Superhydrophobic properties of nonaligned boron nitride nanotube films

A new strategy for making a sensitive sensor for aspirin drug: first-principles investigations by using pure and metal-doped BN nano-heterostructures

The present study used the DFT method to investigate aspirin's intermolecular interactions with boron nitride (BN) nanotubes modified with aluminum, gallium, and zinc. Our experiments obtained adsorption energy of -40.4 kJ/mol for aspirin on BN nanotubes. By doping each of the above metals on the surface of the BN nanotube, the aspirin adsorption energy increased dramatically. For BN nanotubes doped with Al, Ga, and Zn, this energy was -255, -251, and -250 kJ/mol. Thermodynamic analyses proved that all surface adsorptions are exothermic and spontaneous. Nanotubes' electronic structures and dipole moments have been examined following aspirin adsorption. In addition, AIM analysis has been performed for all systems in order to understand how the links were formed. According to the obtained results, BN nanotubes doped with metals, as mentioned previously, have a very high electron sensitivity to aspirin. These nanotubes can therefore be used to manufacture aspirin-sensitive electrochemical sensors.Communicated by Ramaswamy H. Sarma.

Multistage Modulation Formation of Hydrophilic-Hydrophobic Boron Carbon Nitride Nanomaterials

Boron carbon nitride (BCN) ternary compounds are attractive due to their wide applications in adsorption, catalysis, protective coatings, etc. A simple way is provided to synthesize BCN materials with multistage modulation of hydrophilic-hydrophobic properties. Hydrophilic BCN nanoparticles with a contact angle of 31° and nearly superhydrophobic BCN sheets with a contact angle of 145° are obtained. The participation of a CuO additive in the synthesis process has the role of tuning morphologies, components, and properties of BCN materials. The addition of CuO would improve the hydrophobicity of BCN due to its microstructure with enhanced surface roughness. The interaction between melamine and boric acid on the surface of CuO(111) is investigated by first-principles calculations based on density functional theory (DFT). The tuned BCN materials have different photoelectric properties also, and their performance as photocatalysts has been verified in photocatalytic reactions for hydrogen from water. The achieved uniform hydrophilic BCN nanoparticles and hydrophobic BCN sheets have the potential for further practical applications.

Boron nitride nanotube-salt-water hybrid:crystalline precipitation

Molecular dynamics simulation is used to study the transport characteristics of NaCl solution in boron nitride nanotubes (BNNTs). It presents an interesting and well-supported MD study of the crystallization of NaCl from its water solution under the confinement of a 3 nm thick boron nitride nanotube with varied surface charging conditions. The results of the molecular dynamics simulation indicate that NaCl crystallization occurs in charged BNNTs at room temperature when the concentration of NaCl solution reaches about 1.2 M. The reason for this phenomenon is as follows: when the number of ions in the nanotubes is high, the double electric layer that forms at the nanoscale near the charged wall surface, the hydrophobicity of BNNTs, and the interaction among ions cause ions to aggregate in the nanotubes. As the concentration of NaCl solution increases, the concentration of ions when they aggregate in the nanotubes reaches the saturation concentration of the NaCl solution, resulting in the crystalline precipitation phenomenon.

A Simple Method for the Synthesis of a Coral-like Boron Nitride Micro-/Nanostructure Catalyzed by Fe

Catalyzed by Fe, novel a coral-like boron nitride (BN) micro-/nanostructure was synthesized from B₂O₃ by a ball milling and annealing process. Observations of the morphology of the product indicated that the coral-like BN micro-/nanostructure consists of a bamboo-shaped nanotube stem and dense h-BN nanoflakes growing outward on the surface of the nanotube. Experimental results showed that the morphology of the BN nanotube was greatly dependent on the anneal process parameters. With the annealing time increasing from 0.5 h to 4 h, the morphology developed from smooth BN nanotubes, with a diameter size of around 100 nm, to rough, coral-like boron nitride with a large diameter of 3.6 μm. The formation mechanism of this coral-like BN micro-/nanostructure is a two-stage growth process: bamboo-shaped BN nanotubes are first generated through a vapor-liquid-solid (VLS) mechanism and then nanoflakes grow surrounding the surface of the nanotube. Acid pickling and a hydrolysis process were carried out to remove Fe, iron nitrogen and unreacted B₂O₃ impurities.

