Flexible Graphene Nanocomposites with Simultaneous Highly Anisotropic Thermal and Electrical Conductivities Prepared by Engineered Graphene with Flat Morphology

Biowaste-Derived Triboelectric Nanogenerators for Emerging Bioelectronics

Triboelectric nanogenerators (TENGs) combine contact electrification and electrostatic induction effects to convert waste mechanical energy into electrical energy. As conventional devices contribute to electronic waste, TENGs based on ecofriendly and biocompatible materials have been developed for various energy applications. Owing to the abundance, accessibility, low cost, and biodegradability of biowaste (BW), recycling these materials has gained considerable attention as a green approach for fabricating TENGs. This review provides a detailed overview of BW materials, processing techniques for BW-based TENGs (BW-TENGs), and potential applications of BW-TENGs in emerging bioelectronics. In particular, recent progress in material design, fabrication methods, and biomechanical and environmental energy-harvesting performance is discussed. This review is aimed at promoting the continued development of BW-TENGs and their adoption for sustainable energy-harvesting applications in the field of bioelectronics.

Heterojunction of branched benzopyrazine-based polymers coating on graphene for electrochemical sensing of vanillin

Vanillin finds widespread applications in various industries, such as food, pharmaceuticals, and cosmetics. However, excessive intake of vanillin could pose risks to human health. This study detailed the successful creation of a heterojunction of branched benzopyrazine-based polymers coating on graphene (CMP-rGO) through the Sonogashira-Hagihara coupling reaction. Utilizing the CMP-rGO, a novel electrochemical sensor for vanillin detection was developed. Besides, the synthesized materials were validated using standard characterization techniques. Both cyclic voltammetry and differential pulse voltammetry techniques were employed to investigate vanillin's electrochemical characteristics on this sensor. The findings indicated a significant enhancement in vanillin's electrochemical signal responsiveness with the application of CMP-rGO. Under optimal conditions, the sensor demonstrated a linear response to vanillin concentrations ranging from 0.08 to 33 μM and achieved a detection limit as low as 0.014 μM. Also, the constructed electrochemical sensor exhibited excellent selectivity, stability, and reproducibility. It has been effectively employed to detect vanillin in real samples such as human serum, human urine, and vanillin tablets, with a recovery rate of 99.13-103.6 % and an RSD of 3.46-1.26 %. Overall, this innovative sensor offers a novel approach to the efficient and convenient detection of vanillin.

Recyclable and elastic highly thermally conductive epoxy-based composites with covalent-noncovalent interpenetrating networks

High-power electronic architectures and devices require elastic thermally conductive materials. The use of epoxy resin in thermal management is limited due to its rigidity. Here, based on epoxy vitrimer, flexible polyethylene glycol (PEG) chains are introduced into covalent adaptable networks to construct covalent-noncovalent interpenetrating networks, enabling the elasticity of epoxy resins. Compared to traditional silicone-based thermal interface materials, the newly developed elastic epoxy resin shows the advantages of reprocessability, self-healing, and no small molecule release. Results show that, even after being filled with boron nitride and liquid metal, the material maintains its resilience, reprocessability and self-healing properties. Leveraging these characteristics, the composite can be further processed into thin films through a repeated pressing-rolling technique that facilitates the forced orientation of the fillers. Subsequently, the bulk composites are reconstructed using a film-stacking method. The results indicate that the thermal conductivity of the reconstructed bulk composite reaches 3.66 W m-1 K-1, achieving a 68% increase compared to the composite prepared through blending. Due to the existence of covalent adaptable networks, the inorganic and inorganic components of the composite prepared in this work can be completely separated under mild conditions, realizing closed-loop recycling.

Remarkable Toughening of Plastic with Monodispersed Nano-CaCO3: From Theoretical Predictions to Experimental Validation

The structure-property relationship of poly(vinyl chloride) (PVC)/CaCO3 nanocomposites is investigated by all-atom molecular dynamics (MD) simulations. MD simulation results indicate that the dispersity of nanofillers, interfacial bonding, and chain mobility are imperative factors to improve the mechanical performance of nanocomposites, especially toughness. The tensile behavior and dissipated work of the PVC/CaCO3 model demonstrate that 12 wt % CaCO3 modified with oleate anion and dodecylbenzenesulfonate can impart high toughness to PVC due to its good dispersion, favorable interface interaction, and weak migration of PVC chains. Under the guidance of MD simulation, we experimentally prepared a transparent PVC/CaCO3 nanocomposite with good mechanical properties by in situ polymerization of monodispersed CaCO3 in vinyl chloride monomers. Interestingly, experimental tests indicate that the optimum toughness of a nanocomposite (a 368% increase in the elongation at break and 204% improvement of the impact strength) can be indeed realized by adding 12 wt % CaCO3 modified with oleic acid and dodecylbenzenesulfonic acid, which is remarkably consistent with the MD simulation prediction. In short, this work provides a proof-of-concept of using MD simulation to guide the experimental synthesis of PVC/CaCO3 nanocomposites, which can be considered as an example to develop other functional nanocomposites.

