Thermal Conductivity Enhancement Efficiency Research Articles

Self-assembled nest-like BN skeletons enable polymer composites with high thermal management capacity

The lagging development of thermally conductive but electrically insulating materials has become a bottleneck problem for the next generation of advanced high-power density electronic devices. Although second-phase reinforced composites are promising materials for addressing thermal management issues, the inherent mechanism of severe phonon scattering at the interphase results in actual thermal conductivity enhancement efficiency far below expectations. Here, we report a high-performance polymer composite with a nest-like interconnected boron nitride skeleton. This nest-like interconnected BN skeleton without mechanical contact can provide high-efficiency and long-distance phonon transport channel, realizing high thermal conductivity of 1.827 W m−1 K−1 in polymer composite with ultra-low content (4.7 vol%). Meanwhile, the EP/nest-like BS composites possess ideal electrical properties and dimensional stability. In the actual heat dissipation process of LED chips, the optimal composite material as the thermal interface material can display a temperature drop of more than 34.8 % compared to neat epoxy, which proves the broad application prospects of this strategy in advanced electronic devices.

Interweaved filler network in epoxy resin with reduced interface thermal resistance via in-situ high-temperature “welding” for significantly improved thermal conductivity

For heterogeneous integration in harsh environments, polymeric materials are required to integrate excellent insulating property with significant thermal conductivity. Traditional discrete fillers used in polymeric matrix to create thermal pathways introduce numerous contact interfaces, leading to limited thermal conductivity enhancement efficiency (TCE) and unstable dielectric properties. Here, a distinctive strategy, involving the preparation of an interweaved thermally conductive filler with inherent heat channels through self-templated electrospinning and in-situ high-temperature “interface welding”, is proposed to reduce the interface thermal resistance (ITR). The growth of grains at high temperature facilitates the process of “interface welding”, while self-templated electrospinning establishes intrinsic thermal conduction pathways. Consequently, the epoxy resin fortified with this interweaved filler exhibits an exceptionally TCE of 162.15 % and enhanced in-plane thermal conductivity of 3.75 W m−1 K−1 at ultra-low filler ratio of 7.10 vol%. The combination of high electrical insulation of filler and low filler content results in excellent electrical insulating property (>1017 Ω cm) and stable dielectric properties over a frequency range of 103-106 Hz, enabling the successful implementation of heterogeneous integration in challenging environments. This work has the potential to offer a groundbreaking approach for achieving interconnected functional networks within polymer-based composites.

Preparation and properties of phase-change materials with enhanced radial thermal conductivities based on anisotropic graphene aerogels.

In this study, anisotropic graphene aerogels are prepared using the heat-flow method. Then, graphene aerogels with nanosilver particles are prepared via a silver mirror reaction. The aerogels are soaked in paraffin wax and the effects on the properties of the wax are investigated. The thermal conductivity of pure paraffin wax is 0.2553 W m-1 K-1. For the prepared PCM, the aerogel content was 0.92 vol%; this increases to 1.2234 W m-1 K-1, which corresponds to a thermal conductivity enhancement efficiency of 582%. The axial thermal conductivity is 1.4953 W m-1 K-1, which corresponds to a thermal conductivity enhancement efficiency of 746%. The graphene aerogels with the nanosilver particles show high phase-change efficiency. Owing to the significant improvements in the axial and thermal conductivities, the radial and axial heat transfer properties show good consistency suitable for practical applications.

An innovative graphene-based phase change composite constructed by syneresis with high thermal conductivity for efficient solar-thermal conversion and storage

Graphene-based phase change composites hold significant potential for solar energy utilization, but their poor thermal conductivity hinders their practical applications. In this work, an air-dried graphene skeleton (AGS) with excellent thermal conductivity enhancement efficiency was constructed by the ice templating method and syneresis, and the air-dried graphene phase change composite (AGP) was subsequently obtained through vacuum-impregnating n-Docosane (C22) into AGS. The syneresis effectively reduced the phonon scattering between graphene sheets within AGS and increased the density of AGS to 0.1701 g/cm³. Therefore, with a graphene skeleton loading of 23.82 wt.%, AGP exhibited excellent thermal conductivity of 9.867 W/(m K), outstanding electrical conductivity of 68.08 S/cm, and remarkable shape stability. Additionally, AGP demonstrated a melting enthalpy of 188.5 J/g and an outstanding solar-thermal conversion efficiency of 93.98%, showing enormous potential for the utilization of solar energy.

