Fiber Bragg gratings (FBGs) were fabricated in tapered fibers using both the plane-by-plane and phase mask approaches with a femtosecond infrared laser. A thin layer of boron nitride nanotubes (BNNTs) was deposited onto the FBGs through a dip-coating process from a BNNT water solution. The reflection spectra of the FBGs were then recorded when they were placed in ammonia (NH3), hydrogen chloride (HCl) and bromine (Br2) gases. It was demonstrated experimentally that, due to the BNNT coating, the return losses of the FBGs increased when they were surrounded with these hydrophilic gas vapors. However, when the FBGs were in other atmospheres such as air, methanol and acetone vapors, no change in the FBG reflection spectra was observed. The results of this work indicate that BNNT coatings on FBGs can play an important role for hydrophilic gas detection with large measurement range and reusability due to their quick release of adsorbed gases. Moreover, the BNNT coating induced losses with different ammonia gas concentrations were quantitatively measured. It was observed that the Bragg wavelengths of the FBGs remained the same when the FBGs were tested in hydrophilic gases suggesting the proposed device can be used for temperature or strain sensing at the same time. The response of the Bragg wavelength of BNNT coated FBGs to temperature was also studied and it was found that the thin BNNT coating did not affect the FBG's temperature sensitivity. Due to the properties of BNNTs and optical fibers, the proposed fiber sensor can be used in harsh environments.

Fiber Bragg gratings (FBGs) were fabricated in tapered fibers using the plane-by-plane technique and a fs-IR laser. A thin layer of boron nitride nanotubes (BNNTs) was deposited onto the FBGs through a dip-coating process from a BNNT water solution. The reflection spectra of FBGs were then recorded when they were placed above the water solution of ammonia (NH3), hydrogen chloride (HCl) or liquid bromine ( Br2) in an open cylinder container. It was demonstrated experimentally that, due to the thin BNNT coating, the returned losses of FBGs were increased when they were surrounded with such hydrophilic gas vapors, such as ammonia, bromine and hydrogen chloride. However, when the FBGs were in other atmospheres such as air, methanol and acetone vapors, no change of the FBG reflection spectra was observed. The results of this work indicates that BNNT coating on FBGs plays an important role for hydrophilic gas detection with high sensitivity and reusability due to their quick release of adsorbed gases. The proposed sensor has the capacity of multiparameter sensing and can be used in harsh environments.

Boron nitride nanotubes (BNNTs) are predicted to be promising one-dimensional nonlinear optical materials, but to date, only one experimental observation has been made using individual nanotubes. In this work, second harmonic generation (SHG) was achieved from free-standing bulk BNNT sheets and BNNT coatings on silica substrates. Focusing femtosecond infrared (fs-IR) laser pulses with a wavelength of 800 nm onto the BNNT assemblies resulted in strong SHG at a wavelength of 400 nm. It was observed that due to the thickness variation of the BNNT assemblies and orientational alignment of BNNTs in the assemblies, the intensity of the second-harmonic (SH) radiation changed dramatically when different locations on the samples were investigated. Among all the BNNT assemblies tested, the localized SH response and its dependence on the polarization of the excitation fs-IR pulses were the strongest in BNNT coatings produced by a dip-coating process. By measuring the SH response, the uniformity, reproducibility, and efficiency of BNNT deposition processes could be assessed. For applications requiring a high SH response from BNNT assemblies, the process of dip coating is preferred.

We have investigated the potential of three dielectric materials to meet the future demands of green dielectrics: Polycaprolactone (PCL) thermoplastic, polyvinyl alcohol (PVA)-carrageenan (CAR) crosslinked biopolymer, and boron nitride nanotubes (BNNTs) as a nano additive in PVA. Metal-insulator-metal (MIM) capacitors and organic thin film transistors (OTFT) were built with bilayer dielectric stacks of PVA-CAR, PVA-PCL, and PVA-BNNT materials to examine their electrical properties. The PVA-CAR layer uses a cyclic freeze thaw process to crosslink PVA and CAR for superior mechanical and electrical properties to either material alone. The PVA-CAR MIM capacitors showed a dielectric constant of 23, which was found to be consistent with the extracted OTFT gate dielectric characteristics. Of the OTFT devices tested, PVA-CAR OTFT showed highest device currents at low applied biases and produced an ON/OFF ratio of 104-105, both values were highest amongst the tested gate dielectrics. This material is therefore extremely promising for green electronics. The PVA-PCL OTFT had very low leakage current and beneficial hydrophilic properties with comparable electrical properties to the commonly used organic material polytetrafluoroethylene. PVA-BNNT MIM capacitors showed a low dielectric constant of 0.7, and the high resistivity makes this a promising material for shielding or substrates in high frequency applications. All three materials have the potential to fulfil different niches in a sustainable electronics future.

