Boron nitride nanosheet @ quantum‐sized diamond nanocrystal complex/epoxy nanocomposites with enhancing thermal conductivity and sufficient dielectric breakdown strength

Abstract With the development of high‐voltage and high‐power devices in the direction of compactness, lightness and extreme working environments, the contradiction between thermal conductivity and dielectric breakdown strength is becoming more and more obvious. In this work, a novel boron nitride nanosheet with uniformly dispersed diamond nanocrystalline (abbreviated as BA@DN) was prepared via facile acidizing hydroxylation, in situ copolymerization self‐assembly of dopamine and blending process. The obtained hybrid filler was employed to embed into epoxy matrix, showing enhanced thermal conductivity and sufficient dielectric breakdown strength. For example, the through‐plane and in‐plane thermal conductivity of epoxy composite with 5% BA@DN‐2 reaches to 0.56 and 3.824 W/m K, respectively. The study proposes a modified plane thermal conductivity model. Based on calculations, it was found that the modified thermal conductivity of 5% BA@DN‐2 is 3.47 W/m K, which is significantly higher than that of pure EP, specifically 17.35 times higher. These findings are significant in terms of materials science. while its alternating current and direct current dielectric breakdown strength are 48.84 and 136.31 kV/mm, about 85.68% and 99.1% of pure epoxy, respectively. The mechanism of outstanding dielectric breakdown strength was analyzed via dielectric characteristic, partial discharge performance and the theory of quantum size effect. In addition, a modified multi‐core model with a multilevel overlapping interface is presented. Highlights The acidified diamond nanocrystals (DNs) were attached to dopamine‐coated boron nitride nanocrystals by a blending process. The small size effect of DNs allows the epoxy film to have both high thermal conductivity and high insulation properties. A thermal conductivity correction model is proposed to eliminate the effect of graphite layer on the film.