THE APPLICATION OF FAST SCAN CYCLIC VOLTAMMETRY - MECHANISTIC STUDY OF THE INITIAL-STAGE OF ELECTROPOLYMERIZATION OF ANILINE IN AQUEOUS-SOLUTIONS

The initial stage of electropolymerization of aniline in acidic aqueous solution was studied by cyclic voltammetry and digital simulation. The dimer of aniline, p-aminodiphenylamine (ADPA), is the dominant intermediate in the early stages of polymerization, while benzidine is a minor intermediate. Cyclic voltammetric studies at a glassy carbon electrode in aniline solutions of low concentration combined with digital simulation indicated that both inter-mediates, benzidine and p-aminodiphenylamine, are formed through radical-cation-radical-cation coupling pathways. The reduction wave for the aniline radical cation was observed for the first time by working at a low aniline concentration (0.05 mM) and at a scan rate of 200 V s-1. The rate constant for the dimerization of aniline radical cations is about 10(8) M-1 s-1. Because of kinetic control of electropolymerization of aniline, the polymer morphology depended upon scan rate. Scanning electron and scanning tunneling microscopic images of the polyaniline films formed showed that the films produced at fast scan rates were more uniform, compact, and of a more regular structure than those produced at slow scan rates.