Purification and Assembly of DNA-Stabilized Boron Nitride Nanotubes into Aligned Films

Abstract

The liquid phase processing including dispersion, purification, and assembly of boron nitride nanotubes (BNNTs) is important for effectively translating unique properties of BNNTs into assembled solid materials, such as films and fibers. Short single-stranded DNA (ssDNA) has been the biopolymer of choice to achieve efficient sorting and assembly of carbon nanotubes, which are structural analogues to BNNTs. Here, we demonstrated a highly efficient aqueous dispersion of BNNTs using (GT)20 ssDNA and the subsequent removal of non-nanotube impurities from dispersions of as-synthesized BNNT material by a membrane filtration approach. The surface coating of BNNTs by DNA creates uniform dispersions at a nanotube concentration of as high as ≈11.5 mass %, leading to the formation of solid aligned films after solvent evaporation without applied shear, therefore demonstrating the first example of BNNT films produced by spontaneous alignment of nanotubes. Our findings provide important insights for producing macroscopic assemblies of aligned BNNT films for potential applications in thermal interface material and electronic and optoelectronic devices.

Interaction of DNA-Complexed Boron Nitride Nanotubes and Cosolvents Impacts Dispersion and Length Characteristics

“…Additionally, dispersions of 1 mg/mL BNNTs by surfactants (i.e., SDS and SDC) at a final concentration of 1 mass % surfactant were prepared by bath sonication for 24 h in a total volume of 1 mL solvents including DI water and an IPA/water mixture with 50% (v/v) IPA, followed by centrifugation at 17 000 g for 90 min at 19 °C to collect supernatant samples. Comparative study of BNNT dispersions prepared by probe tip sonication was performed based on our previously reported method . Briefly, 1 mg/mL BNNTs was mixed with a total volume of 1 mL of aqueous solution of either 1 mg/mL DNA or 1 mass % of surfactant (i.e., SDC or SDS) and tip-sonicated (model VCX 130, Sonics and Materials, Inc.) in an ice bath for 1 h at a power level of 8 W using a 2 mm diameter probe.…”

“…A stock solution of 10 mass % SDC in DI water was prepared for the DNA/surfactant-exchange reaction of BNNTs. First, solvent exchange was performed by membrane filtration for the stock sample prepared from DNA–BNNT dispersions in an IPA/water mixture with 50% (v/v) IPA using a Microcon centrifugal filter with a molecular weight cutoff (MWCO) of 30 kDa according to our previously reported procedure . After membrane filtration, DNA–BNNT complexes were redispersed in DI water.…”

“…Covalent modification causes permanent and unwanted changes in the B–N lattice structure from sp 2 to sp 3 orbital hybridization that often leads to the deterioration of nanotube properties. , In comparison, noncovalent complexation of BNNTs with surfactants, polymers, small molecules, and biomolecules (often assisted by sonication) has proven to be a simple way of dispersing BNNTs in various solvents, including water. These aqueous dispersions are important for many applications, particularly in biology. − Alternatively, chlorosulfonic acid has been proven to be capable of dispersing BNNTs without the aid of dispersants or sonication due to its optimal interactions with the nanotube surface. , Other promising solvents include dimethyl formamide (DMF), ethanol (EtOH), and isopropyl alcohol (IPA), all of which require the assistance of sonication . Solvents containing amide or hydroxyl groups induce hydrogen-bonding interactions with BNNTs, which exhibit an electron deficiency of B atoms due to partially ionic B–N bonds, thereby leading to dispersion of a low concentration of BNNTs. , Various cosolvents with tunable solubility parameters have been exploited to disperse BNNTs as well; however, this method generally resulted in low-concentration dispersions with poor stability …”

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

“…Thus far, the formation of BNNT liquid crystals has not been attained, possibly because of sample impurities (e.g., hexagonal boron nitride (h-BN) and elemental boron 24 ), which hinder the individualization and alignment of BNNTs. Previous work has suggested spontaneous ordering of DNA-BNNT hybrid systems, but aligned structures were only observed in dried films of DNA-wrapped BNNTs after solvent removal by filtration 25 or evaporation 26 .…”

Boron nitride nanotubes enhance mechanical properties of fibers from nanotube/polyvinyl alcohol dispersions

“…Noncovalent complexation of BNNTs with polymers, surfactants, and biomolecules through adsorption onto the surface of nanotubes is a simple and effective way of producing liquid dispersions of BNNTs. [14][15][16] This approach preserves the intrinsic properties of nanotubes as compared to the covalent functionalization of tubes, which oen causes permanent changes in the B-N lattice structure and subsequent property deterioration. [17][18][19] In recent work, dispersions of BNNTs in solvents, including dimethyl formamide (DMF) and ethanol, have been integrated with polymer matrices to produce composites and bers.…”