2005 W.R. Whitney Award Lecture: Corrosion Stability of Polymer-Coated Metals—New Concepts Based on Fundamental Understanding

The corrosion and de-adhesion of polymers from reactive metal surfaces will be described in this paper. Corrosion protection by polymeric coatings is mainly due to the electronic structure of the electrified interface, which allows the transfer of electrons but not the transfer of ions, and therefore behaves remarkably different from defect sites in the coating at which ion transfer reactions are easily possible. As a result, a strong local variation of the corrosion potential is observed along the interface. The corrosion potential of the buried interface is nowadays routinely detected by the scanning Kelvin probe. Based on such measurements, a detailed model of the de-adhesion reaction has been obtained, which includes steps like ion migration along the interface, electron-transfer reactions at the interface, and subsequent chemical reactions inside the polymer close to the interface. Taking this knowledge into account, surface engineering allows for the design of interfaces with rather superior stability. The rate of electron-transfer reactions is significantly reduced by tailored semiconducting oxides whose band structure is such that, in particular, in the presence of defects within the polymer coating, no electrons will pass the interface. Ion migration is stopped to a large extent by highly cross-linked plasma polymers that are firmly attached to the substrate surface. Finally, the electrified interface may be used to discharge conducting polymer molecules, therefore opening a reservoir for corrosion-inhibiting molecules and generating self-healing intelligent coatings.