Studies in the Electrical Double Layer at Metal/Polymer Interfaces by Scanning Capacitive Probe

A scanning capacitive probe (the Kelvin probe) is applied to studying metal/polymer contacts. Potential drop across the electrical double layer of oriented ionic dipoles at the metal/polymer interface was shown to mainly contribute to measured Volta potentials. Amino groups of epoxy coatings are protonated upon their interaction with hydroxylated metal surfaces; being positively charged, they reduce the Volta potential of the metals. Acid groups of alkyd coatings acquire a negative charge and increase the Volta potentials of the metals. Polyaniline (an electron-conducting polymer) accepts metal's electrons to its Fermi level, thus producing a Schottky barrier. In this case, the potential at the contact does not depend on the metal nature; it approaches the aniline intrinsic redox-potential.