pH-induced mass and volume changes of perchlorate-doped polypyrrole

The mass change of polypyrrole (PPy) due to ion transport was investigated in NaClO4 of various pHs, using an electrochemical quartz crystal nanobalance (EQCN). It was disclosed that the mass of perchlorate-doped PPy (PPy-ClO4) varies with solution pHs. While the mass was increased with lowering pH in general, the greatest mass changes were observed in the pH range of ca. 1.0–2.0 and 10.5–11.5. The magnitude of mass changes with pH was proportional to the film thickness of PPy-ClO4. Repeated acid/base treatments in between pH 1.0 and 11.3 resulted in the retention of ca. 78% of the initial mass response after 100 cycles, which can be compared with ca. 65% retention of the electrochemically induced mass change. In situ atomic force microscopic (AFM) images of PPy in NaClO4 revealed that the volume increase of 12.6% occurs in a solution of pH 1.0, relative to the volume in a solution of pH 11.3.