Hierarchically Multifunctional Polyimide Composite Films with Strongly Enhanced Thermal Conductivity

Bird's-Nest-Inspired, High-Temperature-Resistant Soft Robots with Enhanced Electromagnetic Interference Shielding

The rapid development of aerospace, artificial intelligence, and flexible wearable electronics has led to an increasing demand for multifunctional electromagnetic interference (EMI) shielding materials, especially for lightweight and high-strength biomimetic intelligent actuators. In this study, we present polyolefin elastomer/aramid nanofiber/carbon nanotube (POE/ANF/CNT) composites with a sandwich architecture fabricated via layer-by-layer technology. Actuation is achieved by exploiting the differential thermal expansion coefficients among the layers, where the POE functions as the active layer, while ANFs and CNTs serve as inert reinforcement layers. The bird's-nest-like CNT layer imparts the actuators with repeatable programming capabilities. These intelligent actuators exhibit rapid responses to light, electrical, and thermal stimuli, featuring a low activation energy, high actuation speed, significant deformation, and exceptional fatigue resistance. Inspired by paper cutting and origami techniques, the actuators achieve repeatable morphological programming and complex actuation behaviors. The POE/ANF/CNT composites also demonstrate effective EMI shielding (35.7 dB at 40 wt % CNTs), high tensile strength (39.1 MPa), superior Joule heating performance (301 °C at 20 V voltage), and excellent thermal stabilities (with a maximum decomposition temperature reaching 473 °C). These multifunctional intelligent materials hold significant potential for applications in flexible wearable electronic devices, EMI shielding, and soft robotics.

New Carbon Materials for Multifunctional Soft Electronics

Soft electronics are garnering significant attention due to their wide-ranging applications in artificial skin, health monitoring, human-machine interaction, artificial intelligence, and the Internet of Things. Various soft physical sensors such as mechanical sensors, temperature sensors, and humidity sensors are the fundamental building blocks for soft electronics. While the fast growth and widespread utilization of electronic devices have elevated life quality, the consequential electromagnetic interference (EMI) and radiation pose potential threats to device precision and human health. Another substantial concern pertains to overheating issues that occur during prolonged operation. Therefore, the design of multifunctional soft electronics exhibiting excellent capabilities in sensing, EMI shielding, and thermal management is of paramount importance. Because of the prominent advantages in chemical stability, electrical and thermal conductivity, and easy functionalization, new carbon materials including carbon nanotubes, graphene and its derivatives, graphdiyne, and sustainable natural-biomass-derived carbon are particularly promising candidates for multifunctional soft electronics. This review summarizes the latest advancements in multifunctional soft electronics based on new carbon materials across a range of performance aspects, mainly focusing on the structure or composite design, and fabrication method on the physical signals monitoring, EMI shielding, and thermal management. Furthermore, the device integration strategies and corresponding intriguing applications are highlighted. Finally, this review presents prospects aimed at overcoming current barriers and advancing the development of state-of-the-art multifunctional soft electronics.

3D Network of Liquid Metal-Embedded Graphene via Surface Coating for Flexible Thermal Management

The rapid growth of flexible electronics has led to significant demand for relevant accessories, particularly highly efficient flexible heat dissipators. The fluidity of liquid metal (LM) makes it a candidate for realizing flexible thermal interface materials (TIMs). However, it is still challenging to combine LM with a conductive thermal network to achieve the synchronous improvement of thermal conductivity and flexibility. In this work, highly conductive flexible LM@GN/ANF films are made by coating LM nano-droplets with graphene nanosheets (GN) via sonication, and then they are combined with aramid nanofibers (ANF). The LM@GN/ANF film is found to have a thermal conductivity of 5.67 W m-1 K-1 and a 24.5% reduction in Young's modulus, making it suitable for various flexible electronic applications such as wearable devices and biosensors.

All-Polymer Composite Film with Outstanding Mechanical, Thermal Conductive, and EMI Shielding Performances

Robust polymer-based composites with high thermal conductivity (TC) and electromagnetic interference shielding effectiveness (EMI SE) hold great promise for applications in rapidly developing electronics. Traditional composites containing inorganic fillers often suffer from increases in processing difficulty, density, and significant deterioration in mechanical properties. Herein, we report for the first time a flexible multilayered all-polymer composite of poly(p-phenyl-2,6-phenylene bisoxazole) (PBO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), featuring excellent mechanical strength of 203.9 MPa, in-plane TC of 21.9 W/mK, EMI shielding effectiveness (SE) of 44.2 dB, high-temperature stability, and flame retardancy. The excellent TC, mechanical strength, and flame retardancy of PBO, the remarkable EMI shielding performance of PEDOT:PSS, and the π-π stacking interactions between adjacent layers contribute to the comprehensive properties, which outperform most of the traditional composites of polymers and inorganic fillers reported so far. This full-polymer design may pioneer a new strategy for the preparation of robust and lightweight multifunctional composites.

Analysis of the CPZ/Wnt4 osteogenic pathway for high-bonding-strength composite-coated magnesium scaffolds through transcriptomics

Magnesium (Mg)-based scaffolds are garnering increasing attention as bone repair materials owing to their biodegradability and mechanical resemblance to natural bone. Their effectiveness can be augmented by incorporating surface coatings to meet clinical needs. However, the limited bonding strength and unclear mechanisms of these coatings have impeded the clinical utility of scaffolds. To address these issues, this study introduces a composite coating of high-bonding-strength polydopamine-microarc oxidation (PDA-MHA) on Mg-based scaffolds. The results showed that the PDA-MHA coating achieved a bonding strength of 40.56 ± 1.426 MPa with the Mg scaffold surface, effectively enhancing hydrophilicity and controlling degradation rates. Furthermore, the scaffold facilitated bone regeneration by influencing osteogenic markers such as RUNX-2, OPN, OCN, and VEGF. Transcriptomic analyses further demonstrated that the PDA-MHA/Mg scaffold upregulated carboxypeptidase Z expression and activated the Wnt-4/β-catenin signaling pathway, thereby promoting bone regeneration. Overall, this study demonstrated that PDA can synergistically enhance bone repair with Mg scaffold, broadening the application scenarios of Mg and PDA in the field of biomaterials. Moreover, this study provides a theoretical underpinning for the application and clinical translation of Mg-based scaffolds in bone tissue engineering endeavors.

