Vertically Aligned and Interconnected Boron Nitride Nanosheets for Advanced Flexible Nanocomposite Thermal Interface Materials

3D Printed Leaf-Vein-Like Al2O3/EP Biohybrid Structures with Enhanced Thermal Conductivity

The high computility of electronic components put urgent requirements on the dissipation efficiency of a high thermal conductive substrate. Herein, inspired by the nature structure, leaf-vein-like Al2O3 skeleton was first designed though topology optimization algorithm and manufactured via vat photopolymerization (VPP) 3D printing, then compounded with epoxy (EP) to prepare leaf-vein-like biohybrid structures. The biohybrid structure had a high λ (14.65 Wm-1 K-1 with the solid fraction of 40 vol %), which was 5585% higher than neat EP and 269% higher than the random dispersed Al2O3/EP composite at the same solid amount. Moreover, it further showed a high enhancement in the cooling ecoefficiency of the lighting-emitting diode (LED) cooling system. Compared with 40 vol % random dispersed Al2O3/EP composite as a cooling substrate, the leaf-vein-like biohybrid structure with the same solid fraction reduced the working temperature of LED by 8.9 °C. Our strategy has a significant potential as a viable type and mass-producible bionic cooling substrate.

Highly Interconnected Thermal Conduction Highway for Highly Thermally Conductive and Mechanically Strong Polymeric Composites

Industrial implementation of highly thermally conductive polymeric composites has been hindered by several hurdles, such as the low intrinsic thermal conductivity (TC) of polymers, the use of expensive thermally conductive fillers, and difficulty in processing composites with high filler loading. In this study, we introduce a straightforward fabrication method for a high TC polymeric composite with a programmed internal structure of a highly interconnected thermal conduction highway (HITCH) by the simple addition of partially cured resin fragments into the conventional filler/resin combination. Critical variables, such as the concentration of the added resin fragments and the local concentration of hexagonal boron nitride (hBN) in the HITCH, as well as the packing density of the fragments, were systematically tuned to maximize the TC with the use of the least amount of the filler. Careful choice of the compositions enabled a significant TC enhancement of the composite by 2.6 times (6.5 W/mK) compared to the value of the conventional composite at the same overall concentration of hBN (∼2.5 W/mK). Finally, a composite with high TC (∼12 W/mK) and strong tensile strength (∼22.6 MPa), which is good enough for most practical thermal management applications, could be successfully fabricated with the use of the least amount of the filler (∼34 wt %). The comprehensive study of the HITCH composite here can be easily extended to other combinations with various fillers and matrices and may provide a library to researchers looking for advanced materials for future thermal management systems.

Constructing the Snail Shell-Like Framework in Thermal Interface Materials for Enhanced Through-Plane Thermal Conductivity

Melioration of the through-plane thermal conductivity (TC) of thermal interface materials (TIMs) is a sore need for efficient heat dissipation to handle an overheating concern of high-power-density electronics. Herein, we constructed a snail shell-like thermal conductive framework to facilitate vertical heat conduction in TIMs. With inspiration from spirally growing calcium carbonate platelets of snail shells, a facile double-microrod-assisted curliness method was developed to spirally coil boron nitride nanosheet (BNNS)/aramid nanofiber (ANF) laminates where interconnected BNNSs lie along the horizontal plane. Thus, vertical alignment of BNNSs in the resultant TIM was achieved, exhibiting a through-plane TC enhancement of ∼100% compared to the counterpart with randomly distributed BNNSs at the same BNNS addition (50 wt %). The Foygel's nonlinear model revealed that this unique snail shell-like BNNS framework reduced interfacial thermal resistance by 4 orders of magnitude. Our TIM showed superior interfacial thermal dissipation efficiency, leading to a temperature reduction of 42.6 °C for the LED chip compared to the aforementioned counterpart. Our work paves a valuable way for fabricating high-performance TIMs to ensure reliable operation of electrical devices.

Highly Thermally Conductive and Flexible Thermal Interface Materials with Aligned Graphene Lamella Frameworks

Highly thermally conductive and flexible thermal interface materials (TIMs) are desirable for heat dissipation in modern electronic devices. Here, we fabricated a high-crystalline aligned graphene lamella framework (AGLF) with precisely controlled lamella thickness, pore structure, and excellent intergraphene contact by manipulating the thermal expansion behavior of scanning centrifugal casted graphene oxide films. The rational design of the AGLF balances the trade-off between the thermal conductivity and flexibility of TIMs. The AGLF-based TIM (AGLF-TIM) shows a record thermal conductivity of 196.3 W m-1 K-1 with a graphene loading of only 9.4 vol %, which is about 4 times higher than those of reported TIMs at a similar graphene loading. Meanwhile, good flexibility remains comparable to that of commercial TIMs. As a result, an LED device achieves an additional temperature decrease of ∼8 °C with the use of AGLF-TIM compared to high-performance commercial TIMs. This work offers a strategy for the controlled fabrication of graphene macrostructures, showing the potential use of graphene as filler frameworks in thermal management.

