Characteristic behavior of an electron-transfer reaction across a tributyl phosphate droplet/water interface: Micrometer droplet-size effect

An electron-transfer (ET) reaction between decamethylferrocene in a single tributyl phosphate (TBP) droplet and hexacyanoferrate(III) in the surrounding water phase was investigated by laser trapping, microspectroscopic, and electrochemical techniques. The interfacial ET rate constant (k(obs)) was inversely proportional to the droplet radius (r) at > 5 mu m, but deviated from a linear relationship between k(obs) and r(-1) at r < 5 mu m. The characteristic droplet-size effect was independent of the Galvani potential between the TBP and water phases. The results are discussed in terms of the physical properties of the micrometer-sized TBP droplet/water interface.