Nest-like hetero-structured BNNS@SiCnws fillers and significant improvement on thermal conductivities of epoxy composites

Abstract

Silicon carbide nanowires (SiCnws) were in-situ grown on boron nitride nanosheets (BNNS) to construct a novel kind of nest-like hetero-structured BNNS@SiCnws thermally conductive fillers from natural bamboo leaves and tetraethyl orthosilicate (TEOS) by means of ultrasonic impregnation, sol-gel followed by carbothermic reduction. Then, the thermally conductive & electrically insulating BNNS@SiCnws/epoxy composites were prepared via blending-casting method. When the amount of BNNS@SiCnws-II (65/35, wt/wt) was 20 wt%, BNNS@SiCnws/epoxy composites presented the optimal overall performances. Thermal conductivity coefficient (λ) of BNNS@SiCnws-II (20 wt%)/epoxy composites increased from 0.22 W/mK of pure epoxy matrix to 1.17 W/mK, higher than that of SiCnws/epoxy (0.72 W/mK), BNNS/epoxy (0.82 W/mK) and (BNNS/SiCnws)/epoxy composites (direct mixing BNNS/SiCnws, 65/35, wt/wt, 0.76 W/mK) with the same filler concentration of 20 wt%. Meanwhile, BNNS@SiCnws/epoxy composites presented excellent heat transfer/heat dissipation efficiency, due to synergistic effect of the “line-to-surface” hetero-structure of SiCnws and BNNS, which could significantly improve the formation probability of the thermally conductive paths. Furthermore, the BNNS@SiCnws/epoxy composites possessed favorable electrical insulation, thermostability and ideal mechanical properties. Furthermore, the related surface & volume resistivities, the electric breakdown strength, the glass-transition temperature, the heat resistant index, the flexural strength as well as the impact strength of BNNS@SiCnws-II (20 wt%)/epoxy composites reached to be 3.7 × 1015 Ω, 5.17 × 1015 Ω·cm, 22.1 kV/mm, 126.7 °C, 185.5 °C, 75.7 MPa and 8.2 kJ/m2, respectively.