Thermoresponsive Ionic Liquid/Water Mixtures: From Nanostructuring to Phase Separation.

Area of Science:

• Physical Chemistry
• Materials Science

Background:

• Thermoresponsive systems, particularly water solutions of organic salts, are crucial in various scientific fields.
• Ionic liquids (ILs) are a key class of organic salts with low melting points, exhibiting unique thermoresponsive properties.

Purpose of the Study:

• To review the thermodynamics, structures, and applications of thermoresponsive systems, with a focus on ionic liquids.
• To elucidate the mechanisms of temperature-driven phase transitions (demixing) in these systems.
• To explore current and future applications of these materials.

Main Methods:

• Review of experimental data and computer simulations.
• Analysis of thermodynamic properties (enthalpy and entropy of mixing).
• Investigation of nanoscale inhomogeneity and its relation to phase separation.

Main Results:

• Thermoresponsive systems undergo temperature-driven transitions between homogeneous and biphasic states (IL-rich and solvent-rich phases).
• Phase separation can occur with decreasing temperature (UCST) or increasing temperature (LCST), governed by enthalpy and entropy contributions.
• Nanoscale inhomogeneity (nanostructuring) is linked to these phase separation phenomena.

Conclusions:

• Ionic liquid-based thermoresponsive systems offer tunable phase behavior based on thermodynamic principles.
• These systems have established applications in extraction, separation, and catalysis.
• Future applications are promising in desalination, thermal energy storage, and atmospheric water harvesting.