Controlling the Dynamics of Microstructure Formation in Mixed-Matrix Polymeric-Particle Membranes

Citation

Ford, Rachel Rae (2021) Controlling the Dynamics of Microstructure Formation in Mixed-Matrix Polymeric-Particle Membranes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/fqgq-vd04. https://resolver.caltech.edu/CaltechTHESIS:04192021-200916929

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—but 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—namely, that polymers with different functions often do not mix—the 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.

In 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.

Thesis Files