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In this work, the tensile strength of polyimide/silica composites with the covalently bonded interface (bonded PI/SiO2) is investigated by molecular dynamic simulation. It is found that the nanofiller with smaller size can bring out a larger number of hydrogen bonds and interfacial non‐bond energy in the composites, resulting in higher tensile strength. As the immobilization of the PI chains in the vicinity of SiO2, the covalently bonded interface is found to offer a greater reinforcing effect than the unbonded interface that is confirmed by the self‐diffusion coefficient. The tensile strength of 9 wt.% bonded PI/SiO2 composites is 11.34% higher than that of the unbounded composites. The tensile strength of PI/SiO2 composites is enhanced with the increase of SiO2 concentration up to critical mass percent (Xc), beyond which it will be decreased. To quantitatively predict Xc of PI/SiO2 composites, an empirical equation based on the non‐bond energy of the composites is proposed. The empirical equation showed that the Xc of PI/SiO2 composites ranged from 8.03 to 10.36 wt.%, which is consistent with experimental values. These results provided the understanding of size‐dependent covalently bonded interface structure, which would be beneficial to the design of nanocomposites with excellent mechanical performances. [ABSTRACT FROM AUTHOR]

B Front Cover b : Molecular dynamics simulation is used to investigate the effect of bonded interface on the mechanical performances of the PI/SiO SB 2 sb composites. The interfacial non-bond energy, the number of the hydrogen bonds, tensile strength, Young's modulus and shear modulus are investigated. As the SiO SB 2 sb concentration increased, the non-bond interaction energy between each PI chain and SiO SB 2 sb particle increased and the non-bond interaction energy in the bonded composites are higher than that of the unbonded. [Extracted from the article]