Liquid-liquid interfaces for sensing applications

• Main Author: McIntosh, Alastair Jeffrey Scott
• Other Authors: Welton, Tom ; Goodchild, Sarah
• Published: Imperial College London 2015
• Subjects: 541
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.684263

A series of unfunctionalised and hydroxyl functionalised ionic liquids were synthesised with the aim of developing an ionic liquid based sensing platform. The electrochemical, and interfacial properties, were investigated and characterised to understand their use in a liquid-liquid, ITIES, platform. Electrochemical cells were designed and tested against model systems before the potential windows for the ionic liquid, ITIES, systems were measured. The potential windows were substantially wider than those previously reported. Initial agitation experiments with cytochrome-c showed promising results for the extraction and stabilisation, in the ionic liquids. However, protein ion transfer, under an applied potential, across the interface was not possible with any of the ionic liquids synthesised here. Capacitance results indicated, along with the cytochrome- c agglomeration, a charge build up or diffusion impedance at the interface. To investigate the reasons for this in greater depth pulse gradient stimulated echo NMR was undertaken and combined with fluorescence correlation spectroscopy. In the first reported monitoring, of the effect of an applied electric field on a probe in an ionic liquid by FCS, the results showed a marked 80 - 90 % decrease in diffusivity and an extremely slow relaxation time after the field was removed. After 600 seconds the diffusivity at the electrode surface was found to be unchanged, while the bulk diffusivity reduction had only reduced by 7 %. These results support the application of hole theory to ion diffusion within ionic liquids. Initial theoretical modelling to understand the ion dynamics at the interface provides intriguing evidence to support the development of theoretical tools to investigate interfacial ion dynamics, with what is believed to be the first reported use of a temporal split-step model based approach. This approach is approximately 10 - 20 times faster than previously reported methods.