Interactions in aqueous solutions of imidazolium chloride ionic liquids [Cnmim][Cl] (n = 0, 1, 2, 4, 6, 8) from volumetric properties, viscosity B-coefficients and molecular dynamics simulations

Abstract

© 2018 Elsevier B.V. In this work a systematic study of aqueous diluted solutions (~0.005 < m/mol·kg−1 < ~0.1) of six imidazolium based ionic liquids (IL) [Cnmim][Cl] with different alkyl chain lengths (n = 0, 1, 2, 4, 6, 8) was carried out. Densities and viscosities were measured as a function of IL concentration in the temperature range between 278.15 K and 313.15 K in steps of 5 K. From experimental data, apparent molar volumes, standard partial molar volumes, and viscosity B-coefficients of ILs were derived. The effect of the alkyl chain length on the estimated properties was discussed in terms of ion-ion and ion-solvent interactions. It turned out that the studied cations with longer alkyl side chain (n = 4, 6, 8) can be regarded as structure makers; cations with shortest side chain (n = 0, 1) as structure breakers, whereas [C2mim]+ can be considered as a border line ion. In order to obtain more information about interactions and influence of studied ILs on water structure, computational simulations were performed. For this purpose, DFT calculations using B3LYP-D3 functional and molecular dynamic simulations with OPLS 2005 force field, were applied. Obtained results show that the increase in length of alkyl substituent in imidazolium ring leads to weakening of interactions with water molecules.