pH and redox-responsive oil-in-dispersion emulsions based on disulfide bond surfactant and carbon quantum dots

Stimulus responsive studies of Pickering emulsions are well documented, whereas those of oil-in-dispersion (OID) emulsions are rare and challenging. Here, we propose an alternative strategy by taking advantage of anionic disulfide bond surfactant sodium 11,11'-disulfanediyldiundecanoate (DS-COONa) and anionic carbon quantum dots (CA-CDs) to report a novel emulsion system responsive to pH and redox reagents. In contrast to Pickering emulsions, the CA-CDs do not adsorb at the oil-water interface but remain dispersed in the water phase between disulfide bond surfactant-coated oil droplets due to their high hydrophilicity. Fast demulsification of OID emulsions can be achieved by addition of HCl (8 mM) and reducing agent DL-dithiothreitol (4 mM). After subsequently adding NaOH (8 mM) and hydrogen peroxide (4 mM), a stable emulsion can be achieved by homogenization. The disulfide bond surfactant is sensitive to redox reagents and pH, imparting the formulated OID emulsion with multi-stimuli-responsiveness showing promising applications in oxidation/reduction biphasic catalysis, oil recovery and controllable drug delivery.