Liquid crystals of neat boron nitride nanotubes and their assembly into ordered macroscopic materials

Abstract

Boron nitride nanotubes (BNNTs) have attracted attention for their predicted extraordinary properties; yet, challenges in synthesis and processing have stifled progress on macroscopic materials. Recent advances have led to the production of highly pure BNNTs. Here we report that neat BNNTs dissolve in chlorosulfonic acid (CSA) and form birefringent liquid crystal domains at concentrations above 170 ppmw. These tactoidal domains merge into millimeter-sized regions upon light sonication in capillaries. Cryogenic electron microscopy directly shows nematic alignment of BNNTs in solution. BNNT liquid crystals can be processed into aligned films and extruded into neat BNNT fibers. This study of nematic liquid crystals of BNNTs demonstrates their ability to form macroscopic materials to be used in high-performance applications.

Lyotropic Boron Nitride Nanotube Liquid Crystals: Preparation, Characterization, and Wet-Spinning for Fabrication of Composite Fiber

“…The mechanical strength of the P(VP-r-QVI)/ BNNT composite microfiber was about 16.3 times stronger than the best one prepared from BNNT LCs with CSA. 39 Hence, it was strong enough to hold a coin with a mass of 4.2 g (Figure 4D) and flexible enough to be knotted (Figure S11B in the Supporting Information). The enhanced tensile strength of the P(VP-r-QVI)/BNNT composite microfiber was mainly due to the good alignment and high packing density of the BNNTs, resulting in high friction and stress transfer among neighboring BNNTs, as shown in the top SEM image of Figure 4E, which is taken after removal of the polymeric matrix by combustion.…”

“…As a result, the lab-scale bucky paper, which is only limited to thin films fabricated using the vacuum filtration of BNNT dispersion, has been considered an efficient way to prepare structural BNNT films and polymeric composites . Therefore, material processing methods to prepare highly concentrated dispersion of BNNTs (or dope) should be developed as soon as possible to facilitate related research and industrial productions of multifunctional structural materials like films or textiles (fibers), which can be directly used in piezoelectric, radiation shielding, heat management, and high-temperature ceramic composite applications. ,,, Furthermore, alignment control of BNNTs inside films or textiles should also be developed to provide additional opportunities to realize both direction-dependent functionalities and performance improvements, as demonstrated by an enhancement of electroactive characteristics of aligned BNNTs. , Very recently, Simonsen Ginestra et al achieved a great step for preparing the lyotropic BNNT LCs and neat BNNT microfibers using CSA . However, several issues have persisted, such as the low mechanical property of the spun microfiber, the use of a toxic strong acid, and the lack of understanding of the rheological properties of the BNNT LCs, which need to be addressed for the implementation of BNNT LCs and microfibers in future industrial applications.…”

“…20,37 Very recently, Simonsen Ginestra et al achieved a great step for preparing the lyotropic BNNT LCs and neat BNNT microfibers using CSA. 39 However, several issues have persisted, such as the low mechanical property of the spun microfiber, the use of a toxic strong acid, and the lack of understanding of the rheological properties of the BNNT LCs, which need to be addressed for the implementation of BNNT LCs and microfibers in future industrial applications. Furthermore, in addition to the neat BNNT macroscopic materials, a facile fabrication method for polymeric composite BNNT microfibers, which can synergistically improve the functionality of the fibers, should also be developed to open up new applications of BNNTs.…”

“…20 Therefore, material processing methods to prepare highly concentrated dispersion of BNNTs (or dope) should be developed as soon as possible to facilitate related research and industrial productions of multifunctional structural materials like films or textiles (fibers), which can be directly used in piezoelectric, radiation shielding, heat management, and high-temperature ceramic composite applications. 18,39,41,42 Furthermore, alignment control of BNNTs inside films or textiles should also be developed to provide additional opportunities to realize both direction-dependent functionalities and performance improvements, as demonstrated by an enhancement of electroactive characteristics of aligned BNNTs. 20,37 Very recently, Simonsen Ginestra et al achieved a great step for preparing the lyotropic BNNT LCs and neat BNNT microfibers using CSA.…”

Scalable, Highly Pure, and Diameter‐Sorted Boron Nitride Nanotube by Aqueous Polymer Two‐Phase Extraction

“…The anisotropic, rod‐like nature of BNNT forms a lyotropic liquid crystal phase when dispersed in an appropriate medium. [ 18 ] We prepared an SC dispersion (1 wt.%) of the purified BNNT at a BNNT concentration of 1 mg mL −1 , using a bath sonicator. To reach a sufficient concentration for the liquid crystal formation, we evaporated the water to give a nominal BNNT concentration of ≈ 7 wt.%.…”