Gelation of ionic liquids by small-molecule gelators and their applications

Ionic liquids (ILs) are atypical organic salts with many attractive features such as low melting point, low vapor pressure, high thermal stability, and non-flammability. These desirable traits have enabled them to be used in applications like catalysis, green organic reactions, electrochemical devices, extraction & separation, pharmaceutics, etc. Furthermore, the properties of the ionic liquids can be improved and the range of functional applications expanded if they are used in the form of ionic liquid-gel phase-materials or ionic liquid-gels (IL-gels). Typically, immobilization of ILs is carried out by mixing with different nanoparticles, polymers or small-molecules under appropriate conditions. Gel electrolytes, lubricants, solar cells, fuel cells, sensors, electrochemical devices, drug release, etc., are some of the applications where IL-gels have contributed significantly. Using small molecules to prepare IL-gels is easy, convenient, and similar to preparing organogels or hydrogels from organic solvents or water. The number of IL-gelators is pretty limited when compared to the large number of reported organogelators and hydrogelators. A detailed review focused on IL-gelators and their functional applications have so far not been undertaken. Here, we will provide an up-to-date summary and highlight the successes, challenges, and future opportunities of this emerging research area.