Study on the salting effect of choline chloride on aqueous solutions of imidazolium-based ionic liquids via the isopiestic measurements

In this work, the vapor-liquid equilibrium behavior of aqueous ternary systems composed of choline chloride (ChCl) and imidazolium-based ionic liquids has been investigated using the isopiestic method at 25 °C. The ionic liquids used are 1-butyl-3-methylimidazolium bromide ([C4mim][Br]) and 1-butyl-3-methylimidazolium trifluoromethane sulfonate ([C4mim][CF3SO3]). The effect of ionic liquid anion on water activity, vapor pressure, and isopiestic equilibrium concentrations has been evaluated. The deviation of water iso-activity curves from the linear isopiestic relation has been used as a benchmark to unveil the salting-out or salting-in effect of ChCl on the aqueous solution of ionic liquids. The results show that ChCl plays the role of co-solvent in the studied systems and increases the solubility of the ionic liquids in water, indicating the occurrence of the salting-in phenomenon

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 ([C4mim][HSO4]) and 1-butyl-3-methylimidazolium bromide ([C4mim]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 [C4mim][HSO4] are more considerable than aqueous solutions of [C4mim]Br. However, [C4mim]Br-polymer interactions are more favourable than interactions between [C4mim][HSO4] and the studied polymers.</p

Investigation of Amino Acid–Polymer Aqueous Biphasic Systems

Aiming at gathering further information to evaluate the recently proposed, mechanism of the salt effect in aqueous polymer solutions, experimental vapor–liquid equilibria (VLE), liquid–liquid equilibria (LLE), and volumetric-compressibility measurements were carried out for several polymer–amino acid aqueous systems. The constant water activity lines (obtained through the isopiestic method at 298.15 K) of aqueous polypropylene glycol 400 (PPG400) + alanine or glycine systems, which form aqueous biphasic systems (salting-out effect), have a concave and convex slope, respectively, in the one-phase and two-phase regions. However, all the investigated polyethylene glycols (PEG400, PEG2000, PEG6000, and PEG10000) do not form aqueous biphasic systems with alanine or glycine (salting-in effect) and their constant water activity lines have a convex slope. In the second part of this work, the apparent molar volume and isentropic compressibility of transfer of alanine and glycine from water to aqueous solutions of PEG200, PEG2000, PEG10000, and PPG400 were studied at different temperatures. The third part of this work is concerned with the determination of LLE phase diagrams for several ternary polymer–amino acid aqueous systems containing polymers PPG400 and PPG725 and amino acids alanine, glycine, serine, and proline at different temperatures. On the basis of the obtained cloud point values of aqueous solutions of PPG725 in the absence and presence of various amino acids, it was found that all the investigated amino acids have a salting-out effect on PPG725 in aqueous solutions and entropy is the driving force for biphasic formation