Abstract
Protective polypyrrole films doped with dodecylbenzene sulfonate (DBS) were formed at copper, while carbon nanotubes (CNT) were incorporated within the polymer films with the DBS to give PPy-DBSCNT (polypyrrole films doped with DBS and incorporated CNT). The polymer films were deposited from a 0.05 M DBS solution at a pH of 6.0 at a thin polypyrrole film doped with tartrate, which served as a stable pre-layer. Low corrosion currents of 0.12 and 0.05 μA cm−2 were estimated using Tafel analysis for the PPy-DBS and PPy-DBSCNT films, respectively, while a significant reduction in the concentration of Cu2+ ions from the corroding copper was observed for the polymer-modified copper. The corrosion protection properties were attributed to the doping of the polymer by the large and immobile DBS anions and possibly, by the larger anionic micelles that are formed at a DBS concentration of 9.8 mM in the pyrrole-containing solution. These dopants give a negatively charged surface that repels chloride anions. The additional protective properties afforded by the CNTs appear to be related to the morphology of the CNT-modified polypyrrole coatings, while the functionalized CNTs also provide a negatively charged surface.
Highlights
Conducting polymers, and in particular, polypyrrole coatings, have been used in the corrosion protection of a number of metals and alloys since DeBerry first reported the formation of polyaniline at steel [1]
dodecylbenzene sulfonate (DBS) is well known for its surfactant properties and its ability to disperse carbon nanotubes (CNT) [27]
The same procedure was used to compute the critical micelle concentration (CMC) in the presence of 0.3 M pyrrole, which is the concentration of pyrrole used to form the polypyrrole coatings
Summary
Conducting polymers, and in particular, polypyrrole coatings, have been used in the corrosion protection of a number of metals and alloys since DeBerry first reported the formation of polyaniline at steel [1]. There has been considerable attention devoted to combining carbon nanotubes (CNTs) with conducting polymers, such as polypyrrole, to give composites with enhanced conducting properties and long-term stability [27,28]. Polypyrrole/CNT coatings have been formed at carbon steel from an oxalate salt [31] and at SS304 stainless steel from sulfuric acid [32] In both cases, it was concluded that the polypyrrole/CNT provided better corrosion protection, while Gergely [33] achieved an improvement in the protective properties of alkyd paint coatings with polypyrrole alumina composites applied to cold-rolled steel on adding CNTs. In this study, a polypyrrole/CNT coating was deposited at pure copper and the influence of the added CNTs on the protective properties of the polymer films was evaluated. Dodecylbenzene sulfonate is considerably different to the relatively simple oxalate, benzoate or salicylate salts that have normally been used, as it has surfactant properties and the ability to form micelles [35,36]
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