BN Nanosheet/Polymer Films with Highly Anisotropic Thermal Conductivity for Thermal Management Applications

Enhancing Thermal Conductivity in Polymer Composites through Molding-Assisted Orientation of Boron Nitride

Incrementing thermal conductivity in polymer composites through the incorporation of inorganic thermally conductive fillers is typically constrained by the requirement of high filler content. This necessity often complicates processing and adversely affects mechanical properties. This study presents the fabrication of a polystyrene (PS)/boron nitride (BN) composite exhibiting elevated thermal conductivity with a modest 10 wt% BN content, achieved through optimized compression molding. Adjustments to molding parameters, including molding-cycle numbers, temperature, and pressure, were explored. The molding process, conducted above the glass transition temperature of PS, facilitated orientational alignment of BN within the PS matrix predominantly in the in-plane direction. This orientation, achieved at low filler loading, resulted in a threefold enhancement of thermal conductivity following a single molding time. Furthermore, the in-plane alignment of BN within the PS matrix was found to intensify with increased molding time and pressure, markedly boosting the in-plane thermal conductivity of the PS/BN molded composites. Within the range of molding parameters examined, the highest thermal conductivity (1.6 W/m·K) was observed in PS/BN composites subjected to five molding cycles at 140 °C and 10 MPa, without compromising mechanical properties. This study suggests that compression molding, which allows low filler content and straightforward operation, offers a viable approach for the mass production of polymer composites with superior thermal conductivity.

Piezoelectric materials for neuroregeneration: a review

The purpose of nerve regeneration via tissue engineering strategies is to create a microenvironment that mimics natural nerve growth for achieving functional recovery. Biomaterial scaffolds offer a promising option for the clinical treatment of large nerve gaps due to the rapid advancement of materials science and regenerative medicine. The design of biomimetic scaffolds should take into account the inherent properties of the nerve and its growth environment, such as stiffness, topography, adhesion, conductivity, and chemical functionality. Various advanced techniques have been employed to develop suitable scaffolds for nerve repair. Since neuronal cells have electrical activity, the transmission of bioelectrical signals is crucial for the functional recovery of nerves. Therefore, an ideal peripheral nerve scaffold should have electrical activity properties similar to those of natural nerves, in addition to a delicate structure. Piezoelectric materials can convert stress changes into electrical signals that can activate different intracellular signaling pathways critical for cell activity and function, which makes them potentially useful for nerve tissue regeneration. However, a comprehensive review of piezoelectric materials for neuroregeneration is still lacking. Thus, this review systematically summarizes the development of piezoelectric materials and their application in the field of nerve regeneration. First, the electrical signals and natural piezoelectricity phenomenon in various organisms are briefly introduced. Second, the most commonly used piezoelectric materials in neural tissue engineering, including biocompatible piezoelectric polymers, inorganic piezoelectric materials, and natural piezoelectric materials, are classified and discussed. Finally, the challenges and future research directions of piezoelectric materials for application in nerve regeneration are proposed.

A Thermochromic, Viscoelastic Nacre-like Nanocomposite for the Smart Thermal Management of Planar Electronics

Cutting-edge heat spreaders for soft and planar electronics require not only high thermal conductivity and a certain degree of flexibility but also remarkable self-adhesion without thermal interface materials, elasticity, arbitrary elongation along with soft devices, and smart properties involving thermal self-healing, thermochromism and so on. Nacre-like composites with excellent in-plane heat dissipation are ideal as heat spreaders for thin and planar electronics. However, the intrinsically poor viscoelasticity, i.e., adhesion and elasticity, prevents them from simultaneous self-adhesion and arbitrary elongation along with current flexible devices as well as incurring high interfacial thermal impedance. In this paper, we propose a soft thermochromic composite (STC) membrane with a layered structure, considerable stretchability, high in-plane thermal conductivity (~ 30 W m-1 K-1), low thermal contact resistance (~ 12 mm2 K W-1, 4-5 times lower than that of silver paste), strong yet sustainable adhesion forces (~ 4607 J m-2, 2220 J m-2 greater than that of epoxy paste) and self-healing efficiency. As a self-adhesive heat spreader, it implements efficient cooling of various soft electronics with a temperature drop of 20 °C than the polyimide case. In addition to its self-healing function, the chameleon-like behavior of STC facilitates temperature monitoring by the naked eye, hence enabling smart thermal management.

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.

