Synthesis and Properties of a Series of CO₂ Switchable Surfactants with Imidazoline Group

Abstract Switchable surfactants are environment‐friendly compounds, which can be separated from the system or lose surface activity after completing their function during one stage of a process. In order to study switchable properties of a kind of CO 2 switchable surfactant with an imidazoline group, four 2‐alkyl‐1‐hydroxyethylimidazolines were synthesized by condensation of N ‐(2‐hydroxyethyl)ethanediamine with dodecanoic, tetradecanoic, hexadecanoic, and octadecanoic acids. Then, the series of long‐chain alkyl imidazoline compounds were reacted with dry ice to produce imidazolinium bicarbonates cationic surfactants. The critical micelle concentration (CMC) and surface tension at CMC (γ cmc ) measured by the Wilhelmy plate technique show that these surfactants have excellent surface activity. The changes of conductivity before and after bubbling CO 2 show the conversion between imidazolines and imidazolinium bicarbonates cationic surfactants. Conductivity cycles indicated that these surfactants could be switched by CO 2 reversibly and repeating this three times. However, their switchable function on the emulsification‐demulsification of water‐alkane was dissatisfactory due to the emulsibility of amide which was hydrolyzed from 2‐alkyl‐1‐hydroxyethylimidazoline. Therefore, the application of these switchable surfactants needed to be studied further.