Molecular Dynamics Study on Silane Coupling Agent Grafting to Optimize the Interfacial Microstructure and Physical Properties of Polyimide/Nano-Si3N4 Composites

Polyimide (PI) is widely used in aerospace, electronic packaging, and other fields due to its excellent dielectric and thermophysical properties. However, the performance of traditional PI materials under extreme conditions has become increasingly inadequate to meet the growing demands. To address this, this study designed a PI/Nano-Si₃N₄ advanced composite material and, based on molecular dynamics simulations, thoroughly explored the influence of silane coupling agents with different grafting densities on the interfacial microstructure and their correlation with the overall material's physical properties. The results show that when the grafting density is 10%, the interfacial bonding of the PI/Nano-Si₃N₄ composite is optimized: non-bonded interaction energy increases by 18.4%, the number of hydrogen bonds increases by 32.5%, and the free volume fraction decreases to 18.13%. These changes significantly enhance the overall performance of the material, manifested by an increase of about 30 K in the glass transition temperature and a 49.5% improvement in thermal conductivity compared to pure PI. Furthermore, the system maintains high Young's modulus and shear modulus in the temperature range of 300-700 K. The study reveals that silane coupling agents can effectively enhance the composite material's overall performance by optimizing the interfacial structure and controlling the free volume, providing an efficient computational method for the design and performance prediction of advanced high-performance PI composites.