Dispersion Of Boron Nitride Nanotubes Research Articles

Understanding the role of ultrasonic cavitation assisted casting of boron nitride nanotube-reinforced aluminum matrix composite

Integrating and dispersing one-dimensional (1D) nano reinforcements in metal matrix composites (MMC) is challenging due to their higher specific surface area, strong van der Waals forces within the nano reinforcement, and poor wettability with the matrix. In the present study, ultrasonic cavitation-assisted casting was employed to fabricate boron nitride nanotubes (BNNT)-reinforced aluminum matrix composites. The ultrasonic treatment (UST) demonstrated excellent deagglomeration, and dispersion of BNNTs in molten aluminum along with enhanced grain refinement potency. A remarkable ∼62% grain refinement efficiency in Al-BNNT composite compared to pure Al was achieved owing to the combined effect of UST, BNNT reinforcement and cold rolling. The increase in low-angle grain boundaries (LAGBs) by ∼58% in Al-BNNT composite, as revealed by electron backscatter diffraction (EBSD) maps, demonstrates the pileup of dislocations resulting in strength improvement. The yield strength exhibited a 97% improvement in the BNNT-reinforced composite compared to pure Al. The strengthening is attributed to UST, enhanced dislocation density and efficient bridging effect between BNNTs and the matrix. Thus, the present study constitutes the first successful report on the role of UST in the mechanism of BNNT dispersion, grain morphology and enhanced mechanical properties, including cold rolling of BNNT-reinforced MMC. Successful dispersion of BNNTs by ultrasonic cavitation confirms that UST technology is a promising method for manufacturing high-strength nanoparticle-reinforced lightweight metal matrix composites.

Electrostabilized homogeneous dispersion of boron nitride nanotubes in wide-range of solvents achieved by surface polarity modulation through pyridine attachment

Boron nitride nanotubes (BNNTs) show exceptional physical properties including high mechanical strength and thermal conductivity; however, their applications have been restricted due to limited dispersibility in processing solvents. Here, a novel BNNT dispersion method with exceptional dispersibility in a wide range of solvents has been demonstrated by surface polarity modulation through short-molecule pyridine attachment. Nitrogen atoms in pyridine are selectively bonded to electron-deficient boron atoms of the BNNT surface through Lewis acid-base reaction, which changes the surface polarity of BNNTs from neutral to negative. Re-dispersing pyridine-attached BNNTs (Py-BNNTs) create a thick and stable electronic double layer (EDL), resulting in uniform dispersion of BNNTs in solvents with an exceptional solubility parameter range of 18.5–48 MPa1/2. The uniform dispersion of BNNTs is maintained even after the mixing with diverse polymers. Finally, composites incorporating uniformly-distributed BNNTs have been realized, and extraordinary property enhancements have been observed. The thermal conductivity of 20 wt.% Py-BNNT/epoxy composite has been significantly improved by 69.6% and the tensile strength of 2 wt.% Py-BNNT/PVA has been dramatically improved by 75.3%. Our work demonstrates a simple and facile route to dispersing BNNTs in diverse solvents, consequently leading to selective utilization of BNNT dispersed solvents in various application fields.

Chemical affinity and dispersibility of boron nitride nanotubes.

Boron nitride nanotubes (BNNTs) are electrically insulating nanoparticles that display highly competitive elastic modulus and thermal conductivity. Long presented as potential fillers for nanocomposite applications, their poor dispersibility in most commodity polymers has, however, limited their spread. In this work, the chemical affinity of purified BNNTs, measured in terms of Hansen solubility parameters (HSP), were obtained through sedimentation tests in a wide set of organic solvents, taking into account relative sedimentation time. The parameters obtained were {δd; δp; δh} = {16.8; 10.7; 14.7} ± {0.3; 0.9; 0.3} MPa1/2, with a Hildebrand parameter, δt = 24.7 MPa1/2 and a sphere radius of 5.4 MPa1/2. The solubility parameters were determined considering complete dispersion of the purified nanomaterial, as well as the viscosity and density of the host solvent. These factors, combined with the high purity of the BNNTs, are crucial to minimize the uncertainty of the HSP characterization. Such refined values provide necessary insights both to optimize the solvent casting of unmodified BNNTs, and to orient the surface modification efforts that would be needed to integrate these nanomaterials into a wider range of host matrices.

