Molecular-Level Pore Engineering for Precise Separation via Active Solvent-Mediated Interfacial Polymerization

Polymer membranes typically face various selectivity demands in practical separations. Tuning the selectivity largely relies on regulating the pore size and distribution in membranes without disrupting the integrity of the polymer network. While monomer design or additive incorporation shows advances in pore tuning, homogeneous sub-nanometer pore tuning in polymer matrix remains challenging as traditional solvents act solely as diffusive media, leading to uncontrolled polymerization. Here, we report an active solvent-mediated interfacial polymerization strategy that enables molecular-level pore engineering of membrane selective layer. By utilizing the microemulsion, a special solvent, we show that ∼1 nm microemulsions induces localized quasi-homogeneous polymerization, templating molecular-level pores within the polyamide network. The resulting membranes exhibit excellent water permeance of 58.7 L m^-2 h^-1 bar^-1 with NaCl-Na₂SO₄ selectivity vs. water permeance surpasses the current upper bond. The strategy also works for hollow fiber membranes which show no performance decline even scaling up to 1-inch modules. Positron annihilation spectroscopy, small-angle x-ray scatterings, molecular dynamics, CFD and other experimental results reveal that patterned surface, enhanced free volume and narrower pore size contribute to the enhanced performance. This active solvent-mediated strategy provides a versatile and scalable method for enhancing membrane performance across water treatment and chemical separations.