Rational design of graphene/polymer composites with excellent electromagnetic interference shielding effectiveness and high thermal conductivity: a mini review

• This review concludes the works of composites using graphene as filler loadings to improve the thermal conductivity enhancement and EMI shielding performance • It was found that the graphene frameworks with the anisotropic orientation can achieve higher thermal conductivity enhancement efficiency and EMI SE at lower filler loading • This review also makes prospect for the development trend of graphene/polymer composites with high thermal conductivity and EMI shielding performance in the future The integration and miniaturization of chips lead to inevitable overheating and increasing electromagnetic interference (EMI) problems, which threaten the performance, stability, and lifetime of electronic components. Therefore, it is important to improve the heat dissipation and EMI shielding performance in device packaging for the steady operation of electronic products. In recent years, due to its intrinsic superior thermal conductivity, proper electrical conductivity, light-weight, and structural adjustability, graphene has been widely used as high thermal and conductive fillers incorporated in the polymer matrix to improve the thermal conductivity and electrical conductivity of composites. This review concludes the recent development of graphene/polymer composites by using graphene as fillers to improve the thermal conductivity and EMI shielding effectiveness (EMI SE). The structure of graphene embedded in the composites varies from zero-dimension (0D), one-dimension (1D) to two-dimensions (2D). Moreover, highly thermally and electrically conductive fillers with different dimensions were also modified on the graphene to improve the composite performance. Finally, this review also makes prospects for the development trend of graphene/polymer composites with high thermal conductivity and EMI SE in the future.

Unidirectional thermal conduction in electrically insulating phase change composites for superior power output of thermoelectric generators

Owing to their ability to absorb excess heat within narrow temperature ranges, phase change materials (PCMs) have attracted significant interest in the thermal management of power equipment and energy devices. However, the low thermal conductivity of PCMs severely limit their application in high-power devices. Current methods for increasing the thermal conductivity are generally at the cost of lowering the phase change enthalpy (i.e., latent heat) of PCMs. In this study, we developed phase change composites (PCCs) based on highly oriented aramid nanofiber/boron nitride nanosheets (ANF/BNNS) aerogels impregnated with paraffin; the aerogels were prepared by unidirectional freeze-drying method and were impregnated with the PCM, namely, paraffin, by a vacuum assisted method. The ANF/BNNS PCCs exhibited high thermal conductivity enhancement efficiency (TCEE), ultra-high latent heat retention, and superior electrical insulation. For a loading of 2.21 wt% BNNS, the TCEE and the latent heat retention of the PCCs reached impressive values of 89.2%, and 93.64%, respectively. In addition, the PCCs are highly electrically insulating with an electrical conductivity of <1.17 × 10−14 S cm−1. The PCCs also maintain good shape stability even at temperatures higher than the melting point of the PCM (i.e., paraffin). The ANF/BNNS PCCs were shown to reduce the cold-side temperature of thermoelectric generators by more than 10 °C in comparison to that achieved by those operated by air-cooling, resulting in an approximately 300% increase in power output. These PCCs, with both high latent heat retention and TCEE, offer new opportunities for use as advanced thermal management materials in future high-power devices.

A novel modified expanded graphite/epoxy 3D composite with ultrahigh thermal conductivity

Polymer-based composites with efficient thermal energy dissipation performance can be prospectively applied in electronics and military industry. However, significantly improving the thermal conductivity (TC) of polymer-based composites is still challenging. Herein, 3D sulfanilamide-modified expanded graphite/epoxy (EG-SA/EP) composites with interconnected filler network were successfully prepared by a pre-filling and hot-pressing method. Benefiting from the interconnected network, the composite with 70 wt% EG-SA demonstrated ultrahigh bulk TC of 98 W/m·K (which exceeds some commercially-used metals) and up to 44,445% TC enhancement efficiency. Meanwhile, the EG-SA/EP composites exhibited excellent electromagnetic interference shielding performance of 85 dB (which is sufficient to block 99.9999997% of incident radiation), high electric conductivity of 7153 S/m and excellent thermal infrared response capability (the time to raise surface temperature from 19 to 82 °C is only 3 s). As for the mechanism of heat transfer, the 3D structure of EG-SA maintained through epoxy pre-filling in EG-SA is the main reason for the significantly improved TC. This is because the new method enables EG-SA to build a unique dense interconnected network in composites in the subsequent hot-pressing process, but the traditional direct mixing method easily destroys the inherent micro-3D structure of EG. The above excellent performances endow the EG-SA/EP composites with huge potential application value.

