Preparation and characterization of polyimide/fluorinated silicate nano-hybrid thin films with low refractive indices

A new series of polyimide (PI)-fluorinated silicate nano-hybrid materials with low refractive indices were prepared by the sol-gel process based on the PI derived from 4,4' (hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 4,4'diaminodicyclohexylmethane (DCHM). Triethoxy-1H,1H,2H,2H-tridecafluoro-n-octylsilane (13FTES) and tetraethoxysilane (TEOS) were employed to prepare the silicate precursors. Furthermore, 2-aminopropyl triethoxysilane (APrTEOS) was used as a coupling agent to improve the compatibility between the polymeric and inorganic domains of the nano-hybrid materials. The chemical structures of organo-silicate and hybrid materials were examined with solid state Si-29- and F-19-NMR and IR spectra. The thermal stability of PIs was not deteriolated with increasing the amount of TEOS, whereas it was sacrificed with the increase of 13FTES. The refractive indices of the hybrids can be controlled through the silica content, and low refractive indices were obtained for the prepared hybrid films. The PI/silicate nano-hybrid materials thus obtained are promising for high performance optical devices.