An Innovative Concept of Membrane-Free Redox Flow Batteries with Near-Zero Contact Distance Between Electrodes

Given that the ion-exchange membrane takes up more than 30% of redox flow battery (RFB) cost, considerable cost reduction is anticipated with the membrane-free design. However, eliminating the membrane/separator would expose the membrane-free RFBs to a higher risk of short-circuits, and the dendrite growth may aggravate this issue. The current strategy based on expanding distances between electrodes is proposed to address short-circuit issues. Nevertheless, this approach would decrease the energy efficiency (EE) and could not restrain dendrite growth fundamentally. Herein, an inexpensive and electron-insulating boron nitride nanosheets (BNNSs)-Nylon hybrid interlayer (BN/Nylon) is developed for general membrane-free RFBs to achieve "near-zero distance" contact between electrodes. And the Lewis acid sites (B atoms) in BNNS can interact with the Lewis base anions in electrolytes, enabling a reduced Pb2+concentration gradient. Additionally, the ultrahigh thermal conductivity and mechanical strength of BNNSs promote the uniform plating/stripping process of Pb and PbO2. Compared with conventional soluble lead RFBs, introducing BN/Nylon interlayers boosts EE by ≈38.2% at 25 mA cm-2, and extends the cycle life to 100 cycles. This innovative strategy premieres the application of the BN/Nylon interlayer concept, offering a novel perspective for the development of general membrane-free RFBs.

Smart Bandage Based on a ZIF-8 Triboelectric Nanogenerator for In Situ Real-Time Monitoring of Drug Concentration

For chronic wounds, frequent replacement of bandages not only increases the likelihood of secondary damage and the risk of cross infection but also wastes medication. Therefore, in situ real-time monitoring of the concentrations of residual drugs in bandages is crucial. Here, we propose a novel strategy that combines a triboelectric nanogenerator (TENG) with medical bandages to develop a smart bandage based on zeolite imidazolate framework TENG. During the process of wound healing, the electrical output of TENG changes with the continuous release of drugs. Based on the correlation between the electrical signal of TENG and drug concentration, the concentration of residual drugs in the bandage can be monitored in real-time in situ, guiding medical staff to replace the bandage at the most appropriate time. The smart bandage based on TENG provides a new strategy for in situ real-time monitoring of drug concentration and also provides an ideal and feasible solution for the field of biomedical drug sensing.

Polymeric Nanocomposites of Boron Nitride Nanosheets for Enhanced Directional or Isotropic Thermal Transport Performance

Polymeric composites with boron nitride nanosheets (BNNs), which are thermally conductive yet electrically insulating, have been pursued for a variety of technological applications, especially those for thermal management in electronic devices and systems. Highlighted in this review are recent advances in the effort to improve in-plane thermal transport performance in polymer/BNNs composites and also the growing research activities aimed at composites of enhanced cross-plane or isotropic thermal conductivity, for which various filler alignment strategies during composite fabrication have been explored. Also highlighted and discussed are some significant challenges and major opportunities for further advances in the development of thermally conductive composite materials and their mechanistic understandings.

Cutting-edge developments in zinc oxide nanoparticles: synthesis and applications for enhanced antimicrobial and UV protection in healthcare solutions

This paper presents a comprehensive review of recent advancements in utilizing zinc oxide nanoparticles (ZnO NPs) to enhance antimicrobial and UV protective properties in healthcare solutions. It delves into the synthesis techniques of ZnO NPs and elucidates their antimicrobial efficacy, exploring the underlying mechanisms governing their action against a spectrum of pathogens. Factors impacting the antimicrobial performance of ZnO NPs, including size, surface characteristics, and environmental variables, are extensively analyzed. Moreover, recent studies showcasing the effectiveness of ZnO NPs against diverse pathogens are critically examined, underscoring their potential utility in combatting microbial infections. The study further investigates the UV protective capabilities of ZnO NPs, elucidating the mechanisms by which they offer UV protection and reviewing recent innovations in leveraging them for UV-blocking applications in healthcare. It also dissects the factors influencing the UV shielding performance of ZnO NPs, such as particle size, dispersion quality, and surface coatings. Additionally, the paper addresses challenges associated with integrating ZnO NPs into healthcare products and presents future perspectives for overcoming these hurdles. It emphasizes the imperative for continued research efforts and collaborative initiatives to fully harness the potential of ZnO NPs in developing advanced healthcare solutions with augmented antimicrobial and UV protective attributes. By advancing our understanding and leveraging innovative approaches, ZnO NPs hold promise for addressing pressing healthcare needs and enhancing patient care outcomes.

Sequential Dual Alignments Introduce Synergistic Effect on Hexagonal Boron Nitride Platelets for Superior Thermal Performance

Planarly aligning 2D platelets is challenging due to their additional orientational freedom compared to 1D materials. This study reports a sequential dual-alignment approach, employing an extrusion-printing-induced shear force and rotating-magnetic-field-induced force couple for platelet planarly alignment in a yield-stress support bath. It is hypothesized that the partial alignment induced by a directional shear force facilitates subsequent axial rotation of the platelets for planar alignment under an external force couple, resulting in a synergistic alignment effect. This sequential dual-alignment approach achieves better planar alignment of 2D modified hexagonal boron nitride (mhBN). Specifically, the thermal conductivity of the 40 wt% mhBN/epoxy composite is significantly higher (692%) than that of unaligned composites, surpassing the cumulative effect of individual methods (only 133%) with a 5 times more synergistic effect. For 30, 40, and 50 wt% mhBN composites, the thermal conductivity values (5.9, 9.5, and 13.8 W m-1 K-1) show considerable improvement compared to the previously reported highest values (5.3, 6.6, and 8.6 W m-1 K-1). Additionally, a 3D mhBN/epoxy heat sink is printed and evaluated to demonstrate the feasibility of device fabrication. The approach enables the planar alignment of electrically or thermally conducting 2D fillers during 3D fabrication.

