Influence of polythiophene overoxidation on its physicochemical properties and corrosion protection performances

Abstract

Polythiophene (PT) films were electrosynthesized by galvanostatic mode on stainless steel (SS) electrodes in (CH3CN + 0.1 M LiClO4 + 0.1 M thiophene) organic medium. In order to investigate the influence of the overoxidation on the physicochemical characteristics of the polymer and on its anticorrosion protection properties, samples were subjected to relatively high potentials (+2 V vs Ag/AgCl) to obtain the overoxidized state of polythiophene (OvPT) to be compared to the oxidized as synthesized one (OxPT). Initially, X-ray photoelectron spectroscopy (XPS) and Raman scattering analyses were carried out on the two forms of PT to bring out the elemental and structural changes accompanying the overoxidation process. It has been found that during the overoxidation, there is emergence of lateral groups attached to the polymer skeleton which generate distorted parts. Thus, the increasing number of structural defects causes a reduction of the conjugation length in the polymer chains and consequently a deterioration of its electroactivity, electrochemical stability and conduction properties. On the other hand, the evaluation of the overoxidation influence on the anticorrosion protection performance of PT was achieved by linear polarization and electrochemical impedance spectroscopy (EIS). The loss of adherence and mechanical properties of the polymeric coating decreased its inhibitory efficiency from 95% for OxPT/SS to 15% for OvPT/SS.