Redox-Controllable Interfacial Properties of Zwitterionic Surfactant Featuring Selenium Atoms

Control of interfacial properties (foaming and emulsification) plays an important role in industry. Here we developed a novel redox-responsive surfactant, 3-(11-benzylselanyl-undecyl)-dimethylammonium acetate (BSeUCB), using selenium atoms as an environmentally sensitive group. In a reduced state, BSeUCB aqueous solution showed good foaming and emulsification abilities as well as conventional betaine surfactants. After oxidization, BSeUCB transformed into a bola-type structure because of the presence of a new hydrophilic group (selenoxide), and thus the critical micellar concentration, equilibrium surface/interfacial tension, and molecular area at the interface correspondingly increase from 0.32 mM, 46.43 mN·m(-1), 5.30 mN·m(-1), and 0.61 nm(2) to 4.98 mM, 59.15 mN·m(-1), 18.29 mN·m(-1), and 1.22 nm(2), respectively, resulting in a greater amount of energy input required to produce foam or emulsion, and a less dense adsorption layer, i.e., poor foaming and emulsification ability. Such a conversion was reversibly controlled by simply adding a trace amount (<0.06 wt % of the dispersion) of oxidant (H2O2) and reductant (Na2SO3). The products of the redox reaction did not interfere in the switchability except at the first cycle. The oxidization was generally time-consuming, whereas the reduction was very fast.