Organic coatings capacitance measurements

Instrument limitations must be considered in the measurement of organic coatings because their resistivities are large, 1012 Q cm or more. The input resistance of common potentiostats is usually not more than 10n to 1012 ohms, and if the cell resistance approaches or exceeds the input resistance of the potenti-ostat, a significant fraction of the applied signal will pass across the input impedance and not the cell impedance. In these cases the collected data do not reflect just the impedance of the electrochemical interface, which is a fundamental assumption in almost all data analyses. In fact, the potentiostat input impedance in parallel with the stray capacitance associated with the potentiostat measuring leads will be obtained. 

It should be kept in mind that organic coatings are characterized by low capacitances and very high resistances, demanding work at high frequencies, and it must be assured that the measuring equipment is able to measure such objects (Sects. 16.1 and 16.2 and Refs. [675-681]). 

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