Barrier Effect of the Polymer

It is well known that the less porous the polymer, the better is the barrier effect, and the better the metal is protected against corrosion [41,42]. Unfortunately, native conducting polymers prepared by electropolymerization of a monomer in aqueous media and deposited directly onto the metal are very porous [77]. Moreover, polymer synthesis in aqueous media leads to native films containing large amounts of water, which are detrimental [41,42]. In general, the films are dried in air, but, even after that, the water content remains high. Clearly, submitting the material to thermal treatment, in order to remove all the water inside the polymer and make it more compact, should improve the barrier effect. 

Another effect, which has often been disregarded, concerns the way the electropolymerization of the monomer is carried out, a point which could also explain the differing results reported for the same material, and which is also related to the porosity. In the following, these two points will be illustrated through two electropolymerization examples pyrrole on zinc in the presence of salicylate salts, and pyrrole on iron in the presence of oxalic acid. 

Decrease in Film Porosity Through Heat Treatment 

In conclusion, native films electrosynthesized in aqueous media are strongly hydrated, and are highly porous. Dehydration is essential to improve the barrier effect. 

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