Large-Scale Fabrication of Flexible EVA/EG@PW Phase Change Composites with High Thermal Conductivity for Thermal Management

The working electronic devices and batteries generate a lot of heat, if this heats not release quickly, it will not only have a great impact on the performance of the devices, but also cause certain safety hazards. The passive thermal management based on organic phase change materials (PCMs) stands out due to its excellent temperature regulation capability as well as the buffer protection capability for device overload. In view of these, a series of flexible EVA/EG@PW (EE@P) phase change composites (PCCs) with high thermal conductivity are prepared by efficiently constructing porous skeletons and thermal conductive pathways through sacrificial template method, and introducing paraffin wax (PW) by simple vacuum impregnation technique. The PCC exhibits high thermal conductivity (2.6 W m⁻¹ K⁻¹), high enthalpy (153.5 J g⁻¹), and good flexibility. In addition, the PCC possesses excellent cycling stability and thermal stability. In practical application, the PCC shows good temperature control ability for LED and shows great potential application in the field of thermal management.     

Multifunctional Shape-Stabilized Phase Change Materials with Enhanced Thermal Conductivity and Electromagnetic Interference Shielding Effectiveness for Electronic Devices

A paraffin-based shape-stabilized composite phase change material (CPCM) is fabricated with dramatically enhanced thermal conductivity and excellent electromagnetic interference (EMI) shielding capacity. The as-prepared CPCMs are supported by graphene-based frameworks with many bubble-like micropores that are prepared by the addition of polystyrene microspheres into graphene oxide hydrogel as hard templates. These bubble-like micropores can encapsulate paraffin wax (PW) due to the strong capillary force between the graphene-based framework and PW and leading to enhanced shape stability of the as-prepared CPCMs. Moreover, the continuous thermally and electrically conductive network formed by graphene nanoplatelets endows the as-prepared CPCMs with a high thermal conductivity and an excellent EMI shielding effectiveness. When the ratio of graphene-based framework is 23.0 wt%, the thermal conductivity and latent heat of CPCM reaches 28.7 W m⁻¹ k⁻¹ and 175.8 J g⁻¹, respectively, and the EMI shielding effectiveness is higher than 45 dB in the frequency of 8.2–12.4 GHz. Their outstanding thermal and EMI shielding performance makes the as-prepared CPCMs promising candidates for use in thermal management and EMI shielding of electronic devices.     

Enhanced out-of-plane thermal conductivity of polyimide composite films by adding hollow cube-like boron nitride

Boron nitride nanosheet (BNNS) is widely used in electronic thermal management due to its excellent planar thermal conductivity and insulating properties. However, it is challenging to improve the out-of-plane thermal conductivity of BNNS-doped composites due to the anisotropy of the thermal conductivity of BNNS. Therefore, the BNNS in the matrix must be oriented to obtain composites with high out-of-plane thermal conductivity. In this study, BNNS powders with directional structures were synthesized directly using sodium chloride templates. The as-obtained BNNS powders have a unique hollow cube-like structure with an ultra-low density of 2.67 × 10⁻² g/cm³ and nearly 8 times the volume of the same mass of two-dimensional (2D) BNNS, making it easy to form the out-of-plane thermal conductivity paths in the polymer matrix. In addition, the high out-of-plane thermal conductivity of 4.93 W m⁻¹ K⁻¹ at 23.3 wt% loadings was obtained by doping it into a polyimide (PI) matrix. This value is 9.7 times higher than that of 2D BNNS-doped PI at the same loadings, 17.6 times higher than pure PI, and 6.1 times higher than the thermally conductive PI film sold by DuPont. Therefore, the prepared composite film has great potential for application in electronic thermal management.     