Constructing Gas Transmission Pathways in Two-Dimensional Composite Material ZIF-8@BNNS Mixed-Matrix Membranes to Enhance CO2/N2 Separation Performance

Two-dimensional (2D) nanomaterials, due to their high aspect ratio and high specific surface area, which provide a more tortuous pathway for larger gas molecules, are frequently used in membrane separation. However, in mixed-matrix membranes (MMMs), the high aspect ratio and high specific surface area of 2D fillers can increase transport resistance, thereby reducing the permeability of gas molecules. In this work, we combine boron nitride nanosheets (BNNS) with ZIF-8 nanoparticles to develop a novel material, ZIF-8@BNNS, to improve both CO₂ permeability and CO₂/N₂ selectivity. Growth of ZIF-8 nanoparticles on the BNNS surface is achieved using an in-situ growth method where the amino groups of BNNS are complexed with Zn²⁺, creating gas transmission pathways that accelerate CO₂ transmission. The 2D-BNNS material acts as a barrier in MMMs to improve CO₂/N₂ selectivity. The MMMs with a 20 wt.% ZIF-8@BNNS loading achieved a CO₂ permeability of 106.5 Barrer and CO₂/N₂ selectivity of 83.2, surpassing the Robeson upper bound (2008) and demonstrating that MOF layers can efficiently reduce mass transfer resistance and enhance gas separation performance.

Recent Advances in Limiting Fatigue Damage Accumulation Induced by Self-Heating in Polymer-Matrix Composites

The self-heating effect can be considered as a catastrophic phenomenon that occurs in polymers and polymer-matrix composites (PMCs) subjected to fatigue loading or vibrations. This phenomenon appears in the form of temperature growth in such structures due to their relatively low thermal conductivities. The appearance of thermal stress resulting from temperature growth and the coefficient of thermal expansion (CTE) mismatch between fibers and neighboring polymer matrix initiates and/or accelerates structural degradation and consequently provokes sudden fatigue failure in the structures. Therefore, it is of primary significance for a number of practical applications to first characterize the degradation mechanism at the nano-, micro- and macroscales caused by the self-heating phenomenon and then minimize it through the implementation of numerous approaches. One viable solution is to cool the surfaces of considered structures using various cooling scenarios, such as environmental and operational factors, linked with convection, contributing to enhancing heat removal through convection. Furthermore, if materials are appropriately selected regarding their thermomechanical properties involving thermal conductivity, structural degradation may be prevented or at least minimized. This article presents a benchmarking survey of the conducted research studies associated with the fatigue performance of cyclically loaded PMC structures and an analysis of possible solutions to avoid structural degradation caused by the self-heating effect.

Anisotropic PDMS/Alumina/Carbon Fiber Composites with a High Thermal Conductivity and an Electromagnetic Interference Shielding Performance

The development of polymer-based composites with a high thermal conductivity and electromagnetic interference (EMI) shielding performance is crucial to the application of polymer-based composites in electronic equipment. Herein, a novel strategy combining ice-templated assembly and stress-induced orientation was proposed to prepare polydimethylsiloxane (PDMS)/alumina/carbon fiber (CF) composites. CF in the composites exhibited a highly oriented structure in the horizontal direction. Alumina was connected to the CF, promoting the formation of thermal conductive pathways in both the horizontal and vertical directions. As the CF content was 27.5 vol% and the alumina content was 14.0 vol%, the PDMS/alumina/CF composite had high thermal conductivities in the horizontal and vertical directions, which were 8.44 and 2.34 W/(m·K), respectively. The thermal conductivity in the horizontal direction was 40.2 times higher than that of PDMS and 5.0 times higher than that of the composite with a randomly distributed filler. The significant enhancement of the thermal conductivity was attributed to the oriented structure of the CF and the bridging effect of alumina. The PDMS/alumina/CF composite exhibited an excellent EMI shielding effectiveness of 40.8 dB which was 2.4 times higher than that of the composite with a randomly distributed filler. The PDMS/alumina/CF composite also exhibited a low reflectivity of the electromagnetic waves. This work could provide a guide for the research of polymer-based composites with a high thermal conductivity and an EMI shielding performance.

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.

Emerging Flexible Thermally Conductive Films: Mechanism, Fabrication, Application

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

Recent advances in thermally conductive polymer composites

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

Vertically Aligned Silicon Carbide Nanowires/Boron Nitride Cellulose Aerogel Networks Enhanced Thermal Conductivity and Electromagnetic Absorbing of Epoxy Composites

With the innovation of microelectronics technology, the heat dissipation problem inside the device will face a severe test. In this work, cellulose aerogel (CA) with highly enhanced thermal conductivity (TC) in vertical planes was successfully obtained by constructing a vertically aligned silicon carbide nanowires (SiC NWs)/boron nitride (BN) network via the ice template-assisted strategy. The unique network structure of SiC NWs connected to BN ensures that the TC of the composite in the vertical direction reaches 2.21 W m^-1 K^-1 at a low hybrid filler loading of 16.69 wt%, which was increased by 890% compared to pure epoxy (EP). In addition, relying on unique porous network structure of CA, EP-based composite also showed higher TC than other comparative samples in the horizontal direction. Meanwhile, the composite exhibits good electrically insulating with a volume electrical resistivity about 2.35 × 10¹¹ Ω cm and displays excellent electromagnetic wave absorption performance with a minimum reflection loss of - 21.5 dB and a wide effective absorption bandwidth (< - 10 dB) from 8.8 to 11.6 GHz. Therefore, this work provides a new strategy for manufacturing polymer-based composites with excellent multifunctional performances in microelectronic packaging applications.

