Toward an understanding of volumetric and isentropic compressibility behavior of imidazolium-based ionic liquids in aqueous polymer solutions

A systematic experimental density and sound velocity measurement was carried out for imidazolium-based ionic liquids (ILs) in pure water and in aqueous solutions of 0.03 w/w of water-miscible polymers with different structures and molar masses at T= (288.15, 293.15, 298.15, 303.15 and 308.15) K and p = 84.5 kPa. The ILs under investigation are 1-butyl-3-methylimidazolium hydrogen sulphate ([C(4)mim][HSO4]) and 1-butyl-3-methylimidazolium bromide ([C(4)mim]Br). The effects of temperature, polymer type, and IL anion type on the various volumetric and compressibility properties, such as apparent molar volume, isentropic compressibility, apparent molar isentropic compressibility, and infinite dilution apparent molar properties for transfer of ILs from water to aqueous polymer solution were scrutinised. From the gathered results, ion-water interactions, ion-ion interactions at finite concentration, and water-structure breaking character for aqueous solutions of [C(4)mim][HSO4] are more considerable than aqueous solutions of [C(4)mim]Br. However, [C(4)mim]Br-polymer interactions are more favourable than interactions between [C(4)mim][HSO4] and the studied polymers.