In-Situ Synthesis of Graphene-Like Carbon Encapsulated Copper Particles for Reinforcing Copper Matrix Composites

Owing to the unfavorable wetting and density difference between graphene and copper, it remains challenging to achieve homogeneous dispersion of graphene for utilizing the unique nature of graphene in copper matrix composites. Here, we design an in-situ process to fabricate graphene-like carbon (GLC) reinforcing copper matrix composites: GLC can be directly fabricated on commercial copper particles using modified PECVD method followed by vacuum hot pressing, which is high-efficiency and can be massively produced for graphene reinforced metal matrix composites in industrial level. After hot pressing, the GLC with ultra low content (170 to 350 ppm) can be uniformly dispersed and tightly embedded within the copper matrix. A remarkable thermal conductivity enhancement efficiency of 85% and enhanced thermal conductivity (439 W m-1 K-1), accompanied by the higher wear resistance, can be obtained in our GLC reinforced copper matrix composites. In actual arc ablation performance measurement, the breakdown strength and relative arc ablation resistance of GLC/Cu composites can be significantly improved by 106.5% and 33.3% than pure copper, respectively, demonstrating GLC/Cu composites a promising candidate for application as high voltage electrical contacts.

Flexible thermoplastic polyurethane-carbon nanotube composites for electromagnetic interference shielding and thermal management

• Flexible TPU composites were prepared by NIPS assisted solution mixing method. • Long length MWCNT composites offer a remarkable EMI SE value of 42.5 dB. • Short length MWCNT based composites exhibit excellent thermal management. • Short length MWCNT based composites possess good electromechanical performance. Lightweight, flexible, and thermally conductive electromagnetic interference (EMI) shielding materials have garnered front facet research interest because of urgent demand to address the EM wave pollution. Herein, inspired from the effectiveness of interconnected networks of different types of carbon nanotubes (CNTs), an endeavored to design three types of CNTs based thermoplastic polyurethane (TPU) composites through a facile solution blending with non-solvent induced phase separation (NIPS) strategy. The effect of different length of CNTs on the EMI shielding, electrical and thermal conductivity performance of TPU nanocomposites have been studied explicitly. The composite with long length CNT (10 wt%) offered a remarkable EMI shielding efficiency of 42.5 dB, the electrical conductivity of 1.9 × 10 −3 S/cm, whereas composite with short length CNTs showed a thermal conductivity of 0.51 W/mK and the corresponding thermal conductivity enhancement efficiency exceeded 145% relative to pure TPU. Incorporation of long length CNTs helped to form unique interconnected conductive networks within the TPU matrix that boost more the electron or charge transferability inside the composites, improvement in mechanical properties, EMI shielding, and electrical properties than that of short length CNTs. In contrast, short length CNTs display significant electromechanical performance and heat transferability than that of long length CNTs. The composites showed a high response in electrical conductivity and minor change in EMI shielding efficiency with repeated bending cycles. This work provides a corelated remark of different types of CNT based TPU composites for superior EMI SE and thermal management applications for next generation wearable and stretchable electronics.

In-situ synthesis of graphene-like carbon encapsulated copper particles for reinforcing copper matrix composites

Owing to the unfavorable wetting and density difference between graphene and copper, it remains challenging to achieve homogeneous dispersion of graphene for utilizing the unique nature of graphene in copper matrix composites. Here, we design an in-situ process to fabricate graphene-like carbon (GLC) reinforcing copper matrix composites: GLC can be directly fabricated on commercial copper particles using modified PECVD method followed by vacuum hot pressing, which is high-efficiency and can be massively produced for graphene reinforced metal matrix composites in industrial level. After hot pressing, the GLC with ultralow content (170 to 350 ppm) can be uniformly dispersed and tightly embedded within the copper matrix. A remarkable thermal conductivity enhancement efficiency of 85% and enhanced thermal conductivity (439 W m−1 K−1), accompanied by the higher wear resistance, can be obtained in our GLC reinforced copper matrix composites. In actual arc ablation performance measurement, the breakdown strength and relative arc ablation resistance of GLC/Cu composites can be significantly improved by 106.5% and 33.3% than pure copper, respectively, demonstrating GLC/Cu composites a promising candidate for application as high voltage electrical contacts.

