Boron Nitride Nanotubes Assist the Self-Assembly of Spherical Cholesteric Liquid Crystal Shells of Cellulose Nanocrystals in Water.

Spherical confinement of cholesteric liquid crystal (ChLC) droplets is emerging as an intriguing approach for achieving complex ordered structures for photonic applications and beyond. Previously, this has been achieved primarily through microfluidic assembly utilizing immiscible solvents or immiscible mesogen-solvent systems, such as oil-water or thermotropic liquid crystal-water systems, respectively. Here, we show the spontaneous assembly of spherical ChLC droplets with isotropic cores from lyotropic liquid crystals of mixed nanorods containing boron nitride nanotubes (BNNTs) and cellulose nanocrystals (CNCs) in all-aqueous environments. We show that the mixing of as low as 0.094 vol % of pectin-coated BNNTs with isotropic dispersions of 3.20 ± 0.04 vol % of CNCs enables the self-assembly of spherical ChLC droplets of micrometer size in water. This is potentially caused by the larger-aspect-ratio BNNTs modulating the overall nanorod alignment within the cholesteric shell of the resulting liquid crystal-in-water system of BNNT/CNC mixtures. Specifically, the size and negative charge of pectin-coated BNNTs are compatible with the negatively charged CNC template. By slightly increasing the BNNT concentration up to 0.121 vol %, we observed the thickness of ChLC shells to grow by roughly 53%, suggesting a synergistic liquid crystal phase behavior in BNNT/CNC mixtures. These findings provide important insights into the scalable, water-based self-assembly of mixed nanorod systems with integrated properties in a spherical confinement, broadening applications for photonics, biochemical sensing, optical films, and nanomaterial templating.