Density, Thermal Expansion and Viscosity of Cholinium‐Derived Ionic Liquids

Density and viscosity data of the N-alkyl-N,N-dimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide ionic liquids homologous series [N1 1 n 2(OH)][Ntf2] with n=1, 2, 3, 4 and 5 have been measured at atmospheric pressure in the 283effective molar volume of cations and anions is used to estimate the effective molar volume of the different cations present in this study. The results agree with data for other cation families that show a molar volume increment per CH2 group on the alkyl chain of the cation of about 17.2 cm3 mol−1, except for [N1 1 1 2(OH)]+, which exhibits an outlier behaviour. Molecular dynamics simulation results are used to explain the volumetric behaviour along the homologous series from a molecular perspective. The predictive power of group contribution methods for density and viscosity is also tested.