Tuning Binary Ionic Liquid Mixtures: Linking Alkyl Chain Length to Phase Behavior and Ionic Conductivity

Abstract

The use of mixed salts to generate new composite ionic liquids (ILs) provides a facile means of readily tuning or tailoring the desired properties of ionic media. Despite this, very little information is available about how the structure of the selected ions and composition impacts the properties of salt mixtures. To explore this, six binary IL1–IL2 mixtures based on N-alkyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide salts have been characterized. The physicochemical properties (density, viscosity, and ionic conductivity) and phase behavior of these mixtures are reported. The variation of the alkyl chains lengths on the cations plays a significant role in determining both the phase behavior and the physicochemical properties of the mixtures. Notably, the “tunability” of the properties of the IL mixtures is much easier to control than is found by simply making small structural changes to the ions in a given salt.

Electronic Effects in Organic Chemistry

“…For computations of spectral data, for example, TD-DFT [67,104] is often chosen due to its high cost-benefit ratio although such approaches cannot yet describe excited state potential energy surfaces (PESs) in general [105]. For CAM-B3LYP [110,111] and CAM-PBE0 [112] the results are in excellent agreement with the CR-EOM CCSD(T) results [113] if the asymptotic falloff is 1/r, and for approximations with an asymptotic falloff of 0.65/r only reasonable agreement is obtained. For zinc porphyrin in aqueous solution Govind et al investigated the accuracy of long range-corrected functionals in comparison to high-level CC methods.…”

“…Thus, the question arises whether this carbene content is observable at all in the liquid phase. Nevertheless, its presence could be surmised according to ab initio molecular dynamics simulations [113], where significantly increased C-H and decreased O-H bond lengths have been observed also in the bulk, alleviating the above discussed H/D exchange. Nevertheless, its presence could be surmised according to ab initio molecular dynamics simulations [113], where significantly increased C-H and decreased O-H bond lengths have been observed also in the bulk, alleviating the above discussed H/D exchange.…”

“…In addition, a 1 H NMR spectroscopic study was conducted. In fact, a meta-analysis of the literature shows that ideal mixing behavior, i.e., a linear dependence of both temperature and molar composition, is found with regards to the density of most binary ionic liquid mixtures investigated to date [84,[106][107][108][109][110][111][112][113]. 8).…”

“…It is known that, like the viscosity, the conductivity is not always linearly dependent on the composition of the binary ionic liquid mixture [113,117]. Combined conductivity measurements could show if this "lubrication" is connected to increased ion conductivity or not.…”

Physicochemical and Electrochemical Properties of Novel Ionic Liquids Containing Aprotic Heterocyclic Anions Doped with Lithium Salts

“…More recently, pyrrolidinium-based ILs have attracted interest because of their wide electrochemical windows. [26][27][28][29][30][31] However, few papers have been published related to ILs doped with lithium salts used in lithium-ion battery devices. In those papers, [32][33][34] There are several different approaches to improve the physicochemical and electrochemical properties of promising ILs, such as using additives, making IL mixtures, and designing new ILs.…”