Cotton Candy-Templated Fabrication of Three-Dimensional Ceramic Pathway within Polymer Composite for Enhanced Thermal Conductivity

Protruding Boron Nitride Nanotubes on the Al2O3 Surface Enabled by Tannic Acid-Assisted Modification to Fabricate a Thermal Conductive Epoxy/Al2O3 Composite

Over the past few years, the ability to efficiently increase boron nitride nanotube (BNNT) production has opened up ample research possibilities. BNNT has garnered significant attention for diversifying its industrial applications. However, the problem of poor processability resulting from agglomeration and uneven distribution has emerged as a major challenge to integrating BNNT into the polymer matrix for composite material formation. Utilizing noncovalently attached molecules with various reactive sites can be a logical method to enhance the compatibility of BNNT with different polymers. The present study explored a simple approach to protruding BNNT onto the surface of Al2O3 through tannic acid (TA)-assisted generation of alkyl chains (octadecylamine, ODA) to fabricate Al2O3@ODA-BNNT. The subsequent compounding of Al2O3@ODA-BNNT with epoxy polymer generates interconnected thermal conduction pathways, thereby improving the thermal conduction and mechanical performance of the composites. The current research approach allows for the even distribution of BNNT throughout the polymer matrix, as demonstrated by optical characterization, mechanical performance analysis, and isotropic thermal conductivity analysis. The fabricated epoxy composite by incorporating a 2 wt % (BNNT = 1.3 wt % and ODA = 0.7 wt %) ODA-BNNT exhibited 5.117 W/mK thermal conductivity and 7.43 MPa mechanical stress. Thermal conductivity improved by 2528, 76.56, and 54.7%, while mechanical stress enhanced by 270, 221, and 34% compared to neat polymers without BNNT and virgin BNNT epoxy composites, respectively.

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.

Development and Perspectives of Thermal Conductive Polymer Composites

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

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.

Wood-Derived, Vertically Aligned, and Densely Interconnected 3D SiC Frameworks for Anisotropically Highly Thermoconductive Polymer Composites

Construction of a vertically aligned and densely interconnected ordered 3D filler framework in a polymer matrix is a challenge to attain significant thermal conductivity (TC) enhancement efficiency. Fortunately, many biomaterials with unique microstructures can be found in nature. With inspiration from wood, artificial composites can be rationally designed to achieve desired properties. Herein, the authors report a facile and effective approach to fabricate anisotropic polymer composites by biotemplate ceramization technology and subsequent vacuum impregnation of epoxy resin. The hierarchical microstructure of wood is perfectly replicated in the cellular biomass derived SiC (bioSiC) framework by carbothermal reduction. Owing to the anisotropic architecture of bioSiC, the epoxy composite with vertically aligned dense SiC microchannels shows interesting properties, including a high TC (10.27 W m-1 K-1 ), a significant enhancement efficiency (259 per 1 vol% loading), an outstanding anisotropic TC ratio (5.77), an extremely low coefficient of linear thermal expansion (12.23 ppm K-1 ), a high flexural strength (222 MPa), and an excellent flame resistance. These results demonstrate that this approach is expected to open a new avenue for design and preparation of high performance thermal management materials to address the heat dissipation of modern electronics.

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.

A Novel Branched Al2O3/Silicon Rubber Composite with Improved Thermal Conductivity and Excellent Electrical Insulation Performance

In this paper, we report a thermal conductive polymer composite that consists of silicone rubber (SR) and branched Al₂O₃ (B-Al₂O₃). Owing to the unique two-dimensional branched structure, B-Al₂O₃ particles form a continuous three-dimensional network structure by overlapping each other in the matrix, serving as a continuous heat conductive pathway. As a result, the polymer composite with a 70 wt% filler achieves a maximum thermal conductivity of 1.242 Wm⁻¹ K⁻¹, which is equivalent to a significant enhancement of 521% compared to that of a pure matrix. In addition, the composite maintains a high volume resistivity of 7.94 × 10¹⁴ Ω·cm with the loading of 70 wt%, indicating that it meets the requirements in the field of electrical insulation. Moreover, B-Al₂O₃ fillers are well dispersed (no large agglomerates) and form a strong interfacial adhesion with the matrix. Therefore, the thermal decomposition temperature, residual mass, tensile strength, modulus and modulus of toughness of composites are significantly improved simultaneously. This strategy provides new insights for the design of high-performance polymer composites with potential application in advanced thermal management in modern electronics.

