A scanning Kelvin probe was used to study the metal/polymer contacts for models of epoxy, alkyd and polyaniline coatings. It was shown that the potential drop across the electrical double layer of oriented ionic dipoles at the metal/polymer interface contributes a major part of the measured Volta potentials. The Bronsted acid/base interactions are responsible for the charge separation and the creation of a double electric layer. Polyaniline (an electron-conducting polymer) accepts electrons from the metal to its own Fermi level, thus producing a Schottky barrier. In this case, the Volta potential of the contact does not depend on the metal, but follows the polyaniline flat band potential. Exposure in water vapor neutralizes the potential drop at the interface due to water dipole orientation in a direction opposite to the intrinsic electric field. The kinetics of potential change during water uptake follow Fick's and Nernst's equations. After hydrolysis of the interfacial bonds, activation of the metal surface can takes place. (C) 2004 Elsevier Ltd. All rights reserved.