CO2-responsive Pickering emulsions stabilized by in-situ generated ionic liquids and silica nanoparticles.

Abstract Stimuli-responsive Pickering emulsions have attracted increasing interest because of the advantages of applications in numerous industrial processes. In this work, Pickering emulsions have been obtained by using negatively charged silica nanoparticles in association with very small amount of CO 2 -responsive ionic liquids as stabilizer. Ionic liquids N -alkylimidazole bicarbonates ([C n im]+HCO 3 −, n = 6, 8, 10, 12, 14) are in-situ generated by bubbling CO 2 into aqueous solution of N -alkylimidazoles (C n im, n = 6, 8, 10, 12, 14), and this process is reversible by removal of CO 2 with bubbling of N 2. Thus the Pickering emulsions may be switched multiple times between emulsification and demulsification states by alternatively bubbling and removal of CO 2 at 25 °C. The effect of concentration and alkyl chain length of [C n im]+HCO 3 − on Pickering emulsions is investigated systematically, and the possible mechanism of CO 2 -responsive Pickering emulsion is also studied by conductivity, surface tension, zeta potential, adsorption isotherm, water contact angle and 13C NMR spectroscopy. This CO 2 -responsive Pickering emulsion is cheap, simple, eco-friendly, and may have potential applications in emulsification and demulsification. Graphical abstract For the first time, in situ generated ionic liquids N -alkylimidazole bicarbonates were used as a emulsifier to prepare CO 2 -responsive Pickering emulsions, which may be switched between emulsification and demulsification by alternatively bubbling and removal of CO 2 at room temperature. Unlabelled Image Highlights • Emulsion was stabilized by silica and very small amount of ionic liquids. • Formation and breaking of emulsion was reversible by bubbling and removal of CO 2. • Minimum concentration of Ionic liquids required is 83 times smaller than its CMC. • The possible mechanism for the CO 2 -responsive Pickering emulsion is studied. [ABSTRACT FROM AUTHOR]