Dopant Effects in Polyaniline Inhibition of Corrosion-Driven Organic Coating Cathodic Delamination on Iron

Coatings comprising various volume fractions of particulate polyaniline dispersed in a polyvinylbutyral binder are applied to iron substrates. A scanning Kelvin probe is used to measure substrate potentials in humid air and follow corrosion-driven coating delamination (cathodic disbondment) when aqueous NaCl contacts a coating defect. Emeraldine base has no effect on substrate potential or delamination kinetics. Emeraldine salts (ES) doped using p -toluenesulfonic (HpTS), camphorsulfonic (HCS), phosphoric , and phenylphosphonic acids increase substrate potentials by up to and inhibit delamination with efficiency order of . Dopant salts added to the corrosive electrolyte do not inhibit delamination. It is proposed that inhibition arises primarily from cathodic reduction becoming relocated from the ennobled substrate onto the ES coating. However, and FePP salt films formed at the ES–substrate interface also contribute by hindering interfacial electron transfer.