Morphology and electrical conductivity behavior of electro-deposited conductive carbon black-filled epoxy dispersions near the insulator–conductor transition point

The film morphology and electrical properties of the base-coat in an epoxy-based double electro-deposition system was studied using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and image analysis. The concentration of the conductive carbon black (CCB) was increased to the lower vicinity of the percolation threshold. The re-coatability of the first layer and degree of coverage and the fractal dimension of the second layer were determined using image processing techniques. It was found that the base-coat films behave electrically as a two-layer film. The lower layer behaves conductive and the upper layer behaves capacitive. It was also proved that the current transport through the base-coats during top-coat electro-deposition is not through the resistive elements but occurs mainly by multiple charging and discharging of the capacitive elements present in the base-coat film.