Thermal Conductivity Enhancement of Polymeric Composites Using Hexagonal Boron Nitride: Design Strategies and Challenges

With the integration and miniaturization of chips, there is an increasing demand for improved heat dissipation. However, the low thermal conductivity (TC) of polymers, which are commonly used in chip packaging, has seriously limited the development of chips. To address this limitation, researchers have recently shown considerable interest in incorporating high-TC fillers into polymers to fabricate thermally conductive composites. Hexagonal boron nitride (h-BN) has emerged as a promising filler candidate due to its high-TC and excellent electrical insulation. This review comprehensively outlines the design strategies for using h-BN as a high-TC filler and covers intrinsic TC and morphology effects, functionalization methods, and the construction of three-dimensional (3D) thermal conduction networks. Additionally, it introduces some experimental TC measurement techniques of composites and theoretical computational simulations for composite design. Finally, the review summarizes some effective strategies and possible challenges for the design of h-BN fillers. This review provides researchers in the field of thermally conductive polymeric composites with a comprehensive understanding of thermal conduction and constructive guidance on h-BN design.

Bridging a Gap in Thermal Conductivity and Heat Transfer in Hybrid Fibers and Yarns via Polyimide and Silicon Nitride Composites

The pressing issues of the energy crisis and rapid electronics development have sparked a growing interest in the production of highly thermally conductive polymer composites. Due to the challenges related to the poor processability of hybrid materials and filler distribution to achieve high thermal conductivity, electrospinning is employed to create composite nanofibers and yarns using polyimide (PI) and thermally conductive silicon nitride (SiN) nanoparticles. The thermal performance of the individual nanofibers is evaluated using scanning thermal microscopy (SThM), providing significant insights into their heat transfer performance. Next, the nanofibers are applied as coatings on resistance wires to assess the thermal conductivity and insulation properties. Notably, the samples containing 35 wt.% of SiN exhibit a 25% increase in surface temperature. These innovative materials hold great promise as exceptional candidates for smart textiles and thermal management applications, addressing the growing demand for effective heat dissipation and regulation.

Melt-blown fiber felt for efficient all-weather recovery of viscous oil spills by Joule heating and photothermal effect

Adsorbents play a vital role in responding to marine oil spills, yet effectively cleaning up viscous oil spills remains a technical challenge. Herein, we present a superhydrophobic oil-adsorbing felt prepared using melt-blown technology and functionally enhanced with a photoelectric composite CNT/PANI coating for effectively cleaning up high-viscosity oil spills. By virtue of its superior solar/Joule heating ability and thermally conductive fiber network, p-CNT/PANI@PP notably reduced crude oil viscosity and enhanced the oil diffusion coefficient within pores. Leveraging primarily solar heating and supplemented by Joule heating, p-CNT/PANI@PP demonstrates an impressive in-situ adsorption rate of up to 560 g/h for ultra-high-viscosity crude oil (c.a. 138000 mPa·s), alongside an adsorption capacity of 15.57 g/g. This measure enables efficient viscosity reduction and continuous day-and-night recovery of viscous crude oil, addressing the challenges posed by seasonal fluctuations in seawater temperature and adverse weather conditions. Moreover, a conveyorized collector integrated with an oil-adsorbing felt realizes continuous recovery of viscous oil spills with speed control to tackle varying thicknesses of oil film. Given the top-down material design, superior functionality, and applicability to applications, this work provides a comprehensive and feasible solution to catastrophic large-area viscous oil spills.

Heat transfer mechanism in graphene reinforced PEEK nanocomposites

The thermal conductivity of graphene is in the range of 3000-5000 W m-1 K-1, showing great potential in high thermal conductivity devices. However, the thermal conductivity of graphene-reinforced polymer is typically lower than 10 W m-1 K-1, which is far from theoretical expectations. To understand the mechanisms of heat transfer in graphene-reinforced polymers, this work investigated the effect of graphene addition on the thermal conductive performance of polyetheretherketone (PEEK) matrix. The study examined the number of layers, deflection angles, and interlayer distances using molecular dynamics (MD) simulations. The results showed that the improvement of thermal conductivity of PEEK nanocomposite was not only related to the content of graphene but also to the angle between the benzene ring in the molecular chain of PEEK and the transfer direction of heat flow. Increasing the number of graphene layers is more beneficial to the enhancement of thermal conductivity. In particular, the enhancement of thermal conductivity is most significant when the number of graphene layers is the same, and the interlayer distance is less than the truncation radius.

Improved Through-Plane Thermal Conductivity of Poly(dimethylsiloxane)Composites through the Formation of 3D Filler Foam Using Freeze-Casting and Annealing Processes

The configuration of a continuous and oriented thermal pathway is essential for efficient heat dissipation in the oriented direction. Three-dimensional (3D) conductive filler structures provide a suitable approach for constructing continuous thermal pathways in polymer-based composites. The aluminum nitride/reduced graphene oxide/poly(dimethylsiloxane) (AlN/rGO/PDMS) composite material is made with a 3D foam structure and focuses on reducing GO and forming foam via polyvinyl alcohol (PVA). We analyze the successful fabrication of hybrid fillers and composites using various methods. The fabricated composite with a 3D network filler foam achieves a through-plane thermal conductivity of 1.43 W/mK and achieves 752% higher thermal conductivity compared to pure PDMS, which is superior to composites without 3D foam. The continuous 3D filler structure via freeze-drying and annealing processes provides efficient thermal dissipation in the through-plane direction pathway, which is critical for enhancing thermal conductivity. Therefore, this work produces a polymer composite material with improved thermal conductivity through various processes.

