Physicochemical properties and thermal-responsive phase separation of poly(ethylene glycol)-based ionic liquids

How to design thermal-responsive functional ionic liquids that can respond in a reversible manner still remains a challenge for the construction of ionic liquid-based smart systems, and they easily find appli-cations in various scientific fields, including phase transfer catalysis, smart soft materials, controlled drug delivery and green separation. In this work, a series of PEGylated ionic liquids were prepared, and their structures were confirmed by NMR and FTIR spectra. The thermal properties of these ionic liquids were characterized by DSC and TGA. In addition, their physicochemical properties were measured in detail, including density and viscosity. Different models were used to fit the density and viscosity data. The crit-ical micelle concentrations of the Aerosol OT-based PEGylated ionic liquids were also determined by the surface tension method, and they exhibited good surface activity. Furthermore, these PEGylated ionic liq-uids exhibit typical low critical solution temperature phase behavior. To illuminate the underlying mech-anism of thermal-induced phase separation, temperature-dependent FTIR spectra were used to analyze the interaction between ionic liquids and water molecules. Finally, the thermally regulated PEGylated IL phase separation system was proposed as an efficient strategy to separate heavy metal ions and rare earth metal ions from water media. The results presented here offer key information to design new ther-moresponsive ionic liquids and their applications.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

The design of thermal-responsive functional ionic liquids that can respond reversibly remains a challenge for the construction of smart systems. This study prepared a series of PEGylated ionic liquids and characterized their structures and thermal properties. The physicochemical properties, including density and viscosity, were measured and modeled. The results showed that these PEGylated ionic liquids exhibited good surface activity and low critical solution temperature phase behavior. The interaction between the ionic liquids and water molecules was analyzed to understand the mechanism of thermal-induced phase separation. This study provides valuable information for designing new thermoresponsive ionic liquids and their applications.