Ge Gao,Mingqi Sun,Bing Dai,Lei Yang,Kang Liu,Zhenhuai Yang,Jiecai Han,Jiaqi Zhu
High-performance thermal interface materials are in increasing demand because of the problems of dissipating heat from high-power computing devices. To solve this problem, this study proposes a method of microstructural design through uniaxial compression of graphene foam along the out-of-plane direction. The thermal conductivity of the composites with graphene foam shows an anisotropic growth along the direction of the compressive strain. The in-plane thermal conductivity increases significantly from 0.189 to 1.669 W m −1 K −1 at an extremely low filler content of 2.24 vol%, whereas the out-of-plane thermal conductivity increases slightly to 0.303 W m −1 K −1 . Moreover, the samples exhibit outstanding in-plane thermal conductivity enhanced efficiency, which reaches 415.19% at a 1.29 vol% graphene content. The mechanism of anisotropic thermal conductivity enhancement is revealed by constructing a theoretical model based on a geometrical unit cell simplified from the morphology of graphene foam. This uniaxial compression method of a 3 structure provides a novel direction for improving the thermal conductivity of polymeric matrix composites more controllably.
The anisotropic strain development and releasing process in materials is largely related to their intrinsic mechanical properties and mesoscale grain interactions. Uniaxial compression can induce a large amount activation energy in a system, which builds up anisotropic elastic strain. This is especially common in a hexagonal close-packed (HCP) system. Utilizing the X-ray diffraction technique, we investigated the double-dome shaped evolution of its anomalous anisotropic strain when compressing a polycrystalline HCP–silver–aluminum (Ag 75 Al 25 ) alloy up to 40 GPa. Analysis of the pressure-dependent grain size showed that the anisotropic strain relaxation was accompanied with grain-size refinement. This was a strong indication of microscopic structural anisotropy impacting both the mesoscopic mechanical properties and the macroscopic fracture behavior under uniaxial compression. Our findings provide valuable novel insights for further studies on materials with anisotropic mechanical properties.
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