Self-assembled lyotropic liquid crystal interlayer regulated interfacial polymerization for modulating structure and performance of nanofiltration membranes

Nanofiltration (NF) is a key membrane separation technology that is promising in various chemical and environmental applications. The need for high-performance thin-film composite (TFC) NF membranes, particularly those with enhanced salt selectivity and fouling resistance, necessitates effective strategies for optimizing their fabrication processes-interfacial polymerization (IP). In this study, we demonstrate an effective strategy for fine-tuning of IP process through integrating lyotropic liquid crystals (LLCs), which self-assemble into an interlayer with hexagonal structure on substrates. Performing IP on the LLC-coated substrates leads to the formation of polyamide with characteristic tubular structure. Compared with conventional TFC membranes, the LLC-modulated TFC membranes display doubled water permeability while preserving comparable Na₂SO₄ selectivity, thereby achieving an enhanced water/salt selectivity. Moreover, these membranes demonstrate high ion/ion selectivity (e.g., Na⁺/Ca²⁺ and Li⁺/Mg²⁺) and enhanced fouling resistance, rendering them highly desirable for various separation processes. Further exploration into interfacial structures and mechanisms reveals the pivotal role of the LLC-interlayers in affecting the diffusion of the diamine monomer (i.e., piperazine), thereby resulting in the polyamide layer with the distinctive tubular structure and improved separation properties. Our results highlight the promise and potential of utilizing interlayers with self-assembled structures for creating high-performance NF membranes.