The optical and structural properties of boron nitride nanotube (BNNT) assembly were characterized using optical fiber Bragg grating (FBG) sensors. FBGs were fabricated in tapered fibers with a diameter of less than 30 mu m. After tapered fibers were etched in hydrofluoric acid solution for a few minutes, BNNTs were then deposited on the fibers through a dip-coating process. The Bragg wavelengths of the FBGs were measured before and after BNNT coating such that the effective refractive index (RI) of the guided fundamental HE11 mode in the fiber was obtained. By numerical modeling of the dependence of HE11 mode effective RI on the RI of the surrounding material, both the RI and the air void content of BNNT coating were obtained. To verify the accuracy of the modeling results, a FBG sensor fabricated in a tapered fiber was immerged in various RI standard solutions and the corresponding Bragg wavelengths were measured and compared to numerical simulations. It was shown that the experimental data agreed well with simulation results.

Alberta oilsands asphaltenes (AOAs) are carbonrich hydrocarbons obtained from the heaviest fraction in Alberta oilsands bitumen. They have little value in the current market. Asphaltenes are considered a problematic stream for bitumen transportation and processing, and they may be a potential feedstock for carbon fiber (CF) production. Effort has been devoted by researchers and the oil industry for developing asphaltenes into value-added products, in particular CFs. Major barriers have been identified for the conversion of asphaltenes to CFs. One of them is purification and priming of the AOA feedstock as the raw material varied significantly from extraction and applied isolation technologies. Here, we report the purification of raw AOAs for the purpose of forming AOA-green fibers through electrospinning, the comparison with the non-purified AOA raw materials, and the validation of the potential of conversion of asphaltenes toward CFs. Thermogravimetric analysis, elemental analysis, and scanning electron microscopy were carried out. AOA-green fibers were obtained with the as-received AOAs and the maltene-free AOAs by three optimized electrospinning protocols. These green fibers can be spun to a large size mat with a high degree of alignment through adjusting the collector rotation velocity. The diameters of the obtained AOA-green fibers are mostly in the range of 4-15 mu m. The green fibers from the as-received AOAs could sustain up to 200 degrees C in air but fused with further increase of temperature, while the green fibers from the purified AOAs showed improved mechanical strength and were able to withstand temperatures up to 300 degrees C in air without fusing. This work will be of interest to the CF industry as a potential alternative approach for low-cost precursors.

Recent developments in microelectronic devices have led to rising demand for polymeric nanocomposites that can simultaneously deliver enhanced thermal conduction and electrical insulation. Boron nitride nanotube (BNNT) is one of the most promising fillers for the fabrication of such composites. While being electrically insulating, effective crystal lattice vibrations allow BNNTs to achieve thermal conductivity values that can even surpass that of diamond. However, when BNNTs are surface functionalized and incorporated within polymers, their lattice vibrations are significantly suppressed, resulting in polymeric nanocomposites with thermal conductivity values only a fraction of what BNNTs can achieve in air. The aim of this study is to shed light on the underlying cause of this challenge for thermally conductive, dielectric polycarbonate (PC)/BNNT nanocomposites that were produced using two distinct surface functionalization approaches. By incorporation of BNNTs in PC, the thermal conductivity values were significantly increased. However, depending on nanotubes’ concentration, the thermal conductivity of pristine BNNTs in PC were comparable or superior to those of the functionalized nanotubes. Theoretical analysis and experimental characterization have been conducted to elucidate the fundamental impacts of surface functionalization on the lattice vibrations of BNNTs and their subsequent effects on the thermal properties of dielectric BNNT composites.

Boron nitride nanotubes (BNNTs) are demonstrated for use in optical fiber sensor applications. A BNNT coated tapered optical fiber sensor has been developed to detect various liquids and gases with enhanced sensitivity and selectivity.

Printed electronics provide inexpensive and light weight electrical components to fuel emerging applications. One major challenge is the high temperature required to sinter conductive metal inks, which leads to thermal degradation of the substrate and subsequently poor performance. A boron nitride nanotube (BNNT) interfacial film is reported for thermal management in rapid processing of a printable silver molecular ink platform using intense pulsed light (IPL) sintering techniques. The inclusion of BNNT thin films of varying surface concentrations deposited between the substrate and the printed features reduces thermal damage to the substrate during sintering while simultaneously improving electrical performance, achieving a sheet resistance value as low as 140 mΩ sq −1 . A wide range of sintering energies ranging from 2.0 and 3.2 J cm −2 are investigated along with printed trace widths ranging from 5 mil (0.127 mm) to 20 mil (0.508 mm). Increases in the rate of cooling and in the current carrying capacity are confirmed with the inclusion of the BNNTs. Overall the thin coating of BNNTs presents no drawbacks while significantly improving the electrical properties of IPL sintered conductive traces and thus represents a simple approach that will advance the adoption of IPL for fabricating printed electronic components.

