CO2-switchable multi-headgroup surfactant for oil-in-dispersion emulsions with a reusable aqueous phase

Abstract

Surfactants are widely utilized in various industries, but their amphiphilic nature poses an obstacle to the complete recycling of them from water or oil phases. It is a challenge to design a surfactant that has both good emulsification performance and aqueous-phase recyclable properties. In this paper, we report a novel aqueous-phase recyclable surfactant with multi-headgroups (C3H7-NH (C10COONa)2, di-UAPAba). Di-UAPAba can stabilize oil-in-water emulsions alone at pH ≥ 9 (≥0.3 mM), exhibiting excellent emulsification ability. After adding a trace amount of silica nanoparticles, CO2 switchable oil-in-dispersion emulsions were formed by di-UAPAba at extremely low concentrations (0.01 mM). Reversible demulsification/emulsification was achieved upon CO2/N2 trigger. Moreover, di-UAPAba can be converted into zwitterionic di-UAPAza by bubbling CO2, which entirely enters the aqueous phase with no surfactant residual in the oil phase. Consequently, the emulsions were reformed after di-UAPAba was completely recovered from the aqueous phase. The interfacial behavior of the surfactant and its aqueous recyclable mechanism was analyzed by molecular dynamics simulation. This study introduces a new type of aqueous-recyclable surfactants that can be beneficial in temporary emulsions for oil-soluble products where demulsification is necessary, such as in crude oil production, oil transportation, and multi-phase catalysis.