Xiao-Xue Ma

Ionic Parachor and Its Application in Acetic Acid Ionic Liquid Homologue 1-Alkyl-3-methylimidazolium Acetate {[Cnmim][OAc](n = 2,3,4,5,6)}

Five acetic acid ionic liquids (AcAILs) [C(n)mim][OAc](n = 2,3,4,5,6) (1-alkyl-3-methylimidazolium acetate) were prepared by the neutralization method and characterized by (1)HNMR spectroscopy and differential scanning calorimetry (DSC). The values of their density and surface tension were measured at 298.15 ± 0.05 K. Since the AcAILs can strongly form hydrogen bonds with water, the small amounts of water are difficult to remove from the AcAILs by common methods. In order to eliminate the effect of the trace water, the standard addition method (SAM) was applied to these measurements. As a new concept, ionic parachor was put forward. [OAc](-) was seen as a reference ion, and its individual value of ionic parachor was determined in terms of two extrathermodynamic assumptions. Then, the values of ionic parachors of a number of anions, [NTf(2)](-), [Ala](-), [AlCl(4)](-), and [GaCl(4)](-), were obtained by using the value of the ionic parachor of the reference ion; the parachor and surface tension of the investigated ionic liquids in literature were estimated. In comparison, the estimated values correlate quite well with their matching experimental values.

Study on thermodynamic properties and estimation of polarity of ionic liquids {[Cnmmim][NTf2] (n = 2, 4)}

Two bis(trifluoromethyl sulfonyl)imide ionic liquids [Cnmmim][NTf2] (n = 2, 4) {1-alkyl-2,3-dimethyimidazolium-N,N-bis(trifluoromethyl sulfonyl)imide} were prepared and characterized by 1H NMR spectroscopy and differential scanning calorimetry (DSC). The values of their density, surface tension and refractive index were measured in the temperature range of (298.15 to 338.15 ± 0.01) K and the average contributions to the density, surface tension, and refractive index per methyl group in the alkyl chain and the addition of a methylene group in the imidazolium ring for the ILs were discussed. The dependence of volumetric properties, surface properties and molar refraction on temperature was discussed. Based on Kabos method and Verevkins experimental values, the molar enthalpies of vaporization, ΔHv, for [Cnmmim][NTf2] (n = 2, 4) were estimated. As a new idea, it was put forward that ΔHv can be assumed to consist of two parts: a part corresponds with the induced energy, ΔHvn, and another part corresponds with orientation energy from the permanent dipole moment of the ion pair in ILs, ΔHvμ. The values of ΔHvn were calculated in terms of the Lawson–Ingham equation so that the values of ΔHvμ could be estimated. Using the values of ΔHv, ΔHvn and ΔHvμ, cohesive energy density, δ2 (δ is Hildebrand solubility parameter), the contribution of induced energy, δn2, and the contribution of orientation energy, δμ2, were obtained. If a liquid only has δn then it is a non-polar liquid and if a liquid not only has δn, but also has δμ then it is a polar liquid. Since the ion pairs in ILs have a permanent dipole moment, the ionic liquid has a certain polarity. Therefore, using δμ as the polarity scaling of ILs is very convenient because the values of δμ are very easy to calculate from the enthalpy of vaporization and refractive index data.

Theoretical and experimental determination of the number of water molecules breaking the structure of a glycine-based ionic liquid

The effects of water on the structures of the amino acid ionic liquid (IL) 1-ethyl-3-methylimidazolium glycine ([emim][Gly]) are explored by a classical simulation method. The density and surface tension of the [emim][Gly]–H2O mixture are experimentally studied by a standard addition method. Simulation and experiment show that the density of the [emim][Gly]–H2O mixture reaches the maximum at 2–4 mass% water. Different analysis tools, including radial distribution, an interstice model, and molecular intrinsic characteristic contours are used to describe the structural modifications of the [emim][Gly] and ionic aggregates as a function of the solution concentration. At xw < 0.33 (mole fraction), the isolated water and dimer are located at the interstices formed between the ions, do not modify the network of ILs, and slightly strengthen the interactions between the cation and anion. Consequently, a turnover in the evolution of the IL structures and properties ensues. At 0.33 < xw < 0.50, the formation of relatively large water clusters, such as trimers and tetramers, leads to interstice distention, breakage of the cation–anion network, and gradual loosening of the interactions. With a further increased water concentration, a bicontinuous phase is generated and ionic clusters disperse in a continuous water phase. The size and morphology of the water aggregates are evaluated and analyzed by several statistical functions.