Transparent, superhydrophobic, and flexible polyimide films with robust and durable imide/silica particles surface prepared via a sintering process

Recently, transparent superhydrophobic surfaces have attracted great interest due to their potential applications in various fields, such as skyscrapers, windows, glass doors, displays, and solar panels. However, flexible films with superhydrophobicity and transparency still face challenges in practical applications due to their lack of durability of the properties. Here, we report transparent, superhydrophobic, and flexible polyimide films with robust oligoimide/silica protrusion surface prepared by a simple sintering process, aiming to address the above issues. A transparent polyimide film (PIF) and nano-silica particles modified with an oligoimide (NSOI) were separately prepared, and the sintering between PIF and NSOI were performed to obtain PINSOI samples. Among PINSOIs, the optimal PINSOI-3 sample exhibited excellent superhydrophobicity, optical transmittance and tensile strength. After folding/torsion, sandpaper abrasion, tape peeling and acidic/basic immersion tests, its superhydrophobicity was maintained, indicating excellent mechanical and chemical durability of superhydrophobicity even under harsh conditions. Also, after a standard accelerated weathering test, its superhydrophobicity, transmittance and tensile strength were almost completely maintained, indicating the excellent weathering durability of PINSOI-3. These durability properties of PINSOI-3 could be attributed to that the sintering resulted in strong fusion between the NSOI particles and PIF by chain entanglement. PINSOI-3 showed excellent self-cleaning performance, and it can be applied as a self-cleaning film for flexible or curved solar cells and displays.