On the growth of polypyrrole from solutions of methanol and water

Abstract

Samples of polypyrrole have been prepared electrochemically from solutions of pyrrole and p-sodium toluene sulfonate in mixtures of methanol and water, and the resulting samples have been characterized by optical microscopy, scanning electron microscopy (SEM) and wide-angle X-ray scattering (WAXS). Conductivity measurements have also been made. Incremental addition of methanol to the solvent results in a change in the surface morphology of the film. The film becomes markedly more wrinkled and the usually reported nodular surface texture also changes. This is accompanied by a fall in the electrical conductivity of three orders of magnitude and an almost total loss in the anisotropy of the films as measured by WAXS. In addition to the preparation of films on planar electrodes, growth has also been investigated on linear Pt/Pd wire electrodes. For solvent mixtures containing less than 50% methanol, a disc-shaped film (additional to the film on the linear electrode) grows along the air/solvent interface. The morphology of this growth has also been examined. Although many of these phenomena closely mirror the effect of changing the anodic potential in an aqueous system, the suppression of interfacial growth at high methanol concentrations suggests that the organic solvent does not only affect the polymerization process as a consequence of changes in the oxidation potential of the pyrrole monomer.