Synergistic Rigid Twisted and Fluorinated Architectures in Zwitterionic Poly(arylene ether sulfone) for Ultrahigh Water/Salt Selectivity

High-performance desalination membranes require polymers with optimized free volume and selective transport properties. In this work, the effects of incorporating rigid monomers into zwitterionic poly(arylene ether sulfone) (PAES) membranes on water and salt transport behavior were investigated, grounded in solution-diffusion theory. Three rigid monomers, 9,9-di(4-hydroxyphenyl)fluorene (BHF), 1,1’-binaphthyl-2-phenol (BNP), and 3,6-dihydroxy-9-trifluoromethyl-9-phenylxanthene (3FR), were selected to modify polymer structure. The results demonstrate that the introduction of rigid monomers enhances the free volume and water uptake of the membranes. Notably, the 3FR-based membranes, incorporating both rigid twisted structures and fluorinated groups, exhibited a synergistic effect, significantly improving water diffusion while suppressing salt diffusion. The presence of fluorine atoms in 3FR created stable hydrophobic channels, which not only facilitated rapid water transport but also effectively hindered salt permeation, resulting in superior water/salt selectivity. The study reveals that the combination of rigid and fluorinated structures provides a promising strategy for designing high-performance desalination membranes.