CO₂ and Redox Dual Responsive Pickering Emulsion

Abstract

Herein, we described for the first time a CO₂ and redox dual responsive paraffin oil-in-water Pickering emulsion stabilized by the modified silica nanoparticles with Se-containing tertiary amine, SeTA, in which the tertiary amine serves as a CO₂-sensitive group, and the Se atom serves as a redox-sensitive center. The Pickering emulsion can be reversibly switched between stable and unstable states by bubbling CO₂ and N₂ in the reduced state, or with the addition of H₂O₂ and Na₂SO₃ in the absence of CO₂, because of the adsorption and desorption of SeTA on the silica surface. The former is mainly attributed to a CO₂-controllable electrostatic attraction, resulting from the transition of molecules between cationic and nonionic states; whereas, the latter is ascribed to a redox-tunable hydrogen bonding, originating from the transition of molecules between selenide and selenoxide. However, in the presence of CO₂, redox can only induce a change in the droplet size, not demulsification. These interesting and unique multiresponsive behaviors endow the Pickering emulsion with a capacity for intelligent control of emulsification and demulsification, as well as the droplet size, which may be an asset for a myriad of technological applications in biomedicine, microfluidics, drug delivery, and cosmetics.