Smart Ionic Liquid/water Mixture System with Dual Stimuli-Response to Temperature and CO2

Stimuli-responsive materials have important applications in chemistry and chemical engineering. Here, we synthesized five different polyetheramine-fatty acids (PEFA) ionic liquids (ILs), possessing the dual stimuli-responsive ability to temperature and CO2. These PEFA ILs have reversible lower critical solution temperature (LCST) phase behavior over a wide temperature range of 37–91 °C, and reversible heterogeneous-homogeneous phase transition towards the addition and removal of CO2. Furthermore, the droplet size of the IL—water mixture system increased from 6.5 to 21.0 nm as the temperature increased from 25 to 56 °C, and then recovered to 6.5 nm when the temperature decreased to 25 °C. The addition and removal of CO2 also reversibly modulated the droplet size of the system. Results from nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectra further showed that the temperature-dependent conformation of polyether amine chain in the cation dominates the temperature response, while the reversible formation of bicarbonate and fatty acids (FA) from CO2 and anion controls the CO2-based reversible phase transition. Molecular simulations revealed a microscopic response mechanism of the IL—water system to temperature and CO2, and a synergistic effect between the dual stimuli of temperature and CO2. These findings may provide a basis for the rational design and understanding of ILs-based stimuli-responsive materials and nanoreactors.