Graphene-polyaniline nanocomposite based coatings: Role of convertible forms of polyaniline to mitigate steel corrosion

Abstract

Present work addresses the synthesis of different structural forms of polyaniline (PANI) and their nanocomposites with graphene as functional fillers to epoxy coating for minimizing mild steel corrosion. The π-π interactions between p-phenylenediamine functionalized graphene (fGO) and aromatic rings of in-situ grown covalently linked PANI on fGO facilitated the interfacial wrapping of graphene skeleton by PANI. The chemical, morphological, crystalline, and structural features of fGO-PANI nanocomposites are probed by FTIR, NMR, Raman, XPS, XRD, SEM, and HRTEM analyses. The emeraldine salt form of PANI (PANI-ES) exhibited significantly higher impedance and better corrosion inhibition properties than the emeraldine base (PANI-EB). Graphene skeleton in the fGO-PANI nanocomposite notably enhanced the anticorrosive properties of PANI with a multifold increase in total impedance. The 2D graphene skeleton in fGO-PANI nanocomposites provides excellent surface coverage as a structural barrier and increases the number of possible electron transfer pathways. Moreover, the oxidoreduction properties of PANI make the fGO-PANI-ES nanocomposite highly effective in increasing the impedance by multifolds. The corrosion protective mechanism of fGO-PANI-ES is discussed by emphasizing the role of graphene, different structural forms of PANI, and the dosing of graphene in fGO-PANI nanocomposites. The present work revealed fGO-PANI-ES as a promising material for new generation coatings to mitigate mild steel corrosion, particularly in a maritime environment.