Charge Density Overcomes Steric Hindrance of Ferrocene Surfactant in Switchable Oil‐in‐Dispersion Emulsions

Abstract A ferrocene surfactant can be switched between single and double head form (FcN + C 12 /Fc + N + C 12 ) triggered by redox reaction. FcN + C 12 can neither stabilize an O/W emulsion alone nor an oil‐in‐dispersion emulsion in combination with alumina nanoparticles due to the steric hindrance of the ferrocene group. However, such steric hindrance can be overcome by increasing the charge density in Fc + N + C 12 , so that oil‐in‐dispersion emulsions can be co‐stabilized by Fc + N + C 12 and alumina nanoparticles at very low concentrations (1×10 −7 M (≈50 ppb) and 0.001 wt %, respectively). Not only can reversible formation/destabilization of oil‐in‐dispersion emulsions be achieved by redox reaction, but also reversible transformation between oil‐in‐dispersion emulsions and Pickering emulsions can be obtained through reversing the charge of alumina particles by adjusting the pH. The results provide a new protocol for the design of surfactants for stabilization of smart oil‐in‐dispersion emulsions.