UC Berkeley

The rational design of microporous membrane materials enables exceptional control over the pore-network architecture, pore-wall chemistry, and structural rigidity that together dictate selective mass transport. These materials, which vary in structure from randomly packed microporous polymers to highly ordered porous crystals, discriminate between permeating species based on their size as well as their chemical and physical properties. Microporous membranes are not only a promising answer to the economic and environmental costs associated with industrial chemical separations but also a means to enhance the feasibility of incipient clean-energy technologies from carbon capture to electrochemical energy storage. In this dissertation, I discuss the chemical synthesis, membrane fabrication, and performance of state-of-the-art membrane materials to investigate the underlying structure-property relationships tying chemical design to selective mass transport.

In the first part of this dissertation, I describe my work advancing pure polymer membranes through the production of exceptionally rigid backbone chemistries. I present novel thermally rearranged polymer membranes that feature Tröger’s base units as highly rigid sites of contortion along the polymer backbone. This rigidity enhances diffusive selectivity without sacrificing flux, challenging the permeability-selectivity tradeoffs inherent to polymer membranes. The Tröger’s base thermally rearranged polymer membranes exhibit state-of-the-art performance for air separations.

In the second part of the dissertation, I discuss metal-organic framework (MOF)/polymer composites towards overcoming the permeability/selectivity tradeoffs inherent to pure polymers. First, I demonstrate an alternative synthesis of M2(dobpdc), a family of phase-change adsorbent MOFs, that allows for control over the crystal size down to the nanoscale. Then I demonstrate that incorporating the amine-appended nano mmen-M2(dobpdc) into a polymer membrane selectively increases the CO2 permeability. Subsequently, I describe the growth of sub-micron MOF films at a porous polymer surface through the chemical conversion of sacrificial metal-oxide nanocrystals. Layered membranes can access the full potential of the molecular-sieving crystalline components without sacrificing the processability of the underlying polymer layer.

In the final part of this dissertation, I discuss my work characterizing polyelectrolyte binders for controlled ion transport in sulfur cathodes. In this system, unwanted mass transport of polysulfide components is hindered through strong attractive interactions with an ionically charged polymer binder. I ascertain the nature of those interactions through the use of synchrotron X-ray absorption spectroscopy which, when coupled with predictive molecular dynamics simulations, reveals that the polysulfides ring open to crosslink the binder chains.