Reversible temperature regulation of CO2-responsive ionic liquid microemulsion

Abstract Due to the limitation of anhydrous conditions, the research on anhydrous microemulsion has been developed rapidly. In this paper, CO2/N2-responsive ILs was used as a polar phase instead of water to prepare anhydrous surfactant-free microemulsion (SFME) with ethanol and n-hexane. This research group has previously studied the preparation process and CO2/N2 responsiveness of the ILs. Then the boundary between multi-phase zone and single-phase zone of surfactant free microemulsion system was determined by drop addition. And the single-phase region was divided into three regions: O/W, B.C and W/O by conductivity and uv–vis. N2 was introduced into SFME system at 30℃. Interestingly, we found that there was no separation of oil and water. Through the study on DLS, pH and the mutual solubility of Dipropylamine, ethanol and n-hexane, it was found that demulsification occurred in the system, and the absence of oil-water separation was due to the formation of uniform and transparent mixed solution in the system. Finally, It is found that changing the temperature can make the boundary of the multi-phase zone and the single-phase zone in the three-phase diagram of SFME system move. In addition, temperature also had an effect on the particle size of SFME system.