CO2-responsive O/W microemulsions prepared using a switchable superamphiphile assembled by electrostatic interactions.

A CO2-responsive superamphiphile was designed to form switchable O/W microemulsions of rapid switching responses. The linear structured superamphiphile was assembled via electrostatic interactions between anionic oleic acid and cationic Jeffamine D-230 at a mole ratio of 1:1. Addition of the CO2-responsive superamphiphile and 1-butanol as a co-surfactant led to the spontaneous formation of stable heptane-in-water microemulsions. Treating this stable microemulsion with CO2 for 20 s caused dissociation of the superamphiphile into interfacial inactive components, leading to a complete phase separation of the microemulsion into immiscible oil and water phases. Removing the CO2 from the system by N2 sparging at 60 °C for 10 min converted the phase-separated system into a transparent microemulsion as a result of the in situ formation of the superamphiphile. Compared with the results from previous studies, the O/W microemulsion formed using the current superamphiphile with the co-addition of 1-butanol featured not only a unique thermodynamical stability of nano-sized droplets, but also a desired response to CO2 to achieve a rapid and complete phase separation, and re-microemulsification as desired with N2 sparging, making this CO2-responsive O/W microemulsion a promising candidate for applications such as nanomaterial synthesis, enhanced oil recovery and soil remediation.