Medium-Frequency Results and Discussion

Typical impedance plots are shown in Fig. 4.6. In each plot we find a resistance on the real axis at a high frequency of / ,. This resistance is the sum of the electrolyte resistance Re and the resistance / n of the transmission line where, as discussed in Eqn. 25, 

There is a well-developed Warburg region with a 45° slope that eventually at low frequency turns into a capacitive impedance with a slope close to 90°. The impedance plot in the capacitive region has a slope somewhat less than 90°. This feature has been attributed to dispersion of the values caused by the heterogeneity of the film.  

Under these conditions along the Warburg 45° line, from Eqn. 23 (including R and taking p 1) the theory predicts that 

The parameter p is equal to the volume of the polymer divided by the volume of the aqueous pores. For an electrode of area A and polymer coat of thickness L, the volume of the polymer Vp is given by 

FIGURE 4.6. Typical impedance plots for poylvinylferrocene. The increasing potentials were 0, 25, and 50 mV in the main diagram and 50 and 75 mV in the inset. Lines are drawn at 45°. 

---