Thermodynamic and transport properties of aqueous solutions containing cholinium l-alaninate and polyethylene glycol dimethyl ether 250: Evaluation of solute-solvent interactions and phase separation

Abstract

Cholinium amino acids ([Ch][AA]) are novel, low toxic and biocompatible ionic liquids (ILs) which utilized widely in biotechnological processes. Since, the most of these processes were done in an aqueous media, it is vital to achieve better understanding of the interactions between ILs with other species in this media. In this respect, this work is focused on the investigation of physicochemical properties of the cholinium l-alaninate ([Ch][l-Ala]) in water and in the presence of polyethylene glycol di-methyl ether 250 (PEGDME250) with different mass fractions 0.025–0.125 at T = (288.15–318.15) K under atmospheric pressure (≈85 kPa). Density (ρ), speed of sound (u), viscosity (η), and refractive index of the studied aqueous solutions were experimentally measured. The obtained values from the density and acoustic studies were used for calculating the limiting values for apparent molar volume (Vφ0), apparent molar isentropic compressibility (κφ0), and also the transfer molar volume (ΔtranVφ0) and isentropic compressibility (Δtranκφ0) of [Ch][l-Ala] from water to aqueous PEGDME250 solutions. Also, viscosity A and B-coefficients were obtained from intercept and slope of the linear plot of viscosity data versus IL molarity. Moreover, the hydration number (nH) was computed from the isentropic compressibility and viscosity data. Finally, the solute-solvent interactions in the investigated solutions were evaluated on the basis of changing the above thermodynamic properties from aqueous binary to ternary solutions consist of the [Ch][l-Ala] and PEGDME250. The results indicated that the IL-water interactions become stronger in the presence of PEGDME250 compared to pure water; and in above a critical concentration this ternary solution can be separated into two-phases.