Abstract

AbstractTo develop a convenient and reversible strategy for phase separation and re‐emulsification of surfactant‐based emulsions, we established a method for pH switching of emulsions formed from a pH‐switchable anionic surfactant, potassium dodecyl seleninate (C12SeO2K). Upon acidification, C12SeO2K was protonated to give a precipitate of dodecyl seleninic acid (C12SeO2H); upon basification, C12SeO2H was neutralized restore C12SeO2K. The pH‐switchable window of the emulsion thus obtained was a pH range of 7 to 8. Reversible changes in both interfacial tension by ~10.2 mN m−1, as well as the mechanical, steric, and/or electrical barriers formed by C12SeO2K at the interface of the oil–aqueous solution account for the fully reversible phase separation and re‐emulsification of the C12SeO2K‐based emulsions. A stable emulsion (i.e. the time needed to separate 1 mL of H2O from 6 mL of emulsion at 25 °C is larger than 1 h) could be cycled at least 25 times when the pH was varied between 7 and 8.

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