POTENTIOMETRIC STUDIES OF BILAYERS OF CONDUCTING POLYMERS

A theoretical model describing the dependence of the open-circuit pote ntial on electrolyte concentration for bilayers of conducting polymers is presented. One component of the bilayer is an anion-exchanger, whi le the second one is a cation-exchanging matrix. This model proposes d iagnostic criteria concerning the properties of such bilayers: (i) the presence of redox reactions between component polymers, (ii) the abse nce of such reactions due to hindrances in ion transfer across the out er layer, necessary to maintain the electroneutrality of the polymer, (iii) the presence of defects in the outer coating. This model was app lied to analyze the experimental results in the systems where the cati on exchanging matrix was polypyrrole with poly(4-styrenesulfonate) ion s or with indigo carmine, while poly(N-methylpyrrole) with perchlorate doping ions served as an anion exchanger. Potentiometric measurements were performed in solutions of KCl, MgCl2 and BaCl2. Although the pot entiometric results in BaCl2 solution exhibited more pronounced anioni c responses than in KCI solutions, it was found that during conditioni ng, prior to the potentiometric measurements, both univalent (K+) and divalent (Ba2+) could penetrate the outer PMPy layer. (C) 1998 Elsevie r Science S.A.