Construction of 3D Skeleton for Polymer Composites Achieving a High Thermal Conductivity

Owing to the growing heat removal issue in modern electronic devices, electrically insulating polymer composites with high thermal conductivity have drawn much attention during the past decade. However, the conventional method to improve through‐plane thermal conductivity of these polymer composites usually yields an undesired value (below 3.0 Wm^?1 K^?1). Here, construction of a 3D phonon skeleton is reported composed of stacked boron nitride (BN) platelets reinforced with reduced graphene oxide (rGO) for epoxy composites by the combination of ice‐templated and infiltrating methods. At a low filler loading of 13.16 vol%, the resulting 3D BN‐rGO/epoxy composites exhibit an ultrahigh through‐plane thermal conductivity of 5.05 Wm^?1 K^?1 as the best thermal‐conduction performance reported so far for BN sheet‐based composites. Theoretical models qualitatively demonstrate that this enhancement results from the formation of phonon‐matching 3D BN‐rGO networks, leading to high rates of phonon transport. The strong potential application for thermal management has been demonstrated by the surface temperature variations of the composites with time during heating and cooling.     

Sandwiched epoxy–alumina composites with synergistically enhanced thermal conductivity and breakdown strength

Development of polymer-based composites with simultaneously high thermal conductivity and breakdown strength has attracted considerable attentions owing to their important applications in both electronic and electric industries. In this study, we successfully design novel epoxy-based composites with nano-Al₂O₃/epoxy composite layer sandwiched between micro-Al₂O₃/epoxy composite layers, which show synergistically and significantly enhanced thermal conductivity and breakdown strength. Compared with the traditional composites, the bottleneck that both thermal conductivity and breakdown strength cannot be simultaneously enhanced can be overcome successfully. An optimized sandwiched alumina–epoxy composite with 70 wt% micro-Al₂O₃ fillers in the outer layers and 3 wt% nano-Al₂O₃ in the middle layer simultaneously displays a high thermal conductivity of 0.447 W m^?1 K^?1 (2.4 times of that of epoxy) and a high breakdown strength of 68.50 kV mm^?1, which is 6.3 % higher than that of neat epoxy (64.45 kV mm^?1). The experimental results on the thermal conductivity of multi-layered alumina–epoxy composites were in well accordance with the theoretical values predicted from the series conduction model. This novel technique simultaneously improves thermal conductivity and breakdown strength, which is of critical importance for design of perspective composites for electronic and electric equipments.     

Formation of Cu Nanodots on Diamond Surface to Improve Heat Transfer in Cu/D Composites

Diamond‐dispersed copper matrix (Cu/D) composite materials with different interfacial configurations are fabricated through powder metallurgy and their thermal performances are evaluated. An innovative solution to chemically bond copper (Cu) to diamond (D) has been investigated and compared to the traditional Cu/D bonding process involving carbide‐forming additives such as boron (B) or chromium (Cr). The proposed solution consists of coating diamond reinforcements with Cu particles through a gas–solid nucleation and growth process. The Cu particle‐coating acts as a chemical bonding agent at the Cu–D interface during hot pressing, leading to cohesive and thermally conductive Cu/D composites with no carbide‐forming additives. Investigation of the microstructure of the Cu/D materials through scanning electron microscopy, transmission electron microscopy, and atomic force microscopy analyses is coupled with thermal performance evaluations through thermal diffusivity, dilatometry, and thermal cycling. Cu/D composites fabricated with 40 vol% of Cu‐coated diamonds exhibit a thermal conductivity of 475 W m^?1 K^?1 and a thermal expansion coefficient of 12 × 10^?6 °C^?1. These promising thermal performances are superior to that of B‐carbide‐bonded Cu/D composites and similar to that of Cr‐carbide‐bonded Cu/D composites fabricated in this study. Moreover, the Cu/D composites fabricated with Cu‐coated diamonds exhibit higher thermal cycling resistance than carbide‐bonded materials, which are affected by the brittleness of the carbide interphase upon repeated heating and cooling cycles. The as‐developed materials can be applicable as heat spreaders for thermal management of power electronic packages. The copper‐carbon chemical bonding solution proposed in this article may also be found interesting to other areas of electronic packaging, such as brazing solders, direct bonded copper substrates, and polymer coatings.