Effect of Impregnated Phenolic Resins on the Cellulose Membrane for Polymeric Insulator

In this study, a cellulose membrane (CM) was chemically treated with phenolic (PF) resin to improve its performance as a polymeric insulator. The CM was prepared from kenaf pulp, and the PF was synthesized from oil palm empty fruit (EFB) fibre. Four different concentrations of synthesized PF resin (5, 10, 15, and 20 wt.%) were impregnated under wet or dry conditions. Thermal analysis of the phenolic cellulose membrane (PCM) showed that the samples had good chemical interaction and compatibility. The PF uptake in the wet phenolic cellulose membrane (PCMW) was higher than in the dry phenolic cellulose membrane (PCMD). During the PF uptake, the CM underwent solvent exchange and absorption in wet and dry membranes, respectively. This difference also affected the crosslinking of PCM samples via the formation of methylene bridges. Due to the PF treatment, the PCM showed lower water absorption than CM. The PF concentrations also affect the surface roughness and electrical properties of PCM samples. These findings prove that PCM can be used as a renewable and green polymer electrical insulator.

A Novel Method to Prepare Transparent, Flexible and Thermally Conductive Polyethylene/Boron Nitride Films

The high thermal conductivity and good insulating properties of boron nitride (BN) make it a promising filler for high-performance polymer-based thermal management materials. An easy way to prepare BN-polymer composites is to directly mix BN particles with polymer matrix. However, a high concentration of fillers usually leads to a huge reduction of mechanical strength and optical transmission. Here, we propose a novel method to prepare polyethylene/boron nitride nanoplates (PE/BNNPs) composites through the combination of electrostatic self-assembly and hot pressing. Through this method, the thermal conductivity of the PE/BNNPs composites reach 0.47 W/mK, which gets a 14.6% improvement compared to pure polyethylene film. Thanks to the tight bonding of polyethylene with BNNPs, the tensile strength of the composite film reaches 1.82 MPa, an increase of 173.58% compared to that of pure polyethylene film (0.66 MPa). The fracture stress was also highly enhanced, with an increase of 148.44% compared to pure polyethylene film. Moreover, the addition of BNNPs in PE does not highly reduce its good transmittance, which is preferred for thermal management in devices like light-emitting diodes. This work gives an insight into the preparation strategy of transparent and flexible thermal management materials with high thermal conductivity.

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.

Flame-retardant MXene/polyimide film with outstanding thermal and mechanical properties based on the secondary orientation strategy

With the development of multifunction and miniaturization in modern electronics, polymeric films with strong mechanical performance and high thermal conductivity are urgently needed. Two-dimensional transition metal carbides and nitrides (MXenes) have attracted extensive attention due to their tunable surface chemistry, layered structure and charming properties. However, there are few studies on using MXenes as fillers to enhance polymer properties. In this paper, we fabricate a three-dimensional foam by the freeze-drying method to enhance the interfacial interaction between adjacent MXene sheets and polyimide (PI) macromolecules, and then a composite film with a dense and well-ordered layer-by-layer structure is produced by the hot-pressing process. Based on the secondary orientation strategy, the resultant MXene/PI film exhibits an enhanced thermal conductivity of 5.12 ± 0.37 W m^-1 K^-1 and tensile strength of 102 ± 3 MPa. Moreover, the composite film has good flexibility and flame retardancy owing to the synergistic effect of MXene sheets and PI chains. Hence, the MXene/PI composite film with the properties of flexibility, flame-retardancy, high mechanical strength and efficient heat transmission is expected to be used as the next thermal management material in a variety of applications.

Fanless, porous graphene-copper composite heat sink for micro devices

Thermal management in devices directly affects their performance, but it is difficult to apply conventional cooling methods such as the use of cooling liquids or fans to micro devices owing to the small size of micro devices. In this study, we attempted to solve this problem by employing a heat sink fabricated using copper with porous structures consisting of single-layer graphene on the surface and graphene oxide inside the pores. The porous copper/single-layer graphene/graphene oxide composite (p-Cu/G/rGO) had a porosity of approximately 35%, and the measured pore size was approximately 10 to 100 µm. The internal GO was reduced at a temperature of 1000 °C. On observing the heat distribution in the structure using a thermal imaging camera, we could observe that the p-Cu/G/rGO was conducting heat faster than the p-Cu, which was consistent with the simulation. Furthermore, the thermal resistance of p-Cu/G/rGO was lower than those of the p-Cu and pure Cu. When the p-Cu/G/rGO was fabricated into a heat sink to mount the light emitting diode (LED) chip, the measured temperature of the LED was 31.04 °C, which was less than the temperature of the pure Cu of 40.8 °C. After a week of being subjected to high power (1000 mA), the light intensity of p-Cu/G/rGO decreased to 95.24%. However, the pure Cu decreased significantly to 66.04%. The results of this study are expected to be applied to micro devices for their effective thermal management.

