Synthesis, characterization, and optical properties of uniaxially drawn and gold nanoparticle dispersed fluorinated polyimide films

Abstract

Gold-nanoparticle dispersed fluorinated polyimide films were prepared by thermal curing and uniaxially drawing of poly(amic acid) films containing hydrogen tetrachloroaurate(III) trihydrate (HAuCl4·3H2O) as a dopant. The chemical states, crystallinity, average sizes, and spatial distribution of the gold particles were examined, and the optical and thermal properties of the films were compared with those of the host-polyimide. The gold salt was converted into zero-valent gold particles having high crystallinity after thermal imidization. TEM micrograph showed that the precipitated gold nanoparticles inside the films are larger than those in the surface area, and they have well-defined lozenge or rectangular shapes, which suggest pressed octahedron or rectangular parallelepiped structures of the crystallites. In addition, their long axes are oriented along the drawing direction and the surface direction. The films show much higher absorption in the visible region than the host-polyimide, which is due to the surface plasmon absorption of gold nanoparticles. In addition, significant anisotropy in optical transmittance are observed for the Au-dispersed films. This supports the orientation of precipitated gold nanoparticles having anisotropic shapes along the drawing direction.