Reactive molecular dynamics simulations on the mechanism of the different protection methods of KAPTON during atomic oxygen impact

Abstract

KAPTON-type polyimide (PI) is a crucial polymer that is often used in the aerospace industry, but the high levels of atomic oxygen (AO) in low-earth orbit (LEO) can cause the polymer to deteriorate and peel, so it is especially important to protect PI from AO. Incorporating nano-reinforcements into PI and applying a protective coating to the surface of PI are the two basic strategies for shielding PI from AO impact. Herein, to investigate the effect and mechanism of different protection methods, molecular models of PI reinforced with graphene (Gr) and carbon nanotubes (CNTs) as well as covered by silica (SiO2) and Gr, respectively, are constructed. Reactive molecular dynamics simulations are then performed to explore the degradation mechanisms of PI under AO impact. Results indicated that the addition of CNT and Gr can improve the resistance of PI to AO erosion, and their protective effect is mainly by burying in the PI substrate to prevent the penetration of AO downward. Additionally, the protective effect of covering the PI surface with a protective layer is significantly better than that of mixing nanomaterials into the PI substrate. Meanwhile, the protective effect of the Gr protective layer is weaker than that of SiO2 due to its smooth surface, which tends to slip when AO is incident, and it plays a protective effect mainly by bouncing the incident AO. By comparison, the SiO2 protective layer can be embedded into the substrate due to its serrated structure, which better protects the substrate, and it protects the substrate mainly by absorbing the incident AO. This study provides useful guidance for the identification of promising candidate materials for LEO applications, as well as for the development of molecular design for AO-resistant polymeric materials.