Research on the surface structure engineering of boron nitride nanotubes and mechanism of their regulation on the properties of epoxy composite dielectric

Adding nanofillers to epoxy resin matrices is a common approach to achieve their multi-function, among which boron nitride nanotubes (BNNTs) with one-dimensional nanostructures have attracted much attention because of their ultra-high thermal conductivity, wide energy level band gap, high aspect ratio and mechanical strength. Yet, the strong π-π non-covalent bonding and lip-lip interactions make BNNTs prone to agglomeration in the epoxy resin matrix. Moreover, the different physicochemical properties of BNNTs and epoxy resins as well as the chemical inertness of BNNTs surface lead to the lack of effective interfacial interaction between BNNTs and epoxy resin matrix. Therefore, the performance of the epoxy composite dielectric is not enhanced by simple blending solely, but will even have the opposite effect. To address the problems of BNNTs, in this article, the surface structure of BNNTs was constructed from the perspective of interface modulation by using sol-gel method to coat mesoporous silica (mSiO₂) on BNNTs surface and further introducing silane coupling agent (KH560). The results indicate that constructing the surface structure of BNNTs can optimize the level of interfacial interaction between BNNTs and epoxy resin matrix, which results in stronger interfacial connection and elimination of internal pore phenomenon. The dielectric constant and loss of the composite dielectric prepared in this way were further reduced, reaching 4.1 and 0.005 respectively at power frequency, which was significantly lower than that of pure epoxy resin. At the same time, the mechanical toughness (3.01 MJ/m³) and thermal conductivity (0.34 W/(m·K)) were greatly improved compared with pure epoxy resin. In addition, the unique nano-mesoporous structure of mSiO₂ endowed the composite dielectric with a large number of deep traps, which effectively hinders the migration of electrons, thereby improving the electrical strength of the composite dielectric, and the breakdown field strength reached 95.42 kV/mm. Further, Tanaka multinuclear model was used to systematically investigate the interfacial mechanism of BNNTs surface structure construct on dielectric relaxation and trap distribution of composite dielectrics. The above results indicated that the good interfacial interaction between BNNTs and epoxy resin matrix was crucial for the establishment of the micro-interface structure and the improvement of macroscopic properties of composite dielectrics. This paper offered a novel idea for the multifunctionalities of epoxy resin, and also provided some experimental data support for revealing the correlation between surface properties of nano-fillers, microstructure of composite dielectric and macroscopic properties.