Transparent polyimide nanocomposites with improved moisture barrier using graphene

A facile technique was developed to improve the water barrier properties of transparent polyimide ( PI ) films. Transparent and organo‐soluble PI films were synthesized from an alicyclic tetracarboxylic dianhydride (bicyclo[2.2.2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride) and an aromatic diamine (3,4′‐oxydianiline) in a co‐solvent of dimethylacetamide ( DMAc ) and γ ‐butyrolactone via a one‐step process. Thermally reduced graphene ( RG ) was then blended with the PI in DMAc solution to fabricate PI / RG nanocomposite films without the addition of coupling agent. With the incorporation of only 0.1 wt% highly exfoliated RG in the PI matrix, the resultant PI / RG ‐0.1 nanocomposite exhibited a superior barrier to moisture and retained high transmittance in the visible light region. The surface of PI / RG was more hydrophobic than that of pure PI and simultaneously the water vapor transmission rate was significantly reduced to 13 g m −2  day −1 for the PI / RG ‐0.1 nanocomposite compared to 181 g m −2  day −1 for pure PI . Notably, the PI / RG ‐0.1 nanocomposite also exhibited favorable thermal stability with a lower coefficient of thermal expansion and a higher thermal degradation temperature compared to pure PI . The easy processing of PI solution and RG nanosheets, the good orientation of RG in PI and the excellent barrier and thermal properties of PI / RG make the transparent PI nanocomposite films potential substrate materials in flexible electronic applications .