Tree-Inspired Structurally Graded Aerogel with Synergistic Water, Salt, and Thermal Transport for High-Salinity Solar-Powered Evaporation

Solar-powered interfacial evaporation is an energy-efficient solution for water scarcity. It requires solar absorbers to facilitate upward water transport and limit the heat to the surface for efficient evaporation. Furthermore, downward salt ion transport is also desired to prevent salt accumulation. However, achieving simultaneously fast water uptake, downward salt transport, and heat localization is challenging due to highly coupled water, mass, and thermal transport. Here, we develop a structurally graded aerogel inspired by tree transport systems to collectively optimize water, salt, and thermal transport. The arched aerogel features root-like, fan-shaped microchannels for rapid water uptake and downward salt diffusion, and horizontally aligned pores near the surface for heat localization through maximizing solar absorption and minimizing conductive heat loss. These structural characteristics gave rise to consistent evaporation rates of 2.09 kg m-2 h-1 under one-sun illumination in a 3.5 wt% NaCl solution for 7 days without degradation. Even in a high-salinity solution of 20 wt% NaCl, the evaporation rates maintained stable at 1.94 kg m-2 h-1 for 8 h without salt crystal formation. This work offers a novel microstructural design to address the complex interplay of water, salt, and thermal transport.

Guidelines derived from biomineralized tissues for design and construction of high-performance biomimetic materials: from weak to strong

Living organisms in nature have undergone continuous evolution over billions of years, resulting in the formation of high-performance fracture-resistant biomineralized tissues such as bones and teeth to fulfill mechanical and biological functions, despite the fact that most inorganic biominerals that constitute biomineralized tissues are weak and brittle. During the long-period evolution process, nature has evolved a number of highly effective and smart strategies to design chemical compositions and structures of biomineralized tissues to enable superior properties and to adapt to surrounding environments. Most biomineralized tissues have hierarchically ordered structures consisting of very small building blocks on the nanometer scale (nanoparticles, nanofibers or nanoflakes) to reduce the inherent weaknesses and brittleness of corresponding inorganic biominerals, to prevent crack initiation and propagation, and to allow high defect tolerance. The bioinspired principles derived from biomineralized tissues are indispensable for designing and constructing high-performance biomimetic materials. In recent years, a large number of high-performance biomimetic materials have been prepared based on these bioinspired principles with a large volume of literature covering this topic. Therefore, a timely and comprehensive review on this hot topic is highly important and contributes to the future development of this rapidly evolving research field. This review article aims to be comprehensive, authoritative, and critical with wide general interest to the science community, summarizing recent advances in revealing the formation processes, composition, and structures of biomineralized tissues, providing in-depth insights into guidelines derived from biomineralized tissues for the design and construction of high-performance biomimetic materials, and discussing recent progress, current research trends, key problems, future main research directions and challenges, and future perspectives in this exciting and rapidly evolving research field.

Interfacial Assembly of 2D Graphene-Derived Ion Channels for Water-Based Green Energy Conversion

The utilization of sustained and green energy is believed to alleviate increasing menace of global environmental concerns and energy dilemma. Interfacial assembly of 2D graphene-derived ion channels (2D-GDICs) with tunable ion/fluid transport behavior enables efficient harvesting of renewable green energy from ubiquitous water, especially for osmotic energy harvesting. In this review, various interfacial assembly strategies for fabricating diverse 2D-GDICs are summarized and their ion transport properties are discussed. This review analyzes how particular structure and charge density/distribution of 2D-GDIC can be modulated to minimize internal resistance of ion/fluid transport and enhance energy conversion efficiency, and highlights stimuli-responsive functions and stability of 2D-GDIC and further examines the possibility of integrating 2D-GDIC with other energy conversion systems. Notably, the presented preparation and applications of 2D-GDIC also inspire and guide other 2D materials to fabricate sophisticated ion channels for targeted applications. Finally, potential challenges in this field is analyzed and a prospect to future developments toward high-performance or large-scale real-word applications is offered.

