Abstract Understanding the transport resistance of water molecules in polyamide (PA) reverse osmosis (RO) membranes at the molecular level is of great importance in guiding the design, preparation, and applications of these membranes. In this work, we use molecular simulation to calculate the total transport resistance by dividing it into two contributions: the interior part and the interfacial part. The interior resistance is dependent on the thickness of the PA layer, while the interfacial resistance is not. Simulation based on the 5 nm PA layer reveals that interfacial resistance is the dominating contribution (> 62%) to the total resistance. However, for real-world RO membranes with a 200 nm PA layer, interfacial resistance plays a minor role, with a contribution below 10%. This implies that there is a risk of inaccuracy when using the typical method to estimate the transport resistance of RO membranes, as this method involves simply multiplying the total transport resistance of the simulated value based on a membrane with a 5 nm PA layer. Furthermore, both the interfacial resistance and the interior resistance are dependent on the chemistry of the PA layer. Our simulation reveals that decreasing the number of residual carboxyl groups in the PA layer leads to decreased interior resistance; therefore, the water permeability can be improved at no cost of ion rejection, which is in excellent agreement with the experimental results.

中文翻译：

---

聚酰胺 RO 膜中水传输阻力的分子模拟：界面和内部贡献

摘要 从分子水平了解水分子在聚酰胺（PA）反渗透（RO）膜中的传输阻力对于指导这些膜的设计、制备和应用具有重要意义。在这项工作中，我们使用分子模拟来计算总传输阻力，将其分为两个部分：内部部分和界面部分。内部电阻取决于 PA 层的厚度，而界面电阻则不是。基于 5 nm PA 层的模拟表明，界面电阻是总电阻的主要贡献 (> 62%)。然而，对于具有 200 nm PA 层的真实 RO 膜，界面电阻起次要作用，其贡献低于 10%。这意味着使用典型方法来估计 RO 膜的传输阻力时存在不准确的风险，因为该方法涉及简单地乘以基于具有 5 nm PA 层的膜的模拟值的总传输阻力。此外，界面电阻和内部电阻均取决于 PA 层的化学性质。我们的模拟表明，减少 PA 层中残留羧基的数量会导致内阻降低；因此，可以在不以离子排斥为代价的情况下提高透水性，这与实验结果非常吻合。因为该方法涉及简单地乘以基于具有 5 nm PA 层的膜的模拟值的总传输阻力。此外，界面电阻和内部电阻均取决于 PA 层的化学性质。我们的模拟表明，减少 PA 层中残留羧基的数量会导致内阻降低；因此，可以在不以离子排斥为代价的情况下提高透水性，这与实验结果非常吻合。因为该方法涉及简单地乘以基于具有 5 nm PA 层的膜的模拟值的总传输阻力。此外，界面电阻和内部电阻均取决于 PA 层的化学性质。我们的模拟表明，减少 PA 层中残留羧基的数量会导致内阻降低；因此，可以在不以离子排斥为代价的情况下提高透水性，这与实验结果非常吻合。