Phase variety in ionic liquids: Hydrogen bonding and molecular conformations

Ionic liquids (ILs) have a phase variety due to degrees of freedomof hydrogen bonding and molecular conformations. Liquid, amorphous, and crystal phases of the ILs and their mixtures are connected with the geometrical factors. In the liquid state, the IL nano-structures are spontaneously formed despite their simple molecular structures. The nano-heterogeneity of pure ILs is related to the glass transition at low temperature (LT) and high pressure (HP). Multiple glass transitions are induced by the additive water or under HP. Protic and aprotic ILs indicate crystal polymorphs and/or multiple crystallization pathways at LT or HP. The phase varieties, including metastable phases, are related to molecular conformations. In the IL-water system, the hydrogen bonding of water is modified, and nano-confined water appears in the water-rich region. The static and dynamic behaviors of the nano-confined water in ILs are clarified. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Ionic liquids exhibit phase variety due to the degrees of freedom of hydrogen bonding and molecular conformations, with connections to liquid, amorphous, and crystal phases. The nano-structures of ILs are spontaneously formed in the liquid state, and the phase varieties, including metastable phases, are related to molecular conformations. In the IL-water system, the hydrogen bonding of water is modified, leading to the appearance of nano-confined water with clarified static and dynamic behaviors.