Enhancement of Isotropic Heat Dissipation of Polymer Composites by Using Ternary Filler Systems Consisting of Boron Nitride Nanotubes, h-BN, and Al2O3

In this research article, a poly(dimethylsiloxane) (PDMS)-based composite was postulated adapting an interactive ternary filler system consisting of Al₂O₃, hexagonal boron nitride (h-BN), and boron nitride nanotubes (BNNT) to construct a continuous three-dimensional (3D) structure for thermal attenuation. Al₂O₃ was imposed as a main filler, while h-BN and BNNT were assimilated to form interconnected heat conduction pathways for effective thermal dissipation. The structured framework articulates a profound improvement in isotropic thermal conductivity considering both axial and radial heat dissipation. The presence of h-BN entails uniform heat distribution in a planar mode, eliminating the occurrence of hotspots, while BNNT constructed a connecting phonon pathway in various directions, which insinuates effective overall thermal transport. The generated ternary filler composites attained an isotropic ratio of 1.35 and a thermal conductivity of 7.50 W/mK, which is a 36-fold (∼3650%) increase compared to neat PDMS resin and almost 3-fold (∼297%) that of the Al₂O₃ unary filler composite and ∼53% that of its binary counterpart, partaking interfacial thermal gaps of ∼36.15 and ∼62.24% on practical heating performance relative to its counterparts. Moreover, the incorporation of BNNT on a traditional spherical and planar filler offers an advantage not only in thermal conductivity but also in thermal and structural stability. Improvement in thermal stability is stipulated due to a melting point (T_m) shift of ∼11 °C upon the assimilation of BNNT. Mechanical permeance reinforcement was also observed with the presence of BNNT, showcasing a 31.5% increase in tensile strength and a 53% increase in Young's modulus relative to the singular filler composite. This exploration administers a new insight into heat dissipation phenomena in polymeric composites and proposes a simple approach to their design and assembly.

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.

Vertical Array of Graphite Oxide Liquid Crystal by Microwire Shearing for Highly Thermally Conductive Composites

Excellent through-plane thermally conductive composites are highly demanded for efficient heat dissipation. Giant sheets have large crystalline domain and significantly reduce interface phonon scattering, making them promising to build highly thermally conductive composites. However, realizing vertical orientation of giant sheets remains challenging due to their enormous mass and huge hydrodynamic drag force. Here, we achieve highly vertically ordered liquid crystals of giant graphite oxide (more than 100 µm in lateral dimension) by microwire shearing, which endows the composite with a recorded through-plane thermal conductivity of 94 W m^-1 K^-1 . Microscale shearing fields induced by vertical motion of microwires conquer huge hydrodynamic energy barrier and vertically reorient giant sheets. The resulting liquid crystals exhibit extremely retarded relaxation and impart large-scale vertical array with bidirectional ordering degree as high as 0.82. The graphite array-based composites demonstrate an ultrahigh thermal enhancement efficiency of over 35 times per unit volume. Furthermore, the composites improve cooling efficiency by 93% for thermal management tests compared to commercial thermal interface materials. This work offers a novel methodology to precisely manipulate the orientation of giant particles and promote large-scale fabrication of vertical array with advanced functionalities.

Nanopolyhybrids: Materials, Engineering Designs, and Advances in Thermal Management

The fundamental requirements for thermal comfort along with the unbalanced growth in the energy demand and consumption worldwide have triggered the development and innovation of advanced materials for high thermal-management capabilities. However, continuous development remains a significant challenge in designing thermally robust materials for the efficient thermal management of industrial devices and manufacturing technologies. The notable achievements thus far in nanopolyhybrid design technologies include multiresponsive energy harvesting/conversion (e.g., light, magnetic, and electric), thermoregulation (including microclimate), energy saving in construction, as well as the miniaturization, integration, and intelligentization of electronic systems. These are achieved by integrating nanomaterials and polymers with desired engineering strategies. Herein, fundamental design approaches that consider diverse nanomaterials and the properties of nanopolyhybrids are introduced, and the emerging applications of hybrid composites such as personal and electronic thermal management and advanced medical applications are highlighted. Finally, current challenges and outlook for future trends and prospects are summarized to develop nanopolyhybrid materials.

Significant Improvement of Thermal Conductivity of Polyamide 6/Boron Nitride Composites by Adding a Small Amount of Stearic Acid

This study investigates the effect of adding stearic acid (SA) on the thermal conductivity of polyamide 6 (PA6)/boron nitride (BN) composites. The composites were prepared by melt blending, and the mass ratio of PA6 to BN was fixed at 50:50. The results show that when the SA content is less than 5 phr, some SA is distributed at the interface between BN sheets and PA6, which improves the interface adhesion of the two phases. This improves the force transfer from the matrix to BN sheets, promoting the exfoliation and dispersion of BN sheets. However, when the SA content was greater than 5 phr, SA tends to aggregate and form separate domains rather than being dispersed at the interface between PA6 and BN. Additionally, the well-dispersed BN sheets act as a heterogeneous nucleation agent, significantly improving the crystallinity of the PA6 matrix. The combination of good interface adhesion, excellent orientation, and high crystallinity of the matrix leads to efficient phonon propagation, resulting in a significant improvement in the thermal conductivity of the composite. The highest thermal conductivity of the composite is achieved when the SA content is 5 phr, which is 3.59 W m^-1 K^-1. The utilization of a composite material consisting of 5phr SA as the thermal interface material displays the highest thermal conductivity, and the composite also demonstrates satisfactory mechanical properties. This study proposes a promising strategy for the preparation of composites with high thermal conductivity.

