High transparent polyimide/titania multi-layer anti-reflective hybrid films

In this study, polyimide–titania hybrid thin films (6FDA–6FpDA–4ABA/TiO2, PIT) were prepared from soluble fluorine-containing polyimide and titanium butoxide. The soluble polyimide with carboxylic acid terminal groups (6FDA–6FpDA–4ABA–COOH) was synthesized from the precursor s 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 4,4′-(hexafluoroisopropylidene) dianiline (6FpDA), and 4-aminobenzoic acid (4ABA). Such end groups undergo a condensation reaction with titanium butoxide to provide organic–inorganic bonding and thus prevent macrophase separation. The titania content in the hybrid films was varied from 0 to 90 wt.% (PIT0–PIT90). The effects of TiO2 content on the hybrid film properties and the optimum operating conditions were also investigated. TGA and DSC analysis showed that the decomposition temperature of polyimide was about 468 °C. Td increased as the titania content in hybrid thin films increased. HRTEMM and XRD results indicated the formation of nanocrystalline-titania domains of around 4–11 nm in the hybrid films. AFM, SEM, TEM, and XRD results indicated the formation of well-dispersed nanocrystalline-titania. FTIR spectra indicated that the amidization was complete and that a cross-linked Ti–O–Ti network had formed. UV–vis and n&k analysis showed that the prepared hybrid films had high refractive index (1.931) and good optical properties. Moreover, the prepared polyimide/titania hybrid thin films were further applied to develop a three layer antireflective (AR) coating on glass and PMMA substrates. The results showed that the average reflectance of the AR coating on the glass and PMMA substrates was 0.5% and 0.8%, respectively. The transparency at 550 nm was greater than 90% for both AR coatings.