Correlation between ultrasonic velocity, surface tension, density and viscosity of ionic liquids

Ultrasonic velocity, density, viscosity and surface tension of ionic liquids 1-butyl-3-methyl imadazolium hexafluorophosphate [BMIM][PF6], 1-butyl-3-methyl imadazolium octyl sulfate [BMIM][OcSO4] and 1-ethyl-3-methyl imadazolium methane sulfonate [EMIM][MeSO3] have been measured from 303 K to 333 K. Using these experimental data, inter relationships among ultrasonic velocity, density, viscosity and surface tension have been examined for these ionic liquids. It has been found that (a) ultrasonic velocity (u), surface tension (σ) and density (ρ) can be correlated linearly using equation, log u = ψ log σ/ρ + ξ (with typical values of ψ = 1.61 and ξ = 10.459) (b) surface tension is linearly correlated with viscosity by the relation ln σ = ln a + bη−0.125, where ln a and b are constants. These correlations among physicochemical properties of the ionic liquids can be used to evaluate the properties (viz. ultrasonic velocity) not available in literature.

Research highlights
► Physicochemical properties of ionic liquids have been correlated with two linear correlations.
► In the first correlation, experimental values of surface tension, density and ultrasonic velocity of the ionic liquids have been correlated with the modified form of empirical Auerbach's relation. A good agreement has been observed between experimental and calculated values of ultrasonic velocity.
► The second correlation fits the experimental viscosity with surface tension.
► These observed correlations may be used to calculate several temperature dependent physicochemical properties whose experimental values are not available in literature.