CO2-Responsive Pickering Emulsions Stabilized by a Bio-based Rigid Surfactant with Nanosilica

A novel CO₂-responsive surfactant, maleopimaric acid glycidyl methacrylate ester 3-(dimethylamino)propylamine imide (MPAGN), based on sustainable resource of rosin was synthesized and used to prepare a kind of CO₂-responsive Pickering emulsions with nanosilica. MPAGN can be reversibly responsive to CO₂ and N₂ between active cationic (MPAGNH⁺) and inactive nonionic (MPAGN), leading to adsorb on or desorb from the surface of nanosilica, then stabilize or break emulsion. CO₂-responsive behavior of MPAGN was verified by cycle change of pH and conductivity with bubbling CO₂ and N₂ alternately. The type of adsorption of MPAGNH⁺ at the particle-water interface was explained according to the adsorption isotherms. The mechanisms of stabilization, destabilization, and restabilization of Pickering emulsion were analyzed according to zeta potentials and droplet size. This Pickering emulsion can be reversible between stable and unstable by bubbling CO₂ and N₂ alternately. Moreover, this emulsifier can be recycled when new oil was added after removing the initial oil. Therefore, it not only has economic benefits but also has an environmentally friendly property.