Recent Advances in Design and Preparation of Polymer-Based Thermal Management Material

The boosting of consumer electronics and 5G technology cause the continuous increment of the power density of electronic devices and lead to inevitable overheating problems, which reduces the operation efficiency and shortens the service life of electronic devices. Therefore, it is the primary task and a prerequisite to explore innovative material for meeting the requirement of high heat dissipation performance. In comparison with traditional thermal management material (e.g., ceramics and metals), the polymer-based thermal management material exhibit excellent mechanical, electrical insulation, chemical resistance and processing properties, and therefore is considered to be the most promising candidate to solve the heat dissipation problem. In this review, we summarized the recent advances of two typical polymer-based thermal management material including thermal-conduction thermal management material and thermal-storage thermal management material. Furtherly, the structural design, processing strategies and typical applications for two polymer-based thermal management materials were discussed. Finally, we proposed the challenges and prospects of the polymer-based thermal management material. This work presents new perspectives to develop advanced processing approaches and construction high-performance polymer-based thermal management material.

Anisotropic heat transfer properties of two-dimensional materials

The anisotropic heat transfer properties of two-dimensional materials play an important role in controlled heat transfer and intelligent heat management. At present, there are many references on anisotropic heat transfer of two-dimensional materials, but less systematic review of their development status, problems, and future directions. In this paper, intrinsic anisotropic heat transfer of two-dimensional materials, influencing factors and control means are introduced. The preparation methods of thin film with two-dimensional material and the influence factors of macroscopic anisotropic thermal properties are summarized. The technology of two-dimensional material oriented arrangement in matrix and the influence factors of macroscopic anisotropic thermal properties of the composite are outlined.

Highly Multifunctional and Thermoconductive Performances of Densely Filled Boron Nitride Nanosheets/Epoxy Resin Bulk Composites

In the development of hexagonal boron nitride (h-BN)-based polymeric composites with high thermal conductivity, it is always challenging to achieve a dense filling of h-BN fillers to form a desired high-density thermal transfer network. Here, a series of boron nitride nanosheets (BNNSs)/epoxy resin (EP) bulk composites filled with ultrahigh BNNSs content (65-95 wt %) is successfully constructed through a well-designed mechanical-balling prereaction combined with a general pressure molding method. By means of this method, the highly filled BNNSs fillers are uniformly dispersed and strongly bonded with EP within the composites. As a result, the densely BNNSs-filled composites can exhibit multiple performances. They have excellent mechanical properties, and their maximum compression strength is 30-97 MPa. For a BNNSs/EP composite with filling ultrahigh BNNSs fraction up to 90 wt %, its highly in-plane thermal conductivities (TC) are 6.7 ± 0.1 W m^-1 K^-1 (at 25 °C) to 8.7 ± 0.2 W m^-1 K^-1 (200 °C), respectively. In addition, the minimum coefficient of thermal expansion of BNNSs/EP composites is 4.5 ± 1.3 ppm/°C (only ∼4% of that of the neat EP), while their dielectric constants are basically located between 3-4 along with their dielectric loss tangent values exceptionally <0.3 in the ultrahigh frequency range of 12-40 GHz. Additionally, these BNNSs/EP composites exhibit remarkable cycle stability in heat transfer during heating and cooling processes because of their structural robustness. Thus, this type of densely BNNSs-filled BNNSs/EP composite would have great potential for further practical thermal management fields.

Nanoporous Boron Nitride Aerogel Film and Its Smart Composite with Phase Change Materials

With the advent of the 5G era, electronic systems have become more and more powerful, miniaturized, integrated ,and intelligent. The thermal management of electronic systems requires more efficiency and multiple functions for their practical applications, especially for the portable 5G electronic devices of the future, as the undesired heat can cause thermal discomfort or even thermal injury to people who use these electronic devices. Herein, two thermal management strategies based on boron nitride (BN) aerogel films have been proposed and demonstrated for portable devices. First, a flexible BN aerogel film with high porosity (>96%), large specific surface area (up to 982 m² g^-1), and controllable thickness (in the range from 50 to 200 μm) was fabricated via molecular precursor assembly, sublimation drying, and pyrolysis reaction in sequence. The resulting BN aerogel film individuals, serving as a thermal insulation protecting layer in portable electronics, can significantly reduce heat transfer from electronics to skin. Second, BN phase change composite films, made by dipping BN aerogel films into the melts of the organic phase change materials (e.g., paraffin), can effectively cool the portable electronics as the organic phase change materials filled in the aerogel matrix can serve as a smart thermal-regulator to absorb the undesired heat via solid-liquid phase transition. These two typical strategies of the flexible BN aerogel film-directed thermal management could assist in efforts to miniaturize, integrate, and intelligentialize portable 5G electronic devices in the future.