Wet-resilient graphene aerogel for thermal conductivity enhancement in polymer nanocomposites

Three-dimensional (3D) graphene-based aerogels have significant potential for adsorption, sensors, and thermal management applications. However, their practical applications are limited by their disorganized structure and ultra-low resilience after compression. Some methods can realize a well-aligned structure, however, they involve high costs and complex technology. Herein, a 3D graphene hybrid aerogel with an anisotropic open-cell and well-oriented structure is realized by unidirectional freeze casting, which combines the ‘soft’ (e.g. graphene oxide, Tween-80) and ‘hard’ (e.g. graphene assembly) components to realize full recovery after flattening. A graphene aerogel annealed at a moderate temperature (∼200 °C) can possess superhydrophilicity and outstanding wet-resilience properties, including after being pressed under 40 MPa. Furthermore, the graphene aerogel annealed at a high temperature of ∼1500 °C exhibits excellent thermal conductivity enhancement efficiency in polydimethylsiloxane (PDMS). The resultant nanocomposites clearly demonstrate anisotropic thermal conductivity and promising applications as thermal interface materials. This strategy offers new insights into the design and fabrication of 3D multifunctional graphene aerogels.

Application potential of graphene aerogel in paraffin phase change composites: Experimental study and guidance based on numerical simulation

The current challenge for the application of organic phase change materials is to compromise the conflicting influence of high thermal conductivity matrix content on the heat storage performance and thermal conductivity of phase change composites. Herein, we prepared graphene aerogel (GA) and GA-based paraffin phase change composite (GAP) by the widely reported hydrothermal method and studied the application potential of GA in GAP. The underlying mechanism of paraffin latent heat enhancement caused by GA was discussed from the perspective of the crystallization and phase change process of paraffin. X-ray diffraction and differential scanning calorimetry results showed that as the GA content increased, the paraffin in GAP had an increased crystallinity and exhibited increased latent heat. Activation energy of paraffin's phase change process calculated according to Kissinger model was effectively reduced when GA content was greater than 7.3 wt%, implying a considerable increase in the thermal response rate of GAP. In addition, in order to improve the thermal conductivity enhancement efficiency of GA, thermal conductivity of GAP was predicted by finite element numerical simulation. A good agreement was observed between the experimental and numerical results and some practical suggestions were made for the experimental preparation process.

Ultralight covalently interconnected silicon carbide aerofoam for high performance thermally conductive epoxy composites

With the development of highly integrated electronic devices, there are growing demands for high performance thermal management materials with high thermal conductivity and electrical insulation. Herein, we report thermal properties of epoxy-based SiC aerofoam composites. A novel three-dimensional structure of covalently interconnected porous SiC (3D-SiC) aerofoam is successfully fabricated using 3D reduced graphene oxide foam as a template, and it was embedded in epoxy resin and cured to prepare thermoconductive composites. The formation of covalent SiC linkage and presence of interconnected 3D-SiC aerofoam resulted in thermal conductivity of the epoxy composites as high as 10.26 W·m−1·K−1 at 6.52 vol% of SiC, which calculated as thermal conductivity enhancement efficiency per 1 vol% of filler loading equals to 859%. The 3D-SiC/epoxy composites showed an excellent heat dissipation performance compared to that of a commercial thermal pad. The 3D-SiC/epoxy composite is a highly prospective candidate as next generation thermal dissipating material for electronic devices.

Highly Oriented Graphite Aerogel Fabricated by Confined Liquid-Phase Expansion for Anisotropically Thermally Conductive Epoxy Composites.

