Strategies towards the control of one-dimensional polypyrrole nanomorphology and conductivity

Conducting polypyrrole nanotubes rank among the most conducting polymer materials and find applications in organic electronics and energy conversion devices. They are produced by the chemical oxidation of pyrrole in globular form, which converts to nanotubes or nanofibres in the presence of suitable templates and is often accompanied by a pronounced conductivity increase. This is illustrated by the anionic dye, methyl orange, where the template formation is based on azo-hydrazone tautomerism associated with hydrogen atom transfer caused by the acidity change. In other words, the soluble salt of the dye converts to an insoluble acid, and its one-dimensional aggregates serve as a locus for the adsorption of pyrrole oligomers. This is followed by the growth of polypyrrole chains constituting the nanotube wall. Safranin, a cationic dye, produces a template by a completely different mechanism, the oxidative generation of insoluble safranin oligomers that perform with similar results. Other mechanisms of template formation are also proposed and discussed but mainly organic dyes have a significant potential to support the one-dimensional growth of polypyrrole. The role of surfactants that affect the morphology of templates, and subsequently also of polypyrrole, is demonstrated. (c) 2018 Society of Chemical Industry