Tuning polyamide layer structure via interfacial modulation: Insights from molecular dynamics to membrane design

The interfacial polymerization behavior of polyamide (PA) separation layers is largely constrained by the physicochemical characteristics of the aqueous-organic interface. While previous studies have employed additives (e.g., surfactants) to reduce interfacial tension, most strategies focus on isolated tuning of macroscopic physical parameters, lacking systematic intervention in diffusion pathways, miscible zone structures, and reaction thermodynamics. This study introduced N-butylpyrrolidone (NBP), a novel green interfacial regulator featuring a balanced polar-nonpolar amphiphilic structure. By enhancing interfacial affinity and modulating interfacial tension, it optimized the transport pathways and enrichment behavior of monomers at the interface. Combined molecular dynamics simulations and experimental characterization revealed that trace-level incorporation of NBP expands the miscible zone from 8 Å to 15 Å. It also reduced the diffusion energy barrier for M-phenylenediamine, increasing its interfacial diffusion coefficient by nearly 30-fold. This synergistic modulation induced a morphological transition of the PA layer from a nodular structure to a multilayer leaf-like architecture. The resulting reverse osmosis (RO) membrane achieved a high water flux of 93.11 L·m –2 ·h –1 , while maintaining NaCl rejection above 96%. This work demonstrated that NBP enables simultaneous regulation of interfacial thermodynamics and reaction kinetics at minimal dosage, offering a sustainable strategy for developing high-performance, environmentally friendly RO membranes. • Incorporation of green amphiphilic small molecule NBP modulated the physical microenvironment. • NBP reduced interfacial tension and doubled the width of the miscible zone. • NBP reduced the trans-interfacial energy barrier of MPD. • Interface regulation induced multilayer leaf-like structures, significantly enhancing membrane flux (93.11 L·m -2 ·h -1 ); • Unveiled the structure-function relationship driven by interfacial property-regulated monomer diffusion.