A detailed study has been undertaken of the mechanisms of stress transfer in a nanocomposite consisting of hexagonal boron nitride (hBN) nanotubes (BNNTs) in a poly(vinyl alcohol) (PVA) matrix based upon the use of nonresonance Raman spectroscopy. The structure of the BNNTs was characterized by using transmission electron microscopy (TEM) where it was shown that the majority of the nanotubes had 2-5 walls with some having over 10 walls. The structure and mechanical properties of nanocomposites containing up to 1 wt % of both pristine and hydroxyl-functionalized nanotubes (OH-BNNTs) in PVA were investigated. The dispersion of the BNNTs in the nanocomposites was characterized by using a combination of transmission electron microscopy and Raman mapping. The mechanical properties of the nanocomposites were evaluated by tensile testing, and it was found that the Young's modulus, yield strength, and fracture stress all increased on the addition of the BNNTs. A further improvement in the mechanical properties was obtained for nanocomposites containing the OH-BNNTs. The variation of the Young's modulus of the nanocomposites with volume fraction of the BNNTs was evaluated by using the rule of mixtures, and it was shown that the effective Young's modulus (E-eff) of the BNNTs approached 825 +/- 100 GPa at low volume fractions. The value of E-eff was found to decrease with increasing BNNT volume fraction as the result of nanotube bundling. By use of nondestructive Raman spectroscopy, stress transfer from the PVA matrix to the BNNTs was evaluated from stress-induced shifts of the hBN Raman G band, enabling the analysis of interfacial adhesion in the nanocomposites. Larger band shifts were obtained for the OH-BNNTs indicating a stronger interface between the BNNTs and the PVA matrix and a better dispersion. A value of 1.34 +/- 0.72 was determined from the stress-induced Raman band shifts for the Griineisen parameter of the BNNTs. In consideration of their efficient reinforcement of a polymer at very low additions and unique electrically insulating and thermally conductive properties, BNNTs are shown to have great potential to be used as nanofillers for composites in a number of applications.

Current processes to manufacture nanotubes at commercial scales are unfortunately imperfect and commonly generate undesirable byproducts. After manufacturing, purification is necessary and is a rate and cost determining step in advancing the development of commercial products based on nanotubes. Boron nitride nanotubes (BNNTs) produced without metal catalysts from high-temperature processes are known to contain a significant amount (e.g., 50 wt %) of various boron derivatives. Herein we report a simple yet efficient and scalable process to purify these types of BNNT materials at commercial scales, from a few grams to hundreds of grams, at purity over 85 wt % in a single step. The process relies on a vertically mounted flow tube reactor and scrubber system that can be operated under pure or diluted chlorine gas flow at temperatures up to 1100 degrees C. The main chemical reactions driving the purification are the conversion of boron and BN derivatives into BCl3 and HCl, which are removed as gaseous species, while pristine BNNTs are left behind. The preferential etching of impurities over pristine BNNTs shows the extreme chemical resistance of BNNTs in this harsh environment and opens up new applications for this nanomaterial. The process has been examined at various temperatures, up to 1050 degrees C, and the resulting materials display improved BNNT purity and quality across a range of imaging and spectroscopic assessments. The recommended temperature to optimize quality with yield is 950 degrees C, although higher quality material is obtained at a higher temperature.

Boron nitride nanotubes (BNNTs) are 1-D hollow fibrous nanomaterials. They are thermally stable up to 800 °C in open air and up to 1000 °C in a pure chlorine atmosphere, are electrically insulating, and possess superlative mechanical properties. Since the BNNT assembly is highly porous and easily penetrated by liquids and gases, BNNT thin film coated on optical fiber can be used as a novel sensing medium with enhanced sensitivity and selectivity. In this letter, uniform BNNT films have been successfully coated on optical fibers and tapered optical fibers (TOFs). A BNNT-coated TOF sensor has been developed for various liquids and gases sensing applications. We demonstrated experimentally that the BNNT-coated TOF can be used as a level sensor for liquids, even for those with refractive indices smaller than that of silica such as the organic solvents like acetone, hexane, tetrahydrofuran, ethyl ether, and dimethylformamide. As to gas sensing, HCl was selectively detected with enhanced sensitivity due to its high polarity and good affinity to the OH/NH2 functionalized BNNTs. The BNNT-coated optical fiber sensors can be potentially used at high temperatures and in some harsh environments.