聚合物基热界面材料与导热性能研究进展

随着电子产品的小型化、集成化和功能化发展,功率密度及热流密度急剧上升,器件内巨大的散热和温压压力使电子设备的寿命和可靠性受到影响,因此对器件在运行过程中如何有效散热提出了更为苛刻的要求。开发及使用高性能导热基复合材料（热界面材料,TIM）降低接触热阻是解决电子设备散热问题的有效途径之一,热界面材料创新与优化备受关注。本文从基本的导热机理出发,阐述聚合物基热界面材料结构及导热强化方面最新进展,讨论导热填料和聚合物基体对复合材料性能的影响。重点对微纳结构的导热强化（协同）作用、构筑3D高导热微结构、导热填料和基质间的界面微结构和导热互穿网络结构等进行讨论,为设计高性能导热结构、制备开发新型高性能TIM提供参考。     

Highly anisotropic thermal conductivity of mesogenic epoxy resin film through orientation control

To develop insulating materials with a high thermally conductive anisotropy, planarly aligned mesogenic epoxy (ME) resin film was fabricated by uniaxial coating on a hydrophobic polyethylene terephthalate substrate. Grazing incidence small-angle X-ray scattering (GISAXS) and transmission SAXS measurements exhibited that the films spontaneously formed uniaxially aligned monodomain-like smectic structures by curing on the hydrophobic substrate. Then, an in- and out-of-plane thermal conductivity of 10 and 0.048 W m⁻¹ K⁻¹ and outstanding thermal conductivity anisotropy of 208 have been confirmed, respectively. The ME resin films with high thermal conductivity can be applied as insulating materials for multiple-layer electrical and electronic devices.     

3D printing of copper particles and poly(methyl methacrylate) beads containing poly(lactic acid) composites for enhancing thermomechanical properties

Poly(lactic acid) (PLA) composite filaments with different copper (Cu) contents as high as 40 and 20 wt% of poly(methyl methacrylate) (PMMA) beads have been fabricated by twin-screw extruder for 3D printing. A fused-deposition modeling (FDM) 3D printing technology has been used to print the PLA composites containing hybrid fillers of Cu particles and PMMA beads. The morphology, mechanical, and thermal properties of the printed PLA composites were investigated. The tensile strength was slightly decreased, but storage modulus and thermal conductivity of PLA composites were significantly improved by adding Cu particles in the presence of PMMA beads. The PLA composites with hybrid fillers of 40 wt% of Cu particles and 20 wt% of PMMA beads resulted in thermal conductivity of 0.49 W m⁻¹ K⁻¹ which was three times higher than that of the bare PLA resin. The facilitation of the segregated network of high-thermally conductive Cu particles with the PMMA beads in PLA matrix provided thermally conductive pathways and resulted in a remarkable enhancement in thermal conductivity.     

Simultaneously Improved Thermal Conductivity and Dielectric Properties of NBR Composites by Constructing 3D Hybrid Filler Networks

This work aims to address the heat accumulation issue in electronic components during high-frequency operation through the preparation of novel thermally conductive composites. First, polydopamine (PDA) and in-situ growth of silver (Ag) nanoparticles are applied for the surface modification of graphene oxide (GO) and carbon nanotube (CNT) to prepare pGO@Ag and pCNT@Ag hybrid filler, respectively. Then, nitrile butadiene rubber (NBR) is chosen as the polymeric matrix and simultaneously incorporated with both pGO@Ag and pCNT@Ag to prepare polymeric composites with excellent thermal conductivity (TC) and dielectric constant (ɛ_r). Due to the construction of 3D heat conduction networks by utilizing 2D pGO@Ag and 1D pCNT@Ag, the fabricated NBR composites achieved the maximum TC of 1.0112 W/(mK), which is 636% higher than that of neat NBR (0.1373 W (mK)⁻¹). At the filler loading of 9 vol%, the TC of pGO@Ag/pCNT@Ag/NBR composite is 152% that of GO/CNT/NBR composite (0.6660 W (mK)⁻¹). Moreover, due to electron polarization effect of GO and CNT and micro-capacitor effect of Ag nanoparticles, a large ɛ_r of 147.12 is attained at 10 Hz for NBR composites. Overall, the development of dielectric polymer materials with high TC is beneficial for enhancing the service life and safety stability of the electronic components.     

