Rheology of Pure Ionic Liquids and Their Complex Fluids: A Review

Ionic liquids (ILs) are liquid salts at ambient or lower temperatures and consist of ions and short-lived ion pairs. They are potential alternatives to toxic, hazardous, highly flammable, and volatile solvents for preparing solutions, dispersions, gels, composites, and polymeric melts. ILs have some very interesting and unique characteristics like good chemical and thermal stability and very low vapor pressures. They have good solvation interactions with a wide range of organic, inorganic, and polymeric compounds. They can enhance colloidal stability and the elasticity range of polymers. ILs are environmental friendly, easily recyclable, and structurally similar to the conventional solvents. For optimal performance, it is necessary to fully understand the rheological properties of ILs and their different systems for academic interests such as understanding the ability of ILs as processing aids particularly in film casting, fiber spinning and spraying, comprehension of thermodynamics and dynamics of polymer chains in ILs, analyzing the hydrodynamic volume of dispersed polymer, polymer ILs interactions, characterizing the viscoelastic properties and nanophase-ILs interactions in nanocomposite systems, analyzing the plasticization efficiency, and the final properties of the composite system. The rheological analysis is also important for industrial purposes particularly for designing processing techniques and suitable operating conditions for IL based systems. The aim of this review is to give an overview of the rheological properties of pure ionic liquids and solutions, dispersions, gels, composites, and melts based on ionic liquids.