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

Area of Science:

• Materials Science
• Chemical Engineering
• Polymer Science

Background:

• Polymeric hollow fiber membranes (HFMs) are scalable for gas separations but face limitations in permeance-selectivity tradeoff and microporosity control.
• Existing membranes struggle to achieve high performance for critical gas separations like helium recovery.

Purpose of the Study:

• To engineer a high-performance gas separation layer on HFMs using a novel surface fluorination strategy.
• To overcome the inherent limitations of polymeric membranes through precise nanoscale modification.

Main Methods:

• Surface fluorination of polydimethylsiloxane (PDMS)-coated Matrimid® HFMs using carbon tetrafluoride (CF4) plasma.
• Controlled modification of PDMS surface chemistry and structure by tuning plasma parameters.
• Characterization of the fluorinated layer's composition, chain rigidity, and pore structure.

Main Results:

• Achieved a sub-10 nm fluorinated and crosslinked layer with up to 27.7 mol% fluorine content.
• Enhanced chain rigidity by 5.3-fold and narrowed pore size distribution.
• Record-breaking He/N2 (1202 ± 13) and He/CH4 (1790 ± 12) selectivities with high He permeance (170 ± 2 GPU).
• Demonstrated excellent molecular discrimination for He/CO2 and He/H2, and high selectivity in ternary He/(CO2+CH4) mixed-gas separations.
• Maintained operational stability for 720 hours.

Conclusions:

• Plasma-engineered surface fluorination is a scalable and effective strategy for advanced HFM design.
• This method surpasses perfluoropolymer performance and addresses key challenges in gas separation membranes.
• The approach opens new possibilities for high-performance membranes in industrial gas separation applications.