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.

► Polyimide–titania hybrid materials with up to 90 wt.% titania via sol–gel process.
► The hybrid films are highly transparent.
► Organic–inorganic bonding through the carboxylic acid end groups of polymide.
► Nanocrystalline–titania domains in the hybrid films around 3–4 nm.
► High thermal stability, good surface planarity, tunable refractive index are obtained.