Protection coatings for corrosion control of mild steel using phenolic polymeric deep eutectic solvents

The mitigation of corrosion, especially in coastal regions, stands as a significant social concern necessitating the exploration of environmentally friendly materials. This study introduces phenol-based ionic polymers as both coatings and solution corrosion inhibitors for mild steel. Three methacrylated phenolic deep eutectic monomers (DEMs) bearing catechol and gallol motifs were synthetized for this purpose, taking advantage of polyphenol chemistry. Both the polyphenol DEMs and the UV-photopolymerized ionic polymer coatings formed coordination complexes with iron ions on the surface of the mild steel, resulting in a distinctive colour evolution, transitioning from a non-coloured film to dark purple, characterized by optical imaging and UV-vis absorption analysis. The resulting interfacial complex layer demonstrated exceptional corrosion inhibition efficiency for tannic acid and protocatechuic acid based polymers, achieving efficiencies of 99.84% and 99.54% respectively. Further explanation of this phenomenon involves the investigation of phenolic deep eutectic monomers in solution as model compounds, revealing a purple hue in the solution arising from the complexation between the polyphenol chemistry and the iron ions leached from the steel surface.