DEGRADATION OF POLYIMIDE UNDER ELECTRON IRRADIATION

摘要

Interaction of high energy electrons with spacecraft materials, such as polyimide (PI, Kapton), is known to cause their physical degradation. Despite numerous studies carried out over the past three decades, understanding of the chemical nature of this damage and its effect on PI's electrical and optical properties is still limited. This lack of understanding limits predictive spacecraft models (charging, thermal, etc) to only pristine material properties. This is a major source of error in spacecraft construction and anomaly resolution, since PI properties change after exposure to the space environment. Material aging is comprised of two competing processes: breaking of bonds within the material (damage) and formation of new bonds. Understanding these processes will allow development of a predictive model for materials' optical and chemical properties as a function of exposure to the space environment. In this study, we investigated chemical and optical changes in PI as a function of exposure to simulated space environment. PI films were exposed to simulated geosynchronous Earth orbital (GEO) conditions. Several complimentary characterization techniques were utilized to qualify and quantify radiation induced chemical changes in the material. The surface potential decay method was utilized to monitor material conductivity during recovery process in vacuum. To quantify the concentration of free radicals within the irradiated material, the electron paramagnetic resonance (EPR) technique was used. Changes in the infrared (IR) absorption profile of irradiated materials during the recovery process were identified using the directional-hemispherical reflectance (DHR) technique coupled with Fourier Transform Infrared (FTIR) spectroscopy. Relation of the chemical changes of aged material to alterations of charge transport will be used to help us building a reliable model of the charge transport.