     

Highly Thermoconductive,Thermostable, and Super-Flexible Film by Engineering 1D Rigid Rod-Like Aramid Nanofiber/2D Boron Nitride Nanosheets

Polymer-based thermal management materials have many irreplaceable advantages not found in metals or ceramics, such as easy processing, low density, and excellent flexibility. However, their limited thermal conductivity and unsatisfactory resistance to elevated temperatures (<200 °C) still prevent effective heat dissipation during applications with high-temperature conditions or powerful operation. Therefore, herein highly thermoconductive and thermostable polymer nanocomposite films prepared by engineering 1D aramid nanofiber (ANF) with worm-like microscopic morphologies into rigid rod-like structures with 2D boron nitride nanosheets (BNNS) are reported. With no coils or entanglements, the rigid polymer chain enables a well-packed crystalline structure resulting in a 20-fold (or greater) increase in axial thermal conductivity. Additionally, strong interfacial interactions between the weaved ANF rod and the stacked BNNS facilitate efficient heat flux through the 1D/2D configuration. Hence, unprecedented in-plane thermal conductivities as high as 46.7 W m⁻¹ K⁻¹ can be achieved at only 30 wt% BNNS loading, a value of 137% greater than that of a worm-like ANF/BNNS counterpart. Moreover, the thermally stable nanocomposite films with light weight (28.9 W m⁻¹ K⁻¹/10³ (kg m⁻³)) and high strength (>100 MPa, 450 °C) enable effective thermal management for microelectrodes operating at temperatures beyond 200 °C.     

Dielectric and thermal properties of GFs/PTFE composites with hybrid fillers of Al2O3 and hBN for microwave substrate applications

The alumina/hexagonal boron nitride/glass fibers cloth/Polytetrafluoroethylene (Al₂O₃–hBN/GFs/PTFE) composites were prepared by blending-impregnation followed by hot compression method, and the dielectric, thermal properties of the composites with various hBN fillers content (0–20 wt.%) were investigated. The results show that the thermal conductivity of the composites increase significantly, while the coefficient of thermal expansion (CTE) decrease gradually, with the hBN content increasing. Composite substrates with 20 wt.% hBN exhibited high thermal conductivity as 1.05 W m^?1 K^?1, which is 5.3 times that of pure PTFE. Such compositions may be a promising material in high thermal conductivity copper clad laminate.

     

3D Anisotropic Thermal Conductivity of Exfoliated Rhenium Disulfide

ReS₂ represents a different class of 2D materials, which is characterized by low symmetry having 1D metallic chains within the planes and extremely weak interlayer bonding. Here, the thermal conductivity of single‐crystalline ReS₂ in a distorted 1T phase is determined at room temperature for the in‐plane directions parallel and perpendicular to the Re‐chains, and the through‐plane direction using time‐domain thermoreflectance. ReS₂ is prepared in the form of flakes having thicknesses of 60–450 nm by micromechanical exfoliation, and their crystalline orientations are identified by polarized Raman spectroscopy. The in‐plane thermal conductivity is higher along the Re‐chains, (70 ± 18) W m^?1 K^?1, as compared to transverse to the chains, (50 ± 13) W m^?1 K^?1. As expected from the weak interlayer bonding, the through‐plane thermal conductivity is the lowest observed to date for 2D materials, (0.55 ± 0.07) W m^?1 K^?1, resulting in a remarkably high anisotropy of (130 ± 40) and (90 ± 30) for the two in‐plane directions. The thermal conductivity and interface thermal conductance of ReS₂ are discussed relative to the other 2D materials.     

