Ionic liquid embedded polyimides with ultra-foldability, ultra-flexibility, ultra-processability and superior optical transparency

New generation spacecraft technology requires more and more deployable, light-weight, thin polymer films, in particular novel polyimide materials with high optical transparency, excellent foldability and superior flexibility. In this work, we develop a highly transparent, ultra-foldable, ultra-flexible and ultra-processable polyimide composite material by incorporating 5-8 wt% of ionic liquid 1-ethyl-3-methylimidazolium bis((trifluoromethyl) sulfonyl) imide into colorless polyimide matrices. This 23-mu m-thick polyimide composite film exhibits a high optical transmittance of 90.4% even at 450 nm wavelength and an incredibly low cutoff wavelength of 273 nm. It is an extremely strong and flexible material, with a tensile modulus of 844.6 MPa, a tensile strength of 48.2 MPa, a high elongation at break of 108.4%, and an extraordinary minimum bend radius of 1 mu m. It can be easily folded in half 4 times or twisted by 900 degrees without any crack damages. Moreover, it has a low expense cost and good film processability for industrialization manufacturing. All of these superior performances render this ionic liquid/polyimide composite an ideal structural material for solar sails, solar arrays and thin-film photovoltaics, etc.