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

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

Tailoring the Thermal Conductivity of Rubber Nanocomposites by Inorganic Systems: Opportunities and Challenges for Their Application in Tires Formulation

The development of effective thermally conductive rubber nanocomposites for heat management represents a tricky point for several modern technologies, ranging from electronic devices to the tire industry. Since rubber materials generally exhibit poor thermal transfer, the addition of high loadings of different carbon-based or inorganic thermally conductive fillers is mandatory to achieve satisfactory heat dissipation performance. However, this dramatically alters the mechanical behavior of the final materials, representing a real limitation to their application. Moreover, upon fillers’ incorporation into the polymer matrix, interfacial thermal resistance arises due to differences between the phonon spectra and scattering at the hybrid interface between the phases. Thus, a suitable filler functionalization is required to avoid discontinuities in the thermal transfer. In this challenging scenario, the present review aims at summarizing the most recent efforts to improve the thermal conductivity of rubber nanocomposites by exploiting, in particular, inorganic and hybrid filler systems, focusing on those that may guarantee a viable transfer of lab-scale formulations to technological applicable solutions. The intrinsic relationship among the filler’s loading, structure, morphology, and interfacial features and the heat transfer in the rubber matrix will be explored in depth, with the ambition of providing some methodological tools for a more profitable design of thermally conductive rubber nanocomposites, especially those for the formulation of tires.

Highly Thermal Conductive and Electrical Insulating Epoxy Composites with a Three-Dimensional Filler Network by Sintering Silver Nanowires on Aluminum Nitride Surface

In this study, a new fabrication technique for three-dimensional (3D) filler networks was employed for the first time to prepare thermally conductive composites. A silver nanowire (AgNW)- aluminum nitride (AlN) (AA) filler was produced by a polyol method and hot-pressed in mold to connect the adjacent fillers by sintering AgNWs on the AlN surface. The sintered AA filler formed a 3D network, which was subsequently impregnated with epoxy (EP) resin. The fabricated EP/AA 3D network composite exhibited a perpendicular direction thermal conductivity of 4.49 W m-1 K-1 at a filler content of 400 mg (49.86 vol.%) representing an enhancement of 1973% with respect to the thermal conductivity of neat EP (0.22 W m-1 K-1). Moreover, the EP/AA decreased the operating temperature of the central processing unit (CPU) from 86.2 to 64.6 °C as a thermal interface material (TIM). The thermal stability was enhanced by 27.28% (99 °C) and the composites showed insulating after EP infiltration owing to the good insulation properties of AlN and EP. Therefore, these fascinating thermal and insulating performances have a great potential for next generation heat management application.

Wall Density-Controlled Thermal Conductive and Mechanical Properties of Three-Dimensional Vertically Aligned Boron Nitride Network-Based Polymeric Composites

Polymeric composites with good thermal conductive and improved mechanical properties are in high demand in the thermal management materials. Construction of a three-dimensional (3D) structure has been proved to be an effective method to obtain polymeric composites with improved through-plane thermal conductivity (TC) for efficient thermal management of electronics. However, the TC enhancement of the obtained polymeric composites is limited, mainly due to poor control of the 3D thermal conductive network. Additionally, achieving high thermal conductive properties and enhanced mechanical properties simultaneously is of great challenge for polymeric composites. In this work, a 3D boron nitride framework (BNF) with a well-defined vertically aligned open structure and designed wall density fabricated by a unidirectional freezing technique was applied. The as-prepared BNF/polyethylene glycol (PBNF) composites exhibit enhanced through-plane TC, excellent thermal transfer capability (ΔT_max = 34 °C), and improved mechanical properties (Young's modulus enhancement up to 356%) simultaneously, making it attractive to thermal management applications. Strong correlation between the TC and mechanical properties of the PBNF composites and the wall density of the BNF scaffolds was found, providing opportunities to tune the TC and mechanical properties through the controlling of wall density. Furthermore, the models between TC and Young's modulus of PBNF composites were established by using the data-driven method "sure independence screening and sparsifying operator", which enables us to predict TC and Young's modulus of the polymeric composites for designing promising composite materials. The design principles and fabrication strategies proposed in this work could be important for developing advanced composite materials.

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

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

Significant Reduction of Interfacial Thermal Resistance and Phonon Scattering in Graphene/Polyimide Thermally Conductive Composite Films for Thermal Management

