THE ROLE OF THE COUNTERION IN THE PREPARATION OF POLYPYRROLE FILMS WITH ENHANCED PROPERTIES USING A PULSED ELECTROCHEMICAL POTENTIAL

The use of a pulsed electrochemical potential in the growth of polypyrrole films leads to enhancements in the resultant electrical conductivity, molecular anisotropy and surface smoothness as compared to equivalent films synthesized under constant potential conditions. Such enhancements are only observed when the films are prepared from aqueous electrolytes containing toluene sulfonate or naphthalene disulfonate as the dopant or counter-ion. No improvements in properties result when spherical counter-ions such as BF4- are used. X-ray scattering patterns show that the polypyrrole films with aromatic-based counter-ions are highly anisotropic with the planes of the pyrrole rings lying preferentially parallel to the electrode surface. The values of the pulse length and voltages employed are most important in preparing enhanced films and appear to indicate that these improved films grow as a consequence of a much larger number of equivalent growth sites. These enhancements are highly dependent on the type of counter-ion. The improvement in the molecular order depends upon the changes brought about in the growth mechanism during the doping and undoping process.