CO₂-switchable emulsions with controllable size and viscosity

CO₂-responsive emulsions have attracted considerable attention in recent years because of their biocompatibility and easy removal of CO₂. However, most CO₂-responsive emulsions are only used in stabilization and demulsification processes. In this paper, we report CO₂-switchable oil-in-dispersion (OID) emulsions co-stabilized with silica nanoparticles and anionic NCOONa, in which the required concentrations of NCOONa and silica particles were as low as 0.01 mM and 0.0001 wt%, respectively. Besides reversible emulsification/demulsification, the aqueous phase containing the emulsifiers was recycled and reused with the CO₂/N₂ trigger. More importantly, the properties of the emulsions, such as droplet sizes (40-1020 μm) and viscosities (6-2190 Pa s), were intelligently controlled by the CO₂/N₂ trigger, and meanwhile reversible conversion between OID emulsions and Pickering emulsions was achieved. The present method offers a green and sustainable way to regulate the emulsion states, which enables smart control of emulsions and widens their potential applications.