Atomic oxygen degradation of a fluorine-containing colorless polyimide

Abstract

Colorless polyimides (PIs) are regarded as the most feasible lens materials deployed in aerospace optical systems due to their light weight, flexibility, transparency, and excellent mechanical properties. However, durability towards atomic oxygen (AO) exposure is a chief concern for externally deployed colorless PI films in low Earth orbit (LEO) environments. In this work, we investigated the degradation behavior of a fluorine-containing colorless PI film with a combination of ground-based AO exposure experiments and reactive molecular dynamics (ReaxFF-MD) simulations. The fluorine-containing colorless PI showed linear erosion dynamics and a constant erosion yield (Ey) of ∼1.4 × 10−24 cm3 atom−1. Microscopic investigations demonstrated an increased surface roughness and shag-like appearance after continuous AO exposure. In addition, spectroscopic transformations resulted from elimination and oxidation processes occurring at specific reaction active sites (C=O, CN, CH, and CF, and CC) and the release of volatile substances. Moreover, the exposed fluorine-containing colorless PI films exhibited gradually deteriorating visible light transmission with increased AO fluence. Furthermore, the ReaxFF-MD simulations demonstrated physical sputtering and bombardment-enhanced chemical reaction models. Considering the limited-scale slab and the system thermal dissipation, the experimental and ReaxFF-MD computational results were largely consistent.