Stimuli-Responsive Membranes from Mesophase Templating

水资源短缺是当今世界面临的一个主要问题。随着世界人口的持续增长，水资源变得越来越稀缺，尤其是像美国西南部这样的干旱和半干旱地区的微咸水，要想获得低成本、节能和环境可持续的高级水处理方法，就需要开发和表征新的膜技术。水处理过程通常使用几种类型的膜，包括微滤、超滤、纳滤和反渗透膜。超滤膜在去除悬浮颗粒、病毒和细菌方面起着关键作用。超滤膜也是最常用的分离技术之一，应用于食品加工、化学制造和蛋白质纯化。尽管与工业相关，超滤膜是通过一种称为非溶剂诱导相分离（NIPS）的方法生产的，这需要使用大量的有机溶剂。NIPS工艺生产的膜也具有各向异性，表面孔隙率低，导致膜表面的污垢增加。该项目的总体目标是通过具有成本效益的绿色化学方法开发超滤膜，同时提高其渗透性，以降低水处理的成本和能源。通过本科生研究机会和研究相关课程材料的开发，研究和教育被整合到该项目中。污染的控制，特别是生物污染的控制，一直是污水和水处理研究的一个主要焦点。然而，许多先前提出的克服污垢的方法既不具有成本效益，也无法扩展到不同的化学结构和聚合物。由于过滤过程会导致膜污染，随着时间的推移会减少通量，因此可以利用表面洗涤过程来清洁膜的表面。然而，NIPS膜的低表面孔隙率加剧了污染，不能通过反冲洗完全去除。反冲洗也是过滤过程中一个主要的能耗步骤。需要具有(i)提高渗透性和减少污垢，而不影响排污率的超滤膜，以及（ii）刺激响应行为以帮助表面洗涤的超滤膜。在不需要合成新的或昂贵的化学物质的情况下，以环保的方式生产这些膜的能力仍然是一个突出的技术挑战。PI建议使用无有机溶剂模板方法来解决这些挑战，以生产用于超滤应用的纳米多孔聚合物。两亲嵌段共聚物在含有单体的水和油相的混合物中自组装将用作模板。油相的单体在聚合时，由于疏水性的改变，在温度和pH刺激下会发生构象变化。这种膜的孔径可以通过控制分子量切断和抗污染行为来实现。由于与现有的超滤膜技术相比，纳米级孔隙的密度更高，可以均匀地融入聚合物中，因此该方法生产的膜的渗透性也有望超过商业产品，而不会影响废品率。膜结构将使用偏振光显微镜，小角度x射线散射和透射电子显微镜进行表征。渗透率、分子量切断、结垢和溶质截留将通过压力驱动过滤实验进行检验。该研究结果将为通过绿色化学方法制备具有刺激响应孔的高渗透超滤膜提供基础知识。该奖项反映了美国国家科学基金会的法定使命，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。

Water scarcity is a major issue facing the world today. As the world population continues to grow, water resources become scarcer, particularly brackish water in arid and semi-arid regions such as the southwestern U.S. Adequate access to low-cost, energy-efficient, and environmentally sustainable methods for advanced water treatment requires development and characterization of new membrane technologies. Water treatment processes typically use several types of membranes, including microfiltration, ultrafiltration, nanofiltration, and reverse osmosis membranes. Ultrafiltration membranes play a key role in the removal of suspended particles, viruses, and bacteria. Ultrafiltration membranes are also among the most commonly employed separation techniques, with applications in food processing, chemical manufacturing, and protein purification. Despite their industrial relevance, ultrafiltration membranes are produced by a method called non-solvent induced phase separation (NIPS), which requires the use of large quantities of organic solvents. Membranes produced by the NIPS process are also anisotropic with low surface porosity, leading to increased fouling on the surface of the membrane. The overall goal of this project is to develop ultrafiltration membranes through cost-effective green chemistry, while simultaneously increasing their permeability, to reduce the cost and energy of water treatment. Research and education are integrated in the project through undergraduate research opportunities and the development of research-related course materials. Fouling control, particularly the control of biofouling, has been a major focus of wastewater and water treatment research. However, many previously proposed methods to overcome fouling are neither cost-effective nor extensible to different chemical structures and polymers. Since filtration processes result in membrane fouling that reduces the flux over the time, a surface washing process can be utilized to clean the surface of a membrane. However, the low surface porosity of NIPS membranes intensifies the fouling, which cannot completely be removed through backwashing. Backwashing is also a major energy consumption step in filtration. Ultrafiltration membranes with (i) improved permeability and decreased fouling, without compromising the rejection rate, and (ii) stimuli-responsive behavior to aid in surface washing are needed. The ability to produce these membranes in an eco-friendly manner without the need to synthesize new or costly chemicals also remains an outstanding technological challenge. The PI proposes to address these challenges using an organic-solvent-free templating approach to produce nanoporous polymers for ultrafiltration applications. Amphiphilic block copolymer self-assembly in mixtures of water and an oil phase containing monomers will be used as a template. Monomers in the oil phase, upon polymerization, undergo a conformation-change response to temperature and pH stimuli due to change in hydrophobicity. The pore size of such membranes can be manipulated for controlling the molecular weight cut-off and anti-fouling behavior. Because a higher density of nanometer-sized pores can be uniformly incorporated into the polymers relative to existing ultrafiltration membrane technology, the permeability of membranes produced from this method is also expected to exceed that of commercial products without compromising the rejection rate. Membrane structure will be characterized using polarized light microscopy, small angle X-ray scattering, and treansmission electron microscopy. Permeability, molecular weight cut-off, fouling, and solute rejection will be examined through pressure-driven filtration experiments. The outcome of the study will be foundational knowledge for making high-permeability ultrafiltration membranes with stimuli-responsive pores through a green-chemistry approach.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.