Plasma‐Engineered Sub‐10 nm Surface Fluorination Enables Ultraselective Hollow Fiber Membranes

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Abstract While polymeric hollow fiber membranes (HFMs) offer scalable solutions for gas separations, their performance is fundamentally limited by the permeance‐selectivity tradeoff and imprecise microporosity regulation. Herein, we propose a surface fluorination strategy using carbon tetrafluoride (CF 4 ) plasma to engineer a sub‐10 nm fluorinated and crosslinked layer on polydimethylsiloxane (PDMS)‐coated Matrimid ® HFMs. Through precise modulation of plasma parameters, we achieved controlled substitution of PDMS methyl groups/methyl hydrogen atoms with fluorine species (up to 27.7 mol% F content), 5.3‐fold enhanced chain rigidity via fluorine‐induced interchain interactions and steric hindrance, as well as narrowed pore size distribution with preferential ultra‐micropore filling. The optimized HFM‐50W‐65Pa‐500s membrane exhibits record‐breaking He/N 2 and He/CH 4 selectivities of 1202 ± 13 and 1790 ± 12 with 170 ± 2 GPU He permeance, surpassing perfluoropolymer upper bounds and outperforming previously reported polymeric HFMs. Remarkably, it demonstrates molecular discrimination precision (α(He/CO 2 ) = 56 ± 2.2, α(He/H 2 ) = 4.1 ± 0.2) for pure‐gas and attractive ternary He/(CO 2 +CH 4 ) selectivity of 1005 ± 20 under 40‐bar mixed‐gas conditions while maintaining 720‐h operational stability. This plasma‐engineered fluorination paradigm combines nanoscale precision with industrial scalability, opening new avenues for advanced membrane design.

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