EQCM STUDY OF THE PROCESS OF SILICOMOLYBDIC ANION DOPING IN POLYANILINE FILMS ELECTROSYNTHESIZED IN THE PRESENCE OF VARIOUS ANIONS

A systematic investigation of the electrosynthesis of polyaniline (PAN I) films in the presence of various anions has been carried out. These anions were HSO4-, Cl- and ClO4-. The synthesis was followed by dopin g with SiMo12O404- (SiMo12), which has been proven previously to give very stable and catalytically useful PANI/SiMo12 composites. Another i nterest of this system is that two of the redox systems of SiMo12 appe ar in the potential domain where PANI is conductive, and a third one i s just at the limit where PANI becomes fully reduced. The study is con ducted essentially using the EQCM technique. It is shown that the same amount of doping heteropolyanion is fixed in the film, through an ess entially volume process, in open circuit conditions, or by cycling the electrode potential during the incorporation. However, this last tech nique seems more beneficial to obtain a faster homogeneous dispersion of the dopant anion into the polymer matrix. The results also demonstr ate that films preformed in sulfate media are doped very easily with S iMo12, while the plasticization of the films prepared in perchlorate m edia severely limits this incorporation, whatever the anion (HSO4-, Cl - and ClO4-) present in the incorporation medium. Another important re sult, revealed by EQCM studies, concerns the charge transport properti es of the composite PANI/SiMo12 during its redox processes. It appears , in that case, that proton exchange can constitute the dominant pathw ay even in a mildly acid medium like 0.5 M H2SO4. More generally, it c an be concluded that not only might the nature of the anions in the fi lm compensating the positive sites affect the apparent dissociation co nstant of PANI, but the redox chemistry of the anions also affects the charge transport processes. (C) 1998 Elsevier Science S.A. All rights reserved.