High refractive index organic-inorganic composites with TiO2 nanocrystal

Highly transparent polyimide-nanocrystalline-titania hybrid materials with a relatively high titania content (up to 90 wt.%) have been fabricated via sol-gel process. The organo-soluble polyimide was synthesized from 4,4'-(hexafluoroisopropylidene) diphthalic anhydride, 3,3'-Diaminodiphenyl sulfone, and 4-aminobenzoic acid. Such carboxylic acid end groups could provide the organic-inorganic bonding with titania. The images of atomic force and scanning electron microscope showed the well-dispersed nanocrystalline-titania. The analytical results of transmission electron microscope and X-ray diffractometer indicated that the formation of nanocrystalline-titania domains of around 3-4 nm in the hybrid films. The experimental results suggest that the prepared hybrid films have high thermal stability, good surface planarity, tunable refractive index (1.61<n<2.01), and optical transparency in the visible range. These results indicate that the polyimide-nanocrystalline-titania hybrid materials have potential applications for optical devices. (C) 2012 Elsevier B.V. All rights reserved.