Electrochemistry at Electrified Soft Interfaces – Novel Approaches to Old Problems

This thesis addresses some known difficulties in the field of liquid | liquid electrochemistry by presenting novel means of controlling mass transfer, monolayermodification of the interface, and probing interfacial reactivity. A novel rectangular channel flow electrochemical cell suitable for studying charge transfer at liquid | liquid interfaces is presented. The organic phase is immobilised using a gelling agent, while the aqueous phase flows past the interface. This creates an asymmetric diffusion regime, providing diagnostic criteria to determine, for example, the direction of the ion transfer. One of enduring problems concerning phospholipid adsorption at liquid | liquid interfaces has been the inability to determine and control the exact nature of the adsorbed monomolecular layer. This difficulty is addressed by a combination of the Langmuir-Blodgett technique and the use of an electrochemical cell as a substrate. It is shown that reproducible layers of known surface pressure can be deposited at the interface and that the deposition surface pressure has a great influence on the behaviour of the layer. The latter part of this thesis concerns the study of reactivity at liquid | liquid interfaces. To this end, the potential of ring-disk ultramicroelectrodes as probes for scanning electrochemical microscopy is investigated both theoretically and experimentally. In particular, the disk-generation/ring-collection mode of operation is considered. The interaction of two species with the substrate under investigation can be followed simultaneously from a single tip current-distance measurement to the substrate. This method is then applied to investigate the partitioning of iodine across a liquid-liquid interface. A facile method to determine the lipophilicity of potentially unstable charged products of electron transfer reactions is reported. This is achieved by local electrolysis at a Pt coated micropipette and subsequent transfer of the electrogenerated ions across a polarisable liquid | liquid interface supported at the tip of the micropipette. The formal potential of ion transfer can then be used to give a measure of its relative lipophilicity.