Highly flexible and optical transparent 6F-PI/TiO2 optical hybrid films with tunable refractive index and excellent thermal stability

In this study, a synthesis route was developed for preparing highly transparent novel polyimide-nanocrystalline-titania hybrid optical films with a relatively high titania content (up to 50 wt%) and thickness (20 30 mu m) from a soluble polyimide 6F-poly(p-hydroxy-imide) (6FPI). It has been demonstrated that the introduction of bulky CF3 groups into polyimide backbones enhanced both solubility and optical transparency. Furthermore, the attachment of hydroxyl groups provided the organic-inorganic bonding and resulted in homogeneous hybrid solutions by controlling the mole ratio of titanium butoxide : hydroxyl groups. AFM, SEM, TEM, and XRD results indicated the formation of well-dispersed nanocrystalline-titania. The flexible hybrid films revealed excellent optical transparency in the visible range, good surface planarity, high thermally dimensional stability, and tunable refractive index. A three-layer anti-reflection coating based on the hybrid films was prepared and revealed a reflectance of less than 0.7% in the visible range, indicating its potential optical applications.