Study On Surface Modification Of Polyimide And Preparation Method Of Atomic Oxygen Protective Coating On Kapton Materials

Atomic oxygen?AO?is one of the most important components in low earth orbit?LEO?environment.Chemical property of AO is very active,and can oxide most of polymeric materials.The interaction of AO with Kapton may result in surface erosion,changes in chemical composition,surface morphology and optical properties,and even result in particulate formation and molecular contamination of the spacecraft surfaces.To overcome this problem,inorganic oxide coatings are typically used as AO protective coatings.Kapton surface proves to be technically difficult to deposit hydrophilic coating directly,leading to necessary surface treatment or modification for improved wetting behavior.In the paper,several surface modification methods such as hydrothermal methods and silane coupling agents are used to change the surface properties of Kapton.A uniform Ti O₂/SiO₂ coating was prepared on the substrate by sol-gel method.The property of inorganic oxide coatings and cracking during transportation and storage were studied and analysed.The AO erosion resistance of SiO₂/Ti O₂ coating on Kapton surface was also investigated.The main research achievements are as follows:?1?Hydrothermal method was used for surface modification of Kapton substrate:The apparent morphology,contact angle and transmittance of three different thicknesses Kapton material were investigated.It was found that the wettability of Kapton substrate increased due to the treatment by hydrothermal method.And different hydrothermal conditions should be applied for different samples.?2?SiO₂ coatings were prepared by solvothermal and sol-gel methods: The surface of Kapton substrate was modified using solvothermal method.SiO₂ coatings were prepared on the surface of Kapton by sol-gel method.The surface morphology,contact angle and light transmittance of the coatings were also investigated in this thesis.Experimental results demonstrated that the method was able to effectively improve the adhesion between Kapton film and inorganic oxide coatings.Uniform and free of crack SiO₂ coatings could be obtained by sol-gel method.?3?Environmental effect evaluation of SiO₂ coatings: This paper takes advantage of hydrothermal method and solvothermal for surface modification to increase the wettability of Kapton substrates.Sol-gel method was used to prepare SiO₂ coating on modified Kapton.Using artificial ultraviolet aging experiment device to simulate the natural ultraviolet aging effect under different conditions,the influences of ultraviolet?UV?radiation,radiation time and ambient humidity on the properties of SiO₂ coatings were discussed.The experimental results showed that environmental humidity had obvious effect on SiO₂ coatings.?4?Preparation of SiO₂/Ti O₂ coatings by NH3·H2O and sol-gel method: The surface of Kapton was treated by NH3·H2O and silicon coupling agent to improve the polymer surface wettability.The Ti O₂/SiO₂ multi-layer coatings were prepared on the surface of Kapton by sol-gel method.The optical transmittance and surface morphology of samples were investigated by UV-vis spectroscopy and scanning electronic microscope?SEM?.The results indicated that the Ti O₂/SiO₂ sol could easily form a uniform thin coating on the surface of pretreated Kapton.After AO exposure,the coatings became more compact,without peeling off.The AO erosion yield value of coated Kapton was sharply down and the samples had good optical transparency.