The densities of five imidazolium-based ionic liquids (ILs) (1-butyl-3-methylimidazolium tetrafluoroborate, [C1C4Im][BF4]; 1-butyl-3-methylimidazolium hexafluorophosphate, [C1C4Im][PF6]; 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide, [C1C4Im][Tf2N]; 1-ethyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide, [C1C2Im][Tf2N]; 1-ethyl-3-methylimidazolium ethylsulfate, [C1C2Im][EtSO4]) were measured as a function of temperature from (293 to 415) K and over an extended pressure range from (0.1 to 40) MPa using a vibrating-tube densimeter. Knowledge of the variation of the density with temperature and pressure allows access to the mechanical coefficients:  thermal expansion coefficient and isothermal compressibility. The effects of the anion and of the length of the alkyl chain on the imidazolium ring on the volumetric properties were particularly examined. The mechanical coefficients were compared with those of common organic solvents, water and liquid NaCl. Finally, a prediction model, based on an “ideal” volumetric behavior of the ILs, is proposed to allow calculation of the molar volume of imidazolium-based ionic liquids as a function of temperature.

Several methods for estimating the excess volume and density of ternary liquid mixtures of non-electrolytes from binary data are tested using 27 sets of data from the literature. The mean error of the excess volume estimation is lower than 0.1 cm3 mol-1. The use of the tested methods for estimating the density of ternary mixtures results in a significant reduction of the error compared to the stimation when the mixture is considered to be ideal. In decisive majority of the data sets, the maximum error in the density estimation is lower than 0.1%.

No abstract