Apparent molar volumes and expansivities of aqueous solutions of ionic liquids, l-alkyl-3-methylimidazolium alkyl sulfate at T = (298.15–328.15) K

Densities of some aqueous ionic liquids containing alkyl sulfate anions, 1-ethyl-3-methylimidazolium methyl sulfate, 1-hexyl-3-methylimidazolium methyl sulfate, and 1-hexyl-3-methylimidazolium ethyl sulfate solutions were measured at T = (298.15–328.15) K and at atmospheric pressure. The apparent molar volumes at infinite dilution were found by extrapolation to infinite dilution with using Redlich–Mayer and Pitzer equations. The apparent molar volumes at infinite dilution were used to obtain information about solute–solvent and solute–solute interactions. The temperature dependence of apparent molar volumes were used to calculation of apparent molar expansivities and the Heplerʹs constant values, ( ∂ 2 V ϕ 0 / ∂ T 2 ) P . The Heplerʹs constant values were found very small negative which indicating the ionic liquids under study are predominantly a structure breaker due to hydrophobic hydration of ionic liquids in water. The results were discussed in terms of alkyl chain length and anion size on the volumetric properties on the studied ionic liquids.