Boron nitride, which possesses high thermal conductivity, is often incorporated into polymer matrixes for thermal management. The enhancement in the thermal conductivity depends on the filler shape, size, effective dispersion in the matrix, and interfacial thermal resistance between the filler and matrix, and the last two are the most challenging issues. To address these challenges, in this study two different covalent functionalization approaches on boron nitride nanotubes (BNNTs) with short polyethylene (PE) chains are employed: one based on the Williamson reaction and the other on nitrene [1 + 2] chemistry. The covalent connection between the nanotubes and the polymer is confirmed by Fourier transform infrared, X-ray photoelectron microscopy, tandem thermogravimetric-infrared spectroscopy analysis and energy-filtered transmission electron microscopy. The modification of BNNTs with short polymer chains has resulted in an excellent strategy to modulate the interface in polymer composites. Tuning the interface has a strong influence on thermal transport, and up to an , similar to 250% increase in the thermal conductivity of BNNT-HDPE nanocomposites has been observed when the loading increases from 20 to 40 wt % of PE-modified BNNTs due to the improved dispersion and reduced interfacial thermal resistance. The materials described here show the potential for heat-transfer applications.

Boron nitride nanotubes (BNNTs), like carbon nanotubes (CNTs), possess an impressive collection of properties that motivate their use in composite materials, particularly in areas where CNTs are limited (e.g., high-temperature processing and applications) or unsuitable (e.g., electric insulation). The recent advent of pilot-scale production and of commercial BNNT materials offers improved opportunities to study BNNT science and develop BNNT-based composites and applications. Here, we highlight recent advances in BNNT manufacturing and commercialization and the properties and performance of BNNT-based nanocomposites including polymer, metal, and ceramic composites and envision a future landscape of BNNT applications.

Surface functionalized boron nitride nanotubes (f-BNNTs) with hydroxyl (OH) and amino (NH2) groups are employed as a nanofiller to reinforce polycarbonate (PC), a resin that has widely been used where a combination of transparency and high energy absorption is required, such as in armor, automotive and display technologies. To improve the interfacial compatibility of BNNTs with the PC matrix, BNNTs are treated with bromine in water inducing B-N bond cleavage and subsequent formation of OH and NH2 functional groups on BNNT-surfaces. Samples of 1, 2 and 4 wt% f-BNNT/PC nanocomposite are prepared in a mixture of chloroform and dimethylformamide (DMF). The resulting f-BNNT/PC nanocomposites are processed in two ways: thin film formation from the powder by using a hot-press and plaque formation through melt-mixing-extrusion and compression molding techniques, respectively. The thermal and mechanical properties of the f-BNNT/PC nanocomposites are evaluated and compared with those of neat PC. They exhibit about 4 similar to 8 degrees C improvement in thermal stability and over 30 degrees C higher in anti-oxidation than those of the neat PC. The testing result reveals that the f-BNNT/PC nanocomposite at 1 wt% loading achieves 39% increase in tensile toughness relative to the neat PC. Young's modulus has an improvement by 13% (1 wt%) and 31% (4 wt%), respectively, from the thin-film samples; while about 2% and 13% improvements are observed from the extruded coupons at the same f-BNNT loadings. The transparency of the thin films is shown to decrease with the increase of f-BNNT loading.

The first example of aqueous solutions of boron nitride nanotubes (BNNTs) with switchable stability and without use of surfactants is demonstrated. The as-produced boron nitride nanotubes are both purified and solubilized through an environmentally friendly and scalable approach using water extraction and liquid bromine treatment. This treatment effectively removes elemental boron particles and excess bromine reacts with BNNTs, inducing B-N bond cleavage on the BNNT surface to yield hydroxyl (OH) and amino (NH2) functionalized BNNTs. The resulting functionalized BNNTs form stable aqueous solutions around neutral pH (4 < pH < 8), but readily precipitate in other pH ranges. This switchable solubility is explained in terms of the capability of the functional groups (OH and NH2) to form hydrogen-bonding networks in water. Further, the solubility differences in selected polar organic solvents have been utilized to prepare functionalized BNNTs with higher purity.

Hydroxyl (OH) and amino (NH2) functionalized boron nitride nanotubes (f-BNNTs) were integrated into an epoxy resin (Epon828) to achieve improved mechanical properties. While raw BNNT-composites yielded the largest values for Young’s modulus and appeared to be well mixed, f-BNNTs were found to provide a superior combination of mechanical properties yielding improvements in strain at failure, tensile strength and toughness that were not observed using raw BNNTs. In particular, an increase of 21% in Young’s modulus is observed with 5 wt% of f-BNNT, and increases of 12, 21, and 49% are observed in tensile strength, failure strain, and toughness, respectively, with 2 wt% f-BNNT while a 34% increase in fracture toughness is observed with 3 wt% f-BNNT.