Multilayered ultrahigh molecular weight polyethylene/natural graphite/boron nitride composites with enhanced thermal conductivity and electrical insulation by hot compression

A scalable strategy to fabricate thermally conductive but electrically insulating polymer composites was urgently required in various applications including heat exchangers and electronic packages. In this work, multilayered ultrahigh molecular weight polyethylene (UHMWPE)/natural graphite (NG)/boron nitride (BN) composites were prepared by hot compressing the UHMWPE/NG layers and UHMWPE/BN layers alternately. Taking advantage of the internal properties of NG and BN fillers, the UHMWPE/NG layers played a decisive role in enhancing thermal conductivity (TC), while the UHMWPE/BN layers effectively blocked the electrically conductive pathways without affecting the thermal conductive pathways. The in-plane TC, electrical insulation, and heat spreading ability of multilayered UHMWPE/NG/BN composites increased with the increasing layer numbers. At the total fillers loading of 40 wt%, the in-plane TC of multilayered UHMWPE/NG/BN composites with nine layers was markedly improved to 6.319 Wm⁻¹ K⁻¹, outperforming UHMWPE/BN (4.735 Wm⁻¹ K⁻¹) and pure UHMWPE (0.305 Wm⁻¹ K⁻¹) by 33.45% and 1971.80%, respectively. Meanwhile, the UHMWPE/NG/BN composites still maintained an excellent electrically insulating property (volume resistance~5.40×10¹⁴ Ω cm ; breakdown voltage~1.52 kV/mm). Moreover, the multilayered UHMWPE/NG/BN composites also exhibited surpassing heat dissipation capability and mechanical properties. Our results provided an effective method to fabricate highly thermal conductive and electrical insulating composites.     

A bio-based compatibilizer for improved interfacial compatibility in thermally conductive and electrically insulating graphite/high density poly(ethylene) composites

Graphite is a thermally conductive filler. However, when dispersed into high density poly(ethylene) (HDPE) resin, graphite particles tend to agglomerate and requires a compatibilizer to achieve desired thermal/physical properties. In this study, oleic acid (OA), a bio-based additive and polyethylene-polyamines (PEPA) were used to synthesize a new compatibilizer, PEPA-g-OA, containing numerous  NR₂ groups. The experimental results showed that PEPA-g-OA can significantly improve the compatibility between graphite particles and the HDPE matrix due to uniform dispersion of graphite in the HDPE matrix. When the graphite content was 25 wt%, the thermal conductivity of the composite recorded 1.2 W m⁻¹ K⁻¹ (three times that of neat HDPE) and the volume resistivity was 1.8 × 10⁹ Ω cm, indicating excellent electrical insulation. Compared to the composites with no graphite content, the properties of the composites with 25 wt% graphite content exhibited narrower melting and crystallization peaks, more stable mechanical properties, and higher ultraviolet aging resistance. Synthesized new bio-based compatibilizer and thermally conductive and electrically insulating composites developed in this study can be useful in different industrial fields for the preparation of the next generation composites.     

High thermal conductive shape-stabilized phase change materials based on water-borne polyurethane/boron nitride aerogel

Phase change materials (PCMs) applied in energy storage and temperature control system are important for energy conservation and environmental protection. In this work, structure-adjustable water-borne polyurethane (WPU)/boron nitride (BN) aerogels were synthesized via directional freeze-drying method, and used as supporting scaffolds to confine paraffin wax (PW) and obtain composite phase change materials. The three-dimensional (3D) porous thermal conductivity network of BN was derived by the in-situ ice crystal mound in aerogel, which endows the PW/WPU/BN composite PCM-2.5 with high thermal conductivity (0.96 W m^?1 K^?1) and high energy storage density (140.04 J/g). Shape-stabilized PCMs with high thermal conductivity and excellent electrical insulation prepared by the simple method have great potential for the thermal management of electronic products.     