Highly Thermally Conductive Super-Aligned Boron Nitride Nanotube Films for Flexible Electronics Thermal Management

Flexible electronics toward high integration, miniaturization, and multifunctionality, leading to a dramatic increase in power density. However, the low thermal conductivity of flexible substrates impedes efficient heat dissipation and device performance improvement. In this work, we propose a template-assisted chemical conversion strategy for obtaining boron nitride nanotube (BNNT) films with high thermal conductivity and great flexibility. Aligned carbon nanotube (CNT) films have been adopted as templates; a low-temperature chemical conversion followed by a high-temperature annealing has been carried out to produce a highly ordered BNNT film. Benefiting from the high orientation order, the BNNT film exhibits an exceptional thermal conductivity of 45.5 W m-1 K-1 and presents excellent heat dissipation capability, much superior to the commonly used polyimide film. Furthermore, the BNNT film demonstrated excellent flexibility and high insulation resistance. The test of integration with film resistors demonstrated its potential as a thermally conductive substrate for electronics cooling. This work provides a solution for the effective thermal management of flexible electronics.

Versatile Landscape of Low-k Polyimide: Theories, Synthesis, Synergistic Properties, and Industrial Integration

The development of microelectronics and large-scale intelligence nowadays promotes the integration, miniaturization, and multifunctionality of electronic and devices but also leads to the increment of signal transmission delays, crosstalk, and energy consumption. The exploitation of materials with low permittivity (low-k) is crucial for realizing innovations in microelectronics. However, due to the high permittivity of conventional interlayer dielectric material (k ∼ 4.0), it is difficult to meet the demands of current microelectronic technology development (k < 3.0). Organic dielectric materials have attracted much attention because of their relatively low permittivity owing to their low material density and low single bond polarization. Polyimide (PI) exhibits better application potential based on its well permittivity tunability (k = 1.1-3.2), high thermal stability (>500 °C), and mechanical property (modulus of elasticity up to 3.0-4.0 GPa). In this review, based on the synergistic relationship of dielectric parameters of materials, the development of nearly 20 years on low-k PI is thoroughly summarized. Moreover, process strategies for modifying low-k PI at the molecular level, multiphase recombination, and interface engineering are discussed exhaustively. The industrial application, technological challenges, and future development of low-k PI are also analyzed, which will provide meaningful guidance for the design and practical application of multifunctional low-k materials.

In Situ Synthesis of Rare-Earth Hybridized Functional Core-Shell Architectures from Microporous Salt Templates and Capacitance-Adsorption Correlation Mechanisms

Biochar Porous Carbon (BPC) has become a research hotspot in the fields of energy storage, conversion, catalysis, adsorption, and separation engineering. However, the key problem of pore structure liable to collapse has not yet been addressed effectively. Here, an innovative salt ionic coordination modulation technique is reported to synthesize a new core-shell structure of BPC (Dual-doped porous carbonaceous materials, RHPC3@LaYO3) by the asymmetric load of the f orbital ion, which prevents pore structural collapse. The result shows that the novel asymmetric supercapacitors (ASCs) with an excellent energy density (193.11 Wh·kg-1) and capacitance (267.14 F·g-1) by assembling the prepared porous BPC carrier and RHPC3@LaYO3, which surpass the typical supercapacitor. In order to elucidate the association between adsorption and capacitance, the adsorption coexistence equation (MACE) is constructed with the aim of providing a comprehensive explanation for the mechanism of single-multilayer adsorption. Furthermore, a specific linkage mechanism is discovered using adsorption/ desorption properties to validate the pros/cons of capacitive properties. These results demonstrate the potential of renewable biomass materials as ASCs, which can provide new ideas for the construction of an evaluation approach for the performance of future efficient multi-reaction energy storage devices.

Scalable Fabrication of Structurally Stable Polymer Film with Excellent UV-Shielding, Fluorescent, and Antibacterial Capabilities

This research presents a new approach to facilely fabricating a multifunctional film using polyvinyl alcohol (PVA) as the base material. The film is modified chemically to incorporate various desirable properties such as high transparency, UV-shielding, antibacterial activity, and fluorescence. The fabrication process of this film is straightforward and efficient. The modified film showed exceptional UV-blocking capability, effectively blocking 100% of UV radiation. It also exhibits strong antibacterial properties. Additionally, the film emitted bright blue fluorescence, which can be useful in various optical and sensing applications. Despite the chemical modification, the film retained the excellent properties of PVA, including high transparency (90%) at 550 nm and good mechanical strength. Furthermore, it demonstrated remarkable stability even under harsh conditions such as exposure to long-term UV radiation, extreme temperatures (-40 or 120 °C), or immersion in different solvents. Overall, this work showcases a promising strategy to develop versatile, structurally stable, transparent, and flexible polymer films with multiple functionalities. These films have potential applications in various fields that require protection, such as packaging materials, biomedical devices, and optical components.

