CO₂/Light Dual-Responsive Oil-in-Water Emulsion Stabilized by Hydrophilic Chitosan Polyelectrolyte and Like-Charged...

Hydrophilic polyelectrolytes cannot stabilize emulsions independently; they typically require either hydrophobic modification or synergistic stabilization of emulsions in combination with emulsifiers bearing opposite charges. Herein, a novel oil-in-water emulsion was stabilized by cationic surfactants in combination with similarly charged chitosan polyelectrolytes (CPs) at concentrations as low as 10^-5 M and 1 × 10^-3 wt %, respectively. Surfactant molecules adsorbed at the oil-water interface not only reduced the interfacial tension but also imparted charges to the droplets. The hydrophilic CPs distributed in the aqueous phase between droplets and formed disorderly extended stacks, which significantly enhanced the electrostatic repulsions between oil droplets. Furthermore, the CPs increased the aqueous phase viscosity, thereby reducing water drainage and hindering droplet flocculation and coalescence. This stabilization mechanism was universal, as it applied to different polyelectrolytes and like-charged surfactants. Moreover, CO₂-responsive CPs and photoresponsive azobenzene surfactant endowed the emulsion with dual CO₂/light responsiveness, allowing it to switch reversibly between stable and unstable states upon CO₂ exposure or light irradiation, thus exhibiting potential applications in organic synthesis and functional materials.