Study On Adhesion And Enhancement Mechanism Of Coating And Polyimide Matrix Interface

In Low-Earth Orbit?LEO?environments,atomic oxygen?AO?,ultraviolet light,and charged particle radiation can cause erosion to polyimide?PI?,leading to the changes on the chemical,electrical,thermal,optical,and mechanical properties of the material,causing damage to the spacecraft.A large number of space and ground simulation tests have shown that AO is the most important factor to the surface material of spacecraft in LEO environment.In order to improve the ability of PI to resist atomic oxygen attack,the most common protection technique is to prepare an inorganic coating of SiO₂ or Al₂O₃on its surface.The inorganic oxide directly coated on the surface of hydrophobic PI,due to the large difference polarities between coating and matrix,it is easy to cause cracking and falling off of the coating.In view of the above problems,this paper focuses on the research of the adhesion and enhancement mechanism between the protective coating and polyimide matrix.The surface of the polyimide was modified by the combination of low concentration alkali hydrothermal treatment and silane coupling agent solvothermal method.The coating formation mechanism of sol and the elimination of internal stress were investigated.The main research contents are as follows:1.Study on the surface modification mechanism and treatment method of polyimide film by alkaline solution:To obtain a carboxylic acid functional group for further interfacial reaction,the polyimide surfaces was treated at room temperature and hydrothermal conditions using different alkaline solutions such as NaOH,KOH and NH₃·H₂O.The results show that the NH₃·H₂O solution can effectively improve the surface hydrophilicity of the thinner PI substrate.When the NaOH concentration is 0.05mol/L,the hydrothermal temperature is 120°C,and the time is 90 min,the hydrophilicity of PI substrate can be improved effectively.2.The coating formation mechanism and experimental conditions of the acid or base catalyzed sol was systematically studied:In order to explore the effect of sol on the coating,different sols were prepared by using hydrochloric acid,glacial acetic acid or ammonia.The SiO₂ coating formation process,the sol concentration and the preparation method were investigated.The results show that the catalytic effect of hydrochloric acid was the best,glacial acetic acid being the second.A sol that is diluted from a high concentration to a low concentration has a better coating effect.3.Explore the preparation methods and formation mechanism of the internal stress-free coating:A carboxylic acid functional group formed by PI ring opening is used to prepare a SiO₂ coating with a wrinkled morphology on the PI surface.The presence of pleats can reduce or even avoid the cracking problem between the coating and the substrate due to the difference of thermal expansion coefficients.After the temperature change and bending tests,the coating did not show cracking or falling off,and having a good anti-atomic oxygen ability.4.Surface metallization preparation and characterization of polyimide:Ti,TiO₂,Si and SiO₂ coatings were prepared on the polyimide substrates by RF magnetron sputtering.The optical,hydrophilic and mechanical properties of the samples were analyzed by atomic force microscope,ultraviolet-visible spectrophotometer,contact angle measuring instrument,and tensile machine.After 24 h water resistance test,the chemical bonding and magnetron sputtering coatings showed cracking and falling off.Therefore,the coating must pay attention to the influence of environmental humidity and water vapor during the storage and using process.