Abstract
Homopolymers, copolymers, and bilayers of polyaniline (PANI), with both poly(o-aminoaniline) (POAA) and poly(o-methoxyaniline) (POMA), were synthesized using a cyclic voltammetry technique (CV) on a 304 stainless steel substrate (304SS) from a 1 M H2SO4 solution containing 0.2 M ANI with 0.01, 0.03, and 0.05 M OAA and OMA. Moreover, the synthesis of bilayers was performed with different numbers of cycles ranging from 10 to 50 cycles in order to determine the best number of layers for the best protection efficiency. The formed polymers were characterized by CV, (HNMR)-H-1, UV-vis, FTIR, XPS spectroscopy, and ICP analysis. The surface morphology of the polymer layers was studied using SEM; the morphology results indicated significant differences in the polymer structure. The different voltammograms reflected the different behaviors of each copolymer and bilayer. The effect of the monomer feed ratio during copolymer formation and the change in the number of synthesis cycles during bilayer formation for both the POAA and POMA on the corrosion resistance was investigated in 0.5 M HCl at room temperature using potential-time measurements, Tafel polarization, and EIS spectroscopy. The corrosion tests showed that both POAA and POMA exhibited better protection (reaching similar to 98.8 and similar to 77.9%, respectively) as compared to PANI (similar to 70.2%). On the other hand, copolymers formed from 0.05 M POAA and 0.01 M POMA and bilayers formed from 10ANI/40OAA and 30ANI/20OMA provided the best protection efficiency compared to using polyaniline as a homopolymer.