Skin-Inspired Thermosensitive Tactile Sensor Based on Thermally Conductive and Viscous Interface Composites for Rocks

Achieving high thermal conductivity and exceptional interfacial adhesion simultaneously in thermosensitive tactile recognition sensors poses a significant challenge. A copolymer, poly([[(butylamino)carbonyl]oxy]ethyl-ester)-co-polydimethylsiloxane (referred to as PP), is synthesized and subsequently complexed with alumina particles coated with liquid metal (LMAl₂O₃) to prepare a composite material called PP/LMAl₂O₃ with high thermal conductivity and strong interfacial adhesion to address this challenge. The best thermal conductivity (4.43 W m⁻¹ K⁻¹), electrical insulation (10⁻⁶–10⁻⁷ S m⁻¹), and adhesion properties derived from hydrogen bonding (1316 N m⁻²) are obtained by adjusting the volume fraction of PP and LMAl₂O₃ in PP/LMAl₂O₃. PP/LMAl₂O₃ with high thermal conductivity and high interface adhesion can efficiently transfer heat between thermal flux sensors and the objects being sensed, reliably detecting small thermal flux variations and ensuring accurate thermal flux measurements. In this study, PP/LMAl₂O₃ is used to make up thermosensitive tactile sensor. Surprisingly, PP/LMAl₂O₃ demonstrates high thermal signal sensitivity for tactile recognition applications, allowing the smart thermosensitive tactile sensor system to distinguish unknown rock materials even in the dark. Overall, PP/LMAl₂O₃ may function as a fundamental material in thermosensitive tactile sensors for lithology identification.     

导热高分子材料研究进展

讨论了提高聚合物导热性能的途径－合成高导热系数的结构聚合物，用高导热无机填料对聚合物进行填充复合。综述了导热高分子材料的研究成果：聚合物导热的基本概念和影响其导热性能的因素及导热系数的预测理论；聚合物基导热复合材料的选材、复合技术及其应用。指出了导热高分子材料的研究方向－－纳米导热填料的研究和开发；聚合物树脂基体的物理化学改性；聚合物基体与导热填料复合新技术的研究和开发；复合材料导热模型的建立、导热机理（特别是聚合物基体与导热填料界面的结构与性能对材料导热性能的影响）及导热通路的形成等；探索高导热本体聚合物材料的制备方法和途径等。对导热高分子材料的研究和开发有重要意义。     

Thermoelectric behaviour of melt processed carbon nanotube/graphite/poly(lactic acid) conductive biopolymer nanocomposites (CPC)

The aim of the study was to examine the possible use of conductive polymer composites (CPC) as thermoelectrical material for energy harvesting from temperature gradient. Their ease of processing, low cost and environmental impact compared to typical thermoelectric semiconductor materials were found to be strong advantages for large scale production. Our results show that eGR-CNT hybrid fillers are the most effective to enhance the CPC electrical conductivity up to σ = 4123 S.m^− 1, but that eGR is more effective to improve both thermal conductivity (λ_c = 5.5 W.m^− 1.K^− 1) and seebeck coefficient (S = 17 μV.K^− 1), whereas finally CNT give the best compromise to reach the highest ZT = 7 × 10^− 5 at room temperature. This finding is attributed to the ability of CNT network to allow electron circulation by tunnelling, when junctions are separated by an insulating polymer film (even of some nm thick), whereas phonon scattering at nanointerfaces will prevent their effective transmission through the CPC. Although the intrinsic individual physical properties obtained (σ, λ_c, S) with the different kinds of carbon filler were good, it was not possible to completely uncouple them to maximise ZT. We believe that this value of ZT, too low for commercial application, can be enhanced by increasing the confinement of conducting fillers with exclusion volumes and by decreasing the thermal conductivity of the matrix with voids.     

Water-Processable,Stretchable, Self-Healable,Thermally Stable,and Transparent Ionic Conductors for Actuators and Sensors

For emerging biocompatible, wearable, and stretchable epidermal electronic devices, it is essential to realize novel stretchable conductors with the attributes of transparency, low-cost and nontoxic components, green-solvent processbility, self-healing, and thermal stabililty. Although conducting materials–rubber composites, ionic hydrogels, organogels have been developed, no stretchable material system that meets all the outlined requirements has been reported. Here, a series of P(SPMA-r-MMA) polymers with different ratios of ionic side chains is designed and synthesized, and it is demonstrated that the resulting stretchable ionic conductors with glycerol are transparent, water processable, self-healable, and thermally stable due to the chemically linked ionic side chain, satisfying all of the aforementioned requirements. Among the series of polymer gels, the P(SPMA_0.75-r-MMA_0.25) gel shows optimum conductivity (6.7 × 10⁻⁴ S cm⁻¹), stretchability (2636% of break at elongation), and self-healing (98.3% in 3 h) properties. Accordingly, the transparent and self-healable P(SPMA_0.75-r-MMA_0.25) gels are used to realize thermally robust actuators up to 100 °C and deformable and self-healable thermal sensors.     