High-Performance, Multifunctional, and Designable Carbon Fiber Felt Skeleton Epoxy Resin Composites EP/CF-(CNT/AgBNs)x for Thermal Conductivity and Electromagnetic Interference Shielding

In this work, high-performance epoxy resin (EP) composites with simultaneous excellent thermal conductivity (TC) and outstanding electromagnetic shielding properties are fabricated through the structural synergy of 1D carbon nanotubes and 2D silver-modified boron nitride nanoplates (CNT/AgBNs) to erect microscopic 3D networks on long-range carbon fiber (CF) felt skeletons. The line-plane combination of CNT/AgBNs improve the interfacical bonding involving EP and CF felts and alleviate the phonon scattering at the interface. Eventually, the TC of the EP composites is enhanced by 333% (up to 0.91 W m-1 K-1 ) with respect to EP due to the efficient and orderly transmission of phonons along the 3D pathway. Meanwhile, the unique anisotropic structure of CF felt and exceptional insulating BNs diminishes the electronic conduction between CNT and CFs, which protects the through-plane insulating properties of EP composites. Furthermore, the EP composites present favorable electromagnetic shielding properties (51.36 dB) attributed to the multiple reflection and adsorption promoted by the multiple interfaces of stacked AgBNs and heterointerface among CNT/AgBNs, CF felt and EP. Given these distinguishing features, the high-performance EP composites open a convenient avenue for electromagnetic wave (EMW) shielding and thermal management applications.

Anisotropic Black Phosphorene Structural Modulation for Thermal Storage and Solar-Thermal Conversion

Exploiting novel strategies for simultaneously harvesting ubiquitous, renewable, and easily accessible solar energy based on the photothermal effect, and efficiently storing the acquired thermal energy plays a vital role in revolutionizing the current fossil fuel-dominating energy structure. Developing black phosphorene-based phase-change composites with optimized photothermal conversion efficiencyand high latent heat is the most promising way to achieve efficient solar energy harvesting and rapid thermal energy storage. However, exfoliating high-quality black phosphorene nanosheets  remains challenging, Furthermore, an efficient strategy that can construct the aligned black phosphorene frameworks to maximize thermal conductivity enhancement is still lacking. Herein, high-quality black phosphorene nanosheets are prepared by an optimized exfoliating strategy. Meanwhile, by regulating the temperature gradient during freeze-casting, the framework consisting of shipshape aligned black phosphorene at long-range is successfully fabricated, improving the thermal conductivity of the poly(ethylene glycol) matrix up to 1.81 W m-1  K-1 at 20 vol% black phosphorene loading. The framework also endows the composite with excellent phase-change material encapsulation capacity and  high latent heat of 103.91 J g-1 . It is envisioned that the work advances the paradigm of contrasting frameworks with nanosheets toward controllable structure thermal enhancement of the composites.

High-Performance Graphene Biocomposite Enabled by Fe3+ Coordination for Thermal Management

Emerging biocomposites with excellent heat dissipation capabilities and inherent sustainability are urgently needed to address the cooling issues of modern electronics and growing environmental concerns. However, the moisture stability, mechanical performance, thermal conductivity, and even flame retardancy of biomass-based materials are generally insufficient for practical thermal management applications. Herein, we present a high-performance graphene biocomposite consisting of carboxylated cellulose nanofibers and graphene nanosheets through an evaporation-induced self-assembly and subsequent Fe3+ cross-linking strategy. The Fe3+ coordination plays a critical role in stabilizing the material structure, thereby improving the mechanical strength and water stability of the biocomposite films, and its effect is revealed by density functional theory calculations. The hierarchical structure of the biocomposite films also leads to a high in-plane thermal conductivity of 42.5 W m-1 K-1, enabling a superior heat transfer performance. Furthermore, the resultant biocomposite films exhibit outstanding Joule heating performance with a fast thermal response and long-term stability, improved thermal stability, and flame retardancy. Therefore, such a general strategy and the desired overall properties of the biocomposite films offer wide application prospects for functional and safe thermal management.

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.

Oriented Three-Dimensional Skeletons Assembled by Si3N4 Nanowires/AlN Particles as Fillers for Improving Thermal Conductivity of Epoxy Composites

With the miniaturization of current electronic products, ceramic/polymer composites with excellent thermal conductivity have become of increasing interest. Traditionally, higher filler fractions are required to obtain a high thermal conductivity, but this leads to a decrease in the mechanical properties of the composites and increases the cost. In this study, silicon nitride nanowires (Si3N4NWs) with high aspect ratios were successfully prepared by a modified carbothermal reduction method, which was further combined with AlN particles to prepare the epoxy-based composites. The results showed that the Si3N4NWs were beneficial for constructing a continuous thermal conductive pathway as a connecting bridge. On this basis, an aligned three-dimensional skeleton was constructed by the ice template method, which further favored improving the thermal conductivity of the composites. When the mass fraction of Si3N4NWs added was 1.5 wt% and the mass fraction of AlN was 65 wt%, the composites prepared by ice templates reached a thermal conductivity of 1.64 W·m-1·K-1, which was ~ 720% of the thermal conductivity of the pure EP (0.2 W·m-1·K-1). The enhancement effect of Si3N4NWs and directional filler skeletons on the composite thermal conductivity were further demonstrated through the actual heat transfer process and finite element simulations. Furthermore, the thermal stability and mechanical properties of the composites were also improved by the introduction of Si3N4NWs, suggesting that prepared composites exhibit broad prospects in the field of thermal management.

