Electrochemical corrosion behavior of carbon steel coated by polyaniline copolymers micro/nanostructures

A series of polyaniline (PANI) copolymers micro/nanostructures were prepared in order to investigate the effect of different groups with different hydrophilicities on the corrosion protection behavior of polyanilines. Hydrophilic groups (-SO3H and -COOH) and hydrophobic groups (-CH3 and -C2H5) were introduced into the polyaniline molecular structure by the copolymerization of aniline (ANI) and 3-aminobenzenesulfonic acid, 3-aminobenzoic acid, 3-toluidine and 2-ethyl aniline using ammonium persulfate as an oxidant. The carbon steel coated by the resultant PANI copolymers micro/nanostructures were investigated and compared regarding their electrochemical corrosion in 0.1 M H2SO4. Potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) were used. It was found that neither PANI nor PANI copolymers micro/nanostructures provide anodic corrosion protection for carbon steel, but they can effectively restrict the cathodic reaction. Moreover, the ability to restrict the cathodic reaction depends on the surface wettability of the PANI and PANI copolymers micro/nanostructures. The corrosion protection of PANI and PANI copolymers increased along with their water repellency. A well-fitting correlation between the contact angle (theta) of the PANI or PANI copolymers micro/nanostructures coatings and their corrosion protection efficiency (eta) was found to be eta = 102.22 - 102.78 exp(- theta/84). The PANI copolymer with the hydrophobic -C2H5 group (PANI-C2H5) showed the largest static water contact angle (CA = 125 degrees) and the most effective protection with an inhibition efficiency of 78.98%.