Effect of hydrophobicity and H-bonding abilities of ions on osmotic coefficients of aqueous diethylammonium based protic ionic liquid solutions at 298.15 K

Abstract

The osmotic and activity coefficients of aqueous solutions of diethylammonium based protic ionic liquids (PILs) were determined experimentally using vapor pressure osmometry in the concentration range of (~0.02 to ~0.5) mol·kg−1 at 298.15 K. Osmotic coefficient data show positive deviation from Debye-Hückel limiting law for all the studied PILs. Also a minimum in osmotic coefficient data was observed at higher concentrations and is explained in terms of ion-pair formation. Data of experimental osmotic coefficient were used to obtain activities (aw) and activity coefficients (γ1) of water, mean molal activity coefficient (γ±) of PILs and excess Gibbs free energy change (ΔGE) due to mixing. Observed variations in osmotic coefficients data were explained in terms of hydrophobicity as well as H-bonding. The data of osmotic and activity coefficients were further subjected to analysis through Pitzer ion-interaction model to get an information of ion-ion and ion-solvent interaction to understand ion-pairing, ion hydration and hydrophobic effects in aqueous solutions of PILs. For this, Pitzer ion interaction parameters β(0) and β(1) were estimated and compared with literature data available for other relevant systems. Finally, the results are interpreted in terms ion-ion, ion-solvent interaction along with effect of hydrophobicity on ion-pairing and further discussed the effect of alkyl chain length of anions on solvation behavior of protic ionic liquids in aqueous solutions.