Environmentally Friendlier Printable Conductive and Piezoresistive Sensing Materials Compatible with Conformable Electronics

Flexible and conformable conductive composites have been developed using different polymers, including water-based polyvinylpyrrolidone (PVP), chemical-resistant polyvinylidene fluoride (PVDF), and elastomeric styrene-ethylene-butylene-styrene (SEBS) reinforced with nitrogen-doped reduced graphene oxide with suitable viscosity in composites for printable solutions with functional properties. Manufactured by screen-printing using low-toxicity solvents, leading to more environmentally friendly conductive materials, the materials present an enormous step toward functional devices. The materials were enhanced in terms of filler/binder ratio, achieving screen-printed films with a sheet resistance lower than Rsq < 100 Ω/sq. The materials are biocompatible and support bending deformations up to 10 mm with piezoresistive performance for the different polymers up to 100 bending cycles. The piezoresistive performance of the SEBS binder is greater than double that the other composites, with a gauge factor near 4. Thermoforming was applied to all materials, with the PVP-based ones showing the lowest electrical resistance after the bending process. These conductive materials open a path for developing sustainable and functional devices for printable and conformable electronics.

Enhanced In-Plane Thermal Conductivity and Mechanical Strength of Flexible Films by Aligning and Interconnecting Si3N4 Nanowires

As the rapid development of advanced foldable electronic devices, flexible and insulating composite films with ultra-high in-plane thermal conductivity have received increasing attention as thermal management materials. Silicon nitride nanowires (Si₃N₄NWs) have been considered as promising fillers for preparing anisotropic thermally conductive composite films due to their extremely high thermal conductivity, low dielectric properties, and excellent mechanical properties. However, an efficient approach to synthesize Si₃N₄NWs in a large scale still need to be explored. In this work, large quantities of Si₃N₄NWs were successfully prepared using a modified CRN method, presenting the advantages of high aspect ratio, high purity, and easy collection. On the basis, the super-flexible PVA/Si₃N₄NWs composite films were further prepared with the assistance of vacuum filtration method. Due to the highly oriented Si₃N₄NWs interconnected to form a complete phonon transport network in the horizontal direction, the composite films exhibited a high in-plane thermal conductivity of 15.4 W·m^-1·K^-1. The enhancement effect of Si₃N₄NWs on the composite thermal conductivity was further demonstrated by the actual heat transfer process and finite element simulations. More significantly, the Si₃N₄NWs enabled the composite film presenting good thermal stability, high electrical insulation, and excellent mechanical strength, which was beneficial for thermal management applications in modern electronic devices.

3D-Printed Polyamide 12/Styrene-Acrylic Copolymer-Boron Nitride (PA12/SA-BN) Composite with Macro and Micro Double Anisotropic Thermally Conductive Structures

Anisotropic thermally conductive composites are very critical for precise thermal management of electronic devices. In this work, in order to prepare a composite with significant anisotropic thermal conductivity, polyamide 12/styrene-acrylic copolymer-boron nitride (PA12/SA-BN) composites with macro and micro double anisotropic structures were fabricated successfully using 3D printing and micro-shear methods. The morphologies and thermally conductive properties of composites were systematically characterized via SEM, XRD, and the laser flash method. Experimental results indicate that the through-plane thermal conductivity of the composite is 4.2 W/(m·K) with only 21.4 wt% BN, which is five times higher than that of the composite with randomly oriented BN. Simulation results show that the macro-anisotropic structure of the composite (caused by the selective distribution of BN) as well as the micro-anisotropic structure (caused by the orientation structure of BN) both play critical roles in spreading heat along the specified direction. Therefore, as-obtained composites with double anisotropic structures possess great potential for the application inefficient and controllable thermal management in various fields.

Enhancing thermal conductivity and chemical protection of bacterial cellulose/silver nanowires thin-film for high flexible electronic skin

Silver nanowires (AgNWs) thin films have emerged as a promising next-generation flexible electronic device. However, the current AgNWs thin films are often plagued by high AgNWs-AgNWs contact resistance and poor long-term stability. Here, to enhance the AgNWs stability on the surface of bacterial cellulose (BC), a novel flexible high conductivity thin-film was prepared by spin-coating a layer of polyvinyl alcohol (PVA) on the BC/AgNWs (BA) film. Firstly, BC film with high uniformity to better fit the AgNWs was obtained. It is observed that inadequately protected AgNWs can be corroded when AgNWs together with PVA were attached to the BC surface (BAP film), Yet, a layer of PVA was spin-coated on the surface of BA film, the BC/AgNWs/spin-coated 0.5 % PVA (BASP) thin-film (10.1 μm) exhibits that the PVA interfacial protective layer effectively mitigated the intrinsic incompatibility of BC with AgNWs as well as external corrosion (Na₂S for 3 h) and immobilization of AgNWs, thus having a low conductive sheet resistance of 0.42 Ω/sq., which was better than most of the AgNWs-containing conductive materials reported so far. In addition, the resistance of the BASP thin-film changed little after 10,000 bending cycles, and the conductivity remained stable over BC directly immersed in 0.5 % PVA/AgNWs. This "soft" conductive material can be used to manufacture a new generation of electronic skin.

