Formation of adherent polypyrrole coatings on Ti and Ti-6Al-4V alloy

Highly adherent polypyrrole coatings were electrodeposited at etched Ti and Ti-6Al-4V from 0.2 M oxalic acid and 0.2 M pyrrole at a constant applied potential of 0.8 V versus SCE. The substrates were etched in an alkaline peroxide solution at ambient temperature for a 10 min period prior to the electropolymerization reactions. Chemical etching of the substrate gave rise to an increase in the hydrophilicity of the surface, the formation of a micro-etched surface and the formation of a semiconducting titanium oxide film. There was a considerable increase in the density of nucleation sites for polypyrrole growth at the micro-etched surface. Growth of the polypyrrole proceeded slowly from a high number of nucleation sites at the etched surface to give rise to a highly adherent polypyrrole coating. Adhesion of the polypyrrole coating was attributed to micro-etching of the substrate and the conductivity of the oxide film generated during the chemical etching process.