Phase behavior of aqueous two-phase systems formed with cholinium-based magnetic ionic liquids: Experimental insights and theoretical correlations

In this work, three cholinium-based MILs were synthesized, characterized and successfully applied to construct the magnetically responsive aqueous two-phase system (ATPs). This ATPs combined the advantages of ILs and magnetic responsiveness, and showed great potential in the field of extraction and separation. Phase behavior for the magnetic ionic liquid aqueous two-phase systems (MIL-ATPSs) containing [N 1 1n 2OH] [TEMPO-OSO3] + salts + water was investigated experimentally at different temperatures. Merchuk equation was adopted to fit the experimental binodal data with satisfactory correlation performances. The effects of the structure of MILs, temperature and types of salts on the phase behavior were evaluated. Investigation on the phase separation mechanism showed that the phase formation was affected by the structure and viscosity of MILs. The salting-out effect is recognized as the major force for phase separation, which is closely related to the Gibbs free energy of hydration (ΔhydG) and entropy of hydration (ΔhydS) of salts. In addition, a larger biphasic area was obtained by increasing the temperature, indicating the phase separation process was endothermic and entropically driven. The binodal curve at different temperature confirms that this MIL-ATPs has low critical solution temperature (LCST) phase transition behavior. All these experimentally measured data and the theoretical correlations can provide meaningful and valuable information that may promote further research and application. © 2024 Elsevier B.V.