Grazing Incidence Wide-Angle X-ray Scattering of Water Adsorption in Polyamide Barrier Layers of Reverse Osmosis Membranes

IF 5.1 1区化学 Q1 POLYMER SCIENCE

Macromolecules Pub Date : 2024-12-27 DOI:10.1021/acs.macromol.4c02699

Qinyi Fu, Size Zheng, Nisha Verma, Roberto Gambarini, Tao Wei, Benjamin M. Ocko, Benjamin S. Hsiao

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Abstract

To understand the relationship between the intermolecular structure of aromatic polyamide (PA) scaffold and the water molecules in the barrier layers of reverse osmosis (RO) membranes, a grazing incidence wide-angle X-ray scattering (GIWAXS) study was carried out on freestanding PA thin films at varying relative humidity (RH) conditions. The scattering results were analyzed by an interference scattering model, containing a phase factor between a PA chain and an adsorbed water molecule. This model yielded good fits to the GIWAXS profiles where the water adsorption was found to vary linearly with RH. Atomistic molecular dynamics (MD) simulations were also performed to complement the experimental study. The simulations revealed that a rapid condensation layer initially formed on the PA film surface, followed by the slow water molecule diffusion inside the PA membrane. Sparse adsorbed water, isolated in subnanopores of the PA film adjacent to the polar atoms, even in very low quantities, modifies the X-ray scattering. Atomistic simulations at the microscopic scale provide partial support for several X-ray scattering findings.

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反渗透膜聚酰胺阻挡层水吸附的掠射广角x射线散射

为了了解芳香聚酰胺（PA）支架的分子间结构与反渗透（RO）膜屏障层中水分子的关系，在不同相对湿度（RH）条件下对独立的PA薄膜进行了掠入射广角x射线散射（GIWAXS）研究。通过包含PA链与吸附水分子之间相因子的干涉散射模型对散射结果进行了分析。该模型很好地拟合了GIWAXS剖面，其中发现水吸附与RH呈线性变化。原子分子动力学（MD）模拟也进行了补充实验研究。模拟结果表明，首先在PA膜表面形成一个快速的冷凝层，随后水分子在PA膜内缓慢扩散。稀疏吸附的水，孤立在靠近极性原子的PA膜的亚纳米孔中，即使是非常低的量，也会改变x射线散射。微观尺度上的原子模拟为若干x射线散射发现提供了部分支持。

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来源期刊

Macromolecules 工程技术-高分子科学

CiteScore

9.30

自引率

16.40%

发文量

942

审稿时长

2 months

期刊介绍： Macromolecules publishes original, fundamental, and impactful research on all aspects of polymer science. Topics of interest include synthesis (e.g., controlled polymerizations, polymerization catalysis, post polymerization modification, new monomer structures and polymer architectures, and polymerization mechanisms/kinetics analysis); phase behavior, thermodynamics, dynamic, and ordering/disordering phenomena (e.g., self-assembly, gelation, crystallization, solution/melt/solid-state characteristics); structure and properties (e.g., mechanical and rheological properties, surface/interfacial characteristics, electronic and transport properties); new state of the art characterization (e.g., spectroscopy, scattering, microscopy, rheology), simulation (e.g., Monte Carlo, molecular dynamics, multi-scale/coarse-grained modeling), and theoretical methods. Renewable/sustainable polymers, polymer networks, responsive polymers, electro-, magneto- and opto-active macromolecules, inorganic polymers, charge-transporting polymers (ion-containing, semiconducting, and conducting), nanostructured polymers, and polymer composites are also of interest. Typical papers published in Macromolecules showcase important and innovative concepts, experimental methods/observations, and theoretical/computational approaches that demonstrate a fundamental advance in the understanding of polymers.