Design and Synthesis of New Type I Bicontinuous Cubic Lyotropic Liquid Crystal Monomers Based on the Gemini Framework for Molecular-Size Separation Applications

Wiesenauer, Brian R.

Graduate Thesis Or Dissertation

Design and Synthesis of New Type I Bicontinuous Cubic Lyotropic Liquid Crystal Monomers Based on the Gemini Framework for Molecular-Size Separation Applications Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/ng451h67c

Abstract

The overall objective of this thesis research was the design and synthesis of new type I bicontinuous cubic (Q_I) phase-forming, gemini-shaped lyotropic liquid crystal (LLC) monomers for the preparation of nanoporous polymer membrane materials. These new Q_I -phase LLC monomers were designed to overcome several shortcomings of previously developed Q_I -phase LLC monomers in the Gin research group that include expensive and difficult synthesis, poor film processibility, and limited blendability with additives. The first method for obtaining this objective was the synthesis of six homologues of a new gemini ammonium LLC monomer, two of which exhibit a Q_I phase with water. Both of these LLCs form a robust Q_I phase such that a gel of these materials can be fully infused into a microporous support membrane and then cross-linked to maintain the LLC phase structure. The resulting Q_I -phase polymer film showed a uniform pore size of 0.86 nm in water nanofiltration and desalination experiments. This Q_I monomer platform is less costly and less rigorous to synthesize than previously synthesized phosphonium-based gemini Q_I LLC monomers. These new LLC monomers also have the ability to blend with the hydrophobic, commercially available cross-linkable elastomer vinyl-EPDM (v-EPDM) to form breathable composite barrier materials. In the appropriate composition, melt-infused gemini ammonium monomer/v-EPDM polymer membranes exhibit extremely high pure water vapor fluxes, and high rejection of toxic industrial chemical vapors. A new cross-linkable gemini LLC monomer based on charged imidazolium units was also developed that forms a Q_I phase with glycerol. This new LLC monomer can be solution-cast from MeOH and UV-irradiated to form cross-linked thin-film composite Q_I membranes with slightly larger effective pore size (0.96 nm) than the previous systems. A related goal of this thesis research was to develop methods for systematically tuning the effective pore size of nanoporous Q_I polymer-based materials by using glycerol-based LLC monomer/monomer blends. While a number of these LLC monomer/monomer blends exhibited potential Q_I phases in glycerol, the Q_I LLC phases formed were only relatively stable in the bulk state. Unfortunately, attempts to cross-link these Q_I phase monomer/monomer blends resulted in a small degree of phase disruption and phase separation.

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