Electrosynthesis of PEDOT films at the liquid|liquid interface between two immiscible electrolyte solutions

This thesis provides a fundamental investigation into the electrosynthesis of free-standing  poly(3,4-ethylenedioxythiophene) (PEDOT) thin films at the electrified interface between two  immiscible electrolyte solutions (ITIES). First, the controllable electrosynthesis of PEDOT films at the ITIES was demonstrated using both cyclic voltammetry and chronoamperometry methods. The mechanism of EDOT interfacial electropolymerisation was then resolved using a combination of electrochemical and spectroscopic techniques. It was demonstrated that the interfacial electron transfer (IET) reaction between the aqueous Ce(IV) and the organic EDOT monomer takes places when the interfacial Galvani potential difference (Δ𝑜 𝑤𝜙) is biased positively (> +0.2 V), while the deposition of subsequent EDOT oligomers is favourable when the Δ𝑜 𝑤𝜙 is biased negatively. In addition, it was observed that an ion-interchange reaction occurs when EDOT oligomers are deposited at the ITIES with the complexation of the aqueous electrolyte anion (SO4 2‒ ) at the expense of the organic electrolyte anion, tetrakis(penta-fluorophenyl)borate (TB‒ ). Next, extensive characterisation of the free-standing PEDOT film  was made to analyse the morphology, composition, electrochemcial performance, and biocompatibility of the conducting polymer film. Finally, the influence of the aqueous  electrolyte on the kinetics of nucleation and growth of PEDOT at the ITIES was investigated. The rate of EDOT interfacial electropolymerisation, determined with chronoamperometric  analysis, was shown to be both dependant on the applied Δ𝑜 𝑤𝜙, and the choice of aqueous phase electrolyte. A trend that follows the Hofmeister series was observed where increased rates of interfacial electropolymerisation were recorded with anions of increasing hydrophobicity (SO4 2‒ < MsO‒ < NO3 ‒< ClO4 ‒ ). It is expected that the proposed mechanism of EDOT interfacial electropolymerisation will be generic for many aqueous oxidant/organic monomer combinations. Therefore, the results in thesis can be used to improve the interfacial electrosynthesis of other technologically important conducting polymers beyond PEDOT.