Microfluidic Synthesis of Hybrid TiO2-Anisotropic Gold Nanoparticles with Visible and Near-Infrared Activity

Anisotropic gold nanoparticles (AuNPs), with their unique physical and optical properties, are emerging as smart and key nanomaterials and are being exploited in many crucial fields. To further improve their range of action, anisotropic AuNPs have been coupled with semiconductors, mainly TiO₂ (titania), receiving great interest as powerful platforms both in biomedicine and in catalytic applications. Such hybrid nanoparticles show new properties that arise from the synergic action of the components and rely on NP size, morphology, and arrangement. Therefore, continuous advances in design and fabrication of new hybrid titania@gold NPs (TiO₂@AuNPs) are urgent and highly desirable. Here, we propose an effective protocol to produce multibranched AuNPs covered by a controlled TiO₂ thin layer, exploiting a one-pot microfluidic process. The proposed method allows the in-flow and reliable synthesis of titania-functionalized-anisotropic gold nanoparticles by avoiding the use of toxic surfactants and controlling the titania shell formation. TiO₂@AuNPs have been fully characterized in terms of morphology, stability, and biocompatibility, and their activity in photocatalysis has been tested and verified.

Thermoconductive, Moisture-Permeable, and Superhydrophobic Nanofibrous Membranes with Interpenetrated Boron Nitride Network for Personal Cooling Fabrics

Space cooling occupies a large portion of total building energy consumption, aggravating the energy crisis and restricting human sustainable development, thus an efficient and energy-saving personal cooling technology is in high demand. Recently, thermally conductive fillers, such as boron nitride (BN), are usually enriched to fibrous materials to construct thermal management textiles. However, these fabrication processes are complex and time-consuming, and the resultant materials fail to transmit moisture and resist liquid water. Herein, we develop a facile and scalable methodology to construct highly thermoconductive breathable superhydrophobic nanofibrous membranes to enhance the thermal management of textiles for personal cooling. The strategy causes boron nitride (BN) to be linked with each other along nanofibers, and thus the membranes contain well interpenetrated BN network and remain porous structure simultaneously, improving their thermal conductivity without sacrificing the moisture permeability. In addition, the membranes possess good resistance to water penetration and intriguing superhydrophobicity due to the synergistic effect of the hydrophobic polymeric matrix and improved roughness. As a consequence, the resultant membranes demonstrate outstanding hybrid active-passive cooling performance with ultrahigh in-plane thermal conductivity of 17.9 W m^-1 K^-1, cross-plane thermal conductivity of 0.29 W m^-1 K^-1, and high water vapor transmission (WVT) rate of 11.6 kg m^-2 day^-1, as well as excellent water repellency with water contact angle of 153° and high hydrostatic pressure of 32 kPa, indicating promising utility for the next generation of cooling fabrics.

Highly Flexible Graphene Derivative Hybrid Film: An Outstanding Nonflammable Thermally Conductive yet Electrically Insulating Material for Efficient Thermal Management

In modern society, advanced technology has facilitated the emergence of multifunctional appliances, particularly, portable electronic devices, which have been growing rapidly. Therefore, flexible thermally conductive materials with the combination of properties like outstanding thermal conductivity, excellent electrical insulation, mechanical flexibility, and strong flame retardancy, which could be used to efficiently dissipate heat generated from electronic components, are the demand of the day. In this study, graphite fluoride, a derivative of graphene, was exfoliated into graphene fluoride sheets (GFS) via the ball-milling process. Then, a suspension of graphene oxide (GO) and GFSs was vacuum-filtrated to obtain a mixed mass, and subsequently, the mixed mass was subjected to reduction under the action hydrogen iodide at low temperature to transform the GO to reduced graphene oxide (rGO). Finally, a highly flexible and thermally conductive 30-μm thick GFS@rGO hybrid film was prepared, which showed an exceptional in-plane thermal conductivity (212 W·m^-1·K^-1) and an excellent electrical insulating property (a volume resistivity of 1.1 × 10¹¹ Ω·cm). The extraordinary in-plane thermal conductivity of the GFS@rGO hybrid films was attributed to the high intrinsic thermal conductivity of the filler components and the highly ordered filler alignment. Additionally, the GFS@rGO films showed a tolerance to bending cycles and high-temperature flame. The tensile strength and Young's modulus of the GFS@rGO films increased with increasing the rGO content and reached a tensile strength of 69.3 MPa and a Young's modulus of 10.2 GPa at 20 wt % rGO. An experiment of exposing the films to high-temperature flame demonstrated that the GFS@rGO films could efficiently prevent fire spreading. The microcombustion calorimetry results indicated that the GFS@rGO had significantly lower heat release rate (HRR) compared to the GO film. The peak HRR of GFS@rGO10 was only 21 W·g^-1 at 323 °C, while that of GO was 198 W·g^-1 at 159 °C.