Electrospun polymer nanocomposites for thermal management: a review

Thermal management plays a vital role in technology (electronic and electrical equipment) and life (high-temperature injury). Therefore, thermal regulation has attracted worldwide attention. This review addresses the applications of electrospinning (e-spinning) in the thermal management of polymer matrix composites, mainly involving enhanced thermal conductivity (TC), thermal insulation, and passive daytime radiative cooling (PDRC). In particular, in the regulation of TC, e-spinning can uniformly distribute active fillers in the composites to achieve bidirectional control. The types of active filler and its connection forms in the composites are discussed emphatically. In addition, PDRC without energy consumption is also highlighted. Finally, the current challenges and future development are addressed.

Cross-Linking-Filler Composite Materials of Functionalized Hexagonal Boron Nitride and Polyrotaxane Elastomer

This study demonstrates cross-linking-filler composites in which covalent bonds between the fillers and polymer chains act as the main cross-linking points for the development of flexible and thermally conductive materials. Cross-linking-filler composites are fabricated using functionalized hexagonal boron nitride (hBN) fillers and polyrotaxane, called slide-ring polymers. The hBN particles modified with a carbon layer were produced by plasma processing in hydroquinone aqueous solution and functionalized with isocyanate groups. As the functionalized hBN provides cross-linking points for polyrotaxane, the cross-linking-filler composites can reduce cross-linking agents among polyrotaxane and exhibit considerable flexibility. Young's moduli of the cross-linking-filler composites are much lower than those of previously reported polyrotaxane composites while retaining their toughness. These values are relatively close to those of unfilled polyrotaxane elastomers, despite containing hBN fillers with a content of 50 wt %. Thus, the cross-linking-filler composites exhibit a combination of flexibility and thermal conductivity, which few hBN/elastomer composites have achieved.

Advanced perspectives on MXene composite nanomaterials: Types synthetic methods, thermal energy utilization and 3D-printed techniques

MXene, 2D material, can be synthesized as single flake with 1 nm thickness by using phase change material, polymer and graphene oxide. Meanwhile, the MXene and its composite derivative materials have been applied widely in electro-to-thermal conversion, photo-to-thermal conversion, thermal energy storage, and 3D printing ink aspects. Furthermore, the forward-looking utilization of the MXene nanomaterials in hydrogen energy storage, radio frequency field application, CO₂ capture and remediation of environmental pollution, is explored. This article reveals that the efficiencies of the photo-to-thermal and electro-to-thermal energy conversions with the MXene nanomaterials could reach about 80-90%. In parallel, it is demonstrated that the MXene printed ink has the excellent rheological property and high viscosity and stability of liquid, which contribute to arranging the multi-dimensional architectures with functional materials and controlling the flow rate of the MXene ink in the range of 0.03-0.15 mL/min for speedily printing and various printing structures.

Isotropically Ultrahigh Thermal Conductive Polymer Composites by Assembling Anisotropic Boron Nitride Nanosheets into a Biaxially Oriented Network

The demand for thermally conductive but electrically insulating materials has increased greatly in advanced electronic packaging. To this end, polymer-based composites filled with boron nitride (BN) nanosheets have been intensively studied as thermal interface material (TIM). However, it remains a great challenge to achieve isotropically ultrahigh thermal conductivity in BN/polymer composites due to the inherent thermal property anisotropy of BN nanosheets and/or the insufficient construction of the 3D thermal conductive network. Herein, we present a high-performance BN/polymer composite with a biaxially oriented thermal conductive network by a dendritic ice template. The composite exhibits both ultrahigh in-plane (∼39.0 W m^-1 K^-1) and through-plane thermal conductivity (∼11.5 W m^-1 K^-1) at 80 vol % BN loading, largely exceeding those of reported BN/polymer composites. In addition, our composite as a TIM shows higher cooling efficiency than that of commercial TIM with up to 15 °C reduction of the chip temperature and retains good thermal stability even after 1000 heating/cooling cycles. Our strategy represents an effective approach for developing advanced thermal interface materials, which are greatly demanded for advanced electronics and emerging areas like wearable electronics.

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.

Recent Advances in Thermal Interface Materials for Thermal Management of High-Power Electronics

With the increased level of integration and miniaturization of modern electronics, high-power density electronics require efficient heat dissipation per unit area. To improve the heat dissipation capability of high-power electronic systems, advanced thermal interface materials (TIMs) with high thermal conductivity and low interfacial thermal resistance are urgently needed in the structural design of advanced electronics. Metal-, carbon- and polymer-based TIMs can reach high thermal conductivity and are promising for heat dissipation in high-power electronics. This review article introduces the heat dissipation models, classification, performances and fabrication methods of advanced TIMs, and provides a summary of the recent research status and developing trends of micro- and nanoscale TIMs used for heat dissipation in high-power electronics.

AWI-Assembled TPU-BNNS Composite Films with High In-Plane Thermal Conductivity for Thermal Management of Flexible Electronics

Thermal management of flexible/stretchable electronics has been a crucial issue. Mass supernumerary thermal heat is created in the repetitive course of deformation because of the large nanocontact resistance between electric conductive fillers, as well as the interfacial resistance between fillers and the polymer matrix. Here, we report a stretchable thermoplastic polyurethane (TPU)-boron nitride nanosheet (BNNS) composite film with a high in-plane thermal conductivity based on an air/water interfacial (AWI) assembly method. In addition to rigid devices, it was capable for thermal management of flexible electronics. During more than 2000 cycles of the bending-releasing process, the average saturated surface temperature of the flexible conductor covered with composite film with 30 wt % BNNSs was approximately 40.8 ± 1 °C (10.5 °C lower than that with pure TPU). Moreover, the thermal dissipating property of the composite under stretching was measured. All the results prove that this TPU-BNNS composite film is a candidate for thermal management of next-generation flexible/stretchable electronics with high power density.

