Polyamide reverse osmosis membrane compaction and relaxation: Mechanisms and implications for desalination performance

JS Wu and JL He and JA Quezada-Renteria and JS Le and KY Au and KV Guo and MH Xiao and XY Wang and D Dlamini and HQ Fan and K Pataroque and Y Suleiman and S Shahbazmohamadi and M Elimelech and Y Li and EMV Hoek, JOURNAL OF MEMBRANE SCIENCE, 706, 122893 (2024).

DOI: 10.1016/j.memsci.2024.122893

This work investigates the compaction and relaxation behavior of composite reverse osmosis (RO) polyamide (PA) selective layers, utilizing non -equilibrium molecular dynamic (NEMD) simulations and well -controlled permeation experiments. Composite PA-RO membranes are prepared by interfacial polymerization of para and meta diamine monomer blends to achieve different PA film crosslinking degrees ( CD ). Wet -testing results suggest that "tighter" (higher CD ) composite RO membranes undergo 65 % less compaction and recover 17 % more of their initial permeability (termed "relaxation") when the pressure is relieved compared to lower CD PA layers. NEMD simulations provide a visual and quantitative characterization of PA layer's free volume changes in operando . NEMD simulations also corroborate experimental findings and elucidate the viscoelastic properties of the PA layer that govern compaction and relaxation behavior. The mechanisms of compaction under water permeation derived from NEMD simulations further support the notion of viscous flow of water through interconnected free volume elements (i.e., "pores") within crosslinked PA films.

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