Enhanced in-plane thermal conductivity of polyimide-based composites via in situ interfacial modification of graphene

Interfacial thermal resistance is the main barrier restricting the heat dissipation of thermal management materials in electronic equipment. The interface structure formed by covalent bonding is an effective way to promote interfacial heat transfer. Herein, an integrated composite with multi-aspect covalent bonding beneficial for heat transmission is constructed by polyimide (PI) polymerization with maleimide modified graphene nanosheets (M@GNS). The interfacial structure with low thermal resistance built by covalent bonding and oriented graphene arrangement initiated by the coating process makes the in-plane thermal conductivity of the composite as high as 16.10 W m^-1 K^-1. Finite element simulation and 1000 bending tests are carried out to further verify the performance advantages of the integrated structure in the internal thermal diffusion and long-term use of the composite. M@GNS/PI with integrated structure provides extra heat transfer channels for heat dissipation, possibly providing an effective way to address the traditional thermal accumulation issue of electronic devices.

Nanoarchitectonics of RGO-Wrapped CNF/GO Aerogels with Controlled Pore Structures by PVA-Assisted Freeze-Casting Approach for Efficient Sound and Microwave Absorption

Acoustic absorption materials play an important role in eliminating the negative effects of noise. Herein, a polyvinyl alcohol (PVA)-assisted freeze-casting was developed for controllably fabricating reduced graphene oxide wrapped carbon nanofiber (RGO@CNF)/graphene oxide composite aerogel. During the freeze-casting, PVA was used as an icing inhibitor to control the size of ice crystals. While the concentration of PVA increased from 0 to 15 mg ⋅ ml^-1 , the average pore size of the aerogel was reduced from 154 to 45 μm. Due to the modulation of the pore size and composition, the propagation path and friction loss for sound were optimized, especially at low frequency. For instance, the normalized sound absorption coefficient of RGO@CNF/GO-10 achieves 0.79 (250-6300 Hz). The sample also exhibits a desirable microwave absorbing property whose maximum reflection loss is -47.3 dB (9.44 GHz, d=3.0 mm). Prospectively, this synthetic strategy can be extended to develop other forms of elastic aerogel with a controlled pore size.

Development and Perspectives of Thermal Conductive Polymer Composites

With the development of electronic appliances and electronic equipment towards miniaturization, lightweight and high-power density, the heat generated and accumulated by devices during high-speed operation seriously reduces the working efficiency and service life of the equipment. The key to solving this problem is to develop high-performance thermal management materials and improve the heat dissipation efficiency of the equipment. This paper mainly summarizes the research progress of polymer composites with high thermal conductivity and electrical insulation, including the thermal conductivity mechanism of composites, the factors affecting the thermal conductivity of composites, and the research status of thermally conductive and electrical insulation polymer composites in recent years. Finally, we look forward to the research focus and urgent problems that should be addressed of high-performance thermal conductive composites, which will provide strategies for further development and application of advanced thermal and electrical insulation composites.

Graphene Layer Number-Dependent Heat Transport across Nickel/Graphene/Nickel Interfaces

As a typical two-dimensional material, graphene (Gr) has shown great potential to be used in thermal management applications due to its ultrahigh in-plane thermal conductivity (k). However, low interface thermal conductance (ITC) between Gr and metals to a large extent limits the effective heat dissipation in Gr-based devices. Therefore, having a deep understanding on heat transport at Gr-metal interfaces is essential. Because of the semimetallic nature of Gr, electrons would possibly play a role in the heat transport across Gr-metal interfaces as heat carriers, whereas, However, how much the electron can participate in this process and how to optimize the total ITC considering both electron and phonon transportations have not yet been revealed yet. Therefore, in this work, hydrogenation-treated Gr (H-Gr) was sandwiched by nickel (Ni) nanofilms to compare with the samples containing pure Gr for investigating the interfacial electron behaviors. Moreover, both Gr and H-Gr sets of the samples were prepared with different layer numbers (N) ranging from 1 to 7, and the corresponding ITC was systematically studied based on both time-domain thermoreflectance measurements and theoretical calculations. We found that a larger ITC can be obtained when N is low, and the ITC may reach a peak value when N is 2 in certain circumstances. The present findings not only provide a comprehensive understanding on heat transport across Gr-metal interfaces byconsidering a combined effect of the interfacial interaction strength, phonon mode mismatch, and electron contributions, but also shed new lights on interface strucure optimiazations of Gr-based devices.

