The Effect of Phase Continuity on the Cathodic Delamination Resistance of Polyaniline Based Coatings

Organic coatings based on electrically conducting polyaniline emeraldine salts (ES) and electrically insulating polyvinyl butyral (PVB) are applied to an iron substrate. An investigation is made into how ES phase continuity, and in-coating charge percolation, affect the kinetics and mechanism of corrosion driven cathodic coating delamination. Bilayer coatings are prepared by solution casting continuous ES films onto the substrate, then overcoating with PVB. These are compared with composite coatings of decreased phase continuity, prepared using ES powders dispersed in PVB. Coating delamination is followed using scanning Kelvin probe potentiometry and optical spectrophotometry. At ES coating weights <0.05 mg. cm(-2), delamination rate was inversely proportional to coating weight and slower for bilayer coatings. The same trend was found at higher coating weights for ES doped using camphorsulfonic acid. However, for ES doped with phenylphosphonic acid, bilayer coating delamination rates became independent of ES coating weight >0.05 mg. cm(-2) and were greater than for dispersion coatings. The relationship between cathodic delamination rate and PAni ES continuity is proposed to depend strongly upon the nature and continuity of the interphase formed between the PAni ES coating and iron, and therefore on the dopant anion identity. (c) 2018 The Electrochemical Society.