Research On The Performance Of Polymer Membraneapplied To Space Optics

In order to meet the space technology requirements of large aperture space optical telescope in the future, lightweight thin-film diffraction optical technology would be applied to space optical imaging system. It is difficult to achieve large-aperture diffraction optical membrane element by using traditional inorganic optical materialbecause of its features of heavy/fragile.Light-weight optical membrane in future will give priority to organic polymer materials. These precision optical membrane components which exposure to the space environment, need to not only adapt to the harsh space environment for a long time, but also meet the demand of optical applications.In general, polymer materials prone to degradation in the space environment, thereforeit is difficult to adapt to the space environment for a long time, optical properties, mechanical properties and so onwould alsobe gradually deteriorated. Thus, diffraction optical thin-film material is a key technology of spatial diffraction optical system which needs to be solved.It is hard to findthat can completely meet the all requirements of optical thin film material.The only solution is to improve or modify the non-satisfied performance through a comparative analysis of the main performance. In this paper, the favor polyimide membrane material has been researched. On the basis of excellent comprehensive performance and potential of modified space, polyimide film which meets the demand of optical application in the space environmentwould be studied.The ultimate goal of the research is to obtainmolecular design knowledge of the space optical polyimide film, and meet the requirements of space optical imaging polyimide film on the basis of the relevant performance research. The main research workin the paper includes the following several parts:1. Prefered to the polyimide and analyzed the performance parameters of the optical properties and thermodynamic requirements.Compared with the various organic optical thin film materials which may be used in space optical system, the favor polyimide is choosen to be the modified object of space optical thin film materials.Andthe influence ofvacuum environment, thermal cycling environment, atomic oxygen and other space factorson the spatial optical polyimide film was analyzed.The result showed thatoptical uniformity requirements of optical polyimide filmis given priority to Rayleigh criterion which to meetthe principle of the quarter wave. In addition, the thermal expansion coefficient index theoretically should be close to zero, but it can bereduced by optical focal compensation.2. By molecular designed a series of polyimide film were synthesized and characterized.On the basis of performance parameter analysis of space optical polyimide film,the rigid and flexible, fluoride and non-fluoride, containing hydrogen bonding and non-hydrogen bonding of a series of optical polyimide filmhave been synthesized through the molecular design theory, mainly including PAAF, PAI, PAAA. Laser interferometer, the stress birefringence instrument, spectrophotometer, Fourier Transform infrared spectroscopy(FTIR), thermo-gravimetric analyzer(TGA), thermal mechanical analyzer(TMA), dynamic mechanical analyzer(DMA), gel permeation chromatograph(GPC), electronic universal testing machine and so on havebeen used on the characterization and analysis to the performance. Several conclusions about molecular design were drawnfrom the relationship between structure and performance.We also discussedthe influence mechanism of the rigid structure, containing fluorine groups, hydrogen bondingon the performance of optical polyimide film.3. TMAC/TFBZ polyimide was synthesized throughin-situ silylation method.On the characterization by using FTIR, DMA, TMA test methods, we obtain a soluble, low thermal expansion coefficient(11.4 ppm/℃), high modulus(4.0 GPa), colorless transparent(better than 90%), high performance polyimide film. Wehave discussed the important influence of hydrogen bonding and analyzed the activation mechanism of synthetic route.4. In terms of mechanical properties and thermodynamic properties, polyimide membranewere obtained with high strength and high modulus(strength of 295 MPa, modulus of 10.6 GPa)with the introduction of strong hydrogen bonding interaction.And thermal expansion coefficientof the polyimide film can be adjust to close to zerothrough copolymerization, which would be very beneficial to meet the dimensional stability in the space thermal alternating environment.5. The related parameters of flexible optical polyimide film as aoptical medium have been researched and analyzed, including the optical constants of thin film based on the transmission spectra method, refractive index homogeneity offlexible film and surface roughness of thin film.6. We explored the pattern transfer method of Fresnel lens prepared on polyimide film. It can overcome the difficulties of surface etching process onflexible polyimide film. Finally we won theclear Fresnel patterns steps structure on the surface of the polyimide film.It is analyzed whatthe significanceof modulus and the hydrogen bonding interaction is tothe surface contour accuracy on Fresnel structure.7. In order to obtain higher optical homogeneity of polyimide film, near infrared irradiation uniform heating process and flexible tensile heat treatment process was designedbased on theclassicaltwo-step preparation process of polyimide film, which is very beneficial to improve the optical performance, mechanical properties and thermodynamic performanceof polyimide film.In this paper, the studies on the performance of the space optical polyimide film will not only get a large number of knowledge about molecular design and material design of optical imaging polyimide film, will also provide important material which reserves for the development of the large-aperture space membrane optical system.