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The density and viscosity of synthesized 1-alkyl-3-methylimidazolium iodide ([C n mim]I, n ) 4, 6, 8) were measured in the wide range of temperature of (298 to 393) K. Using a vacuum line, measurements of the viscosity were made under a water-vapor free atmosphere. The viscosity decreases sharply with temperature and increases as the alkyl chain length increases. The molecular dynamics simulation was performed for the densities of these ionic liquids to remedy the lack of literature experimental data. The results are quite in agreement with the experiments, with a maximum deviation of 3.00 % due to [C 8 mim]I at 358 K. The viscosities fit best in the modified Arrhenius, Vogel-Fulcher-Tammann (VFT), and Litovitz equations. The viscosities also fit in the simple linear equation we proposed recently with accuracies comparable with Litovitz and VFT.

Bulk and surface properties of the ionic liquids 1-alkyl-3-methyl-imidazolium iodides ([C(n)mim]I) were simulated by classical molecular dynamics using all atom non-polarizable force field (n = 4, butyl; 6, hexyl; 8, octyl). The structure of ionic liquids were initially optimized by density functional theory and atomic charges obtained by CHELPG method. Reduction of partial atomic charges (by 20% for simulation of density and surface tension, and by 10% for viscosity) found to improve the accuracy, while a non-polarizable force field was applied. Additionally, the simulation ensembles approach the equilibrium faster when the charge reduction is applied. By these refined force field parameters, simulated surface tensions in the range of 323-393 k are quite in agreement with the experiments. Simulation of temperature dependent surface tension of [C(4)mim]I well beyond room temperature (up to 700 K) permits prediction of the critical temperature in agreement with that predicted from experimental surface tension data. Simulated densities in the range of 298-450 K for the three ionic liquids are within 0.8% of the experimental data. Structural properties for [C(4)mim]I were found to be in agreement with the results of Car-Parrinello molecular dynamics simulation we performed, which indicates a rather well-structured cation-anion interaction and occurs essentially through the imidazolium ring cation. Diffusion coefficient changes with alkyl chain length in the order of [C(8)mim]I > [C(6)mim]I > [C(4)mim]I for the cation and the anion. Formation of a dense domain in subsurface region is quite evident, and progressively becomes denser as the alkyl chain length increases. Bivariate orientational analysis was used to determine the average orientation of molecule in ionic liquids surface, subsurface, and bulk regions. Dynamic bisector-wise and side-wise movement of the imodazolium ring cation in the surface region can be deduced from the bivariate maps. Atom-atom density profile and bivariate analysis indicate that the imidazolium cation takes a spoon like configuration in the surface region and the tilt of alkyl group is a function length of alkyl chain exposing as linear as possible to the vapor phase.

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Investigation of the behaviour of deep eutectic solvents (DESs) as novel green solvents in the presence of other solvents is of great interest. In this study the behaviour of a common natural DES, namely choline chloride-glycerol deep eutectic solvent (GDES), was studied in the presence of water. A detailed study of the association of the two solvents was performed by integration of two vibrational spectroscopic methods (FTIR and Raman spectroscopy) followed by multivariate analysis. Moreover, a binary mixture of glycerol (Gly) as one of the liquid constituents of GDES and water was explored under the same conditions. A quintuplet and ternary systems were resolved for GDES-water and Gly-water probes, respectively, using multivariate analysis of global data (multi-technique and multi-experiment data arrangements). The results confirmed that in the presence of water the GDES showed different behaviour from its components. Therefore, a DES can be introduced as an independent solvent with its unique properties. Also, different H-bond interaction energies of GDES and its pure components in the presence of water were shown by theoretical calculations based on a density functional theory framework. To investigate the effects of water on the structure of GDES, molecular dynamics (MD) simulations of GDES-water liquid mixtures were performed at 0.9 mole fraction of water.

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Car–Parrinello molecular dynamics (MD) was carried out to simulate pure [C4mim]PF6 and [C4mim]BF4 ionic liquids and their mixtures with polar water solvent to approach the admixing mechanism as well as hydrophobic and hydrophilic interactions from an electronic point of view. Initially, the results of density functional theory (DFT) on isolated ion pairs with partial charges assigned to atomic centers by various methods were analyzed. Next the trajectory of a 40 ps long Car–Parrinello MD were analyzed under bulk conditions. Water molecule influences substantially the hydrophilic ([C4mim]BF4) ionic liquid and the hydrophobic ([C4mim]PF6) to a different extent, which is evident by probing atomic charges of partnering constituents. The reduction in simulated dipole moment of water upon admixing with hydrophilic ionic liquid is larger than that with the hydrophobic one, which roots from stronger electrostatic screening. Water molecules tend to segregate when mixed with [C4mim]PF6 but mix with [C4mim]BF4 efficiently by interacting with BF4 – anion, which interacts and resides on its cation [C4mim]+. When ionic liquids mixed with water, the average charge on each F atom in BF4 – (PF6 –) anion was −0.3261e (−0.1820e). The simulated charge on each H atom of pure water (0.3290e) can be evidently responsible for the effective H···F interaction in [C4mim]BF4 but ineffective in [C4mim]PF6. These results provide insight into the hydrophilic and hydrophobic character from an electronic point of view.