Structural Engineering of Hierarchical Magnetic/Carbon Nanocomposites via In Situ Growth for High-Efficient Electromagnetic Wave Absorption

Materials exhibiting high-performance electromagnetic wave absorption have garnered considerable scientific and technological attention, yet encounter significant challenges. Developing new materials and innovative structural design concepts is crucial for expanding the application field of electromagnetic wave absorption. Particularly, hierarchical structure engineering has emerged as a promising approach to enhance the physical and chemical properties of materials, providing immense potential for creating versatile electromagnetic wave absorption materials. Herein, an exceptional multi-dimensional hierarchical structure was meticulously devised, unleashing the full microwave attenuation capabilities through in situ growth, self-reduction, and multi-heterogeneous interface integration. The hierarchical structure features a three-dimensional carbon framework, where magnetic nanoparticles grow in situ on the carbon skeleton, creating a necklace-like structure. Furthermore, magnetic nanosheets assemble within this framework. Enhanced impedance matching was achieved by precisely adjusting component proportions, and intelligent integration of diverse interfaces bolstered dielectric polarization. The obtain Fe3O4-Fe nanoparticles/carbon nanofibers/Al-Fe3O4-Fe nanosheets composites demonstrated outstanding performance with a minimum reflection loss (RLmin) value of - 59.3 dB and an effective absorption bandwidth (RL ≤  - 10 dB) extending up to 5.6 GHz at 2.2 mm. These notable accomplishments offer fresh insights into the precision design of high-efficient electromagnetic wave absorption materials.

A Novel Sandwich-Structured Phase Change Composite with Efficient Photothermal Conversion and Electromagnetic Interference Shielding Interface

Stability and multifunctionality greatly extend the applications of phase change materials (PCMs) for thermal storage and management. Herein, CuS and Fe3O4 nanoparticles were successfully loaded onto cotton-derived carbon to develop a multifunctional interface with efficient photothermal conversion and electromagnetic interference (EMI) shielding properties. 1,3:2,4-di-(3,4-dimethyl) benzylidene sorbitol (DMDBS) and expanded graphite (EG) formed an organic/inorganic three-dimensional network framework to encapsulate 1-octadecanol (OD) by self-assembly. Finally, multifunctional shape-stabilized PCMs (SSPCMs) with the sandwich structure were prepared by the hot-press process. Multifunctional SSPCMs with high load OD (91%) had favorable thermal storage density (200.6 J/g), thermal stability, and a relatively wider available temperature range with improved thermal conductivity to support the thermal storage and management realization. Furthermore, due to the synergistic enhancement of two nanoparticles and the construction of the carbon network with cotton carbon and EG, highly efficient photothermal conversion (94.4%) and EMI shielding (68.9 dB average, X-band) performance were achieved at about 3 mm thickness, which provided the possibility of the multifunctional integration of PCMs. Conclusively, this study provides new insights towards integrating solar energy utilization with the comprehensive protection of related electronics.

Design and Implementation of a Flexible Electromagnetic Actuator for Tunable Terahertz Metamaterials

Actuators play a crucial role in microelectromechanical systems (MEMS) and hold substantial potential for applications in various domains, including reconfigurable metamaterials. This research aims to design, fabricate, and characterize structures for the actuation of the EMA. The electromagnetic actuator overcomes the lack of high drive voltage required by other actuators. The proposed actuator configuration comprises supporting cantilever beams with fixed ends, an integrated coil positioned above the cantilever's movable plate, and a permanent magnet located beneath the cantilever's movable plate to generate a static magnetic field. Utilizing flexible polyimide, the fabrication process of the EMA is simplified, overcoming limitations associated with silicon-based micromachining techniques. Furthermore, this approach potentially enables large-scale production of EMA, with displacement reaching up to 250 μm under a 100 mA current, thereby expanding their scope of applications in manufacturing. To demonstrate the function of the EMA, we integrated it with a metamaterial structure to form a compact, tunable terahertz absorber, demonstrating a potential for reconfigurable electromagnetic space.

Application and Development of Smart Thermally Conductive Fiber Materials

In recent years, with the rapid advancement in various high-tech technologies, efficient heat dissipation has become a key issue restricting the further development of high-power-density electronic devices and components. Concurrently, the demand for thermal comfort has increased; making effective personal thermal management a current research hotspot. There is a growing demand for thermally conductive materials that are diversified and specific. Therefore, smart thermally conductive fiber materials characterized by their high thermal conductivity and smart response properties have gained increasing attention. This review provides a comprehensive overview of emerging materials and approaches in the development of smart thermally conductive fiber materials. It categorizes them into composite thermally conductive fibers filled with high thermal conductivity fillers, electrically heated thermally conductive fiber materials, thermally radiative thermally conductive fiber materials, and phase change thermally conductive fiber materials. Finally, the challenges and opportunities faced by smart thermally conductive fiber materials are discussed and prospects for their future development are presented.

Advanced multifunctional IGBT packing materials with enhanced thermal conductivity and electromagnetic wave absorption properties

Insulated-Gate Bipolar Transistors (IGBT) face limitations in high-frequency electronic applications due to heat accumulation and electromagnetic interference issues. To address these challenges, it is crucial to develop packing materials with excellent electromagnetic interference immunity and heat dissipation properties. In this research, a novel epoxy-based packing material (MDCF@C-ZrO2/EP) with high electromagnetic wave absorption and exceptional thermal transport properties was produced by employing a unique three-dimensional carbon structure-induced nanomaterial dispersion strategy. In particular, the three-dimensional MDCF structure effectively prevents packing agglomeration and fosters the formation of an abundant hetero-interface between MDCF and C-ZrO2, leading to improved impedance matching and enhanced electromagnetic wave dissipation capabilities. Remarkably, even at a mere 5 wt% filling level, the material demonstrates an impressive reflection loss value of -58.92 dB and a wide effective absorption bandwidth of 6.68 GHz, effectively covering the entire Ku-band. Additionally, the 3D MDCF@C-ZrO2 significantly enhances the phonon transport path and elevates the thermal conductivity of pure epoxy resin by an impressive ∼ 150%. As a result, this innovative research holds tremendous potential in enabling the application of IGBTs in high-power and high-frequency electronic components, while also contributing to the advancement of next-generation wireless communications and smart devices.

