ELECTROCHEMICALLY INDUCED CHARGE AND MASS-TRANSPORT IN POLYPYRROLE/POLY(STYRENESULFONATE) MOLECULAR COMPOSITES

Polypyrrole/poly(styrenesulfonate) (PP/PSS) molecular composites have been synthesized by the electrochemical polymerization of pyrrole in the presence of sodium poly(styrenesulfonate) (PSS-Na+). Their synthesis and charge transport properties have been investigated by a combination of electrochemical and gravimetric techniques using the Electrochemical Quartz Crystal Microbalance (EQCM). Electropolymerization in water at 0.8 V vs Ag/AgCl yields a partially hydrated polymer complex with sulfonate dopant anions from PSS. Mass transport is found to be cation specific, as expected for a composite system, with the polyelectrolyte chains physically entrapped within the polymer membrane. Frequency responses of the EQCM during electrochemical switching are found to increase with increasing electrolyte cation mass as Li+ congruent-to Na+ < Cs+ < Et4N+ < Bu4N+. Chronogravimetric and chronocoulometric analyses of PP/PSS-Na+ yield apparent diffusion constants, D(app), between 10(-9) and 10(-11) cm2 s-1 for mobile hydrated Na+ species. Though the determinations of these values are complicated by the exact determination of the concentration of electroactive sites (C0*), it is evident that reductive transport processes are faster than oxidative transport processes during switching.