A mini-review on dispersion and functionalization of boron nitride nanotubes

Boron nitride nanotubes (BNNTs) are of intense scientific interest due to their unrivaled physicochemical characteristics, extraordinary thermal, electronic, mechanical, optical properties, and prospective applications in various nanotechnologies. Therefore, they are particular candidates for the development of new materials potentially applied in abundant applications. However, obtaining homogenous composite materials requires a good dispersion of BNNTs, as well in solvents or in the matrix, which still has remained challenging. The preparation of effective dispersions of BNNTs presents a major impediment to the extension and utilization of BNNTs. BNNTs intrinsically tend to bundle and/or aggregate. The prevention of such behavior has been explored by testing various techniques to improve the dispersibility of BNNTs in a variety of solvents. There are mainly two approaches to obtain a good quality dispersion; chemical functionalization and physical interactions. The chemical functionalization technique has been found effective, but deteriorates the intrinsic properties of BNNTs through the introduction of defects on the wall. Physical blending approaches with the ultrasound and high-speed shearing have been proven capable of debundling BNNTs and stabilizing individual BNNTs while maintaining their integrity and intrinsic properties. Attention has been brought to the study of the dispersion of BNNTs in aqueous media and most attention is paid to molecular dynamics (MD) simulation techniques and other physical techniques, as well as to the use of various surfactants and polymers.

Dispersion of Boron Nitride Nanotubes by Pluronic Triblock Copolymer in Aqueous Solution.

Boron nitride nanotubes (BNNTs) have been of interest for their excellent thermal, electrical, and mechanical properties, and they have a broad spectrum of potential applications, such as in piezoelectric materials, reinforcement of materials, and electrothermal insulation materials. For practical use of BNNTs, it is desirable to disperse them in aqueous solution, which improves convenience of handling. However, it is still difficult to make a homogenous and stable BNNT dispersion in aqueous solution, due to their strong van der Waals interactions and hydrophobic surface. To solve these problems, we used Pluronic P85 and F127, which have both hydrophilic groups and hydrophobic groups. Here, we report the wrapped structure of a Pluronic polymer-BNNT dispersion by using small-angle neutron scattering, UV–Vis spectroscopy, thermogravimetric analysis, and atomic force microscopy.

Surfactant-assisted individualization and dispersion of boron nitride nanotubes

Boron nitride nanotubes (BNNTs) belong to a novel class of material with useful thermal, electronic and optical properties. However, the study and the development of applications of this material requires the formation of stable dispersions of individual BNNTs in water. Here we address the dispersion of BNNT material in water using surfactants with varying properties. The surfactants were compared based on the quantity of BNNTs dispersed and the quality of the dispersions, as visualized by AFM and cryo-TEM. All surfactants produce dispersions of individualized or small bundles of BNNTs. Of the surfactants tested, high molecular weight, nonionic surfactants suspend the most BNNTs, while ionic surfactants remove the most h-BN impurities. The surfactant dispersions were further characterized by ensemble measurements, such as UV absorption and photoluminescence, dynamic light scattering (DLS), and zeta potential to investigate dispersion stability and quality. These techniques provide a facile strategy for testing future BNNT dispersions. The results of this study reveal that BNNT dispersions in aqueous solution can be tuned to fit a specific application through surfactant selection.

Theoretic Study on Dispersion Mechanism of Boron Nitride Nanotubes by Polynucleotides.

Due to the unique electrical and mechanical properties of boron nitride nanotubes (BNNT), BNNT has been a promising material for many potential applications, especially in biomedical field. Understanding the dispersion of BNNT in aqueous solution by biomolecules is essential for its use in biomedical applications. In this study, BNNT wrapped by polynucleotides in aqueous solution was investigated by molecular dynamics (MD) simulations. Our results demonstrated that the BNNT wrapped by polynucleotides could greatly hinder the aggregation of BNNTs and improve the dispersion of BNNTs in aqueous solution. Dispersion of BNNTs with the assistance of polynucleotides is greatly affected by the wrapping manner of polynucleotides on BNNT, which mainly depends on two factors: the type of polynucleotides and the radius of BNNT. The interaction between polynucleotides and BNNT(9, 9) is larger than that between polynucleotides and BNNT(5, 5), which leads to the fact that dispersion of BNNT(9, 9) is better than that of BNNT(5, 5) with the assistance of polynucleotides in aqueous solution. Our study revealed the molecular-level dispersion mechanism of BNNT with the assistance of polynucleotides in aqueous solution. It shades a light on the understanding of dispersion of single wall nanotubes by biomolecules.

Effects of Polydopamine Functionalization on Boron Nitride Nanotube Dispersion and Cytocompatibility.