Investigation of Electromagnetic Wave Absorption Properties of Ni-Co and MWCNT Nanocomposites

BACKGROUND

In recent years, severe electromagnetic interference among electronic devices has been caused by the unprecedented growth of communication systems. Therefore, microwave absorbing materials are required to relieve these problems by absorbing the unwanted microwave. In the design of microwave absorbers, magnetic nanomaterials have to be used as fine particles dispersed in an insulating matrix. Besides the intrinsic properties of these materials, the structure and morphology are also crucial to the microwave absorption performance of the composite. In this study, Ni-Co- MWCNT composites were synthesized, and the changes in electric permittivity, magnetic permeability, and reflectance loss of the samples were evaluated at frequencies of 2 to 18 GHz.

METHODS

Nickel-Cobalt-Multi Wall Carbon Nanotubes (MWCNT) composites were successfully synthesized by the co-precipitation chemical method. The structural, morphological, and magnetic properties of the samples were characterized and investigated by X-ray diffractometer (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Vibrating Sample Magnetometer (VSM), and Vector Network Analyzer (VNA).

RESULTS

The results revealed that the Ni-Co-MWCNT composite has the highest electromagnetic wave absorption rate with a reflectance loss of -70.22 dB at a frequency of 10.12 GHz with a thickness of 1.8 mm. The adequate absorption bandwidth (RL <-10 dB) was 6.9 GHz at the high-frequency region, exhibiting excellent microwave absorbing properties as a good microwave absorber patent.

CONCLUSION

Based on this study, it can be argued that the Ni-Co-MWCNT composite can be a good candidate for making light absorbers of radar waves at frequencies 2- 18 GHz.

Liquid metal assisted fabrication of MXene-based films: Toward superior electromagnetic interference shielding and thermal management

The development of thin and flexible films that possess both electromagnetic interference (EMI) shielding and thermal management capabilities has always been an intriguing pursuit, but itisnevertheless a crucialproblemtoaddress. Inspired by the deformability of liquid metal (LM) and film forming capacity of MXene, here we present a series of ternary compositing films prepared via cellulose nanofiber (CNF) assisted vacuum filtration technology. Originating from the highly conductive LM/MXene network, the MLMC film presents a maximum EMI shielding effectiness (EMI SE) of 78 dB at a tiny thickness of 45 μm, together with a high specific EMI SE of 3046 dB mm-1. Meanwhile, these compositing films also deliver excellent flexibility and mechanical reliability, showing no obvious decline in EMI shielding performance even after 1000 bending and 500 folding cycles, respectively. Moreover, notable anisotropic thermal conductive property was successfully achieved, allowing for a highly desirable in-plane thermal conductivity of 7.8 W m-1 K-1. This accomplishment also yielded an exceptional electro-thermal conversion capacity, enabling efficient low-voltage (3 V) heating capabilities. These captivating features are expected to greatly drive the widespread adoption of LM-based films in future flexible electronic and wearable technologies.

Highly Thermoconductive, Strong Graphene-Based Composite Films by Eliminating Nanosheets Wrinkles

Graphene-based thermally conductive composites have been proposed as effective thermal management materials for cooling high-power electronic devices. However, when flexible graphene nanosheets are assembled into macroscopic thermally conductive composites, capillary forces induce shrinkage of graphene nanosheets to form wrinkles during solution-based spontaneous drying, which greatly reduces the thermal conductivity of the composites. Herein, graphene nanosheets/aramid nanofiber (GNS/ANF) composite films with high thermal conductivity were prepared by in-plane stretching of GNS/ANF composite hydrogel networks with hydrogen bonds and π-π interactions. The in-plane mechanical stretching eliminates graphene nanosheets wrinkles by suppressing inward shrinkage due to capillary forces during drying and achieves a high in-plane orientation of graphene nanosheets, thereby creating a fast in-plane heat transfer channel. The composite films (GNS/ANF-60 wt%) with eliminated graphene nanosheets wrinkles showed a significant increase in thermal conductivity (146 W m-1 K-1) and tensile strength (207 MPa). The combination of these excellent properties enables the GNS/ANF composite films to be effectively used for cooling flexible LED chips and smartphones, showing promising applications in the thermal management of high-power electronic devices.

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.

Constructing Hierarchical Polymer Nanocomposites with Strongly Enhanced Thermal Conductivity

The rapid advancement of communication technology has substantially increased the demand for advanced electronic packaging materials with high thermal conductivity and outstanding electrical insulation properties. In this study, we design polyvinyl alcohol/polydopamine-modified boron nitride nanosheet (PVA/BNNS@PDA) nanocomposites with hierarchical structures by combining electrospinning, vacuum filtration deposition, and hot pressing. The modified BNNS@PDA improves the interaction between the filler and the polymer matrix while reducing the interfacial thermal resistance, resulting in superior thermal conductivity, excellent insulation, and perfect flexibility. The PVA/BNNS@PDA nanocomposites possess an ultrahigh in-plane thermal conductivity of 16.6 W/(m·K) at 35.54 wt % BNNS@PDA content. Even after 2000 folds, the nanocomposites do not undergo any crack, showing their ultrahigh thermal conductivity behavior. Furthermore, the nanocomposites exhibit a volume resistivity above 1014 Ω·cm, which is well above the standard for insulating materials. Based on these results, this work provides a novel method to produce nanocomposites with high thermal conductivity, offering a new perspective to design advanced thermal management materials.

Structural design and preparation of Ti3C2Tx MXene/polymer composites for absorption-dominated electromagnetic interference shielding

Electromagnetic interference (EMI) is a pervasive and harmful phenomenon in modern society that affects the functionality and reliability of electronic devices and poses a threat to human health. To address this issue, EMI-shielding materials with high absorption performance have attracted considerable attention. Among various candidates, two-dimensional MXenes are promising materials for EMI shielding due to their high conductivity and tunable surface chemistry. Moreover, by incorporating magnetic and conductive fillers into MXene/polymer composites, the EMI shielding performance can be further improved through structural design and impedance matching. Herein, we provide a comprehensive review of the recent progress in MXene/polymer composites for absorption-dominated EMI shielding applications. We summarize the fabrication methods and EMI shielding mechanisms of different composite structures, such as homogeneous, multilayer, segregated, porous, and hybrid structures. We also analyze the advantages and disadvantages of these structures in terms of EMI shielding effectiveness and the absorption ratio. Furthermore, we discuss the roles of magnetic and conductive fillers in modulating the electrical properties and EMI shielding performance of the composites. We also introduce the methods for evaluating the EMI shielding performance of the materials and emphasize the electromagnetic parameters and challenges. Finally, we provide insights and suggestions for the future development of MXene/polymer composites for EMI shielding applications.

