EFFECT OF ANIONS ON THE NUCLEATION AND GROWTH-MECHANISM OF POLYANILINE

In this work we show that the nucleation and growth mechanism (NGM) of polyaniline (PANI) films depends on the anions present in the electrolyte, the solubility of oligomers formed before the nucleation process and the stirring conditions. The NGM of PAM in an unstirred solution can be explained by assuming that this process is preceded by the formation of a high density oligomeric layer which is located near the electrode/solution interface. A thick oligomeric layer obtained with a high concentration of monomers or with anions of the type HSO4- or SO42-, which form more soluble species with the oligomers. Under these conditions, diffusion-controlled progressive nucleation with three-dimensional growth is found. However, when the monomer concentration is low or ClO4- anions are present, the thickness is decreased and the NGM is either instantaneous nucleation with three-dimensional growth or progressive nucleation with two-dimensional growth.