Electrospun Silk-Boron Nitride Nanofibers with Tunable Structure and Properties

In this study, hexagonal boron nitride (h-BN) nanosheets and Bombyx mori silk fibroin (SF) proteins were combined and electrospun into BNSF nanofibers with different ratios. It was found that the surface morphology and crosslinking density of the nanofibers can be tuned through the mixing ratios. Fourier transform infrared spectroscopy study showed that pure SF electrospun fibers were dominated by random coils and they gradually became α-helical structures with increasing h-BN nanosheet content, which indicates that the structure of the nanofiber material is tunable. Thermal stability of electrospun BNSF nanofibers were largely improved by the good thermal stability of BN, and the strong interactions between BN and SF molecules were revealed by temperature modulated differential scanning calorimetry (TMDSC). With the addition of BN, the boundary water content also decreased, which may be due to the high hydrophobicity of BN. These results indicate that silk-based BN composite nanofibers can be potentially used in biomedical fields or green environmental research.

Novel Functionalized BN Nanosheets/Epoxy Composites with Advanced Thermal Conductivity and Mechanical Properties

The effective dissipation of heat is critical to the performance and longevity of high-power electronics, so it is important to prepare highly thermally conductive polymer-based packaging materials for efficient thermal management. Due to the excellent thermal conductivity of boron nitride nanosheets (BNNSs), the hexagonal boron nitride (hBN) powder was dissolved in a mixed solution of isopropanol and deionized water for ultrasonic exfoliation to obtain hydroxylated BN nanosheets. Then, the prepared BNNS was functionalized with (3-aminopropyl)triethoxysilane (APTES) to enhance its dispersibility and interfacial compatibility in the epoxy resin, which play an important role in the improvement of the thermal conductivity of the composites. Finally, APTES-BNNS was uniformly dispersed in the epoxy resin by solvent mixing, and the oriented APTES-BNNS/epoxy composites were prepared through spin-coating and hot-pressing methods. It was found that APTES-BNNS/epoxy composites prepared herein exhibited significant anisotropic thermal conductivity. The results show that the thermal conductivity of APTES-BNNS/epoxy composites reached 5.86 W/mK at a filler content of 40 wt % and these composites have favorable thermal stability and mechanical properties. The APTES-BNNS/epoxy composite prepared in this paper has excellent thermal management capability and can be applied to the packaging of high-power electronic devices.

Electrostatically assembled carbon dots/boron nitride nanosheet hybrid nanostructures for thermal quenching-resistant white phosphors

Carbon dots (C-dots) are promising and widely applied carbon fluorescent materials for next-generation white light-emitting diodes (WLEDs). However, nonnegligible thermal quenching issues induced by high working temperature of high-power WLEDs severely limit the further development of C-dot phosphors. In this paper, we report an efficient strategy to improve thermal dissipation within C-dot phosphors to solve the thermal quenching problem. C-dots/hexagonal boron nitride nanosheet (BNNS) hybrid nanostructures have been firstly prepared through an electrostatic assembly method. Owing to the effective heat transfer channels established by C-dots/BNNS in a polymer matrix, heat could be dissipated efficiently and the working temperature of WLEDs is reduced by 29 °C, suggesting excellent thermal quenching-resistance properties. Particularly, the hybrids show thermally stable emission without obvious emission loss up to 100 °C. Moreover, the C-dots/BNNS-WLEDs still maintain a high color rendering index of Ra > 89, revealing that the present strategy could promote the exploration of carbon phosphors with thermal quenching resistance for high-quality LED applications.

Increasing heat transfer performance of thermoplastic polyurethane by constructing thermal conduction channels of ultra-thin boron nitride nanosheets and carbon nanotubes

The TPU-based thermally conductive composite reaches a thermal conductivity of 1.35 W m⁻¹ K⁻¹ and increases the tensile strength by at least 300%.