Boosting the Thermoelectric Performance of the Doped DPP-EDOT Conjugated Polymer by Incorporating an Ionic Additive

The thermoelectric (TE) performance of organic materials is limited by the coupling of Seebeck coefficient and electrical conductivity. Herein a new strategy is reported to boost the Seebeck coefficient of conjugated polymer without significantly reducing the electrical conductivity by incorporation of an ionic additive DPPNMe₃Br . The doped polymer PDPP - EDOT thin film exhibits high electrical conductivity up to 1377 ± 109 S cm⁻¹ but low Seebeck coefficient below 30 µV K⁻¹ and a maximum power factor of 59 ± 10 µW m⁻¹ K⁻². Interestingly, incorporation of small amount (at a molar ratio of 1:30) of DPPNMe₃Br into PDPP - EDOT results in the significant enhancement of Seebeck coefficient along with the slight decrease of electrical conductivity after doping. Consequently, the power factor (PF) is boosted to 571 ± 38 µW m⁻¹ K⁻² and ZT reaches 0.28 ± 0.02 at 130 °C, which is among the highest for the reported organic TE materials. Based on the theoretical calculation, it is assumed that the enhancement of TE performance for the doped PDPP - EDOT by DPPNMe₃Br is mainly attributed to the increase of energetic disorder for PDPP - EDOT .     

Silica coating onto graphene for improving thermal conductivity and electrical insulation of graphene/polydimethylsiloxane nanocomposites

Graphene possess extremely high thermal conductivity, and they have been regarded as prominent candidates to be used in thermal management of electronic devices. However, addition of graphene inevitably causes dramatic decrease in electrical insulation, which is generally unacceptable for thermal interface materials(TIMs) in real electronic industry. Developing graphene-based nanocomposites with high thermal conductivity and satisfactory electrical insulation is still a challenging issue. In this study,we developed a novel hybrid nanocomposite by incorporating silica-coated graphene nanoplatelets(Silica@GNPs) with polydimethylsiloxane(PDMS) matrix. The obtained Silica@GNP/PDMS composites showed satisfactory electrical insulation(electrical resistivity of over 10~(13)Ωcm) and high thermal conductivity of 0.497 W m-1K-1, increasing by 155% compared with that of neat PDMS, even higher than that of GNP/PDMS composites. Such high thermal conductivity and satisfactory electrical insulation is mainly attributed to the insulating silica-coating, good compatibility between components, strong interfacial bonding, uniform dispersion, and high-efficiency heat transport pathways. There is great potential for the Silica@GNP/PDMS composites to be used as high-performance TIMs in electronic industry.     

High‐Performance Thermally Conductive Phase Change Composites by Large‐Size Oriented Graphite Sheets for Scalable Thermal Energy Harvesting

Efficient thermal energy harvesting using phase‐change materials (PCMs) has great potential for cost‐effective thermal management and energy storage applications. However, the low thermal conductivity of PCMs (K_PCM) is a long‐standing bottleneck for high‐power‐density energy harvesting. Although PCM‐based nanocomposites with an enhanced thermal conductivity can address this issue, achieving a higher K (>10 W m^?1 K^?1) at filler loadings below 50 wt% remains challenging. A strategy for synthesizing highly thermally conductive phase‐change composites (PCCs) by compression‐induced construction of large aligned graphite sheets inside PCCs is demonstrated. The millimeter‐sized graphite sheet consists of lateral van‐der‐Waals‐bonded and oriented graphite nanoplatelets at the micro/nanoscale, which together with a thin PCM layer between the sheets synergistically enhance K_PCM in the range of 4.4–35.0 W m^?1 K^?1 at graphite loadings below 40.0 wt%. The resulting PCCs also demonstrate homogeneity, no leakage, and superior phase change behavior, which can be easily engineered into devices for efficient thermal energy harvesting by coordinating the sheet orientation with the thermal transport direction. This method offers a promising route to high‐power‐density and low‐cost applications of PCMs in large‐scale thermal energy storage, thermal management of electronics, etc.     

