Owens-Wendt method as a tool to evaluate polarity of polymer-polymer aqueous two-phase systems

Phase separation in polymer-polymer aqueous two-phase systems (ATPS) is driven by polarity differences from intermolecular interactions. In this study, we applied the Owens-Wendt method to evaluate polarity changes during the formation of polymer-polymer ATPS and to characterize their individual phases. Surface energy contributions of polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), high-density polyethylene (PE), polyurethane (PU), polyamide (PA), polyvinyl chloride (PVC), and glass were determined using water (H 2 O) and dimethyl sulfoxide (DMSO) as reference liquids. Afterward, the polarity of both binary polymer/H 2 O and the ternary PEG600/PPG400/H 2 O systems were determined. Binary polymer/water mixtures of PEG600 and PPG400 exhibited distinct behaviours due to the additional methyl group in PPG400, which increases its hydrophobicity relative to PEG600. As polymer concentration increased, the overall polarity of the mixtures decreased for both systems. In PEG600/H 2 O mixtures, dispersive forces increased as hydrogen bonding between polymer and water molecules diminished. Conversely, PPG400/H 2 O mixtures displayed largely constant dispersive contributions, likely due to steric-driven self-aggregation of PPG400 molecules and consistent hydrogen bonding with water across all polymer concentrations. In ternary mixtures, the contact angle measurements indicated that PEG600 increases the mixtures’ polarity through strong hydrogen bonding with H 2 O, whereas PPG400 exhibits lower polarity and weaker interactions with H 2 O molecules. Phase separation was attributed to the formation and disruption of hydrogen bonds within PEG600/H 2 O clusters, occurring when the polarity contrast between these clusters and PPG400 exceeded a critical threshold (Dispersive/Polar (D/P) ratio < 0.24). As polymer concentration increased and H 2 O content decreased, polarity differences diminished, leading to the reestablishment of a monophasic system due to stronger apolar intermolecular interactions between polymer molecules (D/P ratio > 0.50). These findings establish the Owens-Wendt method as a reliable tool for assessing ATPS polarity, even in systems with ultralow interfacial tensions. This study opens new avenues for correlating phase polarity with ATPS formation and solute partitioning, providing a novel approach to better understand and optimize liquid-liquid extraction processes, and supporting the future development of tailored ATPS-based extraction systems with enhanced efficiency and selectivity.