Boron nitride nanotubes (BNNTs) have unique physical properties, of value in biomedical applications; however, their dispersion and functionalization represent a critical challenge in their successful employment as biomaterials. In the present study, we report a process for the efficient disentanglement of BNNTs via a dual surfactant/polydopamine (PD) process. High-resolution transmission electron microscopy (HR-TEM) indicated that individual BNNTs become coated with a uniform PD nanocoating, which significantly enhanced dispersion of BNNTs in aqueous solutions. Furthermore, the cytocompatibility of PD-coated BNNTs was assessed in vitro with cultured human osteoblasts (HOBs) at concentrations of 1, 10, and 30 μg/mL and over three time-points (24, 48, and 72 h). In this study it was demonstrated that PD-functionalized BNNTs become individually localized within the cytoplasm by endosomal escape and that concentrations of up to 30 μg/mL of PD-BNNTs were cytocompatible in HOBs cells following 72 h of exposure.

窒化ホウ素ナノチューブの水中分散と機能化

One-dimensional inorganic nanomaterials such as carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) are of intense scientific and technological interest due to their excellent physiochemical properties and potential applications. Because of strong van der Waals interactions and hydrophobic effects between sidewalls of the nanotubes, pristine nanotubes generally form bundled structures. This makes inorganic nanotubes difficult to incorporate into materials where individual nanotubes are required without damaging their properties. Inspired by recent successful isolation followed by functionalization of CNTs through various methods, dispersion of BNNTs towards applications has been developed via covalent and noncovalent approaches. Especially, wrapping of BNNTs by water-soluble synthetic polymers and biomolecules through weak interactions resulted in well dispersed BNNTs in aqueous solution without any changes in original physicochemical properties for biomedical applications. The nanohybrids composed of BNNTs and the polymers/biomolecules will open attractive opportunities for nanoscience and nanotechnology for next-generation hybrid materials.

Dispersion of boron nitride nanotubes in non‐aqueous solution

Boron nitride nanotubes (BNNTs) were dispersed in an ethyl alcohol solution with polyvinylpyrrolidone (PVP) and Triton X-100 (TX100) as dispersants. The influence of the dispersant content on the dispersity of BNNTs was researched. The dispersion system was characterised by means of a UV–vis spectrophotometer, scanning electron microscopy and transmission electron microscopy. The results indicated that the dispersion effect of TX100 was better than that of PVP. The optimal addition of TX100 and PVP were 3 and 2 wt%, respectively. The precipitation of BNNTs was 8.6 and 12.6% after 48 h, respectively, with PVP and TX100. The disperse mechanism of TX100 and PVP was steric hindrance stabilisation.

Dispersion of boron nitride nanotubes in aqueous solution by simple aromatic molecules.

We report that the simple aromatic molecules successfully disentangle and disperse multi-walled boron nitride nanotubes (BNNTs) in aqueous solutions through pi-pi stacking interactions. Aromatic molecules such as derivatives of naphthalene, anthracene, and pyrene were used as dispersants and components for construction of nanohybrids. Spectroscopic analyses of water-dispersed BNNTs revealed that not only numbers of aromatic rings but also substituted functional groups were essential for dispersion capabilities. It was suggested that greater numbers of aromatic rings and a carboxylic acid as the substituted group showed higher dispersion capabilities among the molecules used in this study. Detailed microscopic analyses using atomic force microscopy and transmission electron microscopy showed certain isolation capabilities of the aromatic molecules for BNNTs in aqueous solution. Moreover, fluorescence spectra indicated that BNNTs and the aromatic molecules have different electronic states after hybrid formation. Our results using the simple aromatic molecules will be utilized as a basic data for dispersion of BNNTs and construction of disentangled BNNT nanohybrids effectively.

Noncovalent functionalization of boron nitride nanotubes using water-soluble synthetic polymers and the subsequent preparation of superhydrophobic surfaces

Noncovalent functionalization of multi-walled boron nitride nanotubes (BNNTs) was achieved through water-soluble synthetic polymers wrapping. This led to the excellent disentanglement and dispersion of BNNTs in an aqueous phase. Various spectroscopic techniques revealed that π-π stacking interactions played the key role for the polymer-functionalization of BNNT. To show a prospective application of polymer-functionalized BNNTs in surface engineering fields, the disentangled BNNTs were used as the raw/starting materials for the creation of superhydrophobic surfaces.

