IONIC TRANSPORT IN POLY(N-ETHYLCARBAZOLE) FILMS, INVESTIGATED BY QUARTZ-CRYSTAL MICROBALANCE AND MIRAGE EFFECT TECHNIQUES

Ionic insertion or removal from a poly(N-ethylcarbazole) (PECBZ) film modified electrode upon doping/dedoping in perchloric acid was studied by the mirage effect and quartz crystal microbalance (QCMB) technique s. The experimental mirage signal while cycling the potential was comp ared to the calculated signal based on an exclusive anion exchange lim ited by diffusion. The mass-charge relation from the QCMB was either o btained during cycling voltammetry or from the mass-charge transfer fu nction measured with a low-level signal. Upon anodic scan, the mass in crease is delayed with respect to the charge increase and the measured mirage signal is lower than the calculated one. Upon cathodic scan, t he mass-charge relation is linear with a slope of 120 g mol(-1) farada y(-1), the measured and calculated mirage signals being identical. It is proposed that, starting from a cathodic potential, a conductor-insu lator boundary moves from the metal to the solution. A large expulsion df protons and a weak insertion of counter-ions result from a transpo rt control by electric migration in the insulator layer where the tran sference number of protons is much larger than that of anions. During the cathodic scan,the side of the film against the solution remains co nducting and anions are easily exchanged with the solution.