Research On Atomic Oxygen Protection Technology For Kapton And Silicone Rubber In Space Environment

Spacecrafts are severely challenged by environmental factors in the low earth orbit（LEO）and therefore,the polymer materials placed higher demands in this environment.Especially,the atomic oxygen（AO）in the space environment can erode polymer materials severely,leading to physical and chemical performance degradation and affect the normal work of spacecraft.Besides,the greater difference between the polymer surface and inorganic coatings is easy to cause a crack in the coating and reduces its AO resistance.In this study,Kapton HN and silicone rubber（SR）are employed as substrates,while Si O₂ sol and modified SiO₂ powders are used to improve AO resistance of the substrates.The physical and chemical properties of the substrates before and after AO exposure are investigated.The main contents of this paper are as follows:（1）Study the optimum condition of treated Kapton with alkalineNaOH solution with different concentrations are used to etch Kapton surface at room temperature or under hydrothermal condition,respectively.The optimum alkali condition is obtained:the concentration of NaOH solution is 0.05 mol/L,and the treatment time is 1h under hydrothermal condition at 120℃.The hydrophilicity of Kapton has been greatly improved by treatment,and maintaining a transmittance.After coating with SiO₂ sol,the bonding force between the Si O₂ coating and Kapton substrate can reach 0 grade and conform to operating requirement.（2）The preparation of protective coatings on the Kapton surface by hyperbranched SiO₂ suspensionThe hyperbranched SiO₂ with organic/inorganic hybrid properties on the Kapton surface can reduce the internal stress between the coating and substrate and increase the effective solid content of the protective coating.The experiment result shows that the hyperbranched SiO₂ coatings possess an excellent adhesion to Kapton substrate.The ultraviolet（UV）aging resistance of coated sample is improved greatly,and the surface of sample is smooth,dense and crack-free after 12 h UV aging test.After AO exposure,the sample surface is still smooth without obvious crackings,and its AO erosion yield decreases significantly compared to pristine Kapton substrate.（3）Improving the hydrophilcity of SR surface by KH-550 hydrolysisTo meet the AO resistance of SR as Fresnel Lens in space environment,the interface adhesion between SiO₂ coating and SR substrate is necessary to be improved.The SR substrate was fully swollen with a mixed solution of toluene and KH-550,and appropriate conditions were explored to completely hydrolyze KH-550 to increase the hydrophilicity of the SR surface.The influence of pH,swelling time and hydrolysis time on the hydrophilicity of SR are investigated.The fully swelling SR substrate is treated in Et OH/water mixed solution with the pH value of 1.0 for 24 h,and the SR sample with excellent hydrophilicity is obtained.After coated by Si O₂ sol,the surface of coated SR is compact and uniform without any obvious cracking after bending.（4）Improving the AO resistance of SR by highly-dispersed SiO₂In order to improve the AO resistance of SR without disrupting its transmittance,a new kind ofhydrophilic SiO₂ dopantis synthesizedbyα,ω-dihydroxy polydimethylsiloxane（hydroxyl silicone oil）and sodium silicate（Na₂SiO₃?9H₂O）through hydrolysis-condensation reaction.After doping,hydrophilic SiO₂ nanoparticles are distributed uniformly in SR.The SiO₂ dopant has minimal impact on the optical performance,mechanical property and solvent resistance of SR.Besides,the sample surface is still smooth,and the surface cracking obviously decrease and even disappear after AO irradiation.