Functional Materials and Innovative Strategies for Wearable Thermal Management Applications

Highlights

This article systematically reviews the thermal management wearables with a specific emphasis on materials and strategies to regulate the human body temperature. Thermal management wearables are subdivided into the active and passive thermal managing methods. The strength and weakness of each thermal regulatory wearables are discussed in details from the view point of practical usage in real-life.

Abstract

Thermal management is essential in our body as it affects various bodily functions, ranging from thermal discomfort to serious organ failures, as an example of the worst-case scenario. There have been extensive studies about wearable materials and devices that augment thermoregulatory functionalities in our body, employing diverse materials and systematic approaches to attaining thermal homeostasis. This paper reviews the recent progress of functional materials and devices that contribute to thermoregulatory wearables, particularly emphasizing the strategic methodology to regulate body temperature. There exist several methods to promote personal thermal management in a wearable form. For instance, we can impede heat transfer using a thermally insulating material with extremely low thermal conductivity or directly cool and heat the skin surface. Thus, we classify many studies into two branches, passive and active thermal management modes, which are further subdivided into specific strategies. Apart from discussing the strategies and their mechanisms, we also identify the weaknesses of each strategy and scrutinize its potential direction that studies should follow to make substantial contributions to future thermal regulatory wearable industries.

MXene/bacterial cellulose/Fe3O4/methyltrimethoxylsilane flexible film with hydrophobic for effective electromagnetic shielding

Electromagnetic (EM) pollution has become a serious problem in modern society as it affects human lives. The fabrication of strong and highly flexible materials for electromagnetic interference (EMI) shielding applications is extremely urgent. Herein, a MXene Ti₃C₂T_x/Fe₃O₄ & bacterial cellulose (BC)/Fe₃O₄&Methyltrimethoxysilane (MTMS) flexible hydrophobic electromagnetic shielding film (SBTF_X-Y, X and Y were the number of layers of BC/Fe₃O₄ and the layers of Ti₃C₂T_x/Fe₃O₄), was fabricated. In the prepared film, MXene Ti₃C₂T_x absorbs a large amount of radio waves through polarization relaxation and conduction loss. Because of its extremely low reflectance of electromagnetic waves, BC@Fe₃O₄, as the outermost layer of the material, allows more electromagnetic waves to incident inside the material. The maximum electromagnetic interference (EMI) shielding efficiency (SE) of 68 dB was achieved for the composite film at 45 μm thickness. What's more, the SBTF_X-Y films show excellent mechanical properties, hydrophobicity and flexibility. The unique stratified structure of the film provides a new strategy for designing high-performance EMI shielding films with excellent surface and mechanical properties.

Advances and mechanisms in polymer composites toward thermal conduction and electromagnetic wave absorption

Polymer composites have essential applications in electronics due to their versatility, stable performance, and processability. However, with the increasing miniaturization and high power of electronics in the 5G era, there are significant challenges related to heat accumulation and electromagnetic wave (EMW) radiation in narrow spaces. Traditional solutions involve using either thermally conductive or EMW absorbing polymer composites, but these fail to meet the demand for multi-functional integrated materials in electronics. Therefore, designing thermal conduction and EMW absorption integrated polymer composites has become essential to solve the problems of heat accumulation and electromagnetic pollution in electronics and adapt to its development trend. Researchers have developed different approaches to fabricate thermal conduction and EMW absorption integrated polymer composites, including integrating functional fillers with both thermal conduction and EMW absorption functions and innovating processing methods. This review summarizes the latest research progress, factors that affect performance, and the mechanisms of thermal conduction and EMW absorption integrated polymer composites. The review also discusses problems that limit the development of these composites and potential solutions and development directions. The aim of this review is to provide references for the development of thermal conduction and EMW absorption integrated polymer composites.

Optimal particle distribution induced interfacial polarization in hollow double-shell composites for electromagnetic waves absorption performance

Tunable designs of polymorphic structured transition metal dichalcogenide (TMDC) demonstrate promising applications in the field of electromagnetic wave absorption (EMW). However, it remains a technical challenge for achieving a balanced relationship between well-matched impedance characteristics and dielectric losses. Therefore, the co-modification strategies of polydopamine coating and wet impregnation are chosen to construct CoS₂ magnetic double-shell microspheres with phase component modulation to achieve the optimized performance. Dopamine hydrochloride forms a coating on the surface of CoS₂ microspheres by self-polymerization and forms a double-shell structure during the pyrolysis process. Then the different metal is doped to generate heterogeneous components in the process of heat treatment. The results show that the cobalt doped double-shell microspheres have an ultra-high electromagnetic wave absorption absorption capacity with an effective absorption bandwidth of 5.04 GHz (1.98 mm) and a minimum reflection loss value of -48.90 dB. The double-shell layer structure and metal ion hybridization can improve the interfacial polarization and magnetic loss behavior, which provides an explicit inspiration for the development of transition metal dichalcogenide and even transition metal compounds with tunable absorption properties.

