Influence of the Solution Ionic Mobility on the Impedance Response of Organic Coatings

PVC (polyvinylchloride) Plastisol films immersed in electrolyte were studied by Electrochemical Impedance Spectroscopy (EIS) and the data were fitted using one-time constant and two time constant equivalent circuits. Very often the electrical behavior of these films is better represented by the second circuit. The first time constant can be associated with the film capacitance and is independent of the immersion solution ionic mobility, whereas the second one could be related with charge separation inside the film pores and depends on cation mobility. Since the physical meaning of the two time constants is acknowledged their presence in EIS measurements should be taken into account when the results are analyzed. Electrochemical Impedance Spectroscopy (EIS) can be used to evaluate coatings. The results obtained can be interpreted with an equivalent circuit composed by a resistor (solution resistance) followed by a capacitor (coating capacitance) in parallel with a resistor (poreresistance).FrequentlytheEISresultsforanintactcoating show a second time constant in the high frequency region. Several interpretations of these results are possible, namely, water-polymer composite response, coating pore structure, charge separation occurring at the film, coating relaxation given by the water entrance, high heterogeneity of the coating and transient instability (early water uptake), interaction between adsorbed electrolyte and the polymer (dipole relaxation) and difference between the coating outer and inner parts