Ionic Liquid-Based Microemulsions with Reversible Microstructures Regulated by CO2.

Abstract

CO2-responsive microemulsions based on ionic liquid 1,1,3,3-tetramethylguanidine-oleic acid (TMG-OA) have been designed to provide an approach for reducing the volatilization of amine in amine-containing microemulsions effectively and exhibit reversible transitions of microstructures. The ionic liquid TMG-OA was prepared by the direct neutralization of oleic acid (HOA) and 1,1,3,3-tetramethylguanidine (TMG, one of volatile and toxic amines). From the investigations of nuclear magnetic resonance hydrogen spectrum, pH, thermogravimetry, and automatic interface tension meter, the excellent properties of switchability, stability, and surface activity of TMG-OA were demonstrated, and then the ionic liquid-based microemulsions with CO2 response were prepared with TMG-OA (surfactant), HOA (oil phase), isopropyl alcohol (IPA, cosurfactant), and water. Interestingly, for microemulsions with a higher IPA content (47.42, 44.48 wt %), sizes of microemulsions are increased upon introducing CO2 and decreased upon addition of N2/65 °C. In addition, for microemulsions with a lower IPA content (26.22 wt %), the new microemulsions with different sizes are regenerated after the phase separation of emulsions generated by introducing CO2, and incomplete recovery of microemulsions can be observed upon addition of N2/65 °C. The reversible microstructures are induced by the swelling behavior and the reduced single phase area, which are caused by the reversible conversion between TMG-OA and HOA components.