Fabricated Electrochemical Sensory Platform Based on the Boron Nitride Ternary Nanocomposite Film Electrode for Paraquat Detection

Hexagonal boron nitride (BN), an effective diffusion material for mass transport, was functionalized with molybdenum disulfide (MoS₂) and Au nanoparticles (Au NPs). Then, the working electrodes with developed nanomaterials were applied to construct an electrochemical paraquat sensor. BN was prepared using a solid-state synthesis method combined with solvent-cutting. The electrochemical properties of the BN/MoS₂/Au NP-based glassy carbon electrode (GCE) were investigated using differential pulse voltammetry and cyclic voltammetry. An excellent response signal to paraquat was found from 0.1 to 100 μM with a limit of detection of 0.074 μM, and it had acceptable reproducibility (relative standard deviation = 2.99%, n = 5) and good anti-interference ability. The modified GCE showed superior performance owing to the synergistic effects among all three given nanomaterials. With the proposed method, paraquat in grass samples from an orchard was then investigated. The results of the electrochemical analysis agreed with those of experiments and obtained a 96.28% confidence level via high-performance liquid chromatography, exhibiting relatively high stability. Therefore, the fabricated sensor can be a candidate for the determination of paraquat.

Synthesis of Sandwich-Like Nanostructure Fillers and Their Use in Different Types of Thermal Composites

Thermally conductive yet electrically insulating two-dimensional boron nitride nanosheets (BNNSs) have been an ideal choice for the enhanced fillers for improving thermal properties of polymer-based composites. As a nanofiller with an ultrahigh aspect ratio, BNNSs result in conspicuous stacking along the planar direction in the preparation of composites, which results in strong anisotropy of heat transfer and suppresses out-plane thermal dissipation. Thus, it is necessary to facilitate the out-plane heat transfer by building a favorable microstructure. Focusing on the structural design of the nanofiller itself here, we have fabricated a novel three-dimensional nanofiller with improved out-plane connections. Carbon nanotubes (CNTs) have been grown in situ on the surface of BNNSs using chemical vapor deposition. Utilizing these sandwich-like nanostructure BNNSs/CNTs as fillers in the composites, we have assembled diverse sorts of composites, such as flexible films, scleroid 3D mats, painted ink, and viscous grease. Simultaneously, their thermal and insulating properties have been evaluated. A nearly 330% enhancement of out-plane thermal conductivity from the control sample filled with pristine BNNS is achieved, and the composite also exhibits good electrical resistivity of above 7.5 × 10¹⁰ Ω mm. The results indicate that the BNNS/CNT filler has superior thermal performance over the original BNNS while maintaining a satisfactory electrical resistivity to avoid short-circuits in high-power electronics. Furthermore, the prepared grease used as a thermal interface material shows impressive heat dissipation performance when applied on a running computer.

Lightweight, Superelastic Yet Thermoconductive Boron Nitride Nanocomposite Aerogel for Thermal Energy Regulation

Conventional three-dimensional (3D) thermal conductors or heat sinks are normally bulky solids with high density, which is cumbersome and not portable to satisfy current demands for soft and flexible electronic devices. To address this issue, here, a lightweight, superelastic yet thermally conductive boron nitride (BN) nanocomposite aerogel is designed by a facile freeze-drying method. The attained aerogel constituting of tailored interconnected binary inorganic-organic network structure exhibits low bulk density (6.5 mg cm^-3) and outstanding mechanical performances for compression, clotting, and stretching. Meanwhile, the aerogel has promising thermal stability and high thermal conductivity over wide temperature ranges (30-300 °C), validating the application even in extremely hot environments. Moreover, the aerogel can serve as a lightweight and elastic heat conductor for the enhancement of thermal energy harvest. Interestingly, during alternate strain loading/unloading under heating, the superelasticity and the anisotropy of thermal conductive transduction make the aerogel enable the elastic thermal energy capture and dynamic regulation. Therefore, our findings provide a potential use for the thermally conductive aerogel in future green energy applications.

Aerogel Perfusion-Prepared h-BN/CNF Composite Film with Multiple Thermally Conductive Pathways and High Thermal Conductivity

Hexagonal boron nitride (h-BN)-based heat-spreading materials have drawn considerable attention in electronic diaphragm and packaging fields because of their high thermal conductivity and desired electrical insulation properties. However, the traditional approach to fabricate thermally conductive composites usually suffers from low thermal conductivity, and cannot meet the requirement of thermal management. In this work, novel h-BN/cellulose-nano fiber (CNF) composite films with excellent thermal conductivity in through plane and electrical insulation properties are fabricated via an innovative process, i.e., the perfusion of h-BN into porous three dimensional (3D) CNF aerogel skeleton to form the h-BN thermally conductive pathways by filling the CNF aerogel voids. When at an h-BN loading of 9.51 vol %, the thermal conductivity of h-BN/CNF aerogel perfusion composite film is 1.488 W·m⁻¹·K⁻¹ at through plane, an increase by 260.3%. The volume resistivity is 3.83 × 10¹⁴ Ω·cm, superior to that of synthetic polymer materials (about 10⁹~10¹³ Ω·cm). Therefore, the resulting h-BN/CNF film is very promising to replace the traditional synthetic polymer materials for a broad spectrum of applications, including the field of electronics.

