Abstract
Ionic liquid crystals occupy an intriguing middle ground between room-temperature ionic liquids and mesostructured liquid crystals. Here, we examine a non-polarizable, fully atomistic model of the 1-alkyl-3-methylimidazolium nitrate family using molecular dynamics in the constant pressure–constant temperature ensemble. These materials exhibit a distinct “smectic” liquid phase, characterized by layers formed by the molecules, which separate the ionic and aliphatic moieties. In particular, we discuss the implications this layering may have for electrolyte applications.
Highlights
The intersection of the fields of ionic liquids and liquid crystals is a relatively new sector of materials science, but has garnered much research in recent years [1,2,3,4], as ionic liquid crystals begin to show promise as useful molecules in tunable conductive materials [5,6] or as greener solvents [7,8], for example
While most ionic liquids lack the extended alkyl chain similar to that found in sodium dodecyl sulfate (SDS), thereby exhibiting only an isotropic liquid phase, addition of an extended tail can promote ordering via micro-phase separation, resulting in mesostructured ionic liquids, ionic liquid crystals
We focus here on providing a detailed analysis of the phase behavior and dynamics using an all-atom model of 1-alkyl-3-methylimidazolium nitrate, compactly notated as [Cn MIm][NO3 ]
Summary
The intersection of the fields of ionic liquids and liquid crystals is a relatively new sector of materials science, but has garnered much research in recent years [1,2,3,4], as ionic liquid crystals begin to show promise as useful molecules in tunable conductive materials [5,6] or as greener solvents [7,8], for example. Liquid crystalline phases are of interest due to their innate mesostructure, arising from energetically- or entropically-driven alignment of molecules, or from phase separation arrested by molecular structure. This results in many different ordered phases [5,9,10,11], including multiple nematic, smectic, and columnar phases [10], among others. While most ionic liquids lack the extended alkyl chain similar to that found in SDS, thereby exhibiting only an isotropic liquid phase, addition of an extended tail can promote ordering via micro-phase separation, resulting in mesostructured ionic liquids, ionic liquid crystals
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