Ionic Liquid MixturesVariations in Physical Properties and Their Origins in Molecular Structure

In order to explore the various possible property trends in ionic liquid mixtures, five different ionic liquids were mixed with <i>N</i>-methyl-<i>N</i>-propylpyrrolidinium bis­(trifluoromethylsulfonyl)­amide ([C₃mpyr]­[NTf₂]), and the viscosities, excess molar volumes, ionic conductivities, and phase diagrams of the mixtures were determined over a range of temperatures. In a number of the mixtures the crystallization of both components was completely suppressed and no melting point was observable. Such mixtures of similar ionic liquids thus have potential for use in low-temperature applications by extending the liquid range to <i>T</i>_g. The molar conductivities and viscosities are described as approximating predictable or “simple” mixing behaviors, while excess molar volumes were found to show a variety of mixing and nonideal mixing effects. Mixture equations for viscosity and conductivity are discussed and analyzed. An immiscibility window was observed in the trihexyl­(tetradecyl)­phosphonium bis­(trifluoromethylsulfonyl)­amide ([P_6,6,6,14]­[NTf₂]) in the [C₃mpyr]­[NTf₂] system in the [C₃mpyr]­[NTf₂]-rich region. Unusual physical properties are exhibited by miscible compositions near the demixing line. These compositions are described as [P_6,6,6,14]­[NTf₂]-like, even up to 0.5 mol fraction of [C₃mpyr]­[NTf₂]

New Insights into Decoupled Cation and Anion Transport and Dynamic Heterogeneity in a Diethyl(methyl)(isobutyl)phosphonium Hexafluorophosphate Organic Ionic Plastic Crystal

Organic ionic plastic crystals (OIPCs) are an emerging family of materials with demonstrated applications in electrochemical devices such as lithium/sodium ion batteries, dye-sensitized solar cells, and hydrogen fuel cells. Herein, we present direct evidence of anion diffusion through a relatively static background of a cation lattice in an ionic plastic crystal compound, [P122i4]­[PF6], in an elevated temperature solid phase. We found all anions are diffusive, whereas only a small population of cations is diffusive. Two anion populations were identified with diffusion coefficients differing by 2 orders of magnitude. The slow-diffusing anion is attributed to the plastic crystal region where the cation forms a relative static background, allowing anions to diffuse possibly through a defect-assisted hopping mechanism

PHYS 99-Transport properties of ionic liquids: Origins in liquid structure

PHYS 99-Transport properties of ionic liquids: Origins in liquid structur

Effect of Fumed Silica on Ion Conduction in Proton-Conducting Nanocomposites

In this work, a series of nanocomposites using polymerized ionic liquid (PolyIL), protic ionic liquids (PILs), and nanosilica were developed. The influence of nanosilica on the physical properties of nanocomposites was studied. The binary PIL/silica composites showed decreased ionic conductivity with the addition of silica. However, in the presence of the polymer, the binary PolyIL/silica and ternary PolyIL/PIL/silica showed increased ionic conductivity with a small amount of silica, resulting from the interactions between silica and the anionic groups of PolyIL. This work demonstrated that while adding silica is unfavorable for ionic liquids, it has the potential to promote ionic conductivity in polymer composites

Dynamic Heterogeneity and Ionic Conduction in an Organic Ionic Plastic Crystal and the Role of Vacancies

Dynamic heterogeneity was investigated for the first time in a conductive organic ionic plastic crystal by molecular dynamics simulation. A minority fraction of ions that possess above-average dynamics were identified in the plastic crystal phase. The signature of this unusual motional behavior is found in the significant increase in the non-Gaussian parameter α­(<i>t</i>). A study by incorporation of vacancies into the crystal structure shows explicit evidence of coexistence of mobile species with an otherwise rigid matrix, which particularly supports the previous explanation on heterogeneous motional narrowing in nuclear magnetic resonance. It is also found that the origin of dynamic heterogeneity here is inseparable from the inherent structural characteristics of organic ions. This work reveals the profound effect brought by heterogeneous dynamics on the conduction mechanism of this material, as well as the important role of defects on ions dynamics

Dynamic Heterogeneity and Ionic Conduction in an Organic Ionic Plastic Crystal and the Role of Vacancies

Dynamic heterogeneity was investigated for the first time in a conductive organic ionic plastic crystal by molecular dynamics simulation. A minority fraction of ions that possess above-average dynamics were identified in the plastic crystal phase. The signature of this unusual motional behavior is found in the significant increase in the non-Gaussian parameter α­(<i>t</i>). A study by incorporation of vacancies into the crystal structure shows explicit evidence of coexistence of mobile species with an otherwise rigid matrix, which particularly supports the previous explanation on heterogeneous motional narrowing in nuclear magnetic resonance. It is also found that the origin of dynamic heterogeneity here is inseparable from the inherent structural characteristics of organic ions. This work reveals the profound effect brought by heterogeneous dynamics on the conduction mechanism of this material, as well as the important role of defects on ions dynamics

Ion structure and dynamics in highly concentrated ionic liquid-alkali metal salt electrolytes

Ion structure and dynamics in highly concentrated ionic liquid-alkali metal salt electrolyte