Research Progress with Membrane Shielding Materials for Electromagnetic/Radiation Contamination

As technology develops at a rapid pace, electromagnetic and radiation pollution have become significant issues. These forms of pollution can cause many important environmental issues. If they are not properly managed and addressed, they will be everywhere in the global biosphere, and they will have devastating impacts on human health. In addition to minimizing sources of electromagnetic radiation, the development of lightweight composite shielding materials to address interference from radiation has become an important area of research. A suitable shielding material can effectively reduce the harm caused by electromagnetic interference/radiation. However, membrane shielding materials with general functions cannot effectively exert their shielding performance in all fields, and membrane shielding materials used in different fields must have specific functions under their use conditions. The aim of this review was to provide a comprehensive review of these issues. Firstly, the causes of electromagnetic/radiation pollution were briefly introduced and comprehensively identified and analyzed. Secondly, the strategic solutions offered by membrane shielding materials to address electromagnetic/radiation problems were discussed. Then, the design concept, technical innovation, and related mechanisms of the existing membrane shielding materials were expounded, the treatment methods adopted by scholars to study the environment and performance change laws were introduced, and the main difficulties encountered in this area of research were summarized. Finally, on the basis of a comprehensive analysis of the protection provided by membrane shielding materials against electromagnetic/radiation pollution, the action mechanism of membrane shielding materials was expounded in detail, and the research progress, structural design and performance characterization techniques for these materials were summarized. In addition, the future challenges were prospected. This review will help universities, research institutes, as well as scientific and technological enterprises engaged in related fields to fully understand the design concept and research progress of electromagnetic/radiation-contaminated membrane shielding materials. In addition, it is hoped that this review will facilitate efforts to accelerate the research and development of membrane shielding materials and offer potential applications in areas such as electronics, nuclear medicine, agriculture, and other areas of industry.

Laminated MXene Foam/Cellulose@LDH Composite Membrane with Efficient EMI Shielding Property for Asymmetric Personal Thermal Management

Facing the increasingly complex and deteriorated environment, people's thermal comfort and health requirements are expanding. Therefore, wearable materials with integrated functions have progressed rapidly due to the fair compatibility for various functions and precise regulation. In this work, a laminated MXene foam/cellulose@LDH composite membrane was fabricated via a facile process consisting of in situ growth, vacuum filtration, and foaming for asymmetrical personal thermal management and electromagnetic interference shielding. In detail, the Zn-Al LDH side shows a high solar reflectance of 0.89 and an infrared emissivity of 0.97 in the atmospheric window, demonstrating the superior radiative cooling property. In contrast, the outstanding radiative warming performance is revealed by the high solar absorption (0.72) and infrared reflectivity (0.55) of the MXene foam. As a result, prominent temperature differences were achieved during the validation test. Compared to the control group, an 18 °C reduction of the Zn-Al LDH side and a 9.6 °C increment of the MXene foam side were observed, bringing out the excellent optical properties and radiative thermal management performances. What is more, due to the outstanding electrical conductivity of MXene, a rapid and prominent temperature rise to 44.2 °C could be expected by applying a low voltage of 1 V to provide active joule warmth. In addition, hydrophobization and the associated stain resistance were explained by the high water contact angles of obtained membranes. The excellent electromagnetic interference shielding performance (43.9 dB) given by the introduction of MXene provides a prospective candidate to replace the common shielding materials. The results, in general, provide a promising strategy for meeting the updating requirements for comfortable living in a world full of potential thermal and health threats.

Research Progress and Application of Polyimide-Based Nanocomposites

Polyimide (PI) is one of the most dominant engineering plastics with excellent thermal, mechanical, chemical stability and dielectric performance. Further improving the versatility of PIs is of great significance, broadening their application prospects. Thus, integrating functional nanofillers can finely tune the individual characteristic to a certain extent as required by the function. Integrating the two complementary benefits, PI-based composites strongly expand applications, such as aerospace, microelectronic devices, separation membranes, catalysis, and sensors. Here, from the perspective of system science, the recent studies of PI-based composites for molecular design, manufacturing process, combination methods, and the relevant applications are reviewed, more relevantly on the mechanism underlying the phenomena. Additionally, a systematic summary of the current challenges and further directions for PI nanocomposites is presented. Hence, the review will pave the way for future studies.

Multifunctional Epoxy-Based Electronic Packaging Material MDCF@LDH/EP for Electromagnetic Wave Absorption, Thermal Management, and Flame Retardancy

The sharp reduction in size and increase in power density of next-generation integrated circuits lead to electromagnetic interference and heat failure being a key roadblock for their widespread applications in polymer-based electronic packaging materials. This work demonstrates a multifunctional epoxy-based composite (MDCF@LDH/EP) with high electromagnetic wave (EMW) absorption, thermal conductivity, and flame retardancy performance. In which, the synergistic effect of porous structure and heterointerface promotes the multiple reflection and absorption, and dielectric loss of EMW. A low reflection loss of -57.77 dB, and an effective absorption bandwidth of 7.20 GHz are achieved under the fillings of only 10 wt%. Meanwhile, a 241.4% enhanced thermal conductivity of EP is due to the high continuous 3D melamine-derived carbon foams (MDCF), which provides a broad path for the transport of phonons. In addition, MDCF@LDH/EP composite exhibits high thermal stability and flame retardancy, thanks to the physical barrier effect of MDCF@LDH combined with the high temperature cooling properties of NiAl-LDH-CO₃ ^2- . Compared with pure epoxy resin, the peak heat release rate and the total heat release rate are reduced by 19.4% and 30.7%, respectively. Such an excellent comprehensive performance enables MDCF@LDH/EP to a promising electronic packaging material.

Bifunctional Liquid Metals Allow Electrical Insulating Phase Change Materials to Dual-Mode Thermal Manage the Li-Ion Batteries

Phase change materials (PCMs) are expected to achieve dual-mode thermal management for heating and cooling Li-ion batteries (LIBs) according to real-time thermal conditions, guaranteeing the reliable operation of LIBs in both cold and hot environments. Herein, we report a liquid metal (LM) modified polyethylene glycol/LM/boron nitride PCM, capable of dual-mode thermal managing the LIBs through photothermal effect and passive thermal conduction. Its geometrical conformation and thermal pathways fabricated through ice-template strategy are conformable to the LIB's structure and heat-conduction characteristic. Typically, soft and deformable LMs are modified on the boron nitride surface, serving as thermal bridges to reduce the contact thermal resistance among adjacent fillers to realize high thermal conductivity of 8.8 and 7.6 W m^-1 K^-1 in the vertical and in-plane directions, respectively. In addition, LM with excellent photothermal performance provides the PCM with efficient battery heating capability if employing a controllable lighting system. As a proof-of-concept, this PCM is manifested to heat battery to an appropriate temperature range in a cold environment and lower the working temperature of the LIBs by more than 10 °C at high charging/discharging rate, opening opportunities for LIBs with durable working performance and evitable risk of thermal runaway.

