**5. Conclusions**

Densities for the binary mixtures of [EMIM][ESO<sup>4</sup> ] + [EMIM][HSO<sup>4</sup> ], [EMIM][ESO<sup>4</sup> ] + [BMIM] [OAc], [EMIM][ESO<sup>4</sup> ] + [BMIM][NtF<sup>2</sup> ] has been measured at 293.15–343.15 K with an interval of 5 K. Isobaric expansivity of all studied IL's have been calculated for temperature ranges from 293.15 to 343.15 K. The corresponding excess molar volume, partial molar volume; excess partial molar volumes; and apparent molar volume have also been calculated. The volumetric behavior of this binary system have been discussed in terms of ion-dipole interaction, packing effect, dipole-dipole interaction, hydrogen bond formation, geometrical fitting of one component into other, charge transfer, electron-electron interaction, and other complex forming interactions. In these mixtures, the forces (that is: dispersion, induction and dipolar forces) between pairs of unlike molecules are less than the forces between like molecules due to the difference in shape and size of the constituent molecules.

## **Acknowledgements**

The authors wish to acknowledge the Department of Science and Technology-SERB (YSS/2015/ DO1546), Government of India and SSN trust for funding the work and also Department of Chemical Engineering for supporting the work.
