Investigation On Free Radical Evolution And Optical Degeneration Of PI Under Combined Irradiation

In this paper, the mechanisms of free radicals formation and optical damage ofpolyimide film under combined irradiation in in space condition is researched by usingmodern analytical methods,such as electron paramagnetic resonance (EPR), opticaltransmittance test, Fourier transform infrared spectroscopy and Raman spectroscopy,and the correspondence between the evolution of free radicals and the recovery ofoptical property is established.The results show that the polyimide molecular chain is broken as the result ofcombined irradiation, leading to the formation of free radicals(g=2.0025),and the gvalue does not change with the energy and the fluence of charge particles. Withirradiation fluence increasing,the population of free radicals increase at first anddecrease subsequently,the optical absorption has the same trend.The value of g inducedby proton or electron is also2.0025, but the types of free radicals are different. theoptical property has declined with the increase of free radicals.the population of free radicals decrease during aging process.The relationship offree-radical population and time follows a sum of an exponential and a linear modeduring the storage, where the exponential part and the linear part represent therecombination and the reaction respectively.The optical property of polyimide alsorecovers in the air with the same trend.The value of time constant τradicalis equal toτoptical,illustrating the degradation of optical property has a direct relationship with freeradicals in material.Compared with combined irradiation,the free radicals induced by electron degradein the air quickly, the time constant is about0.1h, while that of proton is1.2h, and thoseunder combined irradiation are0.49h and0.59h,which illustrate that the recovery rate offree radicals induced by combined irradiation are between electron and.proton.Therecovery rate is related to the energy of irradiation particles.Through the test of Fourier transform infrared spectroscopy and Ramanspectroscopy,it is found that the polyimide molecular chain is broken, the surfacecarbonization of proton irradiation increases with increase of irradiation fluence, that ofcombined irradiation increases at first and decrease subsequently.The free radicals recombination and optical recovery under combined irradiationare different from that of proton or electron irradiation,the population of free radicals ismuch higher than the sum of that under proton and electron irradiation alone.Therefore,the combined irradiation effects are not equal to the sum proton and electronirradiation effects simply, with coupling effects between them.