Opposite Effects Induced by Cholinium-Based Ionic Liquid Electrolytes in the Formation of Aqueous Biphasic Systems Comprising Polyethylene Glycol and Sodium Polyacrylate

Abstract

Cholinium-based ionic liquids ([Ch]-based ILs) were investigated as electrolytes in the formation of aqueous biphasic systems (ABS) composed of polyethylene glycol (PEG) and sodium polyacrylate (NaPA) polymers. Both enhancement and decrease in the liquid-liquid demixing ability induced by electrolytes in PEG-NaPA aqueous biphasic systems were observed. It is shown that the ILs that most extensively partition to the PEG-rich phase tend to act as inorganic salts enhancing the two-phase formation ability, while those that display a more significant partition to the NaPA-rich phase decrease the ABS formation capacity. The gathered results allowed us to confirm the tailoring ability of ILs and to identify, for the first time, opposite effects induced by electrolytes on the PEG-NaPA ABS formation ability. The distribution of the electrolyte ions between the coexisting phases and the polyelectrolyte ion compartmentalization are key factors behind the formation of PEG-NaPA-based ABS.

Influence of Choline Chloride on the Phase Equilibria and Partition Performance of Polymer/Polymer Aqueous Biphasic Systems

“…In instances where phase separation does take place, the separated phases differ widely in the overall polymer concentration, and the phase enriched with the uncharged polymer exhibits notably higher concentrations. In this scenario, due to the dominating influence of the entropy of counterions mixing, the degree of polymerization of the polyelectrolyte does not significantly influence the binodal curve [5,13]. Thus, in the PEG-NaPA systems without adjuvants, the molecular weight of NaPA does not significantly influence the ABS formation ability.…”

“…ABS consists of two water-rich and immiscible phases that can be formed by the combination of at least two different compounds, such as polymers, salts, ionic liquids (ILs), and carbohydrates [3,4]. Polymer-polymer ABS have been the most studied owing to their higher water content, resulting in a biocompatible character, although they have some limitations [4][5][6]. These systems usually present low selectivity due to the low polarity difference between the phases and high phase viscosity because of the polymers' high molecular weight required for liquid-liquid demixing [7].…”

“…When added to the polymeric aqueous solution, these minimal salt concentrations act as electrolytes, which can favor phase separation, depending on the salt nature [8,13]. This is particularly useful for enlarging the combinations of polymers that normally do not undergo liquid-liquid demixing in aqueous media at convenient concentrations for separation [5].…”

“…The addition of small amounts of ILs as adjuvants in polymer-polymer ABS not only allows the phase separation at much lower polymer concentrations and with lower molecular weights but also allows the partitioning tailoring [7,[14][15][16][17][18][19][20]. Within this framework, recent studies have highlighted cholinium chloride as a highly advantageous adjuvant in ABS, surpassing other ILs due to its exceptional biocompatibility, lower toxicity, superior ability to tailor phase behavior, and ability to enhance the extraction of biomolecules while maintaining an environmentally friendly nature [5,9,12,18,19,21].…”

“…Earlier reports have identified opposite effects induced by cholinium chloride ([Ch]Cl) on PEG/NaPA ABS formation, showcasing their remarkable tailoring ability [5,22,23]. To gain deeper insights into these systems, we herein investigate the phase behavior of PEG/NaPA aqueous solutions across varied molecular weights and temperatures, with and without the addition of cholinium chloride.…”