Polypyrrole prepared in the presence of methyl orange and ethyl orange: Nanotubes versus globules in conductivity enhancement

The preparation of highly conducting polymer nanostructures with defined and uniform nanoscale morphologies presents a research challenge. Polypyrrole nanotubes were prepared by the oxidation of pyrrole with iron(III) chloride in the presence of methyl orange. The reactant concentrations and the oxidant-to-pyrrole mole ratio were varied in order to obtain the product with the highest conductivity in good yield. The conductivity increased from 1.55 S cm^-1 for the standard globular morphology to 119 S cm^-1 for nanotubes prepared under optimized conditions. The replacement of methyl orange with the closely related ethyl orange has led exclusively to the globular morphology of polypyrrole but the conductivity still improved to 27.3 S cm^-1. The marked difference in morphology is explained by the ability of methyl orange salt to produce a solid template for the nanotubular growth of polypyrrole under acidic conditions, in contrast to ethyl orange. The latter dye, however, acts similarly to surfactants and it also enhances the conductivity of polypyrrole. The results are discussed in detail on the basis of FTIR and Raman spectra.