Influence mechanism of vacancy defect effects on the intrinsic electronic properties of h-BN and the thermodynamic and dielectric properties of h-BN/PI interfaces

Abstract

Polyimide (PI), known for its excellent properties, has been widely applied across various fields. However, its thermodynamic and dielectric properties require further enhancement. Hexagonal boron nitride (h-BN) is commonly employed as a nano-modifier to enhance the properties of the PI matrix. However, the vacancy defects in h-BN limit the improvement of the composite's properties. In this study, molecular simulation techniques are utilised to investigate the effects of vacancy defects on the electronic properties of h-BN and the interfacial properties of h-BN/PI composites. The simulation results indicate that as the number of vacancy defects increases, the distortion of the h-BN geometric structure becomes more severe. Among the single-atom vacancy defects, N-atom vacancies exert a more significant impact on the geometrical structure and insulating properties of h-BN. Two defect levels are introduced into the energy band structure of the diatomic vacancy defect model, thereby weakening the insulating performance of h-BN. The band structure of the three-atom vacancy defect model undergoes greater changes, with additional defect levels introduced into the band gap, resulting in reduced insulating performance and a semi-metallic state in h-BN. As the number of vacancy defects increases, the thermal conductivity and mechanical properties of the h-BN/PI interface deteriorate. In contrast, B-atom vacancies have a more pronounced effect on interfacial heat transfer, whereas N-atom vacancies more significantly affect mechanical properties. The free volume fraction of the model increases as the vacancy defect rate rises, leading to an increase in the relative dielectric constant of the h-BN/PI interface. This paper comprehensively examines the effects of vacancy defects on the interfacial properties of h-BN/PI composites, providing a foundation for the application of h-BN as a filler in the functional modification of PI.