Electrochemical synthesis of bilayer coatings of poly(N-methylaniline) and polypyrrole on mild steel and their corrosion protection performances

Homopolymer and bilayer coatings of poly(N-methylaniline) (PNMA) and polypyrrole-dodecylsulfate (PPy-DS) have been electropolymerized on a mild steel (MS) surface by the potentiodynamic method in aqueous oxalic acid solutions. In order to include dodecylsulfate ion as dopant in the polypyrrole, sodium dodecylsulfate was also added to the polymerization solution of pyrrole. Characterization of coatings was carried out by the cyclic voltammetry, Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM). Corrosion behavior of the polymer coated MS electrodes was investigated in highly aggressive 0.5 M HCl solution by the Tafel test and electrochemical impedance spectroscopy (EIS) techniques. Corrosion test revealed that among the protective coatings obtained, the PNMA/PPy-DS bilayer exhibited the best corrosion resistance at all immersion times.

► The bilayers of poly(N-methylaniline) and polypyrrole-dodecylsulfate were synthesized. ► These films on mild steel were characterized by cyclic voltammetry, FTIR and FESEM. ► DS dopant allows permeation to cations and decreases the ingress of chloride ions. ► The PNMA/PPy-DS bilayer coating exhibited the best corrosion resistance in 0.5 M HCl. ► The protective properties of polymers was developed by preparing their bilayer coatings.