ELSEVIER Synthetic Metals 84 (1997) 91-92 MICROGRAVIMETRIC AND LASER BEAM DEFLECTION STUDIES OF REDOX REACTIONS IN POLYANILJNE AT VARIOUS CONCENTRATIONS OF DOPING ANIONS K. Koziel a, M. Lapkowski b and E. Vieil c a Institute of Inorganic Chemisby, Technology and Electrochemisby, Silesian Technical University, Gliwice, Poland b Institute of Physical Chemistry and Technology of Poljmers, Silesian Technical University Gliwice, Poland c Laboratoire d’Electrochimie Mole’culaire, SESAM, DRFMC, Centre d’Etudes Nuclkaires, Grenoble, France 1. Introduction It has been proved that the nature and concentration of the supporting electrolyte affects electrochemical and spectro- electrochemical properties of polyaniline [l-3]. Since in the course of the doping process ions and solvent molecules are exchanged between the polymer and the supporting electrolyte we applied quartz crystal microbalance and laser beam deflection techniques in the studies concerning the role of anions in electrochemical oxidation and reduction of polyaniline. 2. Experimental Polyaniline films were deposited on the working electrode from the acidic solution of aniline (0.2 M in 1 M HC1 or HC104) while scanning the potential between -0.2 and tO.7 V (vs. Ag/AgCl). After the synthesis the electrode was rinsed with distilled water and several voltammetric scans in 0.1 M H$iWr204c were carried out in order to remove residual anions from the polymer tilm. Microgravimetric measurements were performed using commercially available 5 MHz quartz crystals with gold layers deposited on both sides. Only one of the gold layers was covered with polyaniline and acted as the working electrode. Changes of the resonance frequency and the current response were recorded simultaneously during voltammetric cycling of polyaniline in the solutions containing 0.1 M H$iW1204c and various amounts of HCl or HC104. The linear dependence of 03796779197/$17.00 Q 1997 Elsevier Science S.A. All rights raened PII SO3794779(96)03851-9 Abstract Quartz crystal microbalance and laser beam deflection techniques were used to study the role of ion exchange in electrochemical oxidation and reduction of polyaniline films synthesized in various acids. Mass changes and beam deflection angles were measured during voltammetric cycling of polyaniline in aqueous solutions containing HdSiW12040 and various amounts of HCI or HC104. The obtained results confhm the initial hypothesis that due to their large size heteropolyanions cannot dope the bulk of the polymer. An increase in the doping anion concentration leads to significant changes of mass and a deflection angle associated with redox reactions in polyaniline. Doping anions as well as protons are exchanged between the polymer and the supporting electrolyte. The contribution of protons and anions depends not only on the concentration but also on the conditions under which the film was synthesized. Keywords: polyaniline, electrochemical doping, quartz crystal microbalance mass changes upon the resonance frequency was confiied by silver electrodeposition. A He-Ne laser (X=632.8 nm) was used as a source of light in beam deflection measurements. The light beam was focused in the vicinity of the working electrode (platinum disk). Deflection angles and voltammetric curves were recorded during electrochemical oxidation and reduction of polyaniline at various concentrations of doping anions. 3. Results and discussion Figure 1 shows mass changes recorded during voltammetric cycling of polyaniline (synthesized in HCl) at various concentrations of doping anions. 1.5 0 0 0.2 0.4 0.6 potential / V 0.8 Fig. 1. Mass changes observed during voltammetric cycling of polyaniline in solutions containing 0.1 M H&W12O4o and HCl. CHcl: (a) 0, (b) 0.001 M, (c) 0.005 M, (d) 0.02 M, (e) 0.1 M