Redox-Responsive Oil-In-Dispersion Emulsions Stabilized by Similarly Charged Ferrocene Surfactants and Alumina Nanoparticles.

A redox-responsive oil-in-dispersion emulsion was developed by using a cationic ferrocene surfactant (FcCOCN) and AlO nanoparticles, in which the required concentrations of FcCOCN and AlO nanoparticles are as low as 0.001 mM (≈0.005 cmc) and 0.006 wt %, respectively. Rapid demulsification can be successfully achieved through a redox trigger, resulting from the transition of FcCOCN from a normal cationic surfactant form into a strongly hydrophilic Bola type form (FcCOCN). Moreover, FcCOCN together with the particles almost resides in the aqueous phase and can be recovered after the reduction reaction. Not only the amount of surfactant and nanoparticles are significantly reduced but also the emulsifier (surfactant and alumina) can be recycled and reused from the aqueous phase, which is a sustainable and economical strategy for various applications.