ELECTROCHEMICAL QUARTZ-CRYSTAL MICROBALANCE STUDIES ON THE ELECTROPOLYMERIZATION PROCESSES OF ORTHO-PHENYLENEDIAMINE IN SULFURIC-ACID-SOLUTIONS

The electropolymerization of ortho-phenylenediamine (o-PD) in 0.10 M H 2SO4, 0.10 M H2SO4 + 0.40 M Na2SO4, and 0.50 M H2SO4 solutions was stu died using an electrochemical quartz crystal microbalance. The poly-(o rtho-phenylenediamine) (PoPD) films were formed during continuous pote ntial cycling between -0.40 V and +0.95 V versus SCE. The decrease in the resonant frequency of the quartz crystals during electropolymeriza tion of phenylenediamine demonstrated that the deposition of the polym er films occurred mainly in the potential range where the monomers wer e anodically oxidized. Dramatic changes in the resonant frequency and the resonant admittance were observed during the redox processes at po tentials below +0.20 V. At least two kinds of deposits could be distin guished in the PoPD films. The surface concentration of the electroact ive sites of the polymer prepared in 0.10 M H2SO4 and in 0.10 M H2SO4 + 0.40 M Na2SO4 solutions were much higher than that prepared in 0.50 M H2SO4. The acidity of the solution rather than the concentration of the anions of the electrolyte was found to have a strong influence on the electropolymerization processes. The results were discussed in the light of the effects of the solubilities of oligomers in solutions du ring the electropolymerization processes and the changes in the struct ures of the initially formed polymer films. (C) 1998 Elsevier Science S.A. All rights reserved.