Effect of Temperature, Alkyl Chain Length and Anions on the Density, Viscosity, Speed of Sound, Surface Tension and Refractive Index of [C2mim][MeSO4], [C2mim][EtSO4], [C2eim][EtSO4], [C3py][BF4], [C4py][BF4], [C4mpy][BF4] and [C6py][BF4] Ionic Liquids

Density, refractive index, viscosity, surface tension, and speed of sound were experimentally determined and analyzed for [C 2 mim][MeSO 4 ], [C 2 mim][EtSO 4 ], [C 2 eim][EtSO 4 ], [C 4 mpy][BF 4 ] and [C n py][BF 4 ] ( n  = 3, 4, 6) at atmospheric pressure and temperatures ranging from 293.15 K to 343.15 K. Expectedly, temperature exhibited the greatest impact on viscosity, as all properties decrease as temperatures increase. Linear temperature-dependent correlations were utilized for density, surface tension, refractive index, and speed of sound, while the Vogel–Fulcher–Tammann (VFT) model was applied to describe the temperature dependence of viscosity. The Laplace-Newton equation was used to calculate isentropic compressibility, and thermal expansion was calculated using the experimental density data. Furthermore, the study examined the impact of anion type and alkyl chain length on the thermophysical properties of the ionic liquids. The results reveal that the physical properties of the ionic liquids are significantly influenced by the anion type, whereas the alkyl chain length has a less significant impact. Density, speed of sound, and surface tension decrease as the length of the alkyl chain increases, while viscosity and refractive index exhibit opposing trends. Additionally, the experimental data obtained in this study is compared to theoretical models for density, surface tension, and speed of sound.