0D surface modification and 3D silicon carbide network construction for improving the thermal conductivity of epoxy resins

With rapid advances in electronic device miniaturization and increasing power density, high thermal conductivity polymer composites with excellent properties are becoming increasingly significant for the progress of next-generation electronic apparatuses. In this work, a new type of three-dimensional (3D) network silicon carbide (SiC) frame and core-shell SiC@SiO₂ (SiC@SiO₂) were successfully prepared. The effects of different filler forms (dispersed particle filler and three-dimensional continuous filler network) on the thermal conductivity of the composites were compared. The composites based on the three-dimensional filler network exhibited evidently better thermal conductivity improvement rates, compared to their traditional counterparts. The thermal conductivity of the epoxy/SiC@SiO₂ composite having a total filler content of 17.0 vol% was 0.857 W/m/K, 328.5% higher than that of pure epoxy resin. Similarly, the thermal conductivity of the EP/3D-SiC composite having a total filler content of 13.8 vol% was 1.032 W/m/K, 416.0% higher than that of pure epoxy resin. The abovementioned stats were proven via molecular simulations. We estimated the interfacial thermal resistance (ITR) of the EP/3D-SiC composite to be 5.98 × 10^?8 m² K/W, which was an order of magnitude lower than that of the epoxy composites without a 3D network. Simultaneously, computerized molecular simulation technology was used to verify the feasibility of the experiment, which provided new ideas for the preparation of other highly thermally conductive materials.     

Thermal conductivity and mechanical properties of thermally conductive composites based on multifunctional epoxyorganosiloxanes and hexagonal boron nitride

As electronics become portable and compact with concomitant thermal issues, the demand for high-performance thermal interface materials has increased. However, the low thermal conductivity of polymers and the poor dispersion of fillers impede the realization of high filler loading composites, and this in turn limits the increase in thermal conductivity. To overcome this, multifunctional epoxyorganosiloxanes (MEOSs) were synthesized and used to fabricate thermally conductive composites in this study. In the first part of this study, the effect of the molecular weights of MEOSs on the curing behaviors of the MEOSs/trimethylolpropane tris(3-mercaptopropioante)/1-methyl imidazole systems was investigated by a DSC analysis. Both the nonisothermal and isothermal curing of the epoxy compositions (ECs) verified that the reaction rate of EC-1 containing MEOS-1 with lower molecular weight was faster than that of EC-2. In addition, mechanical properties of the cured EC-1 were superior to those of its counterpart because of a higher density in crosslinking. In the second part, EC-1 was admixed with h-BN to fabricate thermally conductive (TC) composites. Owing to the low viscosity (1.6 Pa s at 0.1 Hz) of EC-1, a TC-3 composite containing 45 wt% h-BN fillers was obtained, and the in-plane and through-plane thermal conductivity of the cured TC-3 composite reached 3.55 ± 0.29 Wm^?1K^?1 and 1.08 ± 0.08 Wm^?1K^?1, respectively. Furthermore, the tensile modulus of the cured TC-3 was measured as 76.3 ± 6.1 MPa, which was 9.1 times higher than that of the cured EC-1. Both the high thermal conductivity and good mechanical properties of the cured TC-3 composite were ascribed to the percolation of h-BN networks stemming from the high filler loading.     

Conductive and radiative heat transfer inhibition in YSZ photonic glass

A high temperature stable ceramic photonic structure is demonstrated with low thermal conductivity and suppressed external radiative heat transfer. The structure is based on a disordered arrangement of yttria-stabilized zirconia (YSZ) microparticles, called photonic glass (PhG). The prepared YSZ-PhG film exhibits low thermal conductivity of 0.03 Wm⁻¹K⁻¹ comparable to that of the air. The small point contacts of the adjacent YSZ particles are the main cause of such low thermal conductivity. After annealing at 1400 °C for 5 h, the solid thermal conductivity increased to 0.3 Wm⁻¹K⁻¹ at room temperature due to the thermally induced neck formation, associated with an increased contact area between adjacent particles. This thermal conductivity is still much lower than that of conventional YSZ thermal barrier coatings (TBCs) with approximately 1 Wm⁻¹K⁻¹. At the same time, the PhG structure is an efficient scatterer for thermal radiation in the wavelength range between 1 and 6 μm. In an only 100 μm thick structure an average reflection of 84% was obtained. At 1400 °C, the effective thermal conductivity is 0.2 Wm⁻¹K⁻¹. The presented structure is applicable to other oxides with even lower bulk thermal conductivity and can be considered for future TBCs.     

