Effective and Reversible Switching of Emulsions by an Acid/Base-Mediated Redox Reaction.

To develop a fast, effective, and reversible strategy for phase separation and re-emulsification of the surfactant-based emulsions, a strategy for using acid/base-mediated redox reactions was established to switch the emulsions formed from a redox-responsive anionic surfactant of potassium dodecyl seleninate (C12SeO2K). Upon acidification, C12SeO2K was reduced by KI to give didodecyl diselenide (C12Se)2, a state of almost no surface or interfacial activity; upon basification, (C12Se)2 was oxidized by I2 to give C12SeO2K again. The fractional conversion of C12SeO2K in the reversible switching processes was close to 100%. Consequently, an unusually large change in interfacial tension (ΔIFT) as high as ∼27.1 mN m-1 was obtained at a wider concentration range starting from the critical micelle concentration of C12SeO2K; the highest IFT at the oil-water interface was obtained after an almost complete switch-off, giving an oil-aqueous solution interface very similar to that without any emulsifiers, which leads to the effective and fast phase separation of the C12SeO2K-based switchable emulsions.