Membrane technology is uniquely suited to meet the growing need for more sustainable processes due to membranes’ tailorable selectivity and energy efficiency. Efforts to further improve membrane performance and modify them for new applications have found success in academic studies with a versatile class of membranes known as mixed-matrix membranes (MMM). Mixed-matrix membranes combine the strength and controlled morphology of semicrystalline polymeric membranes with superior functionality of a separate material dispersed in the polymer matrix. The strength and toughness of the resulting membranes depends on polymer morphology, including degree of crystallinity and pore structure. Control of the membrane morphology is achieved by kinetically trapping a partially phase separated state, for example, using Nonsolvent Induced Phase Separation (NIPS) to drive liquid-liquid and solid-liquid demixing. However, the processes used to control the polymer morphology are influenced by the functional particles and can result in novel morphologies. In Chapter 2, we used a promising strategy for stably incorporating functional polymeric particles in a structural polymer matrix to investigate the role of the particles during NIPS. The interplay of functional polymeric particle loading and nonsolvent induced phase separation are examined using x-ray diffraction (to deduce the crystal morph adopted by polyvinylidene difluoride, PVDF) and scanning electron microscopy (to observe membrane morphology and the size and distribution of functional particles). We found that the interaction between nonsolvent and functional particles enables a shift in crystal phase usually not attainable with our solvent.
In addition to studying the fundamentals underlying MMM formation, we investigated two applications for novel membrane materials: purification of therapeutic antibodies and size-selective particle capture. Purification of proteins for medical use requires several chromatographic steps in order to produce solutions of sufficient purity. For many years, the gold standard in the field was resin-based packed bed chromatography; however, more recently membrane chromatography has gained prevalence due to its faster processing time, lower cost, and low operating pressure. With these advantages come the drawbacks of low binding capacity and a sensitivity to the concentration of salt ions in the solution. To address these two drawbacks, we investigated the chromatographic abilities of a modified MMM, in Chapter 3, and a novel membrane material comprising an MMM-ceramic composite, in Chapter 4. We discovered that the performance of the modified MMM is dependent on crosslinker chemistry and crosslink density. Upon optimization, the modified membrane demonstrated a binding capacity consistent with the upper range of available literature values as well as reduced sensitivity to salt. In addition, the development of the novel MMM-ceramic composite enables the use of a broader range of polymer matrix compositions for membrane chromatography.
Capture of pathogens from complex fluids, such as blood, has received substantial attention due to rising rates of sepsis and antibiotic resistance. In Chapter 5, we pursued the capture of pathogens from model fluids using the size-based separation capabilities of dendritic ceramic membranes. We found that interactions between the ceramic surface and the suspended particles played a significant role in membrane performance.</p
