A New Method for the Study of Processes at the Liquid-Liquid Interface Using an Array of Microdroplets on a Au Electrode

• Published in: Chemphyschem 2006-12, Vol.7 (12), p.2585-2592
• Main Authors: Simm, Andrew O., Chevallier, François G., Ordeig, Olga, del Campo, F. Javier, Munoz, Francesc X., Compton, Richard G.
• Format: Article
• Language: English
• Subjects: Chemistry; copper; Copper - chemistry; diffusion; Electrochemistry; Electrodes; Electrodes: preparations and properties; Exact sciences and technology; General and physical chemistry; Gold - chemistry; Hydrophobic and Hydrophilic Interactions; interfaces; microdroplets; Oximes - chemistry; Particle Size; Study of interfaces; Surface Properties; Temperature
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200600394

We report the fabrication of partially blocked gold electrodes, with regularly and hexagonally spaced inert hydrophobic blocks on their surface. The hydrophobic blocks, with diameters of 5 μm, are used to support liquid 5‐nonyl‐salicylaldoxime (Acorga‐P50) droplets on the surface. By voltametrically monitoring the transport‐controlled reduction rate of CuII (in pH 5 solution) at the unblocked part of the gold surface it is possible to deduce, via simulation, the parameters controlling the rate of uptake of CuII at the droplet–aqueous solution interface as the droplet “fills up” with CuII. Experimentally, it is recorded that the reduction current increases until the droplet is filled completely; after this, there is no further noticeable effect of the droplet coating. A rigorous theoretical analysis of the transients permits the deduction of partition coefficients between the aqueous solution and the organic‐droplet phase and of diffusion coefficients within the droplet. The partition coefficient for CuII between water and 5‐nonyl‐salicylaldoxime was found to be 200 at 25 °C and the diffusion coefficient of CuII inside the organic phase was determined to be 5×10−11 cm2 s−1. Blocking diffusion: The fabrication of a regular array of microdroplets on a gold electrode surface is studied. By voltametrically monitoring the transport‐controlled reduction rate of CuII at the unblocked part of the electrode (see figure) it is possible to deduce, via simulation, the parameters controlling the rate of uptake of CuII at the droplet–aqueous solution interface as the droplet “fills up” with CuII.