Structure and Thermodynamic Properties of Imidazolium-Based Ionic Liquids with Dicyanamide Anion: A Molecular Dynamics Study

Imidazolium-based Ionic Liquids (ILs) with the dicyanamide anion, [N(CN)2]-, have low melting temperature, high thermal and chemical stabilities, high ionic conductivity and low viscosity making them ideal candidates in the different industrial applications. In this work, the structural and thermodynamic properties of two ILs based on 1-alkyl-3-methylimidazolium cation, [amim]+, (alkyl = methyl and ethyl) and [N(CN)2]-, are studied using molecular dynamics simulations. The non-polarizable all-atom force field was applied to investigate the influence of the effect of changing alkyl side chain from methyl to ethyl and temperature on the behavior of ILs. The quantities such as the radial distribution function, spatial distribution function, the density of IL, molar volume, isobaric thermal expansion coefficient, and enthalpy of vaporization were studied. The density of the [dmim][N(CN)2] is larger than that of the [emim][N(CN)2] at all temperatures because of the relatively higher symmetry and greater packing of [dmim]+ in the liquid state. With increasing alkyl chain length from methyl to ethyl, the electrostatic interactions between ions are weakened and the van der Waals interactions are strengthened, and consequently, the enthalpy of vaporization is decreased.