Rinse-Free Deposition of Molecular Layer-by-Layer (mLbL) Polyamide Reverse Osmosis Membranes

Published

April 29, 2025

Author(s)

Samarpan Deb Majumder, Christopher Stafford, Xitong Liu

Abstract

The molecular layer-by-layer (mLbL) deposition technique enables the fabrication of polyamide-based reverse osmosis membranes with low surface roughness and tunable membrane thickness, but scale-up of the process is challenged by the necessity for rinsing away unreacted monomers after each deposition step. By sensible tuning of monomer concentrations during deposition, we can eliminate the rinsing steps while still producing polyamide membranes with comparable thickness and surface properties. This approach markedly shortens fabrication time and improves reagent efficiency. By measuring the growth rate of the polyamide membrane as a function of deposition cycles and monomer concentration, we demonstrate that we can deliver a more targeted quantity of monomer to the growing film surface while maintaining a linear growth rate profile. Fourier transform Infrared (FTIR) spectroscopy shows a negligible amount of the unreacted (free) carboxylic acids across the monomer concentrations, indicating that the crosslink density of the membrane remains high. Desalination tests reveal that mLbL membranes produced at the lowest monomer concentration (membrane thickness of ≈20 nm) achieved nearly 99% salt rejection within 3 h, while maintaining a flux of 0.1 L m⁻² h⁻¹ bar⁻¹. This modified mLbL approach significantly reduces membrane fabrication time without compromising performance, offering a path towards scalable production of polyamide-based membranes with controlled thickness and low roughness while prioritizing both time and resource efficiency.

Citation

Journal of Membrane Science Letters

Volume

5

Issue

1

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.memlet.2025.100098

Local Download

Keywords

reverse osmosis, membranes, polyamide, molecular layer-by-layer, deposition

Citation

Deb Majumder, S. , Stafford, C. and Liu, X. (2025), Rinse-Free Deposition of Molecular Layer-by-Layer (mLbL) Polyamide Reverse Osmosis Membranes, Journal of Membrane Science Letters, [online], https://doi.org/10.1016/j.memlet.2025.100098, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=959311 (Accessed September 28, 2025)