From 1D Nanofibers to 3D Nanofibrous Aerogels: A Marvellous Evolution of Electrospun SiO2 Nanofibers for Emerging Applications

One-dimensional (1D) SiO2 nanofibers (SNFs), one of the most popular inorganic nanomaterials, have aroused widespread attention because of their excellent chemical stability, as well as unique optical and thermal characteristics. Electrospinning is a straightforward and versatile method to prepare 1D SNFs with programmable structures, manageable dimensions, and modifiable properties, which hold great potential in many cutting-edge applications including aerospace, nanodevice, and energy. In this review, substantial advances in the structural design, controllable synthesis, and multifunctional applications of electrospun SNFs are highlighted. We begin with a brief introduction to the fundamental principles, available raw materials, and typical apparatus of electrospun SNFs. We then discuss the strategies for preparing SNFs with diverse structures in detail, especially stressing the newly emerging three-dimensional SiO2 nanofibrous aerogels. We continue with focus on major breakthroughs about brittleness-to-flexibility transition of SNFs and the means to achieve their mechanical reinforcement. In addition, we showcase recent applications enabled by electrospun SNFs, with particular emphasis on physical protection, health care and water treatment. In the end, we summarize this review and provide some perspectives on the future development direction of electrospun SNFs.

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.

Vertical Alignment of Anisotropic Fillers Assisted by Expansion Flow in Polymer Composites

Orientation control of anisotropic one-dimensional (1D) and two-dimensional (2D) materials in solutions is of great importance in many fields ranging from structural materials design, the thermal management, to energy storage. Achieving fine control of vertical alignment of anisotropic fillers (such as graphene, boron nitride (BN), and carbon fiber) remains challenging. This work presents a universal and scalable method for constructing vertically aligned structures of anisotropic fillers in composites assisted by the expansion flow (using 2D BN platelets as a proof-of-concept). BN platelets in the silicone gel strip are oriented in a curved shape that includes vertical alignment in the central area and horizontal alignment close to strip surfaces. Due to the vertical orientation of BN in the central area of strips, a through-plane thermal conductivity as high as 5.65 W m^-1 K^-1 was obtained, which can be further improved to 6.54 W m^-1 K^-1 by combining BN and pitch-based carbon fibers. The expansion-flow-assisted alignment can be extended to the manufacture of a variety of polymer composites filled with 1D and 2D materials, which can find wide applications in batteries, electronics, and energy storage devices.

Enhanced Thermal Conductivities of Liquid Crystal Polyesters from Controlled Structure of Molecular Chains by Introducing Different Dicarboxylic Acid Monomers

Enhancing thermal conductivity coefficient (λ) of liquid crystal polyesters would further widen their application in electronics and electricals. In this work, a kind of biphenyl-based dihydroxy monomer is synthesized using 4, 4'-biphenyl (BP) and triethylene glycol (TEG) as raw material, which further reacts with three different dicarboxylic acids (succinic acid, p-phenylenediacetic acid, and terephthalic acid, respectively) by melt polycondensation to prepare intrinsically highly thermally conductive poly 4', 4”'-[1, 2-ethanediyl-bis(oxy-2, 1-ethanediyloxy)]-bis(p-hydroxybiphenyl) succinate (PEOS), poly 4', 4”'-[1, 2-ethanediyl-bis(oxy-2, 1-ethanediyloxy)]-bis(p-hydroxybiphenyl) p-phenyldiacetate (PEOP) and poly 4', 4”'-[1, 2-ethanediyl-bis(oxy-2, 1-ethanediyloxy)]-bis(p-hydroxybiphenyl) terephthalate (PEOT), collectively called biphenyl-based liquid crystal polyesters (B-LCPE). The results show that B-LCPE possess the desired molecular structure, exhibit smectic phase in liquid crystal range and semicrystalline polymers at room temperature, and possess excellent intrinsic thermal conductivities, thermal stabilities, and mechanical properties. λ of PEOT is 0.51 W/(m·K), significantly exceeds that of polyethylene terephthalate (0.15 W/(m·K)) which has similar molecular structure with PEOT, and also higher than that of PEOS (0.32 W/(m·K)) and PEOP (0.38 W/(m·K)). The corresponding heat resistance index (T_HRI), elasticity modulus, and hardness of PEOT are 174.6°C, 3.6 GPa, and 154.5 MPa, respectively, and also higher than those of PEOS (162.2°C, 1.8 GPa, and 83.4 MPa) and PEOP (171.8°C, 2.3 GPa, and 149.6 MPa).

Structural evolution of MXenes and their composites for electromagnetic interference shielding applications

Nowadays, the extensive utilization of electronic devices and equipment inevitably leads to severe electromagnetic interference (EMI) issues. Therefore, EMI shielding materials have drawn considerable attention, and great effort has been devoted to the exploration of high-efficiency EMI shielding materials. As a novel kind of 2D transition metal carbide material, MXenes have been widely investigated for EMI shielding in the past few years due to their extraordinary electrical conductivity, large specific surface area, light weight, and easy processability. In view of the great achievements in MXene-based materials for EMI shielding, herein, we reviewed the recent studies on the structural design and evolution of MXenes and their composites for EMI shielding. First, the methods for structural control of MXenes, including HF etching, in situ HF etching, fluorine-free etching, electrochemical etching, and molten salt etching, are systematically summarized. Then we illustrate the fundamental relationship between the microstructure of MXenes and the EMI shielding mechanism. In the following, the effects of different synthesis methods and structures of MXene-based composite materials as well as their EMI shielding performances are comprehensively discussed. Lastly, future prospects for the development of MXene-based composite materials in EMI shielding applications are commented on.

