Volumetric, acoustic and viscometric investigation of some choline amino acid ionic liquids in aqueous solutions of polypropylene glycol 400 and polyethylene glycol 400

Abstract

Present study reports density (ρ), ultrasonic velocity (u), and viscosity (η) for some choline amino acid ionic liquids, [Ch][AA]-ILs, including choline glycine, choline L-valine and choline L-proline in aqueous solutions of two water soluble polymers, i.e. polypropylene glycol 400 (PPG400) and polyethylene glycol 400 (PEG400) with different mass fractions of polymer, w/w = (0.025, 0.050 and 0.075), at 298.15 K under atmospheric pressure (≈85 kPa). The experimental densities and sound speeds were used for calculation the apparent molar volume (Vφ), limiting apparent molar volume (Vφ0), apparent molar isentropic compressibility (κφ), limiting apparent molar isentropic compressibility (κφ0), and also the transfer molar volume (ΔtranVφ0) and isentropic compressibility (Δtranκφ0) of [Ch][AA] from water to aqueous polymer solutions. Moreover, the viscosity B-coefficient, hydration number (nH), transfer viscosity B-coefficient (ΔtranB), free energies of activation per mole of solvent (Δμ10≠) and solute (Δμ20≠) have been computed by the help of experimental viscosities measured for the studied solutions. These quantities are useful for evaluation the ILs solvation behaviour, their structure-making or breaking abilities in the presence of polymer in water medium and also the solute-solute or solute-solvent interactions exists in aqueous ([Ch][AA] + polymer) solutions. The results indicated that the IL-water interactions are more favourable in the presence of PPG400 and follow the order: [Ch][Gly] > [Ch][L-Pro] > [Ch][L-Val]. Inversely, the IL-water interactions become weaker by ILs transferring from water to aqueous PEG400 solutions.