With the development of highly integrated and miniaturized electronic devices, silicone rubber composites with good mechanical flexibility, high thermal conductivity and excellent flame resistance have aroused considerable interest in both industrial and research community. However, the effect of different geometries of thermally conductive fillers on the processing, mechanical and thermal properties as well as flame resistance of silicone rubber composites is still not clear. Herein, liquid silicone rubber (LSR) composites filled with three geometries of thermal conductive fillers i.e. spherical-like aluminum oxide (Al2O3), irregular aluminum nitride (AlN) and 2D boron nitride (BN) sheets were prepared by an extremely simple mechanical-mixing process. As expected, incorporation of BN sheets into LSR matrix produces much higher increase in the viscosity, tensile strength and hardness than the corresponding AlN and Al2O3 fillers, respectively. Typically, at a fixed filler loading of 120 phr, the increased thermal conductivity and heating/cooling efficiency of the BN/LSR composites display much better than the corresponding AlN/LSR and Al2O3/LSR composites, e.g. 316, 124 and 88% improvement in thermal conductivity, respectively. Interestingly, the thermal stability and flame resistance of the three composites present unexpected different phenomena. Compared with the pure LSR, the addition of AlN and Al2O3 exacerbates the thermal degradation of LSR chains, while the presence of BN sheets improves the flame resistance of LSR dramatically, which is attributed to the compact BN/silica residue after burning that effectively restricts the heat and oxygen to attack the inside LSR chains. 

Processing, thermal conductivity and flame retardant properties of silicone rubber filled with different geometries of thermally conductive fillers: A comparative study

Although graphene-based composites have been considered desirable candidates for thermal management applications, their poor electrical insulation restricts their further use in electrical insulation requiring occasions. Fluorinated graphene (FG), a new type of graphene-based material, attracts the attention of researchers due to its excellent electric insulation property. In this work, a novel fluorinated graphene aerogel/polydimethylsiloxane (FGA/PDMS) composite with a tightly-packed structure is constructed via freeze-drying and vacuum impregnation. The fabricated composite shows high compressibility and superior thermal conductivity of 1.41 W/(m·K) with a relatively low FGA loading of 0.28 wt%, 605.6% larger than the original PDMS. Meanwhile, it also maintains excellent insulation properties with an ultra-low electrical conductivity of 2.0 × 10−9 S/cm. 180 times smaller than graphene aerogel/PDMS. The practical excellent heat dissipation performance of the composite functioning as thermal interface material is also verified by a thorough study theoretically and experimentally. Furthermore, the FGA/PDMS composite also behaves with excellent flame retardant properties. 

Tightly-packed fluorinated graphene aerogel/polydimethylsiloxane composite with excellent thermal management properties

A critical review of the preparation strategies of thermally conductive and electrically insulating polymeric materials and their applications in heat dissipation of electronic devices

The development of modern microelectronic devices and chip integration cause electronics devices to generate excessive heat. To overcome such challenges in the near future, designing thermally conductive composites with improved stability, conductivity, and excellent electric insulation properties is critical. In this study, a novel strategy was proposed to construct superior thermally conductive networks with boron nitride nanosheets-Multiwalled carbon nanotubes (BNNS-MWCNT)/ poly(vinyl alcohol) (PVA) nanocomposites through the electrospinning technique and hot-pressing process. BNNS and MWCNT are aligned along with the fiber orientation, and MWCNT, with high length-to-diameter ratio characteristics, can act as a bridging point for uncontacted BNNS. Interestingly, when the mass fraction of BNNS-MWCNT was 20 % and the mass ratio between the BNNS: MWCNT was maintained as 9:1, the resultant BNNS-MWCNT/PVA nanocomposites exhibited an excellent in-plane thermal conductivity of 11.49 W/(m·K) and observed a tremendous heat dissipation capacity than PVA and BNNS/PVA composites. Moreover, the BNNS-MWCNT/PVA recorded excellent electrical insulation properties. The present work provides inspiration for the preparation of composites with low fillers and high thermal conductivity. 

Highly thermal conductivity of PVA-based nanocomposites by constructing MWCNT-BNNS conductive paths

Multi-functionalization of Al2O3 nanoparticles for enhancing thermal conductivity of epoxy natural rubber composites

Thermal conductive polymer composites attract lots of research due to the continuous miniaturization and multi-function of electronic equipment. As a common ceramic, Al2O3 owns relatively high thermal conductivity, high electrical resistivity and satisfactory cost performance, which is considered as the high-quality filler to prepare thermal conductive and electrical insulated composites. This paper reviews current progress in the development of Al2O3 reinforced polymer composites. We firstly summarize the preparation methods of spherical Al2O3, then heat conduction mechanisms and main factors affecting thermal conductivity are introduced. Next, we focus on the common research of Al2O3 in improving the thermal conductivity of polymers, including surface modification, filler hybridization and construction of Al2O3 network by various processing methods, and some emerging applications of thermal conductive polymer composites are introduced subsequently. After a critique of recent studies, we identify several outstanding issues must be addressed if higher thermal conductivity is fully realized.

Recent progress of thermal conductive ploymer composites: Al2O3 fillers, properties and applications

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.

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

ZrB2 is of particular interest among ultra-high temperature ceramics because it exhibits excellent thermal resistance at high temperature, as well as chemical stability, high hardness, low cost, and good electrical and thermal conductivity, which meet the requirements of high-temperature components of hyper-sonic aircraft in extreme environments. As raw materials and basic units of ultra-high temperature ceramics and their composites, ZrB2 powders provide an important way for researchers to improve material properties and explore new properties by way of synthesis design and innovation. In recent years, the development of ZrB2 powders' synthesis method has broken through the classification of traditional solid-phase method, liquid-phase method, and gas-phase method, and there is a trend of integration of them. The present review covers the most important methods used in ZrB2 nanopowder synthesis, focusing on the solid-phase synthesis and its improved process, including modified self-propagating high-temperature synthesis, solution-derived precursor method, and plasma-enhanced exothermic reaction. Specific examples and strategies in synthesis of ZrB2 nano powders are introduced, followed by challenges and the perspectives on future directions. The integration of various synthesis methods, the combination of different material components, and the connection between synthesis and its subsequent application process is the trend of development in the future.

Yuge Ouyang

Papers

Recent progress of thermal conductive ploymer composites: Al2O3 fillers, properties and applications

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

Progress in Preparation of ZrB2 Nanopowders Based on Traditional Solid-State Synthesis.