Morphological investigations of polypyrrole coatings on stainless steel

In this paper, electrochemical polymerization of pyrrole on 316L stainless steel substrates was accomplished using a rotating disc electrode (RDE). By applying various current densities and disc rotation speeds, coatings were produced with the aid of galvanostatic technique. Experiments were performed in an aqueous solution containing 0.2 M pyrrole and 0.1 M oxalic acid. Current densities and disc rotation speed ranges were from 0.05 to 1.0 mA/cm2 and from 0 to 1500 rpm, respectively. Using a scanning electron microscope (SEM), the morphology of polypyrrole coatings was studied, and the morphology diagram was determined. The results obtained showed that various morphologies were obtained by changing the current density and/or disc rotation speed. These results also showed that apart from conventional morphologies of polypyrrole coatings reported in the literature, a new semicrystalline morphology was obtained under the conditions of very low current density (0.05 mA/cm2) and disc rotation speed (≤50 rpm). The degree of crystallinity of this morphology was estimated to be 68% by grazing-incidence small-angle X-ray scattering (GISAXS). The elemental analysis (CHN) revealed the ratio of semicrystalline polypyrrole to oxalic acid dopant to be 4:1.