A Facile Route to Fabricate Highly Anisotropic Thermally Conductive Elastomeric POE/NG Composites for Thermal Management

Abstract

Owing to the demand for directional heat dissipation, some technologies have been developed to fabricate polymer-based composites with anisotropic thermal conductivity, and it has been demonstrated that the anisotropic thermal conductivity of composites can be achieved by varying orientation of fillers. The orientation or directional alignment of fillers in the matrix by using the solution-based methods is an important strategy [18] such as vacuum filtration, [19][20][21][22] spin casting, [23] solution casting, [24,25] magnetic fields, [26] electric fields, [27] and self-assembly. [28][29][30][31] Zhao et al. [29] used self-organization strategy to align thermally reduced graphene oxide (TRG) sheets in poly(benzobisoxazole). The composites presented a thermally conductive anisotropy with a highly effective thermal conductivity of 50 W m −1 K −1 along the TRG aligning direction and the thermal conductivity in the direction perpendicular to the TRG alignment was very low. Kuang et al. [32] utilized two-roll milling to fabricate hexagonal boron nitride nanosheets (BNNS)/silicon rubber composite sheets with anisotropic thermal conductivity, and the sheets showed higher thermal conductivity of 5.47 W m −1 K −1 in the orientating direction of BNNS.However, in many cases, the preferred direction to show a high thermal conductivity is not the direction in which the composites do have a high thermal conductivity. [33] Although many methods have been developed to fabricate polymer composite fibers, films, or sheets which have high in-plane thermal conductivity in the oriented direction of the fillers, [9,[34][35][36] a high thermal conductivity in the through-plane direction is more desired as the case in thermal interfacial materials (TIMs), thermal conduction greases, and thermal conduction electronic substrates. [37][38][39][40][41] It has been reported that the bulk thermal conductivity required for TIM should be larger than 4 W m −1 K −1 , which can only be satisfied by the thermal conductivity in the in-plane direction. [42] Yao et al. [43] used silver nanoparticles to decorate the fillers and to improve the through-plane thermal conductivity of BNNS/SiC nanowire bioinspired composite paper. However, the through-plane thermal conductivity of the composite paper was only 1.80 W m −1 K −1 when the filler content was as high as 90 wt%. Besides, magnetic field, electric field, and chemical vapor deposition can be used to align fillers in low-viscosity matrix fluids, but generally the alignment Highly anisotropic polyolefin elastomer (POE)/natural graphite (NG) composites with high through-plane thermal conductivity and excellent mechanical properties, in which NG sheet perfectly aligns along one direction, are prepared by two-roll milling, hot compression, and mechanical cutting. The through-plane thermal conductivity coefficient of POE/NG composites is markedly improved to be 13.27 W m −1 K −1 at an NG loading of 49.30 vol%. When the composite is used as a thermal management material, it shows excellent heat dissipatin...

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