Thermally Robust Bendable Silicon Dioxide/Polyimide Layered Composite Film Through Catalytic Fluorination

The poor atomic oxygen (AO) resistant property of polyimide (PI) film is the bottom problem for its application in aerospace. Coating SiO2 layer on PI is expected to solve this problem efficiently since SiO2 is inherently resistant to AO. However, the adhesion between PI and SiO2 is weak by their mismatch in polarity, leading to failure of layered SiO2/PI composite film as a result of interlaminar cracking in application. Here, by complexing Fe3+ onto benzimidazole units, polyimide film was modified by catalytic fluorination. It was found that the C—F bond on phenyl group produced in catalytic fluorination was three times as much as that in direct fluorination of original PI. Further, γ-aminopropyl triethoxysilane (APTES) was grafted onto PI through nucleophilic substitution between aromatic C—F and amine on APTES, introducing numerous Si—OH groups on PI surface. Finally, a flat and condense SiO2 layer covalently bonded to PI was obtained with condensation of Si—OH from PI surface and Si sol. As a result, peeling strength between PI and SiO2 layer increased from 3 to 210 cN/cm, which is 70 times higher after modification. Moreover, the SiO2/PI composite film can endure 1000 times of bending and 50 times of thermal cycles (−100 °C to 100 °C) without peeling off or cracking.