Microstructured BN Composites with Internally Designed High Thermal Conductivity Paths for 3D Electronic Packaging

Miniaturized and high-power-density 3D electronic devices pose new challenges on thermal management. Indeed, prompt heat dissipation in electrically insulating packaging is currently limited by the thermal conductivity achieved by thermal interface materials (TIMs) and by their capability to direct the heat toward heat sinks. Here, high thermal conductivity boron nitride (BN)-based composites that are able to conduct heat intentionally toward specific areas by locally orienting magnetically functionalized BN microplatelets are created using magnetically assisted slip casting. The obtained thermal conductivity along the direction of alignment is unusually high, up to 12.1 W m^-1 K^-1 , thanks to the high concentration of 62.6 vol% of BN in the composite, the low concentration in polymeric binder, and the high degree of alignment. The BN composites have a low density of 1.3 g cm^-3 , a high stiffness of 442.3 MPa, and are electrically insulating. Uniquely, the approach is demonstrated with proof-of-concept composites having locally graded orientations of BN microplatelets to direct the heat away from two vertically stacked heat sources. Rationally designing the microstructure of TIMs to direct heat strategically provides a promising solution for efficient thermal management in 3D integrated electronics.

A highly orientational architecture formed by covalently bonded graphene to achieve high through-plane thermal conductivity of polymer composites

Combining the advantages of high thermal conductivities and low graphene contents to fabricate polymer composites for applications in thermal management is still a great challenge due to the high defect degree of exfoliated graphene, the poor orientation of graphene in polymer matrices, and the horrible phonon scattering between graphene/graphene and graphene/polymer interfaces. Herein, mesoplasma chemical vapor deposition (CVD) technology was successfully employed to synthesize vertically aligned graphene nanowalls (GNWs), which are covalently bonded by high-quality CVD graphene nanosheets. The unique architecture leads to an excellent thermal enhancement capacity of the GNWs, and a corresponding composite film with a matrix of polyvinylidene fluoride (PVDF) presented a high through-plane thermal conductivity of 12.8 ± 0.77 W m^-1 K^-1 at a low filler content of 4.0 wt%, resulting in a thermal conductivity enhancement per 1 wt% graphene loading of 1659, which is far superior to that using conventional graphene structures as thermally conductive pathways. In addition, this composite exhibited an excellent capability in cooling a high-power light-emitting diode (LED) device under real application conditions. Our finding provides a new route to prepare high-performance thermal management materials with low filler loadings via the rational design of the microstructures/interfaces of graphene skeletons.

High Conduction Band Inorganic Layers for Distinct Enhancement of Electrical Energy Storage in Polymer Nanocomposites

Dielectric polymer nanocomposites are considered as one of the most promising candidates for high-power-density electrical energy storage applications. Inorganic nanofillers with high insulation property are frequently introduced into fluoropolymer to improve its breakdown strength and energy storage capability. Normally, inorganic nanofillers are thought to introducing traps into polymer matrix to suppress leakage current. However, how these nanofillers effect the leakage current is still unclear. Meanwhile, high dopant (> 5 vol%) is prerequisite for distinctly improved energy storage performance, which severely deteriorates the processing and mechanical property of polymer nanocomposites, hence brings high technical complication and cost. Herein, boron nitride nanosheet (BNNS) layers are utilized for substantially improving the electrical energy storage capability of polyvinylidene fluoride (PVDF) nanocomposite. Results reveal that the high conduction band minimum of BNNS produces energy barrier at the interface of adjacent layers, preventing the electron in PVDF from passing through inorganic layers, leading to suppressed leakage current and superior breakdown strength. Accompanied by improved Young's modulus (from 1.2 GPa of PVDF to 1.6 GPa of nanocomposite), significantly boosted discharged energy density (14.3 J cm-3) and charge-discharge efficiency (75%) are realized in multilayered nanocomposites, which are 340 and 300% of PVDF (4.2 J cm-3, 25%). More importantly, thus remarkably boosted energy storage performance is accomplished by marginal BNNS. This work offers a new paradigm for developing dielectric nanocomposites with advanced energy storage performance.

Performance of Thermal Interface Materials

The thermal interface materials (TIMs) used for improving thermal contacts are considered in terms of the performance, performance consideration criteria, performance evaluation methods, and material development approaches. The performance is described mainly by the thermal contact conductance, which refers to the conductance across the thermal contact surfaces that sandwiches the TIM. This conductance depends on the conformability, thermal conductivity, and small-thickness feasibility. However, the vast majority of published work does not consider this conductance, but only the thermal conductivity within the TIM. The highest TIM performance is exhibited by the thermal pastes and low-melting alloys.

Improving thermal conductivities of textile materials by nanohybrid approaches

The thermal transfer between individual body and the surroundings occurs by several paths such as radiation, evaporation, conduction, and convection. Thermal management is related with the heat transfer between the human body and the surroundings, which aims to keep the body temperature in the comfort range either via preserving or via emitting the body heat. The essential duty of clothing is to contribute to the thermal balance of the human body by regulating the heat and moisture transfer. In the case of poorly controlled body heat, health problems such as hyperthermia and heatstroke along with environmental problems due to higher energy consumption can occur. Recently, research has been focused on advanced textiles with novel approaches on materials synthesis and structure design, which can provide thermal comfort together with energy saving. This review article focuses on the innovative strategies basically on the passive textile models for improved thermal conductivity. We will discuss both the fabrication techniques and the inclusion of carbon-based and boron-based fillers to form nano-hybrid textile solutions, which are used to improve the thermal conductivity of the materials.

