A volumetric and viscosity study for the binary mixtures of 1-hexyl-3-methylimidazolium tetrafluoroborate with some molecular solvents

Information on the interactions between ionic liquids and molecular solvents are essential for the understanding of the function of ionic liquids in related procedures, and excess properties are sensitive probe for these interactions. In this work, excess molar volume (VmE) and excess logarithmic viscosity ((ln η)E) for the binary mixtures of 1-hexyl-3-methylimidazolium tetrafluoroborate ([C6mim][BF4]) with butanone, ethyl acetate, butylamine, and tetrahydrofuran have been determined from density and viscosity measurements in the whole composition range at the temperature of 298.15 K. It is found that for the studied systems, the values of VmE are negative but those of (ln η)E   are positive in the whole concentration range. The VmE values show their minimum at the ionic liquid mole fraction of 0.3, and (ln η)E   values exhibit a maximum at the same composition. The absolute values of VmE follow the sequence: tetrahydrofuran > butanone > ethyl acetate > butylamine for the binary systems, whereas the values of (ln η)E decrease in the order: tetrahydrofuran > butylamine > ethyl acetate > butanone. The results have been analyzed through the ion–dipole interaction, the hydrogen bonding, the packing efficiency and the ion-pairs exist in the ionic liquid.

Research highlights
► Excess molar volumes and excess logarithm viscosities for the binary mixtures of 1-hexyl-3-methylimidazolium tetrafluroborate were determined.
► The absolute values of VmE follow the sequence: THF > butanone > ethyl acetate > butylamine for the binary systems.
► The values of (lnη)E decrease in the order: THF > butylamine > ethyl acetate > butanone.
► Ion-dipole interaction, the hydrogen bond, the packing efficiency and the ion-pairs exist in the ionic liquid are believed to influence the excess properties of the related systems.
► The information obtained in this work allows us to show how physical properties of molecular solvents affect their interaction with the ionic liquid.