Surfactant-Free Microemulsion Based on CO2-Induced Ionic Liquids

A novel surfactant-free microemulsion (SFME) based on CO2-induced ionic liquids (ILs) was prepared. Among them, dipropylamine (DPA) was directly reacted with CO2 to form the ILs that were composed of the ammonium salts and the ammonium carbamate salts, which was confirmed by 13C NMR, Fourier transform infrared, electrical conductivity, and pH. In addition, the purity of ILs was determined by 1H NMR. We used water as a polar phase, ILs as an amphi-solvent, and 1-dodecanol as a nonpolar phase to prepare SFME. The multiphase zone and the single-phase zone of the SFME were obtained from the ternary-phase diagram. Then, the microstructure of the studied SFME was determined to be the O/W type by the staining method. The demulsification process of SFME was explored by means of conductivity, pH, dynamic light scattering, and gas chromatography. Under the introduction of N2, CO2 could be removed, and the ILs could be reversibly restored to DPA, resulting in a change in polarity, which caused most of DPA to transfer into the oil phase, eventually leading to demulsification.