Anisotropic thermal conductive properties of cigarette filter-templated graphene/epoxy composites

An Efficient Method to Determine the Thermal Behavior of Composite Material with Loading High Thermal Conductivity Fillers

Improvement of the thermal conductivity of encapsulant material using doping filler is an important requirement for electronic device packaging. We proposed a simple method for determining the thermal characteristics of composite material that can help save time, increase research performance, and reduce the cost of buying testing equipment. Based on the theory of Fourier law, a general 3D model is simplified into a 2D model, which can then be applied to calculate the thermal conductivity of the tested sample. The temperature distribution inside the sample is simulated by the finite element method using MATLAB software; this is a simple and useful option for researchers who conduct studies on thermal conduction. In addition, an experimental setup is proposed to help determine the extent of thermal conductivity improvement in a sample with doping filler compared to a bare sample. This method is helpful for research on optoelectronics packaging, which relates to the enhancement of thermal conductivity composite material.

Efficient Preconstruction of Three-Dimensional Graphene Networks for Thermally Conductive Polymer Composites

Electronic devices generate heat during operation and require efficient thermal management to extend the lifetime and prevent performance degradation. Featured by its exceptional thermal conductivity, graphene is an ideal functional filler for fabricating thermally conductive polymer composites to provide efficient thermal management. Extensive studies have been focusing on constructing graphene networks in polymer composites to achieve high thermal conductivities. Compared with conventional composite fabrications by directly mixing graphene with polymers, preconstruction of three-dimensional graphene networks followed by backfilling polymers represents a promising way to produce composites with higher performances, enabling high manufacturing flexibility and controllability. In this review, we first summarize the factors that affect thermal conductivity of graphene composites and strategies for fabricating highly thermally conductive graphene/polymer composites. Subsequently, we give the reasoning behind using preconstructed three-dimensional graphene networks for fabricating thermally conductive polymer composites and highlight their potential applications. Finally, our insight into the existing bottlenecks and opportunities is provided for developing preconstructed porous architectures of graphene and their thermally conductive composites.

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.

Thermal insulation fibers with a Kevlar aerogel core and a porous Nomex shell

Kevlar aerogel fibers which inherit the aerogel's brilliant properties of low density, high porosity and large surface area are promising candidates for thermal insulation applications in textiles. To enhance the mechanical strength of Kevlar aerogel fibers, an extra Nomex shell was introduced by a simple coaxial-wet-spinning approach. The resultant coaxial fibers were observed to have a Kevlar aerogel core and a porous Nomex shell. Besides, there also formed an air gap between the core and the shell. This multi-layered coaxial structure with numerous pores inside contributes to the excellent thermal insulation performance of the fibers and their fabrics. The temperature differences between the hot plate and the outer surface of the fabrics were measured to be as high as 80 °C when exposed to a temperature of 300 °C. In addition, these fibers also performed well in thermal stability, and almost did not decompose before 380 °C. Not only that, the breaking strength of the Nomex shell can be up to twice that of the Kevlar core, resulting in a significant improvement in the fiber's mechanical strength. It can be envisaged that the developed coaxial fibers with excellent thermal insulation and endurance properties as well as improved mechanical strength may have broad prospects for thermal insulation at high temperatures.

Excellent Thermally Conducting Ni Plating Graphite Nanoplatelets/Poly(phenylene sulfone) Composites for High-Performance Electromagnetic Interference Shielding Effectiveness

First, nickel particles were deposited on the surface of graphite nanoplatelets to fabricate highly conductive GnPs@Ni core-shell structure hybrid fillers via electroplating. The modified GnPs were blended with polyphenylene sulfone via the solution blending method, followed by the hot-pressing method to achieve high thermally conducting GnPs@Ni/PPSU composites for high performance electromagnetic interference effectiveness. The results showed that in-plane and through-plane thermal conductivity of the composite at the 40 wt% filler loading could reach 2.6 Wm-1K-1 and 3.7 Wm-1K-1, respectively, which were 9.4 and 20 times higher than that of pure PPSU resin. The orientation degree of fillers was discussed by XRD and SEM. Then, heat conduction data were fitted and analyzed by the Agari model, and the heat conduction mechanism was further explored. The testing results also demonstrated that the material exhibited good conductivity, electromagnetic shielding effectiveness and superior thermal stability. Overall, the GnPs@Ni/PPSU composites had high thermal conductivity and were effective electromagnetic shielding materials at high temperatures.

Current Status of Research on the Modification of Thermal Properties of Epoxy Resin-Based Syntactic Foam Insulation Materials

As a lightweight and highly insulating composite material, epoxy resin syntactic foam is increasingly widely used for insulation filling in electrical equipment. To avoid core burning and cracking, which are prone to occur during the casting process, the epoxy resin-based syntactic foam insulation materials with high thermal conductivity and low coefficient of thermal expansion are required for composite insulation equipment. The review is divided into three sections concentrating on the two main aspects of modifying the thermal properties of syntactic foam. The mechanism and models, from the aspects of thermal conductivity and coefficient of thermal expansion, are presented in the first part. The second part aims to better understand the methods for modifying the thermal properties of syntactic foam by adding functional fillers, including the addition of thermally conductive particles, hollow glass microspheres, negative thermal expansion filler and fibers, etc. The third part concludes by describing the existing challenges in this research field and expanding the applicable areas of epoxy resin-based syntactic foam insulation materials, especially cross-arm composite insulation.

Construction of low melting point alloy/graphene three-dimensional continuous thermal conductive pathway for improving in-plane and through-plane thermal conductivity of poly(vinylidene fluoride) composites

As the temperature of hot spots increases in electronic devices, thermal management is a key issue for maintaining a device's reliability and performance. The usual approaches of quickly extracting the heat from the hot spots have focused on aligning two-dimensional filler along the in-plane orientation in the polymer matrix. Meanwhile, improving the through-plane thermal conductivity of polymer-based composites is as important as in-plane thermal conductivity. In this study, poly(vinylidene fluoride) composites with three-dimensional continuous thermal conductive pathways of a low melting point alloy (LMPA)/graphene were prepared through a two-step method. Poly(vinylidene fluoride)@graphene (PVDF@Gr) microspheres were firstly prepared by an in-situ water-vapor induced phase separation method. Subsequently, PVDF@Gr/LMPA composites were obtained by hot-pressing after mixing the LMPA with the PVDF@Gr microspheres. Attributed to the unique solid-liquid phase transition advantage of the LMPA and the good matching of the phonon power spectrum between the LMPA and the graphene, the PVDF@4.8Gr/10LMPA composites with 4.8 vol% graphene and 10.0 vol% LMPA exhibited an outstanding in-plane thermal conductivity of 9.41 W m^-1 K^-1 and through-plane thermal conductivity of 0.35 W m^-1 K^-1, which was nearly increased by 245% and 130% compared to that of the PVDF@4.8Gr composites, respectively. The enhanced elasticity modulus and reduced thermal expansion coefficient were attributed to the LMPA constructing a three-dimensional continuous thermal conductive pathway along with the graphene and reducing interface thermal resistance. This study offeres a straightforward and repeatable method for fabricating highly thermally conductive polymer composites and widens the application of LMPAs in the fields of thermal management.

The combustion synthesis of highly crystalline boron nitride nanosheets and their application in thermoconductive polymeric composites

We report scalable fabrication of single crystalline BNNS by a magnesiothermic reduction combustion synthesis method and their applications in thermoconductive polymeric composites.