Collaborative Research: Liquid Crystal-Templated Chemical Vapor Polymerization of Complex Nanofiber Networks

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Research supported by this grant generates foundational knowledge needed to develop new manufacturing processes for novel polymer films, advancing both science and technology and impacting national prosperity. Chemical vapor polymerization is a process where gas phase chemical species are reacted on surfaces to create thin polymer films. Although chemical vapor polymerization has been widely adopted by industry to create polymer coatings, e.g., for the microelectronics industry, the polymer coatings have been limited to flat films. This award supports fundamental research needed to expand the capabilities of chemical vapor polymerization to large-scale manufacturing of surface coatings with tailored nanoscopic structures, including end-attached nanofiber arrays or “nanograsses”, quasi-two-dimensional networks of interconnected nanofibers or “nanosheets”, and rigid end-attached nanofibers or “bed-of-nanonails”. Potential applications for this next generation of nanostructured coatings include improved adhesives, biomedical sensors, biomaterials for growing replacement organs, and water filtration membranes. This collaborative project provides an outstanding context for the multidisciplinary training of graduate students in next-generation manufacturing processes. The project also integrates an initiative that is focused on the engagement of veteran students in advanced manufacturing research. The scientific approach underlying this project is based on a convergence of ideas from two largely disconnected fields – liquid crystals and chemical vapor polymerization. Specifically, thin films of liquid crystals supported on surfaces are used as dynamic molecular templates to guide the formation of polymeric nanostructures via chemical vapor polymerization. The latter process is achieved by thermal sublimation and pyrolysis of paracyclophanes, which subsequently polymerize into shape-controlled nanostructures templated by the liquid crystal films. The research elucidates the chemical and physical processes that control the formation of newly discovered polymeric morphologies, e.g., nanofiber sheets, that can be accessed at scale by chemical vapor polymerization into liquid crystal films. Fundamental questions regarding the role of topological defects in liquid crystal-templated chemical vapor polymerization are investigated by using multiphase liquid crystal films containing dispersions of microparticles and immiscible oil droplets. Post-synthesis processes are also explored as an approach to achieving an expanded palette of nanostructures and functional properties, e.g., the synthesis of electrically conductive and morphologically tunable nanofiber arrays prepared via post-deposition pyrolysis. Other key aspects of the research revolve around the manufacturing of functional thin films with emergent photoluminescent, electrical, and transport properties. A unifying fundamental challenge underlying the approach is understanding how the information encoded in the atomic-scale structure, e.g., chirality, of reactive monomers is amplified across spatial scales by the liquid crystal during chemical vapor polymerization.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.