Electrochemical interfaces microdroplets, single

In the previous section, we demonstrated the micrometer droplet size dependence of the ET rate across a microdroplet/water interface. Beside ET reactions, interfacial mass transfer (MT) processes are also expected to depend on the droplet size. MT of ions across a polarized liquid/liquid interface have been studied by various electrochemical techniques [9-15,87], However, the techniques are disadvantageous to obtain an inside look at MT across a microspherical liquid/liquid interface, since the shape of the spherical interface varies by the change in an interfacial tension during electrochemical measurements. Direct measurements of single droplets possessing a nonpolarized liquid/liquid interface are necessary to elucidate the interfacial MT processes. On the basis of the laser trapping-electrochemistry technique, we discuss MT processes of ferrocene derivatives (FeCp-X) across a micro-oil-droplet/water interface in detail and demonstrate a droplet size dependence of the MT rate. 

In Sections III and IV, we described droplet size dependencies of the ET and MT rates across microdroplet/water interfaces. Such experiments on single droplets are possible by the laser trapping spectroscopy-electrochemistry technique alone. Besides these experiments, the technique is also highly useful in controlling a reaction efficiency in microdroplets [99,100]. In this section, we describe electrochemically induced dye formation reactions across microdroplet/water interface and demonstrate control of the dye formation reaction yield in micrometer dimension. The effects of microenvironments and additives (surfactant or stabilizer) on dye formation reactions are also described. 

The mass transfer and chemical reaction between a single microdroplet and the surrounding solution phase can be induced by the laser and microcapillary manipulation and microelectrochemistry system. An example of the electrochemically induced mass transfer across a single microdroplet/solution interface is shown in Figure 9.3. If... 

FIGURE 9.3. General scheme of electrochemically induced mass transfer across a single microdroplet/ solution interface. 

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