Preparation and Applications of Polymeric Ultrafiltration Membranes Fabricated through the Mixed Solvent Phase Separation (MSPS) Method

The importance of ultrafiltration (UF) membranes is often undervalued due to their larger pore sizes and broader selectivity, which has led to their common perception as merely support layers for composite membranes, overshadowing their numerous standalone applications. However, UF membranes find diverse applications in water treatment, pharmaceutical purification, biomedical separations, and food and beverage processing, and more. Ongoing developments in materials, fabrication, and process optimization continue to advance the field. Membranes with highly porous and orderly structures are particularly desirable to maximize both selectivity and permeability. UF membranes are most commonly fabricated using phase inversion processes, with the non-solvent induced phase separation (NIPS) and thermally-induced phase separation (TIPS) methods being the most widely adopted methods due to their simplicity and broad applicability. Despite these advantages, membranes fabricated through NIPS and TIPS often suffer from a broad pore size distribution. Various methods exist for creating uniform porous membranes, such as block copolymer self-assembly, track etching, breath figure templating, and lithography. However, these approaches face significant limitations for scale-up, including high processing costs, complex procedures, and material sensitivity. To address these shortcomings while maintaining simplicity and cost efficiency, our group developed the mixed solvent phase separation (MSPS) method. The MSPS method is a modified approach to conventional phase inversion which utilizes the thermodynamics of a mixed solvent system to generate a wide array of arranged porous structures. This work aims to prepare highly porous membranes through the MSPS process and evaluate their performance in three critical applications: oily water separation, desalination via direct contact membrane distillation (DCMD), and extracorporeal membrane oxygenation (ECMO). To meet the specific requirements of each application, three distinct polymer-solvent systems were developed. The resulting membranes were comprehensively characterized and tested in their respective applications, with particular focus on elucidating structure-performance relationships. In addition, the scalability of the MSPS process is demonstrated through the fabrication of large-scale PVDF membranes.