Colorless and transparent polyimide nanocomposite films containing organically modified fillers comprising an organoclay/functionalized-graphene complex.

Aromatic colorless and transparent polyimides (CPIs) are super engineering polymers with excellent mechanical performance and thermal stability, making them particularly suitable for optical displays and electronic materials. In this study, a complex filler was dispersed into poly(amic acid) (PAA) synthesized from dianhydride 5,5'-sulfonylbis(isobenzo-furan-1,3-dione) and diamine bis[4-(3-aminophenoxy) phenyl]sulfone monomers using a solution intercalation method, resulting in the formation of a PAA hybrid. Solutions of this PAA hybrid were thermally imidized through various heat treatments to synthesize CPI hybrid films. A new complex filler containing both clay and graphene was synthesized through organic surface modification of the clay and graphene, and the synergistic effects of the two fillers were investigated. A C16-complex synthesized from an organoclay (hexadecyl-montmorillonite, C16-MMT) and functionalized graphene sheets (hexadecyl-graphene sheet, C16-GS) was used as the complex filler in this study. CPI hybrid films were fabricated by dispersing various loading (0-2.0 wt%) of the C16-complex filler into a CPI matrix, and their thermomechanical properties, filler dispersion morphology, and optical transparency were analyzed based on their filler content. In the CPI hybrid films, the C16-complex exhibited excellent nanoscale dispersion at a filler content of 1.0 wt%, and the corresponding systems showed excellent thermomechanical properties; however, when the filler content exceeded the critical content, filler aggregation occurred, adversely affecting the properties of the hybrid films. In contrast, the optical properties of the hybrid films gradually deteriorated with increasing filler content.