Corrosion protection of iron by polystyrenesulfonate-doped polypyrrole films

Electropolymerized polypyrrole (PPy) has been studied as a protective coating for iron in NaCl 3% corrosive medium. The protection mechanism is of the galvanic type, and the main cause for the loss of protection is the progressive invasion of the film by chloride anions. To reduce exchanges between PPy counter-ions and chloride anions, a composite polyanions/PPy film was used. Polystyrenesulfonate was chosen as a large size counter-ion which could be trapped in the polymer matrix. Due to the negligible mobility of these anions, the film permselectivity changed from anionic to cationic. A significant improvement in PPy film protection efficiency was obtained.