Graphene-based thermally conductive polymer composites are of great importance for the removal of the excess heat generated by electronic devices. However, due to the orientation of graphene sheets in the polymer matrix, the through-plane thermal conductivity of polymer/graphene composites remains far from satisfactory. We here demonstrate a confined liquid-phase expansion strategy to fabricate highly oriented confined expanded graphite (CEG) aerogels. After being incorporated into epoxy resin (EP), the resulting EP/CEG composites exhibit a high through-plane thermal conductivity (4.14 ± 0.21 W m-1 K-1) at a quite low filler loading of 1.75 wt % (0.91 vol %), nearly 10 times higher than that of neat EP resin and 7.5 times higher than the in-plane thermal conductivity of the composite, indicating that the CEG aerogel has a high through-plane thermal conductivity enhancement efficiency that outperforms those of many graphite/graphene-based fillers. The facile preparation method holds great industrial application potential in fabricating anisotropic thermally conductive polymer composites.

Graphdiyne for significant thermal conductivity enhancement at ultralow mass fraction in polymer composites

In thermal management systems, it is quite meaningful to achieve high thermal conductivity enhancement efficiency for polymer-based thermally conductive materials with low content filler. In this work, a novel 2D all-carbon allotrope, graphdiyne (GDY) was attempted as a filler to improve the thermal conductivity of the polymer matrix. The poly(vinylidene fluoride) (PVDF) composite films, with ultralow mass fraction (≤ 1 wt%) GDY, were fabricated by solution blend and hot pressing. As a consequence, the obtained composite film, at only 1 wt% GDY content, exhibited a high in-plane thermal conductivity of 3.86 W m−1K−1, which revealed a 2249% thermal conductivity enhancement compared with neat PVDF. This excellent heat transport performance makes GDY an attractive filler for high-performance composite for electronic cooling applications.

Achieving Significant Thermal Conductivity Enhancement via an Ice-Templated and Sintered BN-SiC Skeleton.

Conventional polymer composites normally suffer from undesired thermal conductivity enhancement which has hampered the development of modern electronics as they face a stricter heat dissipating requirement. It is still challenging to achieve satisfactory thermal conductivity enhancement with reasonable mechanical properties. Herein, we present a three-dimensional (3D), lightweight, and mechanically strong boron nitride (BN)-silicon carbide (SiC) skeleton with aligned thermal pathways via the combination of ice-templated assembly and high-temperature sintering. The sintering has introduced atomic-level coupling at the BN-SiC junction which contributes to efficient phonon transport via the newly formed borosilicate glass BCxN3-x (0 ≤ x ≤ 3) and SiCxN4-x (0 ≤ x ≤ 4) phases, leading to much lower interfacial thermal resistance. Thus, the obtained BN-SiC skeleton shows satisfactory thermal performance. The prepared 3D BN-SiC/polydimethylsiloxane (PDMS) composites exhibit a maximum through-plane thermal conductivity of 3.87 W·m-1·K-1 at a filler loading of only 8.35 vol %. The thermal conductivity enhancement efficiency reaches 220% per 1 vol % filler when compared to pure PDMS matrix, superior to other reported BN skeleton-based composites. The feature of our strategy is to allow the oriented three-dimensional skeleton to be strongly bonded by a sintered ceramic phase instead of polymer-like adhesive, namely, to improve the intrinsic thermal conductivity of the skeleton to the greatest extent. This strategy can be applied to develop novel thermal management materials that are lightweight and mechanically tough that rapidly transfer heat. It represents a new avenue to addressing the heat challenges in traditional electronic products.

Preparation of Anisotropic Aerogels with Pristine Graphene by Heat Flow and Study of Their Effects on Heat Transfer in Paraffin.

In this study, anisotropic graphene/graphene oxide (GO) aerogels (AGAs) were obtained by freeze-drying after direct participation of pristine graphene in the self-assembly of anisotropic gel by the heat flow method. After vacuum microwave treatment, the physical, chemical and structural characteristics of the AGAs were investigated. The results show that AGAs, in which the internal graphene sheets are parallel to the heat flow direction, are successfully prepared. After microwave treatment, the amount of oxygen and nitrogen reduces significantly and the sp2 domain increases. However, at the same time, many fragments and holes are generated in the graphene sheets. The effects of AGAs on the phase transition of paraffin is studied, and the results show that the melting enthalpy, solidification enthalpy and initial melting temperature of AGA/paraffin composites decreases as the GO content in the AGAs increases, whereas the melting range, solidifying range and subcooling degree increases. The highest axial thermal conductivity of the AGA/paraffin composite is 1.45 W/(mK), and the thermal conductivity enhancement efficiency is 884% (AGA content was 0.53 vol %). Compared with previously investigated, similar AGA/paraffin composites, the aerogels fabricated in this study have the obvious advantages of a simple fabrication process, a low cost and a high thermal conductivity enhancement efficiency. These aerogels possess the potential for application in phase-change energy storage (PES), thermal energy management and other fields.

