Preparation And Properties Of POSS Protective Coatings On Flexible Polyimide Surface

Polyimide（PI）films are widely used in aerospace,electronic information,flexible display and other fields due to their excellent heat resistance,good insulation,high strength and light weight.However,in the space environment,PI and its components will be bombarded and eroded by ultra-high vacuum（UHV）,ultraviolet（UV）,atomic oxygen（AO）,cyclic thermal shock and space debris.Among these hazards,AO is the main factor leading to the failure of PI materials.The most common method to prevent AO oxidation erosion is to prepare silicon-containing coating on the surface of PI films.However,there are differences in physical properties such as thermal expansion coefficient and polarity between the coating and the substrate.How to improve the interfacial adhesion and alleviate the cracking and shedding of the coating has always been the research focus of coating-PI composites.Therefore,improving the interfacial adhesion between coating and PI substrate is the focus of this paper,exploring the feasibility of preparing polyhedral oligomeric silsesquioxane（POSS）transition layer on PI surface,and studying POSS-Si O₂composite coating and interfacial adhesion mechanism to reduce the potential risk of coating failure.The main research contents are as follows:（1）Influence of matrix properties and media on the dispersion state of POSS:Chloroform,toluene,acetone,dimethyl sulfoxide（DMSO）and N-methylpyrrolidone（NMP）are selected as dispersion media;metal materials（titanium flakes）,inorganic non-metallic materials（glass flakes,silicon flakes,mica flakes）and polymer materials(PI,polymethyl methacrylate（PMMA）,polycarbonate（PC）are selected as substrates.The effects of dispersion medium and physical properties of substrate on POSS deposition were systematically studied,and the method of uniform deposition of POSS on substrate surface was explored.It was found that the adsorption of POSS by the substrate was beneficial to alleviate the coffee-ring effect.The swelling effect of dispersion medium on the substrate makes the POSS embedded in the substrate surface with the dispersion medium,which restricts the movement of POSS to the contact line and is beneficial to a uniform deposition of coating.（2）Swelling behavior of PI film:PI films were swollen in NMP and DMSO,respectively.The swelling mechanism of films,the effects of solvent types and temperature on the swelling behavior were analyzed.The results show that the dissolution of PI films is anisotropic and the direction of dissolution is perpendicular to the film surface,which is conducive to coating deposition.The film swelling rate varies very little,and the process is similar to case II diffusion,with a maximum swelling of 25%.Within a certain temperature range,the temperature only changes the swelling rate of PI and has no effect on the swelling degree.The swelling process has no effect on the structure of PI films.（3）Uniform deposition of POSS on the surface of PI films and preparation of composite coatings:Tri Silanol Phenyl-POSS is uniformly dispersed within the benign medium and deposited onto the PI surface by tape casting method.The results show that the POSS dispersion forms a uniform casting film on the PI surface after NMP swelling,and the POSS molecules can be further formed into an orderly coating by solvent regulation.The addition of inorganic component Si O₂ or Si C powder to the POSS dispersion helps to improve the resistance of the coating to environmental attack.（4）In situ growth of POSS layers on the surface of PI films:NMP was used as a solvent to silanize the PI surface,and an amino POSS layer was formed on the PI surface by adjusting the hydrolytic condensation rate.Due to the improvement of swelling and wettability of PI film surface by NMP,aminopropyltriethoxysilane（APTES）can be uniformly grafted onto PI surface and hydrolyzed to form amino-POSS layer.The existence of POSS layer is beneficial to the uniform extension of Si O₂ sol.The prepared Si O₂/POSS composite coating has excellent anti-AO properties.