Properties Of Transparent Polyimide Materials Under The Coupling Effect Of Stress Field And Electron Irradiation

Polyimide materials have been widely used in the aerospace field due to their excellent properties.Colorless transparent polyimide has become an important candidate material for space optical imaging systems,solar sails,flexible solar cells and other components.In the course of serving in space,spacecraft will not only be bombarded and eroded by high-energy particles such as electrons,protons,and ions,but also be subjected to the stress generated by the cold and heat cycle,structural support and space debris impact.Under the combined action of these factors,the structure of the material will be degraded and damaged,resulting in the decline of device performance and shortening life.Therefore,the preparation of transparent radiation-resistant polyimide with excellent performance and the study of its damage behavior under the coupling effect of electro-irradiation and stress field have very important research value,and could provide theoretical and data support for the prediction of radiation damage of transparent polyimide in complex space environment.In this thesis,ionic liquid was introduced into the system by physical doping to prepare three kinds of flexible transparent polyimide films.The structure and performance changes of these three polyimides under different stress and electron irradiation coupling states were studied.The specific research contents are as follows:Firstly,some chemical structures including trifluoromethyl,ether bond and lipid ring were introduced into molecular chains by homopolymerization and copolymerization,and a series of polyimide films with different ionic liquid doping systems were prepared.Three PI films(PI_6FDA-TFMB,PI_6FDA-FAPB and PI_{CBDA,6FDA-6FODA})with excellent comprehensive performance were screened out by testing their optical and mechanical properties.The transmittance of these three PI films at 600 nm is higher than 90.8%,and the tensile strength is higher than 60 MPa.Secondly,ultraviolet visible（UV-Vis）spectrometer,universal electronic testing machine,thermogravimetric analyzer and scanning electron microscope were used to investigate the performance changes of the PIs under different stress and electron irradiation coupling states.The results show that the optical,mechanical and thermal properties of the three kinds of PI will decrease under the coupling effect of stress and electron irradiation.PI_{CBDA,6FDA-6FODA} has the best comprehensive performance under the coupling effect.Under electron irradiation of5×10¹⁵ cm^-2,the transmittance reduction at 600 nm is only 2.2%.Under the coupled field of 15%initial strain and 5×10¹⁵ cm^-2 electron irradiation,the transmittance reduction at 600 nm is only2.3%.Under 5×10¹⁵ cm^-2 electron irradiation,the tensile strength only decreased by 10.3%,and the temperature of 5%mass loss only decreased by 9.41%.Meanwhile,the stress did not further aggravate the damage of its thermal stability.Finally,the structures of PIs under different stress-electron irradiation coupling states were characterized by Fourier infrared spectrometer,X-ray elemental analyzer and X-ray diffractometer.The results show that electron irradiation can cause ring opening and bond cleavage of PI imide rings,among which C-N bond cleavage is more likely to occur,and the coupling effect of tensile stress generally aggravates the cleavage of imide rings.Under low dose electron irradiation,the coupling effect of tensile stress could promote the cross-linking of C-C bond to some extent.Under high dose irradiation,the fracture of C-C bond will dominate,resulting in the decrease of C-C bond content.The C-C bond of PI_6FDA-TFMB was broken more seriously than that of PI_{CBDA,6FDA-6FODA} and PI_6FDA-FAPB at the dose of 5×10¹⁵ cm^-2.