pH‐Controllable Redox Responsive Amphiphilic Viologens for Switchable Emulsions

A pH and redox dual responsive amphiphilic viologen is synthesized, which can be reversibly transformed among the zwitterionic (SVa), monovalent anionic (SV+), and divalent anionic (SVH2+) forms upon pH variation, exhibiting pH‐controllable redox responsive properties. Switchable Pickering emulsions with different droplet size and viscosity are prepared by the mixture of hydrophilic silica nanoparticles and the viologens (SV+ or SVH2+) at acidic conditions, while such combination yielded an oil‐in‐dispersion emulsion at neutral pH value. Not only can rapid reversible demulsification/stabilization of the Pickering emulsions be achieved by redox reactions, but the rate of redox‐demulsification can also be controlled by pH trigger. The dual‐responsive amphiphilic viologens have potential applications in developing intelligent colloid materials and molecular logic systems. Switchable emulsions are stabilized by silica nanoparticles and the pH and redox dual‐responsive viologens, in which not only can reversible demulsification/stabilization of the Pickering emulsions be achieved by redox reactions, but the droplet size and rate of redox‐demulsification can also be controlled by pH trigger.