Functionalization, Dispersion, and Cutting of Boron Nitride Nanotubes in Water

High-quality boron nitride nanotubes (BNNTs) were functionalized for the first time with water-soluble and biocompatible PEGylated phospholipid [methoxy-poly(ethylene glycol)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N conjugates (mPEG-DSPE)]. We found that BNNTs can be suspended in water for more than 3 months without precipitation. By comparing the dispersion stability of mPEG-DSPE/BNNTs in various solvents and the related Hansen solubility parameters, we found that polarized and hydrogen bonds between water and the hydrophilic mPEG play important roles in maintaining stable dispersion of BNNTs and preventing aggregation of mPEG-DSPE/BNNTs in the solutions. This has led to the formation of composite films with well-dispersed BNNTs and the coating of self-assembled monolayer (SAM) BNNTs. Furthermore, the lengths of these functionalized BNNTs can be shorterned, for the first time, from >10 μm to ∼500 nm by ultrasonication. Experiments suggest that effective dispersion of BNNT in solution is necessary for such cutting, where effective energy transfer from the sonicator to nanotubes is achieved. Our results will form the basis for stable functionalization, dispersion, and effective cutting of BNNTs with water-soluble and biocompatible PEGylated phospholipid, which are important for biomedical and composite applications.

Fabrication of Al-Matrix Composites Reinforced with Amino Functionalized Boron Nitride Nanotubes

Amino functionalized boron nitride nanotubes were used as the reinforcement material for the fabrication of Al-matrix composites using powder metallurgy process. It was found that the mechanical properties of these composites were improved significantly as compared to pure Al composites fabricated under similar conditions. The microhardness of these composites was found to improve by five times and compressive strength by 300% as compared to pure Al composites under similar processing conditions. The enhanced mechanical properties of these composites can be attributed to the proper dispersion of boron nitride nanotubes (BNNTs) in Al matrix and the formation of a strong interfacial bonding between BNNTs and Al matrix under the processing conditions. High-resolution transmission electron microscopy studies revealed the formation of transition layer of AlB2 which might lead to a better load transfer from Al matrix to the BNNTs. Further, these composites are believed to withstand high temperatures as compared to Al matrix composites reinforced with carbon nanotubes and, therefore, can be used for applications where lightweight and high strength materials are desired with stability at elevated temperatures.

Dispersion of boron nitride nanotubes in aqueous solution with the help of ionic surfactants

We report that ammonium oleate surfactants can help the dispersion of multiwalled boron nitride nanotubes (BNNTs) in water to form a BNNT solution stable for several months, which was due to the non-covalent functionalization of nanotube surfaces. Fourier Transform Infrared Spectroscopy (FTIR) and Photoluminescence (PL) analysis with synchrotron radiation source revealed that this BNNT aqueous solution preserves the intrinsic optical properties of BNNTs.

Preparation of Boron Nitride Nanotubes Aqueous Dispersions for Biological Applications

While in the last years applications of carbon nanotubes in the field of biotechnology have been largely proposed, biomedical applications of boron nitride nanotubes (BNNTs) are yet totally unexplored. BNNTs have very interesting physical properties that should be exploited in the biomedical field. At this date, studies on their biocompatibility are completely missing and the first issue behind this investigation is the dispersion of BNNTs in aqueous solutions. In this paper the authors propose, for the first time, a technique for obtaining BNNT stable dispersions suitable for biological applications, based on polyethyleneimine (PEI) water solutions. Based on authors' knowledge, in vitro testing performed on human neuroblastoma cell line (SH-SY5Y) is the first study of interaction between BNNTs and living material. Experimental results showed a satisfactory cell viability up to a concentration of 5.0 μg/ml PEI-BNNTs in the cell culture medium.

A Novel Approach from Infrared to Ultraviolet Emission Enhancement in Yb3+, Er3+:CaF2 Nanofilms

While in the last years applications of carbon nanotubes in the field of biotechnology have been largely proposed, biomedical applications of boron nitride nanotubes (BNNTs) are yet totally unexplored. BNNTs have very interesting physical properties that should be exploited in the biomedical field. At this date, studies on their biocompatibility are completely missing and the first issue behind this investigation is the dispersion of BNNTs in aqueous solutions. In this paper the authors propose, for the first time, a technique for obtaining BNNT stable dispersions suitable for biological applications, based on polyethyleneimine (PEI) water solutions. Based on authors' knowledge, in vitro testing performed on human neuroblastoma cell line (SH-SY5Y) is the first study of interaction between BNNTs and living material. Experimental results showed a satisfactory cell viability up to a concentration of 5.0 microg/ml PEI-BNNTs in the cell culture medium.