Molecular dynamics simulation studies of the structure and antifouling performance of a gradient polyamide membrane
Molecular dynamics simulation studies of the structure and antifouling performance of a gradient polyamide membrane
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梯度聚酰胺膜结构及防污性能的分子动力学模拟研究
DOI：
10.1039/c9cp03798e
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发表时间：
2019-09-28
影响因子：
3.3
通讯作者：
Zhou, Yongfeng
中科院分区：
文献类型：
--
作者：
Li, Ke;Li, Shanlong;Zhou, Yongfeng
薄膜复合反渗透膜表面的聚酰胺（PA）层是膜基海水淡化技术的核心。近年来，分子动力学模拟已越来越多地用于揭示PA层的物理化学性质。然而，目前报道的全原子PA层模型没有表现出层的结构特性的梯度变化，它们只能代表PA层的最内部区域。借助我们最近开发的通用工具包“MembrFactory”，本文报道了一种建模方法，可用于构建PA层的梯度交联模型和表面接枝模型。建立了PA层的全原子模型，其中交联度（DC）沿厚度方向沿着呈梯度变化。PA层模型的结构和水分子在其中的传输动力学进行了系统的研究，使用平衡分子动力学模拟。我们发现PA层模型的界面区DC最低，水分子的自扩散能力最强。同时，孔隙大小在该区域分布较广。随后，我们用PEG涂层对PA层模型表面进行改性，其覆盖率约为75%。径向分布函数分析表明，水分子更倾向于与PEG中的氧原子配位。此外，两个污染分子，1-乙基-2-甲基苯和正癸烷，被选择来研究PEG改性的PA层的抗氧化性能。通过分析污染物的运动轨迹和计算平均力的势能，我们发现PEG改性PA层的抗静电性能不仅与污染物的疏水性和粒径有关，还与PEG层的覆盖率有关。
The polyamide (PA) layer on the surface of thin-film-composite reverse osmosis membranes is the core aspect of membrane-based desalination technology. In recent years, molecular dynamics simulations have been increasingly used to disclose the physicochemical properties of the PA layer. However, the currently reported all-atom PA layer models do not exhibit gradient variation of the structural properties of the layer, and they can only represent the innermost region of the PA layer. With the help of our recently developed universal toolkit "MembrFactory", this paper reports a modeling method that can be used to construct a gradient crosslinking model and surface grafting model for the PA layer. A fully atomistic model of the PA layer was constructed, in which the degree of crosslinking (DC) was changed gradiently along the thickness direction. The structure of the PA layer model and the transport dynamics of the water molecules within it were systematically investigated using equilibrium molecular dynamics simulations. We found that the DC is the lowest and the water molecules have the strongest self-diffusion ability in the interfacial region of the PA layer model. Meanwhile, the pore size is distributed widely in the region. Subsequently, we modified the surface of the PA layer model with PEG coatings, and their coverage ratio was around 75%. The radial distribution function analysis showed that water molecules prefer to coordinate with the oxygen atoms in PEG. Furthermore, two contaminant molecules, 1-ethyl-2-methyl benzene and n-decane, were selected to investigate the antifouling properties of the PEG-modified PA layer. By analysing the trajectories of the pollutants and calculating the potential of the mean force, we found that the antifouling performance of a PEG-modified PA layer is not only related to the hydrophobicity and the size of the pollutant, but is also related to the coverage ratio of the PEG layer.