Effects Of Proton And Electron Irradiation On Novastrat Transparent PI Film

In this paper,based on the application of Novastrat type transparent polyimide（PI）thin film on the space thin film camera,the 120 keV proton and 100 keV electron irradiation experiments were conducted respectively using a space charged particle irradiation simulation device,and the changes in the optical and mechanical properties of the films were summarized.The changes in the intramolecular groups of the PI films were analyzed by means of FTIR and XPS,combined with means of SEM,EPR and XRD,the microscopic mechanism of the irradiation damage of the PI films was revealed.Irradiation experiments showed that under proton irradiation,the spectral transmittance of PI film in the visible light band decreased with increasing irradiation fluence.When the fluence reached 4E15cm^-2,the transmittance around 500 nm decreased by 24%,and he average transmittance decreased by 9.387%.The SEM observation showed that the surface of the PI film was no longer flat after proton irradiation,and there were more folds and macroscopic defects.At the same time,the mechanical properties of the PI film were significantly degraded,and the tensile strength decreased from 278 MPa to 115 MPa,the elongation at break decreased from 11%to 4.0%.The effects of electron irradiation on the optical properties and mechanical properties of PI film were obviously weaker than that of proton irradiation.When the beam density is 1E12cm^-2/s,the spectral transmittance decreased with the increase of fluence.The SEM analysis of the tensile fracture of the PI films reveals that the surface of the PI film is prone to delamination under proton irradiation,and there were a lot of micro-cracks between the proton-affected area and the substrate.The fracture of this area is not synchronous with the matrix fracture.The comprehensive analysis using DSC,FTIR,XPS and Raman spectroscopy showed that proton irradiation destroyed the carbonyl,ether,C-F and imide rings in the PI molecular structure within the proton range,and then generated O=C=O and other unsaturated groups,causing carbonization of the surface layer.XRD analysis showed that there was a structure similar to that of C₁₃N₁₄H₈ crystal in the carbonized layer.This layered structure was weak in resistance to interlaminar tearing,resulting in a drastic decrease in mechanical properties.The comprehensive analysis showed that the electron irradiation caused the molecular chain ether bonds and carbonyl groups to break,generated a large number of pyrolytic carbon radicals in the PI film,and then degraded the molecular chains through a free radical reaction and generates O=C=O groups.