Bridge-type 1D/2D boron nitride enhances the thermal management capability of polymer composites

A bridge-type structure is constructed in the composite fibers by integrating 1D/2D boron nitride, which shows superior heat dissipation properties.

Chemical Vapor Deposition Mechanism of Graphene-Encapsulated Au Nanoparticle Heterostructures and Their Plasmonics

Direct encapsulation of graphene shells on noble metal nanoparticles via chemical vapor deposition (CVD) has been recently reported as a unique way to design and fabricate new plasmonic heterostructures. But currently, the fundamental nature of the growth mechanism of graphene layers on metal nanostructures is still unknown. Herein, we report a systematic investigation on the CVD growth of graphene-encapsulated Au nanoparticles (Au@G) by combining an experimental parameter study and theoretical modeling. We studied the effect of growth temperature, duration, hydrocarbon precursor concentration, and extent of reducing (H₂) environment on the morphology of the products. In addition, the influence of plasma oxidation conditions for the surface oxidation of gold nanoparticles on the graphene shell growth is evaluated in combination with thermodynamic calculations. We find that these parameters critically aid in the evolution of graphene shells around gold nanoparticles and allow for controlling shell thickness, graphene shell quality and morphology, and hybrid nanoparticle diameter. An optimized condition including the growth temperature of ∼675 °C, duration of 30 min, and xylene feed rate of ∼10 mL/h with 10% H₂/Ar carrier gas was finally obtained for the best morphology evolution. We further performed finite-element analysis (FEA) simulations to understand the equivalent von Mises stress distribution and discrete dipolar approximation (DDA) calculation to reveal the optical properties of such new core-shell heterostructures. This study brings new insight to the nature of CVD mechanism of Au@G and might help guiding their controlled growth and future design and application in plasmonic applications.

Green and sustainable cellulose-derived humidity sensors: A review

Cellulose, as the most abundant natural polysaccharide, is an excellent material for developing green humidity sensors, especially due to its humidity responsiveness as a result of its rich hydrophilic groups. In combination with other components including carbon materials and polymers, cellulose and its derivatives can be used to design high-performance humidity sensors that meet various application requirements. This review summarizes the recent advances in the field of various cellulose-derived humidity sensors, with particular attention paid to different sensing mechanisms including resistance, capacitance, colorimetry and gravity, and so on. Furthermore, the roles of cellulose and its derivatives are highlighted. This work may promote the development of cellulose-derived humidity sensors, as well as other cellulose-based intelligent materials.

Graphene-Based Films: Fabrication, Interfacial Modification, and Applications

Graphene-based film attracts tremendous interest in many potential applications due to its excellent thermal, electrical, and mechanical properties. This review focused on a critical analysis of fabrication, processing methodology, the interfacial modification approach, and the applications of this novel and new class material. Strong attention was paid to the preparation strategy and interfacial modification approach to improve its mechanical and thermal properties. The overview also discussed the challenges and opportunities regarding its industrial production and the current status of the commercialization. This review showed that blade coating technology is an effective method for industrial mass-produced graphene film with controllable thickness. The synergistic effect of different interface interactions can effectively improve the mechanical properties of graphene-based film. At present, the application of graphene-based film on mobile phones has become an interesting example of the use of graphene. Looking for more application cases is of great significance for the development of graphene-based technology.

Highly Thermal Conductive Poly(vinyl alcohol) Composites with Oriented Hybrid Networks: Silver Nanowire Bridged Boron Nitride Nanoplatelets

With the increasing demand for thermal management materials in the highly integrated electronics area, building efficient heat-transfer networks to obtain advanced thermally conductive composites is of great significance. In the present work, highly thermally conductive poly(vinyl alcohol) (PVA)/boron nitride nanoplatelets@silver nanowires (BNNS@AgNW) composites were fabricated via the combination of the electrospinning and the spraying technique, followed by a hot-pressing method. BNNS are oriented along the in-plane direction, while AgNWs with a high aspect ratio can help to construct a thermal conductive network effectively by bridging BNNS in the composites. The PVA/BNNS@AgNW composites showed high in-plane thermal conductivity (TC) of 10.9 W/(m·K) at 33 wt % total fillers addition. Meanwhile, the composite shows excellent thermal dispassion capability when it is taken as a thermal interface material of a working light-emitting diode (LED) chip, which is certified by capturing the surface temperature of the LED chip. In addition, the out-of-plane electrical conductivity of the composites is below 10^-12 S/cm. The composites with outstanding thermal conductive and electrical insulating properties hold promise for application in electrical packaging and thermal management.

