Composition of the microemulsion and its influence on the polymerisation and redox activation of PEDOT

The electrochemical formation of poly-3,4-ethylenedioxythiophene (PEDOT) layers in a highly concentrated bicontinuous (BC) microemulsion of the hydrophobic monomer 3,4-ethylenedioxythiophene (EDOT) and an aqueous electrolyte containing a commercial nonionic surfactant is studied with respect to the polymerisation kinetics, capacitive behaviour, doping level and morphology. It is found that polymerisation occurs under charge transfer control and could be described formally by means of a model for instantaneous nucleation and 3D growth. Post-polymerisation treatments of the polymer layers by means of potentiostatic pulses or by utilising the phase behaviour of the microemulsion are applied in order to obtain PEDOTs with high doping levels, close to γ=0.3. The effect of the electrochemical or physicochemical post-polymerisation procedures is related to leaching out of trapped microemulsion residuals. Capacity experiments performed in the BC microemulsion show that adsorption of the hydrophobic oil (EDOT) occurs at the metal electrode ∣ solution interface. In combination with the special BC character of the microemulsion and its high monomer content (26 wt.% EDOT), this effect allows for initiation of the polymerisation process at very low positive potentials (E>0.7 V). The possibility for a polymer growth enhancement under pulse potentiostatic conditions is explored in both BC and oil-in-water (OW) microemulsions. A thickness dependent enhancement effect is established in the case of pulse polymerisation in the OW microemulsion. Pulse synthesis in the BC microemulsion is found to inhibit the PEDOT polymerisation.