Comparison of Properties of Colorless and Transparent Polyimide Nanocomposites Containing Chemically Modified Nanofillers: Functionalized-Graphene and Organoclay

Poly(amic acid) (PAA) was synthesized from dianhydride 4,4-(4,4-isopropylidenediphenoxy)bis(phthalic anhydride) and diamine bis [4-(3-aminophenoxy) phenyl] sulfone. Colorless and transparent polyimide (CPI) hybrid films were synthesized through thermal imidization after dispersing nanofillers using an intercalation method in a PAA solution. C16-GS and C16-MMT, in which hexadecylamine (C16) was substituted on graphene sheet (GS) and montmorillonite (MMT), respectively, were used as nanofillers to reinforce the CPI hybrid films. These two nanofillers were admixed in varying loadings of 0.25 to 1.00 wt%, and the morphology, thermal properties, and optical transparency of the hybrid films were investigated and compared. The results suggest that the thermal properties of the CPI hybrid films can be improved by adding only a small amount of nanofiller. Transmission electron microscopy results of the CPI hybrid film containing two types of fillers suggested that the fillers were well dispersed in the nano-size in the matrix polymer; however, some of the fillers were observed as agglomerated particles above the critical concentration of 0.50 wt%.

Highly Thermally Conductive Polymer/Graphene Composites with Rapid Room-Temperature Self-Healing Capacity

Composites that can rapidly self-healing their structure and function at room temperature have broad application prospects. However, in view of the complexity of composite structure and composition, its self-heal is facing challenges. In this article, supramolecular effect is proposed to repair the multistage structure, mechanical and thermal properties of composite materials. A stiff and tough supramolecular frameworks of 2-[[(butylamino)carbonyl]oxy]ethyl ester (PBA)-polydimethylsiloxane (PDMS) were established using a chain extender with double amide bonds in a side chain to extend prepolymers through copolymerization. Then, by introducing the copolymer into a folded graphene film (FGf), a highly thermally conductive composite of PBA-PDMS/FGf with self-healing capacity was fabricated. The ratio of crosslinking and hydrogen bonding was optimized to ensure that PBA-PDMS could completely self-heal at room temperature in 10 min. Additionally, PBA-PDMS/FGf exhibits a high tensile strength of 2.23 ± 0.15 MPa at break and high thermal conductivity of 13 ± 0.2 W m^-1 K^-1; of which the self-healing efficiencies were 100% and 98.65% at room temperature for tensile strength and thermal conductivity, respectively. The excellent self-healing performance comes from the efficient supramolecular interaction between polymer molecules, as well as polymer molecule and graphene. This kind of thermal conductive self-healing composite has important application prospects in the heat dissipation field of next generation electronic devices in the future.

Interconnected MXene/Graphene Network Constructed by Soft Template for Multi-Performance Improvement of Polymer Composites

The multi-functionalization of polymer composites refers to the ability to connect multiple properties through simple structural design and simultaneously achieve multi-performance optimization. The large-scale design and mass production to realize the reasonable structure design of multifunctional polymer composites are urgently remaining challenges. Herein, the multifunctional MXene/graphene/polymer composites with three-dimensional thermally and electrically conductive network structures are fabricated via the utilization of the microstructure of the soft template, and a facile dispersion dip-coating approach. As a result, the polymer composites have a multi-performance improvement. At the MXene and graphene content of 18.7 wt%, the superior through-plane thermal conductivity of polymer composite is 2.44 W m^-1 K^-1, which is 1118% higher than that of the polymer matrix. The electromagnetic interference (EMI) shielding effectiveness of the sample reaches 43.3 dB in the range of X-band. And the mechanical property of the sample has advanced 4 times compared with the polymer matrix. The excellent EMI shielding and thermal management performance, along with the effortless and easy-to-scalable producing techniques, imply promising perspectives of the polymer composites in the next-generation smart electronic devices.

Emerging Flexible Thermally Conductive Films: Mechanism, Fabrication, Application

Effective thermal management is quite urgent for electronics owing to their ever-growing integration degree, operation frequency and power density, and the main strategy of thermal management is to remove excess energy from electronics to outside by thermal conductive materials. Compared to the conventional thermal management materials, flexible thermally conductive films with high in-plane thermal conductivity, as emerging candidates, have aroused greater interest in the last decade, which show great potential in thermal management applications of next-generation devices. However, a comprehensive review of flexible thermally conductive films is rarely reported. Thus, we review recent advances of both intrinsic polymer films and polymer-based composite films with ultrahigh in-plane thermal conductivity, with deep understandings of heat transfer mechanism, processing methods to enhance thermal conductivity, optimization strategies to reduce interface thermal resistance and their potential applications. Lastly, challenges and opportunities for the future development of flexible thermally conductive films are also discussed.

Recent advances in thermally conductive polymer composites

Polymer matrix composites (PMCs) with high thermal conductivity (TC) play an important role in improving the heat dissipation capacity of a new generation of electronic devices, particularly for 5G and aviation applications. Over the last few decades, considerable efforts have been made in the fabrication of highly thermally conductive PMCs. Advances in the thermal conduction mechanism of polymer composites are induced to, and then commonly used thermally conductive fillers are presented. In the following, the factors affecting the TC of polymer composites are discussed in detail, including fillers, interfaces, polymer matrices and processing technologies. Special attention is paid to the thermally conductive fillers. Then, some application areas of thermally conductive polymer composites are introduced. Finally, the deficiencies and future development trends in this research field are put forward. It is expected that this review will provide some beneficial inspiration in improving the TC of PMCs.