Ultrafast Fabrication of Graphene-Reinforced Nanocomposites via Synergy of Steam Explosion and Alternating Convergent-Divergent Flow

Producing high-quality graphene and polymer/graphene nanocomposite is facing the problems of complex procedure, low efficiency, and serious resource waste. To explore a new fabrication approach with high efficiency and low cost is crucial for solving these technical issues, which becomes a current research hotspot and also a great challenge. Herein, a one-step melt mixing strategy based on the synergy of steam explosion and alternating convergent-divergent flow, is innovatively developed to fabricate high-density polyethylene (HDPE)/graphene nanocomposites using industrial-grade expanded graphite (EG) without chemical agents and complex procedures. The co-action of the external force derived from elongational melts and the internal force generated by steam explosion make EG ultrafastly exfoliate into few-layer graphene nanosheets (GNS) and simultaneously disperse in melts within 4 min. The as-produced GNS have a lateral size of over 5 µm and a minimum thickness of 1.4 nm, can introduce super heterogeneous nucleation to HDPE macromolecules and greatly increases nanocomposite crystallinity up to 86.5%. Moreover, plentiful HDPE crystallites and well-dispersed GNS jointly form an improved thermally-conductive network, making nanocomposites with a rapid-respond ability in solar-to-thermal conversion and heat dissipation. This facile strategy will facilitate the development of scalable production and wide application of high-performance graphene and highly-filled nanocomposites.

High-Performance Joule Heating and Electromagnetic Shielding Properties of Anisotropic Carbon Scaffolds

Highly efficient electrical heaters along with excellent electromagnetic interference (EMI) shielding properties are urgently required for the progress of miniaturization electronics, artificial intelligence, and smart heating management setups. Herein, lignin removal, which comprises two efficient and versatile steps, followed by carbonization produces multifunctional carbon monoliths derived from natural wood. The obtained carbonized wood exhibits a high specific surface area (655.14 m²/g) and electrical (17.5 S/cm) and thermal conductivity (0.58 W/m·K), superhydrophilicity (contact angle of ∼0°), and excellent EMI shielding ability and Joule heating performance. The high electrical conductivity renders a low-voltage-actuated Joule heating performance and fascinating EMI shielding effectiveness of 55 dB, primarily resulting from the absorption mechanism. Moreover, regulation of the carbonized woods derived from the longitudinal to the radial direction enables transformation of hydrophilicity, strong thermal conductivity, and absorption-dominated EMI shielding to hydrophobicity, thermal insulation, and reflection-dominated EMI shielding. This is attributed to the unique anisotropic microstructure of carbon scaffolds. It is believed that these multifunctional carbon scaffolds can be used for intelligent electronics, EMI shielding, and thermal heating instruments.

Enhanced Thermal Conductivity in Oriented Polyvinyl Alcohol/Graphene Oxide Composites

Polymer composites have attracted increasing interest as thermal management materials for use in devices owing to their ease of processing and potential lower costs. However, most polymer composites have only modest thermal conductivities, even at high concentrations of additives, resulting in high costs and reduced mechanical properties, which limit their applications. To achieve high thermally conductive polymer materials with a low concentration of additives, anisotropic, solid-state drawn composite films were prepared using water-soluble polyvinyl alcohol (PVA) and dispersible graphene oxide (GO). A co-additive (sodium dodecyl benzenesulfonate) was used to improve both the dispersion of GO and consequently the thermal conductivity. The hydrogen bonding between GO and PVA and the simultaneous alignment of GO and PVA in drawn composite films contribute to an improved thermal conductivity (∼25 W m^-1 K^-1), which is higher than most reported polymer composites and an approximately 50-fold enhancement over isotropic PVA (0.3-0.5 W m^-1 K^-1). This work provides a new method for preparing water-processable, drawn polymer composite films with high thermal conductivity, which may be useful for thermal management applications.

Anisotropic Electrical Conductivity of Oxygen-Deficient Tungsten Oxide Films with Epitaxially Stabilized 1D Atomic Defect Tunnels

Materials having an anisotropic crystal structure often exhibit anisotropy in the electrical conductivity. Compared to complex transition-metal oxides (TMOs), simple TMOs rarely show large anisotropic electrical conductivity due to their simple crystal structure. Here, we focus on the anisotropy in the electrical conductivity of a simple TMO, oxygen-deficient tungsten oxide (WO_x) with an anisotropic crystal structure. We fabricated several WO_x films by the pulsed laser deposition technique on the lattice-matched (110)-oriented LaAlO₃ substrate under a controlled oxygen atmosphere. The crystallographic analyses of the WO_x films revealed that highly dense atomic defect tunnels were aligned one-dimensionally (1D) along [001] LaAlO₃. The electrical conductivity along the 1D atomic defect tunnels was ∼5 times larger than that across the tunnels. The present approach, introduction of 1D atomic defect tunnels, might be useful to design simple TMOs exhibiting anisotropic electrical conductivity.

