Stimuli-Responsive Membranes from Mesophase Templating

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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.