Anion Effect on Phase Separation of Polyethylene Glycol-8000–Sodium Salt Two-Phase Systems

Aqueous two-phase systems (ATPSs) are formed when two nonionic polymers, or a single polymer and salt, are mixed in water above a specific concentration, resulting in the emergence of phase separation and the formation of two immiscible aqueous phases. The solvent properties of the aqueous media within the phases of ATPSs rely on the specific composition of the co-solutes and the arrangement of the hydrogen bond network within each phase. Here, we investigate the anion effect of various sodium salts on the enhancement or destabilization of polyethylene glycol (PEG)–salt ATPS formation. Relatively small changes in ATPS ionic composition were shown to result in significant changes in solute partitioning. Additionally, we previously established that the arrangement of hydrogen bonds within the coexisting phases of ATPSs is different, as evidenced by Attenuated Total Reflection—Fourier Transform Infrared (ATR-FTIR) spectroscopic analysis of OH-stretch bands. The hydrogen bond arrangement was shown to abruptly change at concentrations below the threshold of macroscopic phase separation in the ATPSs. Using dynamic light scattering (DLS), we observed a correlation between these abrupt changes in H-bond arrangement and the detection of agglomerate formation in both polymer–polymer and polymer–salt systems.