Synthesis of a polypyrrole film on a non-conducting substrate; the influence of the oxidant and acid concentration

Thin films of conducting polypyrrole are deposited on a non-conducting substrate by dipping the substrate in a pyrrole solution and subsequently in an oxidising solution containing Fe(ClO4)3 and HClO4. In this last step pyrrole is polymerised by Fe3+. Calculations on the influence of the acid concentration on the Fe3+ hydrolysis equilibria are in good agreement with UV/VIS and pH measurements. These calculations and experiments in which HClO4 is replaced by LiClO4, show that the polymerisation rate of pyrrole is determined by the perchlorate concentration and not by the acid concentration. We conclude that the perchlorate ions promote the dimerisation of the radical cations by reducing the electrical repulsion between the radical cations; therefore the dimerisation of the radical cations is the rate-determining step.