Fabrication Of Surface SiO₂-coated Polyimide Films Prepared Via A Novel Interpenetrating Network Approach And Its Atomic-oxygen Resistance Properties

Polyimide(PI),a high molecular polymer containing imide groups in the main chain of the molecule,is widely used in aerospace aircraft solar cell substrates,thermal control coatings and circuit insulation protection and other fields because of its good thermal stability,chemical stability,radiation resistance,high insulation and excellent mechanical properties,which become one of the indispensable materials to ensure the normal operation of aircraft.Since the 21st century,human beings have increasingly relied on the technical support provided by aerospace to observe astronomy and meteorology,exploration geology,daily communications and navigation,and explore the mysteries of the universe.However,there has high flux and strong oxidizing atomic oxygen(AO)in the low earth orbit(LEO)environment,which can quickly corrode the polymer on the surface of the spacecraft,and seriously affect the life and performance of the spacecraft,meaning that pristine PI is increasingly unable to meet the high service life requirements for high-precision,high-integration,and high-power development in the aerospace field.Therefore,the preparation of films with good resistance to atomic oxygen and without damaging the excellent properties inherent in PI has attracted widespread attention.Based on the traditional protective coating method for preparing atomic oxygen resistant PI,this paper innovatively developed two unique methods,the limit interpenetrating network method and the in-situ interpenetrating network method.Among them,the limited interpenetrating network method uses nanofibers with high porosity and fine and uniform pores for controlled adsorption of TEOS,which avoids the agglomeration of polyamic acid(PAA)gel and resists the warping and bulging phenomenon of SiO2 on the surface of the composite film.Compared with pristine PI,the AO resistance of the composite film prepared via this method is significantly improved,showing an only 6.07×10-26 cm3 O atom-1 corrosion yield after the irradiation test with an AO cumulative flux of 7×1021 O atoms cm-2.The in-situ interpenetrating network method replaces the types of nanofibers involved in the limit interpenetrating network method,and innovatively uses PAA/TEOS nanofiber membranes.Utilizing the swelling properties of PAA/TEOS nanofiber membrane in the bottom wet film,a unique interpenetrating network transition layer was created,showing the three-layer microstructure of SiO2@PI/SiO2-IPN@PI,almost reaching the effect of ’Blur interface’ which greatly improves the interface adhesion and mechanical bending resistance.At the same time,this method can also control the thickness of nanofibers by controlling the electrospinning conditions,to control the thickness of the surface SiO2.After the irradiation experiment with an AO cumulative flux of 7×1021 O atoms cm-2,the surface roughness of the film prepared by this in-situ interpenetrating network approach is only 20.2nm,which is more than 94%lower than that of pristine PI.The lowest mass loss of SiO2@PI/SiO2-IPN@PI film is 0.28 mg cm-2,and its erosion yield is only 2.319×10-26 cm3 O atom-1,which improved by more than one order of magnitude compared with pristine PI in resistance to atomic oxygen.In addition,the PI films coated with SiO2 on the surface prepared by the above two methods have relatively excellent tensile properties,visible light transmittance and significantly improved thermal stability than PI.