Polypyrrole impedance response

As expected, the impedance responses obtained in practice do not fully match that of the model of Fig. 9.13. However, as shown by the typical case of Fig. 9.14 which illustrates the response obtained for a 5 mol% ClO -doped polypyrrole electrode in contact with a LiC104-propylene carbonate solution (Panero et al, 1989), the trend is still reasonably close enough to the idealised one to allow (possibly with the help of fitting programmes) the determination of the relevant kinetics parameters, such as the charge transfer resistance, the double-layer capacitance and the diffusion coefficient. 

Fig. 9.14 The ac impedance response of a Q04-doped polypyrrole electrode over a frequency range extending from 0.006 Hz to 6.5 kHz.

By comparing impedance results for polypyrrole in electrolyte-polymer-electrolyte and electrode-polymer-electrolyte systems, Des-louis et alm have shown that the charge-transfer resistance in the latter case can contain contributions from both interfaces. Charge-transfer resistances at the polymer/electrode interface were about five times higher than those at the polymer/solution interface. Thus the assignments made by Albery and Mount,203 and by Ren and Pickup145 are supported, with the caveat that only the primary source of the high-frequency semicircle was identified. Contributions from the polymer/solution interface, and possibly from the bulk, are probably responsible for the deviations from the theoretical expressions/45... 

Polypyrrole has the potential to provide an effective method for reagentless transduction by immobilization of the ssDNA probe within the polymer matrix. Significant differences in the impedance profile of ssDNA and dsDNA have been demonstrated [59]. The differences in the impedance profile are purportedly based on intercalation differences of the polymer with ssDNA compared to dsDNA. The exact mechanism for impedimetric change resulting from conducting polymer films has not been identified, although it is likely linked, much like the impedimetric response of pure DNA, to the change in ion density that accompanies the double strand compared to the... 

A pH sensor, based on a.c. conductivity measurements of a thin polymer film, has been developed. The sensor consists of a planar interdigitated electrode array coated with a polypyrrole multilayer, built-up using the Langmuir-Blodgett technique. Impedance spectroscopy has been used to investigate the complex admittance of the device when exposed to aqueous solutions of different pH. The experimental data have been fitted to the theoretical response of an equivalent electrical network of capacitors and resistors. A response over the pH range 3.5 to 8 has been measured. 

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