Electrochemical approach to evaluate the interlayer adhesion of organic coatings

Abstract In this work we used the electrochemical impedance spectroscopy (EIS) to quantify the interlayer adhesion of coatings. Different automotive basecoat/clearcoat systems were tested on their interlayer adhesion with EIS. For EIS measurements, two thin electrode stripes of an electroconductive ink were applied between two coating layers. The impedance measurements were conducted to find out the effect of moisture on the interlayer adhesion. The data obtained show a strong sensitivity of the interlayer impedance on the outer air humidity and point out at the possibility of following the water accumulation in the interlayer and the formation of the conductive paths. Such phenomena lead to the adhesion loss and delamination between the coating layers. We found that the interlayer adhesion loss follows the same trend as the changes of the activation energy of the ion mobility, which can be derived from the interlayer resistance, measured with EIS. For the verification of EIS measurements blister test measurements were carried out. With this method, it is possible to evaluate directly the interlayer adhesion of coatings. A good correlation was found between EIS and blister test data.