High Thermal Conductivity Nanocomposites Based on Conductive Polyaniline Nanowire Arrays on Boron Nitride

With the development of soft electronics, conductive composites are garnering an increasing amount of attention. The electrical conductivity, thermal conductivity, and electrical stability of conductive composites are all very important. In particular, the thermal conductivity of conductive composites is critical to the stability of their conductive properties. However, little is reported on thermal management in conductive systems. Herein, sufficiently hydroxylated boron nitride nanosheets (BN‐OH)@polyaniline (PANI) composite nanosheets with a high thermal conductivity and outstanding conductance stability are reported. PANI nanowire arrays are aligned vertically on BN‐OH. This well‐ordered nanostructure provides the means to form a good conductive and thermally conductive path. Notably, the composite through‐plane thermal conductivity is 2.1 W m^?1 K^?1(≈1000% that of pure PANI) and that the resistivity of the composite is 1.38 Ω cm. Importantly, the resistivity of the composite remains unchanged after 1 h of work. The results show that this composite has prospective applications for use in soft electronics.     

Exceptional thermal interface properties of a three-dimensional graphene foam

We have uncovered some unusual thermal interface properties of a three-dimensional, flexible and interconnected graphene foam (GF). The thermal interfacial resistance of GF at Si–Al interface is as low as 0.04 cm²K W⁻¹, which is one order of magnitude lower than conventional thermal grease and thermal paste-based thermal interfacial material (TIM). The thermal contact resistance was found to dominate the overall interfacial resistance of GF-based TIM, in as much as the bulk thermal conductivity of GF is rather high. The contact pressure-dependent thermal interfacial resistance of GF exhibits an asymptotic behavior, which converges into a plateau value at an ultralow contact pressure (∼0.1 MPa). Significantly, the GF-based TIM has shown a superior performance to vertically aligned carbon nanotubes currently held as the gold standard (at least ∼75% improvement in thermal interfacial resistance at Si–Al interface), thus providing a strong candidate for the next generation of high-performance carbon-based TIM.     

Preparation of Graphene-Based Hydrogel Thermal Interface Materials with Excellent Heat Dissipation and Mechanical Properties

Heat dissipation has become an essential factor affecting the performance and operating life of electronic devices as the development of modern electronic devices continues to miniaturize and integrate to increase power density. The development of new thermal interface materials has been the key solution to heat dissipation. Herein, a high thermal conductive graphene-based hydrogel (G/PVP-PVA) with an interpenetrating network is successfully constructed by physical cross-linking combined with the freeze–thaw process. The effect of the preparation parameters on its all-around performance is evaluated in detail. When the graphene dosage is 0.33%, the maximal tensile stress of the hydrogel is 322.4 kPa, the self-recovery is 95.4%, and the thermal conductivity is as high as 1.486 W m⁻¹ K⁻¹. The cooling simulation experiment shows that the hydrogel can adhere closely to the wall to reduce the air thermal resistance effectively, and the cooling rate is as high as 5.04 °C min⁻¹. The simulation experiment of the human body cooling shows that its cooling rate is 1.10 °C min⁻¹, while that for a commercial hydrogel is 0.27 °C min⁻¹. The G/PVP-PVA can give a practically potential solution for the thermal management of flexible electronic products and provides a new material for an efficient medical cooling application.     

Functionalized few-layered graphene nanoplatelets for superior thermal management in heat transfer nanofluids

The superior thermal conductivity and lightweight of graphene flakes make them materials of choice for advanced heat transfer applications, especially for transport of electricity from sustainable power stations such as concentrating solar power plants. In view of the excellent thermal conductivity of graphene or graphene-like nanomaterials (3000–5000 W m⁻¹ K⁻¹), their dispersion into conventional host fluids such as water (0.613 W m⁻¹ K⁻¹) or ethylene glycol (0.25 W m⁻¹ K⁻¹) can significantly improve fluid heat transfer characteristics. The two-dimensional structure and high surface area as well as the cost-efficient carbon-based material make graphene nanoplatelets (GNPs) suitable for large-scale applications in colloidal thermal conductive fluids. For an efficient dispersion of GNPs in base fluids, intrinsically hydrophobic GNPs were acid treated to obtain highly concentrated (4 wt.%) graphene-based nanofluids. Investigations on various GNP sizes and reaction parameters showed significant influences on the resulting thermal conductivity values of the nanofluid. After 14 h measurements in a dormant system, the most efficient nanofluid reached a thermal conductivity of 0.586 W m⁻¹ K⁻¹ (the base fluid of 0.391 W m⁻¹ K⁻¹) and a low viscosity of 6.39 cP resulting in an overall efficiency improvement of 77%, when compared to the base fluid without particles.     