Highly Thermally Conductive Fluorinated Graphene Films with Superior Electrical Insulation and Mechanical Flexibility

Graphene-based heat-spreading films have captured high attention in academic study and commercial applications because of their extremely high thermal conductivity and desired flexibility. However, the electrical conductivity limits their utilizations in many electronic fields. Herein, to address this problem, fluorinated graphene (F-graphene) that is exfoliated from commercial fluorinated graphite was first used to prepare the flexible free-standing composite film via vacuum filtration of uniform poly(vinyl alcohol)-assisted F-graphene suspension. The well-organized alignment of F-graphene lamellas makes the composite film show an ultrahigh in-plane thermal conductivity of 61.3 W m^-1 K^-1 at 93 wt % F-graphene. Despite at such high filler loading, the fabricated F-graphene film still possesses a superior electrical insulation property. Therefore, these results suggest that F-graphene, as the novel thermally conductive filler, demonstrates fascinating characters in the preparation of a thermally conductive yet electrically insulating nanocomposite.

Dual stimuli-responsive supramolecular boron nitride with tunable physical properties for controlled drug delivery

The new concept of modifying and tailoring the properties of existing two-dimensional (2D) nanomaterials by invoking the assembly of supramolecular networks upon association with a adenine-functionalized macromer (A-PPG) has significant potential to facilitate the development of highly water-dispersible few-layered 2D nanosheets. In this study, we propose that water-soluble A-PPG directly self-assembles into a long-period stacking-ordered lamellar structure over the surface of hexagonal boron nitride (BN) in aqueous solution, due to the efficient non-covalent interactions between A-PPG and BN nanosheets. The layer number of BN nanosheets can be easily tuned by altering the mass ratio of the A-PPG and BN blend, and the resulting exfoliated nanosheets also exhibit excellent temperature/pH-responsive behavior, biocompatibility and extremely high drug-loading capacity (up to 36.2%), features that are highly desirable yet exceedingly rare in traditional 2D nanomaterials. Importantly, in vitro drug release studies showed the drug-loaded nanosheets function as a stable nanocarrier with excellent stability and drug entrapment under normal physiological conditions. Increasing the environmental temperature to 40 °C or decreasing the pH to 5.5 triggered rapid release of the encapsulated drug from the drug-loaded nanosheets, suggesting this newly developed material has potential as a novel multi-responsive 2D nanocarrier to safely deliver drugs and effectively facilitate controlled drug release under specific microenvironmental conditions. This study provides new insight towards the promising application of this system in controlled release drug delivery systems.

Multifunctional Thermal Management Materials with Excellent Heat Dissipation and Generation Capability for Future Electronics

Thermal management materials (TMMs) used in electronic devices are crucial for future electronics and technologies such as flexible electronics and artificial intelligence (AI) technologies. As future electronics will work in a more complicated circumstance, the overheating and overcooling problems can exist in the same electronics while the common TMMs cannot meet the demand of thermal management for future electronics. In this work, nacre-mimetic graphene-based films with super flexibility and durability (in over 10,000 tensile cycles), excellent capability to dissipate excess heat (20.84 W/(m·K) at only 16-22 μm thickness), and outstanding heating performance to generate urgent heat for electronics under extremely cold conditions are fabricated by a facile solution casting method, and the fabricated composites are proved to be superior multifunctional TMMs for the thermal management in electronic chips. In addition, the application of the paper-like films with high in-plane thermal conductivity to a flexible heat spreader and film heater is demonstrated by simulation using a finite volume method, which shows the high importance of the in-plane thermal conductivity in thermal management of electronics.

Self-healable poly(acrylic acid-co-maleic acid)/glycerol/boron nitride nanosheet composite hydrogels at low temperature with enhanced mechanical properties and water retention

Many living tissues possess excellent mechanical properties and water retention which enable them to self-heal at room temperature even below the freezing temperature of water. To mimic the unique features of living tissue, a poly(acrylic acid-co-maleic acid) composite hydrogel with enhanced mechanical properties and remarkable water retention was fabricated under accessible conditions. The hydrogel is functionalized by amino group modified boron nitride nanosheets (BNNS-NH2)/glycerol and exhibits self-healing abilities at low temperature. The self-healing process occurs through the re-establishing of hydrogen bonds and metal coordination interactions at the damaged surfaces. Its anti-freezing abilities enable the hydrogel to self-heal at -15 °C, and the self-healing efficiency based on tensile strength reaches up to ∼70%. Moreover, glycerol also endows the hydrogel with long-lasting water retention, which remains a water content of ∼99 wt% for more than 30 days. Meanwhile, the simultaneous introduction of BNNS-NH2 and glycerol significantly improved the mechanical properties of the hydrogel, which displays great stretchability (∼474%), tensile strength (∼151.3 kPa), stiffness (Young's modulus of ∼62.75 kPa) and toughness (∼355.13 kJ m-3). It is anticipated that these novel hydrogels will develop many fields and be exploited for new applications in extensive external environments.