Methyl red dye in the tuning of polypyrrole conductivity

Abstract

Polypyrrole was prepared by the oxidation of pyrrole with iron(III) chloride in aqueous medium in the presence of methyl red dye. While the acid form of dye had no effect on the polypyrrole synthesis, the presence of its sodium salt increased the conductivity from 1–5 S cm−1 up to 84 S cm−1 for the polymerizations carried out with variable dye concentration at 20 °C. When the reaction temperature was reduced to −50 °C, the conductivity increased up to 104 S cm−1. At temperatures below −20 °C, the polymerization took place in frozen reaction medium, in ice. The morphology of polypyrrole was mainly globular and often converted to particles of irregular size and shape. It was concluded that one-dimensional morphology, nanotubes or nanofibers characteristic of polypyrrole, is not an automatic prerequisite for the high conductivity of this polymer.