MONTE-CARLO SIMULATION OF 2-DIMENSIONAL GROWTH OF CONDUCTIVE ZONES IN INTERCONVERSION OF CONDUCTING POLYMER-FILMS INVOLVING RANDOM MORPHOLOGY

Morphological effects of the interconversion of conductive polymers on anodic voltammograms were estimated by Monte Carlo simulation when the film had a random distribution of electroactive and electroinactive sites. The simulation was based on the propagation theory of the conductive zone under charge-transfer control. The electroactive site was assigned either to a conductive (oxidation) or to a non-conductive (reduction) state. The non-conductive site contact with the conductive site was converted electrochemically into a conductive state in linear sweep voltammetry. When the composition ratio, p, of the electroactive sites ranged from 0.5 to 0.7, various patterns of the conductive zone were observed and appeared visually to be fractal. The current density at p = 0.59 had maximum fluctuation, depending on the initial distribution of the electroactive sites. Then the growing length of the conductive front was ten times longer than the film thickness, indicating that the front wandered in the film. The conversion ratio changed dramatically at p ranging from 0.56 to 0.62. Electric percolation from the film surface to the electrode occurred at p > 0.56. From variations of the variance of the current, the peak current and the conversion ratio with p, the voltammogram was classified into the following three controlled processes: Nernstian boundary condition control for 0 < p < 0.56; morphological control for 0.56 < p < 0.62; and charge-transfer control at the interface between the conductive and non-conductive sites for p > 0.62. © 1990.