Electrochemistry of conductive polymers XXIII: polyaniline growth studied by electrochemical quartz crystal microbalance measurements

Polyaniline (PAn) growth has been studied in 0.50 M H2SO4 containing 0.030 M aniline using an electrochemical quartz crystal microbalance in situ during potentiodynamic and potentiostatic growth experiments. A quantitative analysis of the in situ gravimetric data and the faradaic charge suggests that the oxidative deposition of aniline is made of a few different steps with different mechanisms. The nucleation processes were observed during the first few potential cycles leading to the formation of short chain oligomers. Then, the number of electrons transferred for deposition approached to about 2.4 for each aniline molecule, suggesting that the number of electrons transferred for polymer growth almost agrees with the generally accepted stoichiometry. In later stages of polymerization, the number of electrons involved became less than 1.0, indicating that the PAn growth follows the autocatalytic mechanism. Analysis of weight data also suggests that there must be a change in polymer morphology as well as in growth mechanisms.