Collaborative Research: Molecular-level Understanding of Small Molecule Transport in Glassy Polymers Exhibiting Configurational Free Volume

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Many new membrane materials have been developed in recent years; however, very few of them have made it to industrial applications, mainly due to lack of durability and robustness under realistic operating conditions. This research project aims to develop a molecular-level understanding of transport mechanisms in membrane materials and to inform the development of the next generation of membrane materials that can compete with traditional energy-intensive gas separations technologies. The types of membrane materials that will be investigated have a molecular structure that creates permanent, non-collapsible voids (free volume) in the material. The free volume is available for selective gas sorption, and the molecular structure around the voids helps the material to maintain its free volume and separation performance, unlike current separation membranes. The scientific knowledge generated by this research should enable significant advances in separation membranes that will meet the needs for a broad range of industrial applications. The research project serves as a training ground for undergraduate and graduate students to perform cutting edge research and will engage students from groups underrepresented in STEM fields. The researchers will also engage in well-structured education and outreach activities, including developing new courses, formulating educational and research components for high school students, giving presentations at a public "research night" event, and creating an educational video streaming for general public. The goal of this research project is to elucidate how conformation- and configuration-based free volume contribute, individually and synergistically, to the membrane transport properties. The research hypothesis is that configurational free volume is much more stable than conformational free volume, and thus it provides unprecedented resistance to physical aging and plasticization even under harsh conditions, i.e., at high temperature and in chemically challenging environments. Iptycene-based polymers with specifically, yet systematically, varied free volume architecture will be synthesized, and the effect of configurational free volume on molecular transport will be studied. Fundamental transport properties (i.e., sorption, diffusion and permeation) will be investigated experimentally and theoretically under both ambient and harsh conditions. Finally, atomistic simulations will be performed to elucidate the underlying transport mechanism in polymers with configuration-based free volume and the effect of nano-confinement. The outcome of this project will be improved membranes for industrial gas separations, especially under harsh conditions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.