Lightweight and thermally conductive thermoplastic polyurethane/hollow glass bead/boron nitride composites with flame retardancy

Polymeric composites with low density and high thermal conductivity (TC) are greatly demanded in some specific applications such as aeronautics, astronautics, and deep-sea exploration. It is a great challenge to obtain lightweight and thermally conductive polymer composites because the heat fillers have high density (>2 g/cm³) Herein, lightweight and thermally conductive thermoplastic polyurethane/hollow glass bead/boron nitride composites (TPU/HGB/BN) were prepared with the construction of a 3D BN network under the assistance of ultralightweight HGB by a solution-mixing and hot-pressing method. A 3D BN heat network has been constructed in the TPU matrix due to the alignment of the BN platelets along with the HGB microspheres during hot-pressing, which leads to a higher TC (5.34 W/mK) of the TPU/HGB/BN composites with a low density of 1.23 g/cm³, which is close to the density of pure TPU (1.20 g/cm³). In addition, the TPU/HGB/BN composites show good thermal stability with TC losses of 4.24% and 2.22%, respectively, even after treated for 50 hot-cold cycles and heated at 80 °C for 50 h. Moreover, the limiting oxygen index (LOI) of the TPU/HGB/BN composites is 51%, and they can extinguish in 8 s after ignition and exhibit enhanced flame retardancy. This work presents a simple method to design and prepare lightweight, flame retardant and thermally conductive composite materials, which can be used as lightweight thermal management materials.     

3D interconnected high aspect ratio tellurium nanowires in epoxy nanocomposites: serving as thermal conductive expressway

Heat removal via thermal management materials is attracting more and more attention in the electronic industry. Conventional particle/polymer thermal conductive composites require a high filler loading ratio (>30 vol %), which cause severe thermal interfacial resistance and mechanical issue. In this work, we fabricate tellurium nanowires (NWs)/epoxy nanocomposites via a facile bar coating method. According to Agari model and Maxwell–Eucken model, the as-synthesized ultra-long NWs with high aspect ratio (>100) construct the 3D interconnected thermal conductive network better in resin matrix to facilitate the heat transfer process. The results show that at a low loading ratio of 2.4 vol %, this nanocomposite exhibits the out-of-plane and in-plane thermal conductivity of 0.378 and 1.63 W m⁻¹ K⁻¹, respectively, which is 189 and 715% higher than that of pure epoxy resin. Importantly, good stability, and flexibility of nanocomposites are well maintained. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47054.     

Improvements in thermal conductivity and mechanical properties of HDPE/nano-SiC composites by the synergetic effect of extensional deformation and ISBS

A new melt blending method under synergy of extensional deformation and in-situ bubble stretching for high-density polyethylene (HDPE) thermally conductive composites filled by nano silicon carbide (nano-SiC) was reported. Effects of loadings and mixing time of azodicarbonamide (AC) foaming agent on the properties of the composites were experimentally studied. Scanning electron microscopy imaging showed that the nano-SiC particles dispersed uniformly in the HDPE matrix with the addition of AC. The complex viscosity and storage modulus increased with increasing AC content and decreased with increasing mixing time. The mechanical properties of the composites improved with the addition of AC and proper mixing times. The thermal conductivity of the composites increased from 0.2 to 0.7 W m⁻¹ K⁻¹ without any damage to the mechanical properties when the mixing time increased from 2 to 6 min. These results showed that the new mixing technique enables us to prepare particle-filled thermally conductive polymer composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47648.