The developing flexible electronic equipment are greatly affected by the rapid accumulation of heat, which is urgent to be solved by thermally conductive polymer composite films. However, the interfacial thermal resistance (ITR) and the phonon scattering at the interfaces are the main bottlenecks limiting the rapid and efficient improvement of thermal conductivity coefficients (λ) of the polymer composite films. Moreover, few researches were focused on characterizing ITR and phonon scattering in thermally conductive polymer composite films. In this paper, graphene oxide (GO) was aminated (NH₂-GO) and reduced (NH₂-rGO), then NH₂-rGO/polyimide (NH₂-rGO/PI) thermally conductive composite films were fabricated. Raman spectroscopy was utilized to innovatively characterize phonon scattering and ITR at the interfaces in NH₂-rGO/PI thermally conductive composite films, revealing the interfacial thermal conduction mechanism, proving that the amination optimized the interfaces between NH₂-rGO and PI, reduced phonon scattering and ITR, and ultimately improved the interfacial thermal conduction. The in-plane λ (λ _||) and through-plane λ (λ _⊥) of 15 wt% NH₂-rGO/PI thermally conductive composite films at room temperature were, respectively, 7.13 W/mK and 0.74 W/mK, 8.2 times λ _|| (0.87 W/mK) and 3.5 times λ _⊥ (0.21 W/mK) of pure PI film, also significantly higher than λ _|| (5.50 W/mK) and λ _⊥ (0.62 W/mK) of 15 wt% rGO/PI thermally conductive composite films. Calculation based on the effective medium theory model proved that ITR was reduced via the amination of rGO. Infrared thermal imaging and finite element simulation showed that NH₂-rGO/PI thermally conductive composite films obtained excellent heat dissipation and efficient thermal management capabilities on the light-emitting diodes bulbs, 5G high-power chips, and other electronic equipment, which are easy to generate heat severely.

Highly Compressible, Thermally Conductive, yet Electrically Insulating Fluorinated Graphene Aerogel

Carbon-based aerogels have drawn substantial attention for a wide scope of applications. However, the high intrinsic electrical conductivity limits their potential thermal management application in electronic packaging materials. Herein, a highly compressible, thermally conductive, yet electrically insulating fluorinated graphene aerogel (FGA) is developed through a hydrofluoric acid-assisted hydrothermal process. The macroscopic-assembled FGA constituting of tailored interconnected graphene networks with tunable fluorine coverage shows excellent elasticity and fatigue resistance for compression, despite a low density of 10.6 mg cm^-3. Moreover, the aerogel is proved to be highly insulating, with the observed lowest electrical conductivity reaching 4 × 10^-7 S cm^-1. Meanwhile, the aerogel exhibits prominent heat dissipation performance in a typical cooling procedure, which can be used to fabricate thermoconductive polymer composites for electronic packaging.

A Dual-Crosslinked and Anisotropic Regenerated Cellulose/Boron Nitride Nanosheets Film With High Thermal Conductivity, Mechanical Strength, and Toughness

The highly thermo-conductive but electrically insulating film, with desirable mechanical performances, is extremely demanded for thermal management of portable and wearable electronics. The integration of boron nitride nanosheets (BNNSs) with regenerated cellulose (RC) is a sustainable strategy to satisfy these requirements, while its practical application is still restricted by the brittle fracture and loss of toughness of the composite films especially at the high BNNS addition. Herein, a dual-crosslinked strategy accompanied with uniaxial pre-stretching treatment was introduced to engineer the artificial RC/BNNS film, in which partial chemical bonding interactions enable the effective interfiber slippage and prevent any mechanical fracture, while non-covalent hydrogen bonding interactions serve as the sacrifice bonds to dissipate the stress energy, resulting in a simultaneous high mechanical strength (103.4 MPa) and toughness (10.2 MJ/m³) at the BNNS content of 45 wt%. More importantly, attributed to the highly anisotropic configuration of BNNS, the RC/BNNS composite film also behaves as an extraordinary in-plane thermal conductivity of 15.2 W/m·K. Along with additional favorable water resistance and bending tolerance, this tactfully engineered film ensures promised applications for heat dissipation in powerful electronic devices.

Reinforcing effects of aminosilane-functionalized h-BN on the physicochemical and mechanical behaviors of epoxy nanocomposites

The results of this study confirm the possibility of the directional regulation of operational properties of epoxy composites by the use of small additives of hexagonal boron nitride (h-BN), providing the creation of epoxy composites with high performance properties. The effectiveness of h-BN surface modification by γ-aminopropyltriethoxysilane and the formation of strong chemical bonds at the polymer matrix/filler interface has been proved, which ensures an increase in physico-mechanical characteristics of epoxy composites: bending stress increases by 142% and bending modulus increases by 52%, strength increases by 53% and tensile elastic modulus increases by 37%, toughness increases by 400% and Brinell hardness increases by 96%, compared with an unfilled plasticized epoxy composite.

Highly flexible few-layer Ti3C2 MXene/cellulose nanofiber heat-spreader films with enhanced thermal conductivity

Highly flexible MXene/cellulose nanofiber heat-spreader films with enhanced thermal conductivity were fabricated via simple vacuum assisted filtration.