Potentiometric Responses of Poly(pyrrole) Films Surface Modified by Nafion

Abstract

The influence of surface modification with Nafion layer on potentiometric characteristics of conducting polymer (CP) films was studied. In this article the possibility of inducing the permselective, cationic responses of both anion- and cation-exchanging layers is presented. From theoretical considerations it follows that the effect of coating of CP with permselective cation-exchanging layer on potentiometric responses of the bilayer system is exclusively dependent on the ion-exchanging properties of the inner phase. For the bilayer of two cation-exchanging films the cationic responses are expected, whereas for the anion-exchanging inner layer the open circuit potential changes will reveal the properties of modifying film, the CP will serve as an electrical signal transducer only. Experimental results obtained for poly(pyrrole) layers doped with chloride (PPyCl) and hexacyanoferrate(II) ions (PPyFeCN) are discussed. The polymer doped with a chloride ions is well-known anion-exchanging membrane, whereas the latter is a cation-exchanging one. Applying the cation exchanging, ion-conductive Nafion layer on the top of poly(pyrrole) results in an increase of slope of the characteristic recorded for PPyFeCN layer from 35.7 to 58.1 mV/dec, although the linear responses were in the latter case limited to the range from 2×10−5 to 2×10−3 mol/L, i.e., to the modifying layer permselectivity region. For PPyCl film the type of potentiometric characteristic was reversed from the anionic of slope −70.6 mV/dec to cationic 33.1 mV/dec, the cationic responses were observed within the concentration range from 10−5 to 2×10−3 mol/L. The results obtained point to exclusion anions from the ion-exchange process, which for PPyCl means the possibility of total reversing the anionic characteristic to the cationic one. The cationic selectivity of tested bilayer systems was compared.