Pickering emulsions stabilized by surfactant particles with smart responses to pH and metal-ligands

A new Pickering emulsion system responded to external factors, pH and metal ligands, was provided using surfactant particles as stabilizers. Rhamnolipids, a kind of biosurfactant, widely acted as emulsifier for constructing emulsions. Herein, the deprotonated form of rhamnolipids was used to combine with certain metal ions, e.g., Cu2+, to generate the Rha-Cu particles with partial wettability as stabilizer to prepare O/W Pickering emulsions. The Pickering emulsions exhibited long-term stability in a wide temperature range, 3–80 °C, and could resist high ionic strength. Owing to the smart response of Rha-Cu particles to some environmental factors, the reversible transformation between the emulsions stabilized by rhamnolipids and Rha-Cu particles were conveniently manipulated by changing pH or introducing metal ligands. This property may express many advantages in the application fields which need the convenient transitions between emulsified and demulsified forms.