Preparation and Characterization of Polyimide/ZnO Nano-hybrid Films Exhibiting High Refractive Indices

Abstract

A series of polyimides (PIs) / zincoxide (ZnO) nano-hybrid materials exhibiting high transparency, high refractive indices, and low wavelength dispersions were prepared by the in situ thermal decomposition method. First, the optical properties of six kinds of matrix PIs were investigated, and a fully aromatic PI derived from 4,4'-(hexafluoroisopropylidene) diphthalic dianhydride (6FDA) and 9,9-bis (4-aminophenyl) fluorene (BAFL) and a semi-aromatic PI derived from 3,3';4,4'-biphenyl tetracarboxylic dianhydride (BPDA) and 4,4'-diaminodicyclohexylmethane (DCHM) were chosen as transparent matrices. Secondly, two types of ZnO precursors, which are thermally decomposed into ZnO, were chosen, and the thermal decomposition behaviors of the ZnO precursors dissolved in PI films was examined by far-infrared (Far-IR) and variable temperature mid-infrared (IR) spectra. The PI/ZnO hybrid films prepared from Zn(NO3)26H2O as a ZnO precursor exhibit yellowish coloration, though the transparency of the hybrid films was significantly improved by using a preheated Zn(NO3)26H2O at 110 °C as a ZnO precursor or using a soluble PI solutions in place of poly(amic acid) solutions. The PI/ZnO hybrid films exhibited high thermal degradation temperatures, and 6FDA-BAFL and BPDA-DCHM/ZnO hybrid films exhibited higher refractive indices by up to +0.0037 (+0.25 %) and +0.0130 (+1.10 %), respectively, compared with the pristine PIs. In the case of BPDA-DCHM, the effect of hybridization with ZnO on the increase in the refractive index at infinite wavelength (n∞) relative to the coefficient of wavelength dispersion (D) is more significant than that of modifying the chemical structures of PIs.