Long-term protective mechanism of poly(N-methylaniline)/phosphate one-step electropolymerized coatings for copper in 3.5% NaCl solution

Highlights: • N-methylaniline was electropolymerized on copper in a single step procedure. • Phosphate facilitated the formation of strong anchored coating. • Long-term protection resulted from anodic protection and barrier effects. • Electronic structure of PNMA altered with phosphate. • Diffusion of ions inside composite coating was hugely suppressed. -- Abstract: Cauliflower-like phosphate-intercalated poly(N-methylaniline) (PNMA) composite coatings were electropolymerized on copper surface in a facile one-step procedure for preventing the substrate from corrosion in 3.5% NaCl solution. The composite (PNMA-5P) with 5 mM phosphate in supporting electrolyte exerted superior properties in thickness, conductivity and adhesive strength. Long-term anti-corrosion capacity of PNMA-5P coating was evaluated by morphological, electrochemical, wettability and solution analyses. Multi-scale simulations were employed to distinguish the deposition and protection mechanism of as-prepared coatings for copper in the corrosive solution. Morphological observation indicated that PNMA-5P coating is stable with hydrophobic characteristic during 30 days immersion in NaCl solution. Electrochemical analyses revealed that PNMA and PNMA-5P coatings behaved as a barrier against mass/charge exchange, and therefore impeded copper corrosion effectively. Phosphate reinforced the anodic protection of composite, for which PNMA-5P coating earned the superior anti-corrosion ability for copper in the long-term immersion as compared to the pristine control. Theoretical calculations in electron- and atom-scale evidenced that phosphate was stabilized among PNMA chains via electrostatic force and facilitated the stretched deposition of polymer on copper surface. Time-dependent diffusion trajectories supported that in-situ ions were confined in local region for the compact structure, favorable barrier and anodic protection effects of composite coating.