Understanding Aromatic Motif Structure and Filtration Relationships of Polyamide Barrier Layers in Reverse Osmosis Membranes

反渗透膜包括薄的纳米多孔聚合物（聚酰胺）阻挡层，其负责在脱盐过程中从水中分离离子。聚酰胺阻挡层通常通过称为界面聚合的化学反应过程形成。聚酰胺层的分子结构取决于发生界面聚合的实验条件。了解各种工艺条件如何影响聚酰胺层的微观结构，从而影响过滤性能，可以开发出更好的反渗透膜材料。例如，具有最佳交联度和受控微结构的更具渗透性的聚酰胺阻隔层具有提高渗透性、保持高选择性和降低淡水生产成本的潜力。尽管阻挡层的技术重要性，但分子水平的结构-性能-工艺关系尚未完全显现。该项目整合了实验和计算方法，以描述反应单体，反应和加工条件以及后处理如何改变聚酰胺薄膜的结构。还将评估超高压操作对聚酰胺层分子结构的影响。 该项目预计将导致开发用于海水淡化的新型节能纳米结构材料，这将减少反渗透过程的环境和经济负担，并减轻全球水资源短缺的威胁。反渗透膜的界面聚合芳香族聚酰胺屏障层中。将完成三项研究活动。任务1将研究聚酰胺薄膜中的芳香族分子基序结构和性能之间的关系，作为界面聚合中不同反应单体和反应和加工条件的函数。任务2将检验某些溶剂可以更有效地影响聚酰胺支架的交联结构的假设，即，在链端和主链之间以不同的方式，从而产生不同的水通道分布。任务3将描述超高压反渗透过程中聚酰胺阻隔层的结构变化。一套实验和计算的方法将结合起来，揭示功能芳环和非均匀交联网络结构的形成之间的各向异性空间相互作用的新见解。将采用最先进的表征方法，包括掠入射广角和小角X射线散射和原子对分布函数使用同步辐射。分子模拟任务将应用介观耗散粒子动力学，蒙特卡罗随机反应模型，和原子分子动力学模拟方法。该项目还有望揭示通过溶剂活化后处理生产节能界面聚合阻隔层的新方法，并提高超高压反渗透工艺的脱盐效率。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Reverse osmosis membranes include a thin, nanoporous polymer (polyamide) barrier layer that is responsible for separating ions from water in desalination processes. The polyamide barrier layer is typically formed through a chemical reaction process called interfacial polymerization. The molecular structure of the polyamide layer depends on the experimental conditions under which the interfacial polymerization occurs. Understanding how various process conditions influence the polyamide layer microstructure and, thus, the filtration performance can lead to the development of better reverse osmosis membrane materials. For example, more permeable polyamide barrier layers with an optimal degree of cross-linking and controlled microstructures have the potential to improve the permeance, maintain high selectivity, and reduce the costs of freshwater generation. Despite the technical importance of the barrier layer, the molecular level structure-property-process relationships have yet to fully emerge. This project integrates experimental and computational methods to describe how reacting monomers, reaction and processing conditions, and post-treatments change the structure of the polyamide thin films. The effects of ultrahigh-pressure operation on the polyamide layer molecular structure will also be evaluated. The project is expected to lead to the development of new energy-efficient nanostructured materials for water desalination, which will reduce the environmental and economic burden of reverse osmosis processes and mitigate the threat of global water scarcity.The objective of this research is to investigate fundamental issues, concerning atomic- and molecular-scale interfacial phenomena and engineering, in interfacially polymerized aromatic polyamide barrier layers of reverse osmosis membranes. Three research activities will be completed. Task 1 will investigate aromatic molecular motif structure and property relationships in polyamide thin films as functions of different reacting monomers and reaction and processing conditions in interfacial polymerization. Task 2 will test the hypothesis that certain solvents can more effectively influence the cross-linked structure of the polyamide scaffold, i.e., in a different manner between chain ends and backbone, thus creating a different water-channel distribution. Task 3 will characterize structural changes in polyamide barrier layers by ultrahigh-pressure reverse osmosis processes. A suite of experimental and computational approaches will be combined to reveal new insights into the anisotropic steric interactions between the functional aromatic rings and the formation of inhomogeneous cross-linked network structures. State-of-the-art characterization methods will be employed, including grazing-incident wide-angle and small-angle X-ray scattering and atomic pair distribution function using synchrotron radiations. The molecular modeling tasks will apply mesoscopic dissipative particle dynamics, Monte Carlo with stochastic reaction model, and atomistic molecular dynamic simulations methods. This project is also expected to reveal new approaches to produce energy-efficient interfacial polymerization barrier layers through solvent activation post-treatment and improve the desalination efficiency of ultrahigh-pressure reverse osmosis processes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.