Electrochemical Impedance Spectroscopy (EIS) is now widely used for organic coating evaluation. The water uptake or coating degradation can be followed by EIS measurements. We discuss in this paper the classical impedance behavior of organic coatings and we link this impedance to some of their physical properties. Thus, it was demonstrated that, as the glass transition (Tg) induces a higher ionic mobility, EIS is a powerful tool to detect it. We also propose a simple procedure to investigate if a resistance is due to a flaw or to ionic mobility within the coating bulk. Finally, the case of high-Tg epoxy clear-coat is presented and a good correlation is found between EIS and Differential Scanning Calorimetry.
Key-words : Organic Coatings, Glass Transition, Electrochemical Impedance Spectroscopy