The ohmic response of bromophenol blue (BPB) doped polypyrrole (ppy) films obtained by in situ resistance measurements was studied to evaluate the pH effect on their analytical properties. BPB molecules were inserted into the ppy matrix by electrochemical synthesis onto digitized gold electrodes. Ppy-BPB films do not present decrease in the linear ohmic resistance when increasing pH values over the pH range 1.5-11.0, displayed by an increase in resistance after immersion in pH 7.5. The nonlinear behavior is a disadvantage for the application of the ppy-BPB film as pH sensor, however, meaningful information about the interaction between the dopant and the conjugated polymer can be obtained from the system. The ohmic behavior of the ppy-BPB films are explained in terms of the equilibrium between neutral and anionic dye species embedded in the ppy matrix. This work brings important contributions to the development of efficient conducting polymer-based sensors.
polypyrrole; bromophenol blue; ohmic properties; doped films
