Polypyrrole films electrochemically doped with dodecylbenzenesulfonate for copper protection

Polypyrrole films doped with dodecylbenzenesulfonate (PPy-DBS) were prepared for effective copper protection by galvanostatical method on an underlayer of polypyrrole doped with oxalate (PPy-C2O4), because PPy-DBS could not be obtained directly on the copper surface by electrochemical methods. Their anticorrosion performance in 3.5% NaCl solution was compared with that of the bilayer PPy-C2O4 coatings with equal thickness. The well-protected time is more than 500 h even for PPy-DBS films with a thickness of only 15 mu m, which is 5 times longer than that of PPy-C2O4 films. Furthermore, the corrosive current on PPy-DBS electrode drops by 2 orders of magnitude compared with PPy-C2O4 electrode. It could be that DBS- is difficult to eject from PPy films because of its large size. Consequently, it obstructs the corrosion ions (Cl-) from penetrating the PPy films and hinders the oxalate from escaping so that the healing ability of PPy could be maintained for a long term. The obstructing effect was confirmed by electrochemical impedance spectroscopy and energy-dispersive X-ray spectroscopy. The results demonstrate that PPy-DBS films on an underlayer of PPy-C2O4 have a potential application to protect copper. (c) 2007 The Electrochemical Society.