Controlling Thermodynamic and Kinetic on Ion-Mediated Nonsolvent-Induced Phase Separation.

Polar Clean has emerged as a promising sustainable solvent for membrane fabrication; however, its high boiling point and strong affinity for polymers pose significant challenges for solvent removal and structural preservation. Here, we introduce a nonthermal ion-mediated phase separation (IMPS) strategy that decouples solvent extraction from thermal processing via coupled thermodynamic and kinetic effects. The influence of chloride salts (CaCl2, NaCl, NH4Cl) on poly-(ether sulfone) membrane formation was systematically examined. Cloud-point analysis showed that kosmotropic salts destabilize the dope by shifting the binodal boundary to lower water concentrations, while kinetic analysis revealed that rapid demixing forms dense vitrified skin layers that hinder solvent release in additive-free systems. This kinetic limitation was alleviated by hydrophilic additives (PEG/PVP), which suppressed skin densification and enhanced pore connectivity. The optimized NH4Cl/PEG system achieved 99.8% solvent removal and a flux of 782 ± 17 LMH bar-1, and an MWCO of 79 kDa, representing a 1.8-fold improvement over DI water controls, and exhibited a highly interconnected porous morphology. IMPS thus provides a robust, energy-efficient platform for sustainable membrane fabrication with mechanistic tunability beyond conventional green-solvent limitations.