Membrane technology is uniquely suited to meet the growing need for more sustainable processes due to membranes\u2019 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.
\r\n\r\nIn 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.
\r\n\r\nCapture of pathogens from complex fluids, such as blood, has received substantial attention due to rising rates of sepsis and antibiotic resistance. \tIn 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.
", "doi": "10.7907/9w23-ax66", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14123", "collection": "thesis", "collection_id": "14123", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04192021-200916929", "type": "thesis", "title": "Controlling the Dynamics of Microstructure Formation in Mixed-Matrix Polymeric-Particle Membranes", "author": [ { "family_name": "Ford", "given_name": "Rachel Rae", "orcid": "0000-0001-9844-1557", "clpid": "Ford-Rachel-Rae" } ], "thesis_advisor": [ { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Diallo", "given_name": "Mamadou S.", "clpid": "Diallo-Mamadou-S" } ], "thesis_committee": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Wei", "given_name": "Lu", "clpid": "Wei-Lu" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Diallo", "given_name": "Mamadou S.", "clpid": "Diallo-Mamadou-S" } ], "local_group": [ { "literal": "Resnick Sustainability Institute" }, { "literal": "div_chem" } ], "abstract": "Polymer membranes are increasingly important in energy generation, water purification, and resource recovery. Control over chemistry, morphology, and mechanical properties gives organic polymers unparalleled advantages for membrane technology\u2014but only if these complementary functions can be married into a cohesive material. Herein I have sought to expand upon the chemical tools for integrating diverse polymers into multifunctional membrane materials, making them easily tunable to various applications. To overcome a fundamental challenge in polymer science\u2014namely, that polymers with different functions often do not mix\u2014the functional polymer is grown in situ in a solution containing a preformed scaffold polymer, a method pioneered by co-advisor Mamadou Diallo. The hierarchical structure of the resulting mixed matrix polymeric-particle (M2P2) membrane is governed by the kinetic competition between polymerization and phase separation of the functional polymer from the scaffold polymer. This competition is quenched by immersion in a nonsolvent, which rapidly solidifies the material to trap the metastable structure formed during synthesis.
\r\n\r\nIn my quest to understand how these competing processes interact to inform multifunctional membrane design, I developed a general method for studying transient structure using ultra-small angle neutron scattering (Chapter II), working closely with Kornfield Group alumnus Dr. Joey Kim. I then investigated the synergistic effects of incorporating different functional polymer architectures in M2P2 membranes (Chapter III), working with fellow graduate student Orland Bateman. By combining low-generation dendrimers with randomly hyperbranched oligomers bearing similar chemical functionality, we can systematically tune the characteristic length of domains formed during synthesis. In the final chapter I discuss the main conclusions and describe future directions for understanding structure during processing in M2P2 membranes. My thesis ultimately provides a broadly relevant platform for membrane design and synthesis, one in which the favorable properties of different polymers may be combined to strike a balance between function, stability, and ease of fabrication.
", "doi": "10.7907/fqgq-vd04", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" } ]