The growth, morphology and corrosion resistance of modified films of polypyrrole
Electroactive, or 'conductive', polymers are a rapidly expanding area of research with
proposed applications ranging from batteries or electronic circuitry to artificial muscles
and actuators. An emerging application for these materials is as constituents of
corrosion resistant coatings. An important factor in any corrosion resistant coating is
the level of porosity it possesses. Minimisation of porosity may be highly desirable for
the production of highly protective films.
This work aims to study methods for controlling the porosity of polypyrrole films for
their possible use as corrosion resistant coatings. It has been observed that surfactants
can modify the structure and morphology of polypyrrole on inert substrates such as
platinum or indium-tin oxide glass, and on the non-inert substrate mild steel. This has
involved the study of the conditions necessary for polymer deposition on mild steel
where the tendency for metal dissolution competes with the polymerisation reaction.
Corrosion studies were carried out, firstly, to assess the corrosion potentials for such
films and, secondly, via Tafel extrapolation to determine the effects of film thickness
and anionic surfactant concentration on the corrosion rates obtained. Further corrosion
studies were performed on polypyrrole films with additions of molybdate corrosion
inhibitor species and anionic surfactants. It was found that polypyrrole with additions
of anionic surfactants had little or no effect on the corrosion characteristics of mild steel
in saline environments. However, in the presence of molybdate and certain levels of
surfactants, excellent corrosion resistance characteristics were observed.
It is proposed that the reduction of polypyrrole occurs at large negative corrosion
potentials, resulting in the formation of an insulating polymer film that is incapable of
acting as a site for displaced corrosion reactions around which many of the theories of
electro active polymer corrosion protection have previously been based.