(403b) Sub-10 Nm Glassy Amorphous Perfluoropolymers for Desalination and Solvent Dehydration.

Thin-film composite (TFC) membranes based on 20 – 200 nm cross-linked polyamides are state-of-the-art membranes for desalination and solvent dehydration. The polyamides swell little in water and have a strong-size sieving ability to achieve high selectivity. Advanced polymers have been designed and synthesized to improve the water/salt or water/solvent separation properties. However, the new polymers usually face challenges in fabrication into TFC membranes and stability with time. Herein we show that glassy amorphous perfluoropolymers (such as TeflonAF and Hyflon AD40) can be fabricated into TFC membranes with a selective layer of less than 10 nm. The membranes were characterized for contact angle and selective layer thickness. Increasing the polymer concentration in the coating solutions from 0.05 wt% to 0.1 wt% increases the selective layer thickness from 4.2 to 7.5 nm. For example, a membrane containing 7.5 nm Teflon AF2400 on PES support shows water permeance of 0.10 ± 0.01 LMH/bar and rejection of NaCl, Na₂SO₄, Li₂SO₄, and MgSO₄ of 44.5%, 95.2%, 99.9%, and 59.8%, respectively. Moreover, AF2400/PVDF TFC has shown excellent stability in a wide range of organic solvents, providing a path to study its applications for organic solvent dehydration. For example, a TFC membrane prepared using 0.5 wt% Teflon AF2400 has a selective layer thickness of 32.8 nm and shows water and methanol permeance 9.0 ± 1.0 and 3.1 ± 0.2, respectively. Additionally, perfluoropolymer-based membranes show excellent antifouling properties and stability against chlorine due to their low surface energy and inertness. Though the membranes show lower water permeance than intensively engineered commercial polyamide-based membranes, these perfluoropolymer-based membranes can be optimized and may have promise for desalination and solvent dehydration.