Enhanced thermal-conductive and anti-dripping properties of polyamide composites by 3D graphene structures at low filler content

In this work, 3D graphene structures constructed by graphene foam (GF) were introduced into polyamide-6 (PA6) matrix for the purpose of enhancing the thermal-conductive and anti-dripping properties of PA6 composites. The GF were prepared by one-step hydrothermal method. The PA6 composites were synthesized by in-situ thermal polycondensation method to realize PA6 chains covalently grafted onto the graphene sheets. The 3D interconnected graphene structure favored the formation of the consecutive thermal conductive paths or networks even at relatively low graphene loadings. As a result, the thermal conductivity was improved by 300% to 0.847 W·m⁻¹·K⁻¹ of PA6 composites at 2.0 wt% graphene loading from 0.210 W·m⁻¹·K⁻¹ of pure PA6 matrix. The presence of self-supported 3D structure alone with the covalently-grafted PA6 chains endowed the PA6 composites good anti-dripping properties.     

Enhanced thermal conductivity of Cu matrix composites reinforced with Ag-coated β-Si3N4 whiskers

Cu matrix composites reinforced with 10 vol.% Ag-coated β-Si₃N₄ whiskers (ASCMMCs) were prepared by powder metallurgy method. With the aim of improving the thermal conductivity of the composites, a quite thin Ag layer was deposited on the surface of β-Si₃N₄ whiskers. The results indicated that thermal conductivity of ASCMMCs with 0.30 vol.% Ag (0.30ASCMMCs) reached up to 273 W m⁻¹ K⁻¹ at 25 °C, which was 98 W m⁻¹ K⁻¹ higher than that of Cu matrix composites reinforced with uncoated β-Si₃N₄ whiskers (USCMMCs). The Ag coating could promote the densification of composites, reduce the aggregation of β-Si₃N₄ whiskers and enhance the Cu/Si₃N₄ interfacial bonding, therefore it could efficiently enhance the thermal conductivity of Cu matrix composites reinforced with β-Si₃N₄ whiskers (SCMMCs).     

The effect of interfacial state on the thermal conductivity of functionalized Al2O3 filled glass fibers reinforced polymer composites

Rapidly increasing packaging density of electronic devices puts forward higher requirements for thermal conductivity of glass fibers reinforced polymer (GFRP) composites, which are commonly used as substrates in printed circuit board. Interface between fillers and polymer matrix has long been playing an important role in affecting thermal conductivity. In this paper, the effect of interfacial state on the thermal conductivity of functionalized Al₂O₃ filled GFRP composites was evaluated. The results indicated that amino groups-Al₂O₃ was demonstrated to be effective filler to fabricate thermally conductive GFPR composite (1.07 W/m K), compared with epoxy group and graphene oxide functionalized Al₂O₃. It was determined that the strong adhesion at the interface and homogeneous dispersion of filler particles were the key factors. Moreover, the effect of interfacial state on dielectric and thermomechanical properties of GFRP composites was also discussed. This research provides an efficient way to develop high-performance GFRP composites with high thermal conductivity for integrated circuit packaging applications.     

