Conductivity and association of imidazolium and pyridinium based ionic liquids in methanol

New Local Composition Model for Correlating of the Molar Conductivity of Ionic Liquid-Solvent Systems over the Whole Concentration Range

Considering that traditional electrolyte models are limited to use in the solvent-rich region, the development of new models to describe the molar conductivity (Λm) over the whole concentration range of ionic liquid (IL)-solvent systems is a meaningful study. Based on the idea of local composition and the law of independent ion migration, a new model is proposed in this study and used to successfully correlate the relationship between Λm and composition over the whole concentration range for 18 IL-solvent systems with satisfactory fitting accuracy. Meanwhile, the electrical conductivity (κ) of the systems is estimated using the calculated Λm. Moreover, the strength of anion-cation, anion-solvent, and cation-solvent interactions in the systems is explored by the obtained energy parameters, and the effect of the solvent on the interactions is investigated. The proposed model provides a new method to accurately describe the conductivity property of IL-solvent systems over the whole concentration range.

3D structure of the electric double layer of ionic liquid-alcohol mixtures at the electrochemical interface

Mixtures of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate with amphiphilic cosolvents, such as methanol and ethanol, nanoconfined between graphene walls are studied by means of molecular dynamics simulations and the results are compared with those of the pure ionic liquid and its mixtures with water confined in the same conditions. We investigate the adsorption of cosolvent molecules at the graphene walls as well as their distribution across the system. The results show that, due to a higher affinity of the polar groups to be close to the anions in combination with the electrostatic and excluded volume interactions, there exists a high tendency of the OH groups to lie close to the anode, inducing small changes in the first cation layer. The orientation of cosolvent molecules is found to be closely related to the alignment of the molecular dipole moment. We also investigate the lateral ionic distribution in the layers close to the electrodes, which shows a structural transition from liquid-like lamellar ordering to solid-like hexagonal patterns as the size of the cosolvent molecules increases leading to smaller position fluctuations of the ions. The dependence of the specific patterns on the nature of the electrodes is also studied. This study strongly suggests that the ionic patterns formed in the first ionic layers next to the charged interfaces are universal since their existence does not crucially depend on the atomic composition of the interfacial material, but only on the net charge density of the considered ionic layer, which significantly changes the ionic mobility in this region.

Influence of the anion on the properties of ionic liquid mixtures: a molecular dynamics study

Big anions enhance the non-polar network in IL mixtures, while smaller ones win the competition for the imidazolium cation.

MD simulation study of the diffusion and local structure of n-alkanes in liquid and supercritical methanol at infinite dilution

The diffusion coefficients of 14 n-alkanes (ranging from methane to n-tetradecane) in liquid and supercritical methanol at infinite dilution (at a pressure of 10.5 MPa and at temperatures of 299 K and 515 K) were deduced via molecular dynamics simulations. Values for the radial distribution function, coordination number, and number of hydrogen bonds were then calculated to explore the local structure of each fluid. The flexibility of the n-alkane (as characterized by the computed dihedral distribution, end-to-end distance, and radius of gyration) was found to be a major influence and hydrogen bonding to be a minor influence on the local structure. Hydrogen bonding reduces the flexibility of the n-alkane, whereas increasing the temperature enhances its flexibility, with temperature having a greater effect than hydrogen bonding on flexibility. Graphical abstract The flexibility of the alkane is a major influence and the hydrogen bonding is a minor influence on the first solvation shell; the coordination numbers of long-chain n-alkanes in the first solvation shell are rather low.

Interactions in the ionic liquid [EMIM][FAP]: a coupled experimental and computational analysis

IR spectroscopy and DFT calculations were combined to explore the anion conformers and access the hydrogen-bonding phenomenon in RTIL [EMIM][FAP].

Probing structural patterns of ion association and solvation in mixtures of imidazolium ionic liquids with acetonitrile by means of relative1H and13C NMR chemical shifts

Competition between ion solvation and association in mixtures of imidazolium ionic liquids and molecular solvents can be systematically addressed by the analysis of relative chemical shift variation with mixture composition.