Rational assembly of mussel-inspired polydopamine (PDA)-Zn (II) complex nanospheres on graphene oxide framework tailored for robust self-healing anti-corrosion coatings application

There are increasing demands for self-healing anti-corrosion coatings with high efficiency and durability in various industrial applications. Recently, eumelanin polymers especially polydopamine (PDA)-based nanostructures have been served as a mussel-inspired strategy to provide such requirements due to the intrinsic adhesive nature of amines and catechols along with its film-forming ability. Nevertheless, direct embedment of hydrophilic PDA nanoparticles into polymer coatings could eventually trigger corrosion as a consequence of the osmotic pressure exerted beneath the coating. In the present work, we have adopted a rational design for constructing robust self-healing epoxy composites via a tailor-made procedure including oxidative polymerization of dopamine over the graphene oxide (GO) framework and subsequent loading of Zn (II) corrosion inhibitor. The triple-function of GO as a template for polymerization of dopamine; simultaneously being a nanoreservoir for storage of corrosion inhibitors and eventually as an impermeable barrier is very crucial. Curiously, the as-prepared GO-PDA and GO-PDA-Zn nanocomposites exhibit different ion-capturing/releasing properties derived from opposite charges developed on them. This property not only declines the permeation of aggressive species into the coating matrix but also facilitates the release of divalent zinc ions or PDA through an on-demand manner when local corrosion initiates at the damaged zone. The propensity of PDA to anchor ferrous or ferric ions generated from anodic reactions in one hand and Zn (II) to form zinc hydroxide compounds at cathodic sites, on the other hand, endows the GO-PDA-Zn nanocomposite with high efficiency in reducing the corrosion current as measured by polarization and EIS analyses. More importantly, the outstanding self-healing function of GO-PDA/EP and GO-PDA-Zn/EP composite coatings was proved with impedance measurements on scratched coatings immersed in saline solution.