IONIC EXCHANGE OF A CONDUCTING-POLYMER FILM WITH THE SOLUTION DURING THE CYCLIC-VOLTAMMETRY PROCESS

Two theoretical approaches to the interpretation of the EQCM data for the charging-discharging process in electron-conducting polymer film c oated electrodes have been proposed, with their application to systems without attached charged groups or fixed charges. The first model tre ats cations and anions inside the polymer phase as ''free'' mobile spe cies, whose exchange with the solution may be retarded due to low valu es of the interfacial exchange constants. Depending on its value for t he anion transfer, three limiting regimes of the charging process have been found: (I)complete ionic equilibrium with the solution, (2) ''ir reversible anion transfer'', and (3) ''cation compensation'', the elec tronic charge in the two former regimes being dominantly balanced by t he counterion as opposed to the colon process taking place in the latt er. Theoretical EQCM curves upon cyclic variation of the potential may possess a complicated shape, with a pronounced ''first cycle'' and '' relaxation'' effects as well as considerable hysteresis, the mass at t he anodic scan being greater than that at the cathodic branch for the anion exchange constants between regimes 2 and 3. Another model propos es the existence of two different forms of ions inside the film - ''fr ee'' and ''bound'' - with possible kinetic limitations for their mutua l transformation but a complete equilibrium between the ''free'' ions and the solution. The corresponding theoretical EQCM plots demonstrate the great variety of shapes depending on the maximum amount and therm odynamical stability of ''bound'' species as well as on the kinetic ex change parameters. This model has made it possible to reproduce most o f the features of experimental stabilized EQCM curves for PPy: nonmono tonic variation of the film mass (''coion'' type at low charges and '' counterion'' type at higher charges), with a drastic change in the mas s versus charge slope at the cathodic scan and a flat extremum in the anodic branch as well as a lower mass at the cathodic scan at very low charges and a crossing point of the branches.