Anion Specific Effects Drive the Formation of Li-Salt Based Aqueous Biphasic Systems

Aqueous biphasic systems (ABSs) can form when mixing water with two compounds such as polymers, ionic liquids, or simple salts. While this phenomenon has been known for decades and found applications in various fields biology, recycling, even more recently electrochemistry, the physics behind formation of ABSs remains ill-understood. It was demonstrated that be composed salts sharing same cation (Li+) but different anions (sulfonamide halide). Interestingly, their could not explained by position within chaotropic/kosmotropic series rather proposed to originate from an anion size mismatch, albeit these never measured yet owing lack a proper experimental methodology. Here, we combine techniques molecular simulations assess specific effects (size, shape, hydrophobic/hydrophilic character) correlate them ABSs. We demonstrate while mismatch is prerequisite Li-salts based ABSs, shape also play important role, providing general guidelines forming new potential future applications.