Estimation of speed of sound of ionic liquids using surface tensions and densities: A volume based approach

The limited availability of experimental data and their quality have been preventing the development of predictive methods and Computer Aided Molecular Design (CAMD) of ionic liquids (ILs). Based on experimental speed of sound data collected from the literature, the inter-relationship of surface tension (σ), density (ρ), and speed of sound (u) has been examined for imidazolium based ILs containing hexafluorophosphate (PF₆), tetrafluoroborate (BF₄), bis(trifluoromethanesulphonyl) amide (NTf₂), methyl sulphate (MeSO₄), ethyl sulphate (EtSO₄), and trifluoromethanesulphonate (CF₃SO₃) anions, covering wide ranges of temperature, 278.15–343.15 K and speed of sound, 1129.0–1851.0 m s⁻¹. The speed of sound was correlated with a modified Auerbach's relation, by using surface tension and density data obtained from volume based predictive methods previously proposed by the authors. It is shown that a good agreement with literature data is obtained. For 133 data points of 14 ILs studied a mean percent deviation (MPD) of 1.96% with a maximum deviation inferior to 5% was observed. The correlations developed here can thus be used to evaluate the speeds of sound of new ionic liquids.