Fundamental Investigation of Surfactant-Assembly-Regulated Interfacial Polymerization (SARIP) for Fabricating Next-Generation Membranes for Precise Solute-Solute Separation

膜在工业中用于从混合物（溶液）中分离组分。大多数膜用于从溶液中去除溶质（溶解的分子）。例如，废水处理过程有时使用膜来去除污染物，并且海水淡化通常涉及使用反渗透膜来从海水中去除盐。膜也可以用来将溶质彼此分离，这被称为“分子筛”。“分子筛是制药、石化和能源行业的重要分离工艺。例如，从海水或盐水中提取锂（电池的重要材料）需要高精度的分子筛。能够选择性地分离化学上相似的溶质的膜具有大体积和低成本制造的挑战性。一个主要的挑战是分子筛膜必须具有非常小的孔，小于纳米，尺寸均匀。研究人员计划开发一种通过化学控制孔径均匀性来制造分子筛膜的适应性方法。该方法将容易获得的化学品（表面活性剂和单体）结合在支撑材料层上方的油-水界面处。表面活性剂与油和水的相互作用导致表面活性剂在两者之间积聚。积聚的表面活性剂自发地形成柔性孔的网络，其允许单体通过到达载体材料。单体随后形成包含膜的均匀孔层。膜结构和化学成分，以及它们形成的过程，将被描述为了解这种方法是如何工作的。这种用于形成均匀的亚纳米聚合物孔的方法预计是廉价、高效的，并且与用于膜制造的现有基础设施兼容。该项目的成果将迅速推动膜技术和分离科学的发展，取代能源密集型和昂贵的工业分离方法。该项目还将通过范德比尔特暑期学院为高中生提供教育机会，包括本科生研究经验、研究生和本科生课程指导以及实践研讨会。该项目的目标是开发一种通用方法，用于通过界面聚合在纳滤膜的聚酰胺活性层中形成高度均匀的孔（自由体积）。研究人员假设，界面聚合过程可以通过在己烷/水界面引入动态自组装的、高度组织化的表面活性剂“网络”来调节，这有望导致形成具有增强的孔径均匀性的聚酰胺活性层。进一步预期孔径的均匀性将导致具有用于精确溶质-溶质分离的超锐选择性的膜。研究人员称这种新方法为表面组装调节界面聚合（SARIP）。研究人员将通过三个研究目标来验证这一假设并揭示伴随的机制。第一个目标的重点是证明，选定的表面活性剂可以锐化薄膜复合聚酰胺（TFC-PA）膜的选择性。将评估具有不同亲水电荷基团或不同长度的疏水尾部的表面活性剂。其次，研究人员将评估表面活性剂官能团和结构对SARIP形成的TFC-PA纳滤膜材料性质和性能的影响。最后，将确定在不存在和存在聚合（与酰氯）的情况下，表面活性剂自组装对胺在己烷/水界面上扩散的动力学的影响。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。

Membranes are used in industry to separate components from a mixture (a solution). Most membranes are used to remove solutes (dissolved molecules) from the solution. For example, wastewater treatment processes sometimes use membranes to remove contaminants, and seawater desalination often involves using a reverse osmosis membrane to remove salts from seawater. Membranes can also be used to separate solutes from each other, which is called "molecular sieving." Molecular sieving is an important separation process for the pharmaceutical, petrochemical, and energy industries. For example, membrane-based extraction of lithium (an important material for batteries) from seawater or brine requires high-precision molecular sieving. Membranes capable of selectively separating chemically similar solutes are challenging to manufacture in large volumes and at low cost. A primary challenge is that molecular sieve membranes must have exceedingly small pores, less than a nanometer, that are uniform in size. The investigators plan to develop an adaptable method for manufacturing molecular sieve membranes by chemically controlling pore size uniformity. The method combines readily available chemicals (surfactants and monomers) at an oil-water interface above a layer of support material. The interactions of the surfactants with both the oil and water causes the surfactants to accumulate in between the two. The accumulated surfactant spontaneously forms a network of flexible pores that allow the monomers to pass through to the support material. The monomers subsequently form a homogenous layer of pores comprising the membrane. The membrane structure and chemical composition, as well as the processes by which they are formed, will be characterized to understand how the approach works. This method for forming uniform, sub-nanometer polymer pores is expected to be both inexpensive, efficient, and compatible with existing infrastructure for membrane manufacturing. The outcomes of this project will rapidly advance the current state-of-the-art in membrane technology and separation science, serving to displace more energy-intensive and costly industrial separation methods. The project will also provide educational opportunities including undergraduate research experiences, graduate and undergraduate course-based instruction, and hands-on workshops for high school students through the Vanderbilt Summer Academy.The goal of this project is to develop a universal approach for forming highly uniform pores (free volume) in the polyamide active layer of nanofiltration membranes formed via interfacial polymerization. The investigators hypothesize that the interfacial polymerization process can be regulated by introducing a dynamically self-assembled, highly organized "network" of surfactants at the hexane/water interface, which is expected to result in the formation of a polyamide active layer with enhanced pore-size homogeneity. The uniformity in pore size is further expected to result in membranes with ultra-sharp selectivity for precise solute-solute separations. The investigators call this novel approach surfactant-assembly-regulated interfacial polymerization (SARIP). The investigators will test the hypothesis and uncover the attendant mechanisms through three research objectives. The first objective focuses on demonstrating that selected surfactants can sharpen the selectivity of thin film composite polyamide (TFC-PA) membranes. Surfactants with different hydrophilic charge groups or hydrophobic tails of varying length will be evaluated. Second, the investigators will assess the impact the surfactant functional groups and structures have on the SARIP-formed TFC-PA nanofiltration membrane material properties and performance. Finally, the impact of surfactant self-assembly on the kinetics of amine diffusion across the hexane/water interface in the absence and presence of polymerization (with acid chloride) will be determined. The development of a universal, scalable approach for fabricating membranes with highly uniform free volumes is expected to advance membrane technologies for sub-nanometer scale solute separations.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.