Establishing Liquid Crystals of Boron Nitride Nanotubes for Aligned Assemblies

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Manufacturing strong and multifunctional nanomaterial-based films and fibers with improved alignment and properties enables many applications, including thermal management materials and protective fabrics. Lyotropic liquid crystals of nanomaterials with long-range order and fluidity are recognized as a promising precursor to produce solid assemblies with improved alignment and performance. This award supports fundamental research to provide the framework for establishing liquid crystals of boron nitride nanotubes – a lightweight nanomaterial with excellent thermal conductivity while being an electrical insulator. These material properties meet the critical need for manufacturing electrically insulating thermal interface materials for the next generation electronics and solar cells as well as high strength fibers for protective textiles. Aligned assemblies from this new material system are desirable for a wide array of applications from electronics, energy, aerospace, defense, to thermal packaging industries. Therefore, results from this research will benefit the U.S. economy and society. This research involves several disciplines including manufacturing, liquid crystal science, nanotechnology, and engineering. The multidisciplinary approach will simultaneously advance scientific discovery and a broadly inclusive, innovative, next-generation science and engineering workforce.The liquid crystals of boron nitride nanotubes for manufacturing aligned assemblies have not yet been achieved. This research is to fill the knowledge gap on the liquid crystalline phase behavior and the controlled assembly of boron nitride nanotube films and fibers with ordered structures for performance improvement. The cellulose nanocrystal matrix – a renewable and low-cost nanomaterial that is known to form chiral nematic liquid crystals – will be utilized as a structural template for forming liquid crystals of boron nitride nanotubes. Additionally, stable liquid dispersions of boron nitride nanotubes will be achieved by noncovalent complexation with biopolymers. This approach will preserve the intrinsic properties of nanotubes and further stabilize them in cellulose nanocrystal dispersions. The phase transition of liquid crystals will be investigated by rheology and optical microscopy and the assembled films and fibers will be characterized by various imaging techniques, mechanical testing, and thermal conductivity measurements. Combined, this research will test the broad hypothesis that lyotropic, chiral nematic liquid crystals can be obtained from the cellulose nanocrystal-templated nanotube system and the ordered liquid crystalline structures can be translated into solid assemblies for property enhancement, thus establishing the structure-processing-property relationships of the new nanomaterial system.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.