Thermal Flow Self-Assembled Anisotropic Chemically Derived Graphene Aerogels and Their Thermal Conductivity Enhancement.

In this study, we investigated the directional heating of graphene oxide (GO) dispersion to generate a temperature gradient and form a simulated “ocean current” inside the dispersion so that GO sheets could be aligned in a directional manner and then reduced and self-assembled into anisotropic reduced graphene oxide (rGO) gel. After freeze-drying and varying degrees of vacuum microwave treatment, anisotropic chemically derived graphene aerogels (AGAs) were obtained. Through performance detection and the analysis of the results, it was verified that the AGAs with certain characteristics of “ocean current” were prepared in this experiment, and its axial direction has obvious directional arrangement. After being treated by vacuum microwave for a short time (1 min.), the axial thermal conductivity of the composite materials (AGA-adsorbed paraffin) was observed to be 1.074 W/mK, and the thermal conductivity enhancement efficiency was 995%; as compared with similar thermal conductivity enhancement composites that were found in previous studies, the proposed method in this paper has the advantages of simple processing, high efficiency, and energy conservation.

Construction of 3D interconnected diamond networks in Al-matrix composite for high-efficiency thermal management

Realizing high-efficiency thermal management is of great significance for the fast growth of high-performance electronic devices. Herein, three-dimensional (3D) diamond networks (DN) are proposed as highly thermal conductive reinforcements for Al-matrix composite by template-directed chemical vapor deposition (CVD) on Cr-modified Cu foams. The diamond networks with dense and uniform structure were further incorporated with pure Al by gas pressure infiltration (GPI). Results showed that the diamond skeletons were uniformly and integrally distributed in the dense Al matrix with a compact interfacial bonding and limited interface product after GPI process. A relatively high thermal conductivity of 315.7 W/mK was achieved at a low diamond loading of 4.6 vol.%, which was equivalent to 54% enhancement compared to pure Al. The synthesized diamond networks with high quality and continuous structure can act as high-efficiency heat transfer pathways to ensure most of heat being transferred through the 3D diamond skeletons, which effectively reduced the phonon-boundary scatterings. As a consequence, the fabricated composite shows a great superiority in both thermal conductivity and thermal conductivity enhancement efficiency as compared with the conventional Al-matrix composites reinforced with even higher volume fraction of diamond particles. The construction of 3D interconnected diamond networks in metal-matrix composites might open new doors for the design and preparation of high-efficiency thermal management materials.

3D Vertically Aligned BNNS Network with Long-Range Continuous Channels for Achieving a Highly Thermally Conductive Composite.

Construction of a three-dimensional (3D) vertically aligned filler network in a polymer matrix has been believed to be an effective method to attain a large through-plane thermal conductivity enhancement at relatively low filler loading. However, it is still a challenge to construct a vertically aligned filler network composed of many long-range continuous pore channels in a polymer matrix for the high-flux heat-conduction. To address this problem, herein, nanofibrillated cellulose (NFCs) assisted unidirectional freeze-drying of a boron nitride nanosheets (BNNSs) slurry was used to prepare a novel epoxy composite containing a 3D vertically aligned BNNS network with long-range continuous pore channels. The vertically aligned and nacre-mimetic channels make the composite possess a high through-plane thermal conductivity of 1.56 W m-1 K-1 at an extremely low BNNSs loading of 4.4 vol %, and a significant thermal conductivity enhancement efficiency of 167.3 per 1 vol % filler. Therefore, we think this work is expected to give a significant insight into the preparation of polymer composite with high heat-conduction efficiency to address the heat dissipation of modern electronics.