Smart Emulsions Stabilized by a Multi‐headgroup Surfactant Tolerant to High Concentrations of Acids and Salts

Abstract

Retaining emulsions stable at high acidity and salinity is still a great challenge. Here, we report a novel multi‐headgroup surfactant (C₃H₇−NH⁺(C₁₀COOH)₂, di‐UAPAc) which can be reversibly transformed among cationic, anionic and zwitterionic forms upon pH variation. Stable oil‐in‐dispersion (OID) emulsions in strong acidity (pH=2) can be co‐stabilized by low concentrations of di‐UAPAc and silica nanoparticles. High salinity at pH=2 improves the adsorption of di‐UAPAc on silica particles through hydrogen bonding, resulting in the transformation of OID emulsions into Pickering emulsions. Moreover, emulsification/demulsification and interconversion between OID and Pickering emulsions together with control of the viscosity and droplet size can be triggered by pH. The present work provides a new protocol for designing surfactants for various applications in harsh aqueous media, such as strong acidity and high salinity, involved in oil recovery and sewerage treatments.