Research On Atomic Oxygen Duration Structure And Properties Of Optical Polyimide Films For Space Application

Polyimide(PI)film is widely used in the aerospace field because of its excellent mechanical properties and good thermal properties,but there are very few reports on its application in space optical imaging.To use PI film for space imaging,the re-quirements for the anti-AO performance,optical homogeneity,dimensional stability and mechanical properties of the PI film are extremely demanding.The main research contents of the dissertation are as follows:1.This paper realizes that the optical homogeneity of the 100mm diameter low thermal expansion coefficient stretch-resistant PI film meets the Rayleigh criterion,which has the potential for applications in the imaging field.In addition to the optical homogeneity,the tensile strength of the PI is 285 MPa,which is?2.6 times the tensile strength of the PMDA-ODA PI film;the coefficient of thermal expansion is about 3.2ppm·K^-1,which is comparable to that of the Novastrat?905 type PI and is one order of magnitude lower than that of the commercial PI films.These excellent basic prop-erties reserve more space to further improve the space adaptability of PI film.2.In order to further improve the mechanical properties of the hybrid film from the perspective of the bulk,this study uses BPDA and DABA as bulk dianhydride and diamine.The two are co-condensed with the NH₂-POSS prepared by the hydrolysis co-condensation method to obtain a series of hybrid PI films with different NH₂-POSS content.It is found that when the irradiation dose of AO reaches 4.22×10²⁰O atom·cm^-2,the AO volumetic erosion yield of the hybrid film with a content of30wt%is 0.23×10^-24cm³·atom^-1,which is 2.7%that of unmodified pristine PI film.3.When the AO radiation dose reaches 4.22×10²⁰ O atom·cm^-2,the AO volu-metic erosion yield of the(A2+B3)type hybrid film with a content of 30wt%is0.09×10^-24cm³·atom^-1,which is only 1%that of unmodified pristine PI film.It is worth mentioning that 30wt%HBPSi-PI still maintains good mechanical properties,with a tensile strength and an elongation at break of 211.4 MPa and 6.9%,respectively.Under the premise of acceptable transmittance,increasing the thickness of the hybrid film can prolong the service life of the hybrid film.Compared with the pure film,the transmittance reduction of the 30wt%hybrid film is suppressed after 24 hours of AO irirradiation.The transmittance change at 600 nm is only about 10.8%.4.Mechanically robust optical homogeneous PI films with desirable AO erosion duration are fabricated by initially synthesizing amine-functionalized hyperbranched polysiloxane(NH₂-HBPSi),then reinforcing the pristine polyimide skeleton with it via copolycondensation reactions.X-ray diffraction patterns of NH₂-HBPSi/PI hybrid films suggests that the NH₂-HBPSi are smoothly blocked into the PI chains.NH₂-HBPSi macromolecule imparts desirable AO survivability to the resulting hy-brids.The mass loss per unit area of hybrid films has a downward trend with rising NH₂-HBPSi content and AO dose before the complete silica protective layer is formed.It has been proven by the experiments in an underground simulated AO environment.It decreases to 1%of that of pristine polyimide when NH₂-HBPSi accounts for 30%of the solid content after 24 h AO attack.The stable optical homogeneity that can meet the Rayleigh criterion is achieved in a 30wt%HBPSi PI film,mainly due to the selection of the best process parameters.Meanwhile,30wt%HBPSi PI demonstrates satisfactory mechanical properties,with a tensile strength and elongation at break of228.9 MPa and 7.3%,respectively.The characterization of scanning electron mi-croscopy confirms that pristine polyimide is substantially eroded after AO exposure while the surface morphology of 30wt%HBPSi polyimide shows no evident change.5.When the fluence of AO reached 4.22×10²⁰ O atom·cm^-2,the AO volumetic erosion yield of the(A2'+B3'+C4)type hybrid film with a content of 30wt%is0.27×10^-24cm³·atom^-1,which is only 3.2%that of unmodified pristine PI film.The transmittance reduction of the 30wt%hybrid membrane is suppressed after 24 hours of AO irirradiation The transmittance change at 600 nm is only about 11.75%.This may provide more room for the hybrid membrane to meet the transmittance require-ments after AO irirradiation and extend the service life of the hybrid membrane in the LEO environment.In this paper,a comprehensive improvement on the spatial adaptability of the BPDA-DABA matrix PI film has been made.The effects of three different types of polysiloxane structures on the spatial adaptability of the BPDA-DABA matrix optical PI film are studied.And the research results of this paper will lay the foundation for the application of PI hybrid film in the field of space imaging.