Stitching Graphene Sheets with Graphitic Carbon Nitride: Constructing a Highly Thermally Conductive rGO/g-C3N4 Film with Excellent Heating Capability

Driven by the evolution of electronic packaging technology for high-dense integration of high-power, high-frequency, and multi-function devices in modern electronics, thermal management materials have become a crucial component for guaranteeing the stable and reliable operation of devices. Because of its admirable in-plane thermal conductivity, graphene is considered as a desired thermal conductor. However, the promise of graphene films has been greatly weakened as the existence of grain boundaries lead to a high extent of phonon scattering. Here, a stitching strategy is adopted to fabricate an rGO/g-C₃N₄ film, where 2D g-C₃N₄ works as a linker to covalently connect adjacent rGO sheets for expanding the size of graphene and forming an in-plane rGO/g-C₃N₄ heterostructure. The in-plane thermal conductivity of the rGO/g-C₃N₄ film reaches 41.2 W m^-1 K^-1 at a g-C₃N₄ content of only 1 wt %, which increased by 17.3% compared to pristine rGO. The interfaced thermal resistance between rGO and g-C₃N₄ is further examined by non-equilibrium molecular dynamics simulations. Furthermore, owing to the unique light absorption and welding ability of g-C₃N₄, the rGO/g-C₃N₄ film presents superior solar-thermal and electric-thermal responses to controllably regulate the chip temperature against overcooling. This work provides a facile approach to construct a large-sized rGO sheet and combines heat dissipation and heating capability in the same thermal management material for future electronics.

Small-Nanostructure-Size-Limited Phonon Transport within Composite Films Made of Single-Wall Carbon Nanotubes and Reduced Graphene Oxides

Nanocarbon materials have been widely used for nanoelectronics and energy-related applications. In this work, composite films consisting of reduced graphene oxides (rGOs) and single-wall carbon nanotubes (SWCNTs) are synthesized and studied for their in-plane thermal conductivities. Different from pristine carbon nanotubes or graphene with decreased thermal conductivities above 300 K, the in-plane thermal conductivities of these composite films are found to follow the trend of the specific heat of graphene from 100 to 400 K, i.e., monotonously increasing at elevated temperatures. Such a trend can often be found within amorphous solids but has seldom been observed for nanocarbon. This unique temperature dependence of thermal conductivities is attributed to the largely restricted phonon mean free paths within the graphene sheets that mainly contribute to the in-plane thermal transport. The highest in-plane thermal conductivity among samples with different synthesis conditions is 62.8 W/(m·K) at 300 K. Such a high thermal conductivity, combined with its unique temperature dependency, can be ideal for applications such as flexible film-like thermal diodes based on the junction between two materials with a large contrast for their temperature dependence of the thermal conductivity.

Recent progress in the development of thermal interface materials: a review

Modern electronic devices are characterized by high-power and high-frequency with excessive heat accumulation. Thermal interface materials (TIMs) are of crucial importance for efficient heat dissipation to maintain proper functions and lifetime for these devices. The most promising TIMs are those polymer-based nanocomposites consisting of polymers and low-dimensional materials with high thermal conductivity (TC). This perspective summarizes the recent progress on the thermal transport properties of newly discovered one-dimensional (1D) nanomaterials and two-dimensional (2D) nanomaterials as well as three-dimensional (3D) nanostructures consisting of these 1D and 2D nanomaterials. Moreover, the applications of various nanomaterials in polymer nanocomposites for advanced TIMs are critically reviewed and the mechanism of TC enhancement is analysed. It is hoped that the present review could provide better understanding of the thermal transport properties of recently developed 2D nanomaterials and various 3D nanostructures as well as relevant polymer-based TIMs, shedding more light on the thermal management research.

Conducting Polyetheretherketone Nanocomposites with an Electrophoretically Deposited Bioactive Coating for Bone Tissue Regeneration and Multimodal Therapeutic Applications

The use of polyetheretherketone (PEEK) has grown exponentially in the biomedical field in recent decades because of its outstanding biomechanical properties. However, its lack of bioactivity/osteointegration remains an unresolved issue toward its wide use in orthopedic applications. In this work, graphene nanosheets have been incorporated into PEEK to obtain multifunctional nanocomposites. Because of the formation of an electrical percolation network and the π-π* conjugation between graphene and PEEK, the resulting composites have achieved 12 orders of magnitude enhancement in their electrical conductivity and thereby enabled electrophoretic deposition of a bioactive/antibacterial coating consisting of stearyltrimethylammonium chloride-modified hydroxyapatite. The coated composite implant shows significant boosting of bone marrow mesenchymal stem cell proliferation in vitro. In addition, the strong photothermal conversion effect of the graphene nanofillers has enabled laser-induced heating of our nanocomposite implants, where the temperature of the implant can reach 45 °C in 150 s. The unique multifunctionality of the implant has also been demonstrated for photothermal applications such as enhancing bacterial eradication and tumor cell inhibition, as well as bone tissue regeneration in vivo. The results suggest the strong potential of our multifunctional implant in bone repair applications as well as multimodal therapy of challenging bone diseases such as osteosarcoma and osteomyelitis.