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

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 CO2-responsive ionic liquids as stabilizer. Ionic liquids N-alkylimidazole bicarbonates ([C(n)im]+HCO3-, n = 6,8,10,12,14) are in-situ generated by bubbling CO2 into aqueous solution of N-alkylimidazoles (C(n)im, n = 6, 8, 10, 12, 14), and this process is reversible by removal of CO2 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 CO2 at 25 degrees C. The effect of concentration and alkyl chain length of [C(n)im]+HCO3- on Pickering emulsions is investigated systematically, and the possible mechanism of CO2-responsive Pickering emulsion is also studied by conductivity, surface tension, zeta potential, adsorption isotherm, water contact angle and C-13 NMR spectroscopy. This CO2-responsive Pickering emulsion is cheap, simple, eco-friendly, and may have potential applications in emulsification and demulsification. (C) 2018 Elsevier B.V. All rights reserved.