A Through-Thickness Arrayed Carbon Fibers Elastomer with Horizontal Segregated Magnetic Network for Highly Efficient Thermal Management and Electromagnetic Wave Absorption

Multifunctional thermal management materials with highly efficient electromagnetic wave (EMW) absorption performance are urgently required to tackle the heat dissipation and electromagnetic interference issues of high integrated electronics. However, the high thermal conductivity (λ) and outstanding EMW absorption performance are often incompatible with each other in a single material. Herein, a through-thickness arrayed NiCo₂O₄/graphene oxide/carbon fibers (NiCO@CFs) elastomer with integrated functionalities of high thermal conductivity, highly efficient EMW absorption, and excellent compressibility is reported. The NiCO@CFs elastomer realizes a high out-of-plane thermal conductivity of 15.55 W m⁻¹ K⁻¹, due to the through-thickness vertically aligned CFs framework. Moreover, the unique horizontal segregated magnetic network effectively reduces the electrical contact between the CFs, which significantly enhances impedance matching of NiCO@CFs elastomer. As a result, the vertically arrayed NiCO@CFs elastomer synchronously exhibits ultrabroad effective absorption bandwidth of 8.25 GHz (9.75–18 GHz) at a thickness of 2.4 mm, good impedance matching, and a minimum reflection loss (RL_min) of −55.15 dB. Given these outstanding findings, the multifunctional arrayed NiCO@CFs elastomer opens an avenue for applications in EMW absorption and thermal management. This strategy of constructing thermal/electrical/mechanical pathways provides a promising way for the high-performance multifunctional materials in electronic devices.     

Study on thermal properties of graphene foam/graphene sheets filled polymer composites

The polymer composites composed of graphene foam (GF), graphene sheets (GSs) and pliable polydimethylsiloxane (PDMS) were fabricated and their thermal properties were investigated. Due to the unique interconnected structure of GF, the thermal conductivity of GF/PDMS composite reaches 0.56 W m⁻¹ K⁻¹, which is about 300% that of pure PDMS, and 20% higher than that of GS/PDMS composite with the same graphene loading of 0.7 wt%. Its coefficient of thermal expansion is (80–137) × 10⁻⁶/K within 25–150 °C, much lower than those of GS/PDMS composite and pure PDMS. In addition, it also shows superior thermal and dimensional stability. All above results demonstrate that the GF/PDMS composite is a good candidate for thermal interface materials, which could be applied in the thermal management of electronic devices, etc.     

Porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2: A novel strategy towards making ultrahigh temperature ceramics thermal insulating

Transition metal diborides based ultrahigh temperature ceramics (UHTCs) are characterized by high melting point, high strength and hardness, and high electrical and thermal conductivity. The high thermal conductivity arises from both electronic and phonon contributions. Thus electronic and phonon contributions must be controlled simultaneously in reducing the thermal conductivity of transition metal diborides. In high entropy (HE) materials, both electrons and phonons are scattered such that the thermal conductivity can significantly be reduced, which opens a new window to design novel insulating materials. Inspired by the high entropy effect, porous HE (Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2)B₂ is designed in this work as a new thermal insulting ultrahigh temperature material and is synthesized by an in-situ thermal borocarbon reduction/partial sintering process. The porous HE (Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2)B₂ possesses high porosity of 75.67%, pore size of 0.3–1.2 μm, homogeneous microstructure with small grain size of 400–800 nm, which results in low room temperature thermal diffusivity and thermal conductivity of 0.74 mm² s⁻¹ and 0.51 W m⁻¹ K⁻¹, respectively. In addition, it exhibits high compressive strength of 3.93 MPa. The combination of these properties indicates that exploring porous high entropy ceramics such as porous HE (Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2)B₂ is a novel strategy in making UHTCs thermal insulating.     

Microstructure and properties of the Si3N4/silica aerogel composites fabricated by the sol–gel method via ambient pressure drying

Si₃N₄ particle reinforced silica aerogel composites have been fabricated by the sol–gel method via ambient pressure drying. The microstructure and mechanical, thermal insulation and dielectric properties of the composites were investigated. The effect of the Si₃N₄ content on the microstructure and properties were also clarified. The results indicate that the obtained mesoporous composites exhibit low thermal conductivity (0.024–0.072 Wm^− 1 K^− 1), low dielectric constant (1.55–1.85) and low loss tangent (0.005–0.007). As the Si₃N₄ content increased from 5 to 20 vol.%, the compressive strength and the flexural strength of the composites increased from 3.21 to 12.05 MPa and from 0.36 to 2.45 MPa, respectively. The obtained composites exhibit considerable promise in wave transparency and thermal insulation functional integration applications.