Reversible-Tuning Krafft Temperature of Selenium-Containing Ionic Surfactants by Redox Chemistry

An easy, effective, and reversible strategy for tuning the Krafft temperature (K_T) of selenium-containing ionic surfactants, with head groups ranging in nature from anionic to amphoteric, has been achieved for the first time via the redox chemistry of selenium. After oxidation with H₂O₂, the selenide group was converted to a more hydrophilic selenoxide group. This made the oxidized forms of the surfactants more water-soluble, which results in a marked reduction in the K_T. In contrast, the hydrophilic selenoxide was restored to its reduced form of selenide via reduction reaction, which allowed the K_T value to return to its initial value. By alternating the oxidization and reduction treatments, the K_T of the selenium-containing surfactants in this work could be reversibly switched over 5–10 cycles without causing obvious adverse distortions.