Preparation And Properties Of Colorless Transparent Polyimide Composites

With the rapid development of space exploration technology,various deployable structures,such as solar sails,solar arrays,thin film photovoltaics,sunshields of space telescopes,have been wide applied in the new generation spacecraft to save storage space and reduce launch costs.Soft polymer films have gained a wide range of research interests as an essential part of this deployable structure.Polyimide has always been regarded as one of the best polymer film materials.Due to its good chemical resistance,excellent thermal properties,excellent radiation resistance and mechanical properties,it has been widely used in spacecraft,such as aircraft solar sails and solar arrays of basic structural materials and insulation materials,radiation shielding materials and wave-transparent materials.However,conventional polyimide materials are yellow in color and have low light transmittance,which greatly limits applications in space optical components such as space optical lenses and solar arrays.Therefore,the development of new polyimide materials with high optical transparency,excellent foldability and flexibility is of great scientific significance and urgent application requirements.Ionic liquid(IL)have attracted widespread attention due to their unique properties,including high heat,non-flammability,low melting point,excellent solubilizing power,excellent chemical stability and negligible vapor pressure.Researchers have used different methods to combine polyimide(PI)with ionic liquid(IL)to prepare thin film materials for different applications.In this paper,an ionic liquid(IL)is combined with a colorless polyimide(CPI)to prepare a film material with excellent comprehensive properties.In this study,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 colorless polyimide composite film exhibits a high optical transmittance of 88.5 ? 90.4% at 400 ? 450 nm wavelength and an incredibly low cutoff wavelength of 273 nm.At the same time,it also has excellent mechanical properties,with a tensile strength of 48.2 MPa,a high elongation at break of 108.4%,and an extraordinary minimum bend radius of 1 ?m.It can be folded multiple times in succession or twisted by 900 degrees without any crack damages.Moreover,it has a low expense cost and good processability for industrialization manufacturing.Thanks to these superior performances,the ionic liquid/polyimide composite becomes an ideal structural material for solar sails,solar arrays and thin-film photovoltaics,etc.In this paper,a transparent conductive film material with excellent flexibility and foldability property is prepared by combining silver nanowires with this composite material.The electric resistance of this transparent conductive film is increased by only 7.6% after repeated inward bending 10,000 times,and its bending radius is only 500 ?m.In addition,after 10,000 times of completely folding,the electric resistance of the transparent conductive film material increases by 1.12 times,and no breakage is observed on the surface of the film.As a result,we have confirmed that the composite material has excellent durability and feasibility.In addition,the composite material is further subjected to high dose radiation to detect the practicability of this composite material in outer space.