Molecular structure-tuned stability and switchability of CO2-responsive oil-in-water emulsions

Abstract

HypothesisPseudo-Gemini surfactants (PGS) possessing switchable and recyclable features have drawn increasing attention on generating high-performance CO2-responsive emulsions for wide range and versatile applications. However, there is a lack of fundamental understanding on how the molecular structure of PGS affects the stability and switchability of emulsions. We hypothesize that the length and type of the spacer in PGS play a decisive role in controlling interfacial and switching properties. ExperimentsTwo series of PGS with different spacers were prepared through electrostatic association between amines and oleic acid. The interfacial activity and CO2-responsive properties of corresponding emulsions were systematically investigated by well-designed experiments and molecular dynamics simulations. FindingsIncreasing the spacer length to allow the bent configuration leads to more tight arrangement of oleic molecules, consequently improving the interfacial activity. In addition, the introduction of amino group into the spacer dramatically promotes CO2 response of resulting PGS due to ehanced migration of the spacer from the interface to the aqueous phase after CO2 addition. These results are inspiring in designing controllable CO2-responsive emulsions for a wide range of industrial applications (e.g., enhanced oil recovery and oil-contaminated soil remediation).