From pore-confined to surface-controlled interfacial Polymerization: Strategic interfacial repositioning for high-performance fully aromatic polyamide membranes

Reverse osmosis (RO) membranes face an inherent trade-off between permeability and selectivity, hindering the simultaneous optimization of water flux and solute rejection. This study presents a straightforward and effective strategy, termed as pre-rinse regulated interfacial polymerization (PRIP), to overcome this limitation by strategically repositioning the oil-water interface from within the support pores to above the support surface. This repositioning is achieved through a brief pre-rinse with hexane of the m-phenylenediamine (MPD)-impregnated support before trimesoyl chloride (TMC) addition. The resulting PRIP membranes exhibit pronounced leaf-like structures, leading to an increased effective permeation area. Mechanistically, the hexane pre-rinse transitions interfacial polymerization from a pore-confined to a surface-controlled regime by shifting the oil–water interface above the support surface. This transition in reaction interface promotes the formation of more crumpled polyamide (PA) films with optimized water transport pathways. Remarkably, this straightforward modification produces membranes with water permeance of 4.2 L m⁻² h⁻¹ bar⁻¹, a 60 % improvement over the control, while simultaneously enhancing NaCl rejection from 98.9 % to 99.4 %. The consistent performance improvements observed across different support materials and organic solvents demonstrate the versatility of the method. This work provides new insights into controlling interfacial reaction dynamics to effectively overcome the permeability-selectivity trade-off in RO membranes.