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

Abstract

In this study, polyimide–titania hybrid thin films (6FDA–6FpDA–4ABA/TiO 2, 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 TiO 2 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. T d 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.