Characterization of polyaniline–polypyrrole composite coatings on low carbon steel: a XPS and infrared spectroscopy study

Polyaniline–polypyrrole composite coatings were electrochemically synthesized on low carbon steel under aqueous conditions. The coatings were characterized using X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy. The structure of the coatings was analyzed as a function of electrochemical deposition parameters (molar feed ratio of monomers and reaction time). The infrared spectroscopic analysis showed that a passive layer of iron(II) oxalate is formed at short reaction times. This inorganic layer undergoes dissolution thereby allowing the polymeric coatings to be formed on steel substrates. The infrared spectroscopy also showed significant changes in the chemical structure of the composite coatings when compared with the homopolymeric coatings. X-ray photoelectron spectroscopy was used to study the chemical composition of the coatings and also the amount of dopants (oxalate ions) incorporated into the polymeric coatings.