite coatings were demonstrated by a suite of characterization methods, including bending, folding, and adhesion tests. Moreover, a high electromagnetic interference shielding (EMI) effectiveness of 73.3 dB is achieved for SA-chitosan/AgNW composite coatings at a thickness of only 10 μm due to the ultrahigh electrical conductivity. Additionally, we further demonstrated that such conductive composite inks can be used for fabricating functional textiles for a variety of applications with high performance, such as EMI shielding, Joule heating, and strain sensing. The robust and highly conductive inks prepared by this simple and environmental-friendly method hold great promise as important material candidates for the potential large-scale manufacturing of flexible and wearable electronics.

Directional Electromagnetic Interference Shielding Based on Step-Wise Asymmetric Conductive Networks

Some precision electronics such as signal transmitters need to not only emit effective signal but also be protected from the external electromagnetic (EM) waves. Thus, directional electromagnetic interference (EMI) shielding materials (i.e., when the EM wave is incident from different sides of the sample, the EMI shielding effectiveness (SE) is rather different) are strongly required; unfortunately, no comprehensive literature report is available on this research field. Herein, Ni-coated melamine foams (Ni@MF) were obtained by a facile electroless plating process, and multiwalled carbon nanotube (CNT) papers were prepared via a simple vacuum-assisted self-assembly approach. Then, step-wise asymmetric poly(butylene adipate-co-terephthalate) (PBAT) composites consisting of loose Ni@MF layer and compact CNT layer were successfully fabricated via a facile solution encapsulation approach. The step-wise asymmetric structures and electrical conductivity endow the Ni@MF/CNT/PBAT composites with unprecedented directional EMI shielding performances. When the EM wave is incident from Ni@MF layer or CNT layer, Ni@MF-5/CNT-75/PBAT exhibits the total EMI SE (SET) of 38.3 and 29.5 dB, respectively, which illustrates the ΔSET of 8.8 dB. This work opens a new research window for directional EMI shielding composites with step-wise asymmetric structures, which has promising applications in portable electronics and next-generation communication technologies.

A Surface-Confined Gradient Conductive Network Strategy for Transparent Strain Sensors toward Full-Range Monitoring

The development of transparent and flexible sensors suitable for the full-range monitoring of human activities is highly desirable, yet presents a daunting challenge due to the need for a combination of properties such as high stretchability, high sensitivity, and good linearity. Gradient structures are commonly found in many biological systems and exhibit excellent mechanical properties. Here, we report a novel surface-confined gradient conductive network (SGN) strategy to construct conductive polymer hydrogel-based stain sensors (CHSS). This CHSS showed an ultrahigh stretchability of 4000% strain, transparency above 90% at a wavelength of 600 nm, as well as skin-like Young's modulus of 40 kPa. Impressively, the sensitivity was improved to 3.0 and outstanding linear sensing performance was achieved simultaneously in the ultrawide range of 0% to 4000% strain with a high R-square value of 0.994. With the help of SGN strategy, this CHSS was able to monitor both large-scale and small-scale human motions and activities. This SGN strategy can open a new avenue for the development of novel flexible strain sensors with excellent mechanical, transparent, and sensing performance for full-range monitoring of human activities.

Structural Design Strategies of Polymer Matrix Composites for Electromagnetic Interference Shielding: A Review

With the widespread application of electronic communication technology, the resulting electromagnetic radiation pollution has been significantly increased. Metal matrix electromagnetic interference (EMI) shielding materials have disadvantages such as high density, easy corrosion, difficult processing and high price, etc. Polymer matrix EMI shielding composites possess light weight, corrosion resistance and easy processing. However, the current polymer matrix composites present relatively low electrical conductivity and poor EMI shielding performance. This review firstly discusses the key concept, loss mechanism and test method of EMI shielding. Then the current development status of EMI shielding materials is summarized, and the research progress of polymer matrix EMI shielding composites with different structures is illustrated, especially for their preparation methods and evaluation. Finally, the corresponding key scientific and technical problems are proposed, and their development trend is also prospected.

Superhydrophobic, mechanically durable coatings for controllable light and magnetism driven actuators

Although some groundbreaking work has proved the feasibility of non-contact Marangoni propulsion generated by combination of the superhydrophobicity and photothermal effect, there are still challenges including the strong interfacial adhesion, multifunctional structural design and superior durability. In this paper, a simple two-step spraying method is used to prepare superhydrophobic and multi-functional fluorinated acidified carbon nanotubes (F-ACNTs)/Fe₃O₄ nanoparticles/polydimethylsiloxane (PDMS) coatings. The introduction of Fe₃O₄ nanoparticles and F-ACNTs not merely improve the surface roughness but also endow the coating with the outstanding magnetic property and photothermal conversion performance. The PDMS can reduce the surface energy and also improve the interfacial adhesion between the nanofillers and the substrate (the filter paper). The superhydrophobicity can be maintained when the material experiences abrasion, near-infrared (NIR) light irradiation and acid treatment, exhibiting outstanding durability. The highly stable superhydrophobic coating introduces a thin layer of air to decrease the drag force between the filter paper and the water surface, and can be used for controlled self-propelled light-driven motion and magnetic-driven motion. The movement can be manipulated by adjusting the direction of the incident NIR light and magnetic field. In particular, the superhydrophobic and superoleophilic coating based actuators can be easily driven to the oil-contaminated area on the water surface by using a magnet for high efficiency oil removal. This work provides a simple and universal strategy for developing intelligent and multi-responsive actuators possessing promising applications in various fields such as environmental protection, micro-robots and biomedicine.

Superhydrophobic and Flexible Silver Nanowire-Coated Cellulose Filter Papers with Sputter-Deposited Nickel Nanoparticles for Ultrahigh Electromagnetic Interference Shielding

Superhydrophobic, flexible, and ultrahigh-performance electromagnetic interference (EMI) shielding papers are of paramount importance to safety and long-term service under external mechanical deformations or other harsh service environments because they fulfill the growing demand for multipurpose materials. Herein, we fabricated multifunctional papers by incorporating sputter-deposited nickel nanoparticles (NiNPs) and a fluorine-containing coating onto cellulose filter papers coated with silver nanowires (AgNWs). AgNW networks with sputter-deposited NiNPs provide outstanding magnetic properties, electrical conductivity, and EMI shielding performance. At an AgNW content of 0.109 vol % and a NiNP content of 0.013 mg/cm², the resultant papers exhibit a superior EMI shielding effectiveness (SE) of 88.4 dB. Additionally, the fluorine-containing coating endows the resultant papers with a high contact angle of 149.7°. Remarkably, the obtained papers still maintain a high EMI SE even after 1500 bending cycles or immersion in water, salt, or strong alkaline solutions for 2 h, indicating their outstanding mechanical robustness and chemical durability. This work opens a new window for designing and implementing ultrahigh-performance EMI shielding materials.