Phase Behavior of 1-Dodecyl-3-methylimidazolium Fluorohydrogenate Salts (C₁₂MIm(FH)_nF, n = 1.0–2.3) and Their Anisotropic Ionic Conductivity as Ionic Liquid Crystal Electrolytes

Abstract

The effects of the HF composition, n, in 1-dodecyl-3-methylimidazolium fluorohydrogenate salts (C(12)MIm(FH)(n)F, n = 1.0-2.3) on their physicochemical and structural properties have been investigated using infrared spectroscopy, thermal analysis, polarized optical microscopy, X-ray diffraction, and anisotropic ionic conductivity measurements. The phase diagram of C(12)MIm(FH)(n)F (n vs transition temperature) suggests that C(12)MIm(FH)(n)F is a mixed crystal system that has a boundary around n = 1.9. For all compositions, a liquid crystalline mesophase with a smectic A interdigitated bilayer structure is observed. The temperature range of the mesophase decreases with increasing n value (from 61.8 °C for C(12)MIm(FH)(1.0)F to 37.0 °C for C(12)MIm(FH)(2.3)F). The layer spacing of the smectic structure decreases with increasing n value or increasing temperature. Two structural types with different layer spacings are observed in the crystalline phase (type I, 1.0 ≤ n ≤ 1.9, and type II, 1.9 ≤ n ≤ 2.3). Ionic conductivities parallel and perpendicular to the smectic layers (σ(||) and σ([perpendicular])) increase with increasing n value, whereas the anisotropy of the ionic conductivities (σ(||)/σ([perpendicular])) is independent of the n value, since the thickness of the insulating sheet formed by the dodecyl group remains nearly unchanged.

Nickel-Dithiolene Ion-Pair Compounds Showing Thermotropic Liquid Crystal Behaviors and Alkyl Chain Length Dependent Electrochemical Properties

“…Ionic liquid crystals show intriguing combining features of both cations and anions in a single material (5), some of which differ significantly from those of conventional liquid crystals with neutral organic compounds (46,7). For instance, an ionic liquid crystal is a promising anisotropic ion-conductive material (8) and can be used as an anisotropic medium (such as the solvent, the electrolyte, and the template) for electrochemistry due to its anisotropic structural organization and ionic character (9,10). The most common method for design of ionic liquid crystals is the attachment of one or multiple long alkyl chains to imidazolium (11,12), pyridinium (13)(14)(15), quaternary ammonium (16,17), and quaternary phosphonium cores (18)(19)(20), and a minimum length of the tail, usually dodecyl chain at least, is generally required for such a system.…”

Fluorohydrogenate Ionic Liquids, Liquid Crystals, and Plastic Crystals

“…Effects of the HF composition, n (1.0 ≤ n ≤ 2.3), on the formation of ionic liquid crystal was investigated in combination with C 12 C 1 im + [91]. The phase diagram of [C 12 C 1 Im][(FH) n F] (n vs transition temperature) suggests that [C 12 C 1 Im] [(FH) n F] is a mixed crystal system that has a boundary around n = 1.9.…”

Cholesteryl-containing ionic liquid crystals composed of alkylimidazolium cations and different anions

“…In fact, ILs can be appropriately designed to obtain liquid crystalline. For example, many imidazolium-based ILCs can be generated simply by increasing the alkyl chain length to increase the self-organization character [14,15]. The structure of ILs goes through a transition from spatially heterogeneous to ILCs due to the increased van der Waals interactions between the increased alkyl length of cationic side-chains, which is observed by Ji et al using coarse-grained molecular dynamics simulations [16].…”