Determination of the dopant weight fraction in polyaniline films using a quartz-crystal microbalance

The electrical conductivity of polyaniline depends on factors such as degree of oxidation, type of protonation, and dopant weight fraction. The last of these factors is connected with the loss of mass during the deprotonation of polyaniline, and can thus conveniently be determined in situ by the use of a quartz microbalance. This is illustrated in the present paper which concerns the determination of the weight fraction of acid in thin polyaniline films prepared by the chemical oxidation of aniline in the aqueous solutions of sulfuric and phosphoric acids. It is illustrated that the deprotonation-reprotonation processes are fast, complete, and reversible. Polyaniline has sulfate counter-ions in 0.1 M sulfuric acid while, in 0.5-1 M sulfuric acid, hydrogen sulfate counter-ions are present. The quartz microbalance involving polyaniline films can be used in the sensing of the acidity.