High-Performance Thermal Interface Materials with Magnetic Aligned Carbon Fibers

Thermal interface materials with high thermal conductivity and low hardness are crucial to the heat dissipation of high-power electronics. In this study, a high magnetic field was used to align the milled carbon fibers (CFs, 150 μm) in silicone rubber matrix to fabricate thermal interface materials with an ordered and discontinuous structure. The relationship among the magnetic field density, the alignment degree of CFs, and the properties of the resulting composites was explored by experimental study and theoretical analysis. The results showed higher alignment degree and enhanced thermal conductivity of composites under increased magnetic flux density within a certain curing time. When the magnetic flux density increased to 9 T, the CFs showed perfect alignment and the composite showed a high thermal conductivity of 11.76 W/(m·K) with only 20 vol% CF loading, owing to the ordered structure. Meanwhile, due to the low filler loading and discontinuous structure, a low hardness of 60~70 (shore 00) was also realized. Their thermal management performance was further confirmed in a test system, revealing promising applications for magnetic aligned CF–rubber composites in thermal interface materials.

3D Printing of Nacre-Inspired Structures with Exceptional Mechanical and Flame-Retardant Properties

Flame-retardant and thermal management structures have attracted great attention due to the requirement of high-temperature exposure in industrial, aerospace, and thermal power fields, but the development of protective fire-retardant structures with complex shapes to fit arbitrary surfaces is still challenging. Herein, we reported a rotation-blade casting-assisted 3D printing process to fabricate nacre-inspired structures with exceptional mechanical and flame-retardant properties, and the related fundamental mechanisms are studied. 3-(Trimethoxysilyl)propyl methacrylate (TMSPMA) modified boron nitride nanoplatelets (BNs) were aligned by rotation-blade casting during the 3D printing process to build the "brick and mortar" architecture. The 3D printed structures are more lightweight, while having higher fracture toughness than the natural nacre, which is attributed to the crack deflection, aligned BN (a-BNs) bridging, and pull-outs reinforced structures by the covalent bonding between TMSPMA grafted a-BNs and polymer matrix. Thermal conductivity is enhanced by 25.5 times compared with pure polymer and 5.8 times of anisotropy due to the interconnection of a-BNs. 3D printed heat-exchange structures with vertically aligned BNs in complex shapes were demonstrated for efficient thermal control of high-power light-emitting diodes. 3D printed helmet and armor with a-BNs show exceptional mechanical and fire-retardant properties, demonstrating integrated mechanical and thermal protection.

Controlled Vertically Aligned Structures in Polymer Composites: Natural Inspiration, Structural Processing, and Functional Application

Vertically aligned structures, which are a series of characteristic conformations with thickness-direction alignment, interconnection, or assembly of filler in polymeric composite materials that can provide remarkable structural performance and advanced anisotropic functions, have attracted considerable attention in recent years. The past two decades have witnessed extensive development with regard to universal fabrication methods, subtle control of morphological features, improvement of functional properties, and superior applications of vertically aligned structures in various fields. However, a systematic review remains to be attempted. The various configurations of vertical structures inspired from biological samples in nature, such as vertically aligned structures with honeycomb, reed, annual ring, radial, and lamellar configurations are summarized here. Additionally, relevant processing methods, which include the transformation of oriented direction, external-field inducement, template method, and 3D printing method, are discussed in detail. The diverse applications in mechanical, thermal, electric, dielectric, electromagnetic, water treatment, and energy fields are also highlighted by providing representative examples. Finally, future opportunities and prospects are listed to identify current issues and potential research directions. It is expected that perspectives on the vertically aligned structures presented here will contribute to the research on advanced multifunctional composites.

Beyond homogeneous dispersion: oriented conductive fillers for high κ nanocomposites

Rational design of structures for regulating the thermal conductivities (κ) of materials is critical to many components and products employed in electrical, electronic, energy, construction, aerospace, and medical applications. As such, considerable efforts have been devoted to developing polymer composites with tailored conducting filler architectures and thermal conduits for highly improved κ. This paper is dedicated to overviewing recent advances in this area to offer perspectives for the next level of future development. The limitations of conventional particulate-filled composites and the issue of percolation are discussed. In view of different directions of heat dissipation in polymer composites for different end applications, various approaches for designing the micro- and macroscopic structures of thermally conductive networks in the polymer matrix are highlighted. Methodological approaches devised to significantly ameliorate thermal conduction are categorized with respect to the pathways of heat dissipation. Future prospects for the development of thermally conductive polymer composites with modulated thermal conduction pathways are highlighted.

Advances in Studies of Boron Nitride Nanosheets and Nanocomposites for Thermal Transport and Related Applications

Hexagonal boron nitride (h-BN) and exfoliated nanosheets (BNNs) not only resemble their carbon counterparts graphite and graphene nanosheets in structural configurations and many excellent materials characteristics, especially the ultra-high thermal conductivity, but also offer other unique properties such as being electrically insulating and extreme chemical stability and oxidation resistance even at elevated temperatures. In fact, BNNs as a special class of 2-D nanomaterials have been widely pursued for technological applications that are beyond the reach of their carbon counterparts. Highlighted in this article are significant recent advances in the development of more effective and efficient exfoliation techniques for high-quality BNNs, the understanding of their characteristic properties, and the use of BNNs in polymeric nanocomposites for thermally conductive yet electrically insulating materials and systems. Major challenges and opportunities for further advances in the relevant research field are also discussed.

