(262b) Liquid Crystalline Phase Behavior of Boron Nitride Nanotube Aqueous Dispersion

Boron nitride nanotubes (BNNTs), one-dimensional nanomaterials, possess a remarkable combination of mechanical, thermal, and optical properties that are incomparable with other materials. Their ability to self-assemble into long-range ordered domains, at high concentrations in different solvents, opens up exciting possibilities for the development of novel functional materials and devices with unprecedented properties and performance. However, obtaining highly concentrated and stable dispersions of BNNTs in different solvents remains a challenge due to the strong van der Waals attractions between adjacent nanotubes and the presence of large quantities of non-tubular impurities in the as-synthesized BNNTs. In this study, we announce the successful preparation of surfactant-assisted highly concentrated BNNT aqueous liquid crystalline dispersions, up to 18 mass% BNNTs. Polarized light microscopy (PLM) reveals the Schlieren texture of highly birefringent nematic liquid crystals. We identify the critical concentrations of BNNTs at which the phase transitions occur, which can aid in the design and optimization of BNNT-based materials. This study demonstrates that aqueous BNNT liquid crystals can be processed into transparent thin films. Scanning electron microscopy (SEM) and PLM reveal high BNNT alignment in the shearing direction, demonstrating control of macroscopic morphology and structure. The successful synthesis of highly concentrated BNNT aqueous liquid crystalline dispersions represents a significant advancement in the field and paves the way for the development of novel BNNT macroscopic materials for textiles, thermal management, electrical insulation, biomedical, and aerospace applications.