Finding the path to better desalination Polyamide membranes have been used in large-scale desalination for decades. However, because of the thinness of the membranes and their internal variability, it has been hard to determine which aspects of the membranes most affect their performance. Culp et al. combined electron tomography, nanoscale three-dimensional (3D) polyamide density mapping, and modeling of bulk water permeability with zero adjustable parameters to quantify the effect of 3D nanoscale variations in polymer mass on water transport within the polyamide membrane (see the Perspective by Geise). They found that variability in local density most affects the performance of the membranes. Better synthesis methods could thus improve performance without affecting selectivity. Science, this issue p. 72; see also p. 31 Electron tomography reveals how inhomogeneities in pore distributions affect performance of water filtration membranes. Biological membranes can achieve remarkably high permeabilities, while maintaining ideal selectivities, by relying on well-defined internal nanoscale structures in the form of membrane proteins. Here, we apply such design strategies to desalination membranes. A series of polyamide desalination membranes—which were synthesized in an industrial-scale manufacturing line and varied in processing conditions but retained similar chemical compositions—show increasing water permeability and active layer thickness with constant sodium chloride selectivity. Transmission electron microscopy measurements enabled us to determine nanoscale three-dimensional polyamide density maps and predict water permeability with zero adjustable parameters. Density fluctuations are detrimental to water transport, which makes systematic control over nanoscale polyamide inhomogeneity a key route to maximizing water permeability without sacrificing salt selectivity in desalination membranes.

中文翻译：

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内部不均匀性的纳米级控制增强了海水淡化膜中的水传输

寻找更好的海水淡化之路 数十年来，聚酰胺膜一直用于大规模海水淡化。然而，由于膜的厚度及其内部可变性，很难确定膜的哪些方面对其性能影响最大。卡尔普等人。结合电子断层扫描、纳米级三维 (3D) 聚酰胺密度映射和体积水渗透率建模，零可调参数，以量化聚合物质量的 3D 纳米级变化对聚酰胺膜内水传输的影响（参见 Geise 的观点） . 他们发现局部密度的变化对膜的性能影响最大。因此，更好的合成方法可以在不影响选择性的情况下提高性能。科学，这个问题 p。72; 另见第 31 电子断层扫描揭示了孔隙分布的不均匀性如何影响水过滤膜的性能。通过依赖于膜蛋白形式的明确定义的内部纳米级结构，生物膜可以实现非常高的渗透性，同时保持理想的选择性。在这里，我们将这种设计策略应用于海水淡化膜。一系列聚酰胺脱盐膜——在工业规模的生产线上合成，加工条件不同，但保留了相似的化学成分——显示出增加的水渗透性和活性层厚度，同时氯化钠选择性不变。透射电子显微镜测量使我们能够确定纳米级三维聚酰胺密度图并以零可调参数预测水渗透率。密度波动不利于水的传输，这使得对纳米级聚酰胺不均匀性的系统控制成为在不牺牲海水淡化膜中盐选择性的情况下最大化水渗透性的关键途径。