Spider Web-Inspired Graphene Skeleton-Based High Thermal Conductivity Phase Change Nanocomposites for Battery Thermal Management

Phase change materials (PCMs) can be used for efficient thermal energy harvesting, which has great potential for cost-effective thermal management and energy storage. However, the low intrinsic thermal conductivity of polymeric PCMs is a bottleneck for fast and efficient heat harvesting. Simultaneously, it is also a challenge to achieve a high thermal conductivity for phase change nanocomposites at low filler loading. Although constructing a three-dimensional (3D) thermally conductive network within PCMs can address these problems, the anisotropy of the 3D framework usually leads to poor thermal conductivity in the direction perpendicular to the alignment of fillers. Inspired by the interlaced structure of spider webs in nature, this study reports a new strategy for fabricating highly thermally conductive phase change composites (sw-GS/PW) with a 3D spider web (sw)-like structured graphene skeleton (GS) by hydrothermal reaction, radial freeze-casting and vacuum impregnation in paraffin wax (PW). The results show that the sw-GS hardly affected the phase transformation behavior of PW at low loading. Especially, sw-GS/PW exhibits both high cross-plane and in-plane thermal conductivity enhancements of ~ 1260% and ~ 840%, respectively, at an ultra-low filler loading of 2.25 vol.%. The thermal infrared results also demonstrate that sw-GS/PW possessed promising applications in battery thermal management.

Epoxy Composites with High Thermal Conductivity by Constructing Three-Dimensional Carbon Fiber/Carbon/Nickel Networks Using an Electroplating Method

Heat dissipation problem is the primary factor restricting the service life of an electronic component. The thermal conductivity of materials has become a bottleneck that hinders the development of the electronic information industry (such as light-emitting diodes, 5G mobile phones). Therefore, the research on improving the thermal conductivity of materials has a very important theoretical value and a practical application value. Whether the thermally conductive filler in polymer composites can form a highly thermal conductive pathway is a key issue at this stage. The carbon fiber/carbon felt (CF/C felt) prepared in the study has a three-dimensional continuous network structure. The nickel-coated carbon fiber/carbon felt (CF/C/Ni felt) was fabricated by an electroplating deposition method. Three-dimensional CF/C/Ni/epoxy composites were manufactured by vacuum-assisted liquid-phase impregnation. By forming connection points between the adjacent carbon fibers, the thermal conduction path inside the felt can be improved so as to improve the thermal conductivity of the CF/C/Ni/epoxy composite. The thermal conductivity of the CF/C/Ni/epoxy composite (in-plane K∥) is up to 2.13 W/(m K) with 14.0 wt % CF/C and 3.70 wt % Ni particles (60 min electroplating deposition). This paper provides a theoretical basis for the development of high thermal conductivity and high-performance composite materials urgently needed in industrial production and high-tech fields.

Epoxy composite with high thermal conductivity by constructing 3D-oriented carbon fiber and BN network structure

As electronic devices tend to be integrated and high-powered, thermal conductivity is regarded as the crucial parameter of electronic components, which has become the main factor that limits the operating speed and service lifetime of electronic devices. However, constructing continuous thermal conductive paths for low content particle fillers and reducing interface thermal resistance between fillers and matrix are still two challenging issues for the preparation of thermally conductive composites. In this study, 3D-oriented carbon fiber (CF) thermal network structures filled with boron nitride flakes (BN) as thermal conductive bridges were successfully constructed. The epoxy composite was fabricated by thermal conductive material with a 3D oriented structure by the vacuum liquid impregnation method. This special 3D-oriented structure modified by BN (BN/CF) could efficiently broaden the heat conduction pathway and connected adjacent fibers, which leads to the reduction of thermal resistance. The thermal conductivity of the boron nitride/carbon fiber/epoxy resin composite (BN/CF/EP) with 5 vol% 10 mm CF and 40 vol% BN reaches up to 3.1 W m⁻¹ K⁻¹, and its conductivity is only 2.5 × 10⁻⁴ S cm⁻¹. This facile and high-efficient method could provide some useful advice for the thermal management material in the microelectronic field and aerospace industry.

As electronic devices tend to be integrated and high-powered, thermal conductivity is regarded as the crucial parameter of electronic components, which is the main factor that limits the operating speed and service lifetime of electronic devices.

Solar-assisted isotropically thermoconductive sponge for highly viscous crude oil spill remediation

Efficiently cleaning up high-viscosity crude oil spills is still a serious global problem. In this paper, a composite filler PPy-polydopamine/BN (PPB) with high photothermal effect and high thermal conductivity was first prepared. Then the polyurethane sponge is decorated with polydimethylsiloxane and PPB to obtain a solar-assisted isotropically thermoconductive adsorbent (PPB@PU), which exhibits remarkable stability and durable mechanical properties. Meanwhile, the PPB@PU sponge has good thermal conductivity, and its surface temperature rises to 91°C in just 1 min under irradiation (1 sun). Therefore, the PPB@PU sponge can quickly heat and adsorb the crude oil contacted by the surface, significantly speed up the crude oil recovery process, and the adsorption capacity is as high as about 45 g/g. Finally, the oil adsorption method of the three-dimensional adsorbent is demonstrated, which provides a new idea for the subsequent development of advanced oil spill adsorbent.

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PPB@PU sponge exhibits good superhydrophobic/lipophilicity and mechanical stability

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PPB@PU sponge has outstanding photothermal conversion and thermal conductivity

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PPB@PU sponge can efficiently recover heavy oil for large-scale oil spill cleanup