Optimization routes for high electrical conductivity of polypyrrole nanotubes prepared in presence of methyl orange

- Optimization routes for high electrical conductivity (up to 91.6 S cm−1) and specific surface (up to 67.6 m2 g−1) of polypyrrole nanotubes were proposed.
- Concentration of methyl orange in polymerization solution strongly influences both the diameter (ranging from 60 to 900 nm) and the shape (circular or rectangular cross-section) of synthesized polypyrrole nanotubes.
- The detailed mechanism of methyl orange effect during the polymerization process was explained in terms of behaviour of planar aromatic sulfonic acids.
- A power law describing dependency of electrical conductivity on nanotube diameter for this class of materials is reported.

The synthesis of polypyrrole nanotubes using methyl orange as a structure guiding agent is a popular method for obtaining electrically conductive material of nanostructured morphology. This work presents certain route of chemical synthesis, where the experimental conditions were optimized in order to obtain a material with high conductivity (up to 91.6 S cm−1) and specific surface area (up to 67.6 m2 g−1) via modification of two parameters: a) the methyl orange concentration (from 0.5 mM to 25 mM) and b) the polymerization temperature (from −5 °C to 35 °C). The synthesized material was then characterized by scanning electron microscopy, energy X-ray dispersive spectroscopy, nitrogen physisorption, Fourier-transform infrared and Raman spectroscopies and measurement of electrical conductivity. It was found, that the concentration of methyl orange in polymerization solution strongly influences both the diameter (ranging from 60 to 900 nm) and the shape (circular or rectangular cross-section) of synthesized polypyrrole nanotubes. Moreover, while at low concentrations of methyl orange in the native liquor the resulting nanotubes are accompanied by globular form of polypyrrole, at higher concentrations the composite of polypyrrole nanotubes with acidic form of methyl orange is produced. The detailed mechanism of methyl orange role during the polymerization process was explained in terms of behaviour of planar aromatic sulfonic acids. As for the polymerization temperature, it has stronger influence on the morphology than on the chemical composition of resulting polypyrrole nanotubes. Finally, we report a universal relation - a power law describing dependency of electrical conductivity on nanotube diameter for this class of materials.

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