Synergistic Enhanced Thermal Conductivity and Crack Resistance of Reactor Epoxy Insulation with Boron Nitride Nanosheets and Multiwalled Carbon Nanotubes

Epoxy composites with high thermal conductivity, excellent dielectric, and mechanical properties are very promising for solving epoxy cracking faults in reactors and for extending their service life. In this work, we report on epoxy composites enhanced by ternary fillers of boron nitride nanosheets (BNNSs), multiwalled carbon nanotubes (MWCNTs), and silica (SiO₂) nanoparticles. The obtained BNNSs/MWCNTs/SiO₂/epoxy composites exhibit a high thermal conductivity of 0.9327 W m^-1 K^-1, which is more than 4-fold higher than that of pure epoxy. In addition, the resultant composites present an improved mechanical strength (from 2.7% of epoxy to 3.47% of composites), low dielectric constant (4.6), and low dielectric loss (0.02). It is believed that the integration of multifunctional properties into epoxy composites provides guidance for optimizing the design of high-performance materials.

Metal Oxide Nanoparticles and Nanotubes: Ultrasmall Nanostructures to Engineer Antibacterial and Improved Dental Adhesives and Composites

Advances in nanotechnology have unlocked exclusive and relevant capabilities that are being applied to develop new dental restorative materials. Metal oxide nanoparticles and nanotubes perform functions relevant to a range of dental purposes beyond the traditional role of filler reinforcement-they can release ions from their inorganic compounds damaging oral pathogens, deliver calcium phosphate compounds, provide contrast during imaging, protect dental tissues during a bacterial acid attack, and improve the mineral content of the bonding interface. These capabilities make metal oxide nanoparticles and nanotubes useful for dental adhesives and composites, as these materials are the most used restorative materials in daily dental practice for tooth restorations. Secondary caries and material fractures have been recognized as the most common routes for the failure of composite restorations and bonding interface in the clinical setting. This review covers the significant capabilities of metal oxide nanoparticles and nanotubes incorporated into dental adhesives and composites, focusing on the novel benefits of antibacterial properties and how they relate to their translational applications in restorative dentistry. We pay close attention to how the development of contemporary antibacterial dental materials requires extensive interdisciplinary collaboration to accomplish particular and complex biological tasks to tackle secondary caries. We complement our discussion of dental adhesives and composites containing metal oxide nanoparticles and nanotubes with considerations needed for clinical application. We anticipate that readers will gain a complete picture of the expansive possibilities of using metal oxide nanoparticles and nanotubes to develop new dental materials and inspire further interdisciplinary development in this area.

Effects of boron nitride nanotube content on waterborne polyurethane-acrylate composite coating materials

Waterborne polyurethane-acrylate (WPUA) is a promising eco-friendly material for adhesives and coatings such as paints and inks on substrates including fibers, leather, paper, rubber, and wood. Recently, WPUA and its composites have been studied to overcome severe problems such as poor water resistance, mechanical properties, chemical resistance, and thermal stability. In this study, composite films consisting of WPUA and rod-type boron nitride nanotubes (BNNTs), which have excellent intrinsic properties including high mechanical strength and chemical stability, were investigated. Specifically, BNNT/WPUA composite films were synthesized by mixing aqueous solutions of BNNT and WPUA via facile mechanical agitation without any organic solvents or additives, and the optimal content of BNNTs was determined. For the 2.5 wt% BNNT/WPUA composite, the BNNTs were found to be well distributed in the WPUA matrix and this material showed the overall best performance in terms of water resistance, thermal conductivity, and corrosion resistance. Owing to these advantageous properties and their environmentally friendly nature, BNNT/WPUA composite coating materials are expected to be applicable in a wide variety of industries.

Boron Nitride Nanotube (BNNT) Membranes for Energy and Environmental Applications

Owing to their extraordinary thermal, mechanical, optical, and electrical properties, boron nitride nanotubes (BNNTs) have been attracting considerable attention in various scientific fields, making it more promising as a nanomaterial compared to other nanotubes. Recent studies reported that BNNTs exhibit better properties than carbon nanotubes, which have been extensively investigated for most environment-energy applications. Irrespective of its chirality, BNNT is a constant wide-bandgap insulator, exhibiting thermal oxidation resistance, piezoelectric properties, high hydrogen adsorption, ultraviolet luminescence, cytocompatibility, and stability. These unique properties of BNNT render it an exceptional material for separation applications, e.g., membranes. Recent studies reported that water filtration, gas separation, sensing, and battery separator membranes can considerably benefit from these properties. That is, flux, rejection, anti-fouling, sensing, structural, thermal, electrical, and optical properties of membranes can be enhanced by the contribution of BNNTs. Thus far, a majority of studies have focused on molecular simulation. Hence, the requirement of an extensive review has emerged. In this perspective article, advanced properties of BNNTs are analyzed, followed by a discussion on the advantages of these properties for membrane science with an overview of the current literature. We hope to provide insights into BNNT materials and accelerate research for environment-energy applications.

Characterization of plasma and gas-phase chemistry during boron-nitride nanomaterial synthesis by laser-ablation of boron-rich targets

In this work, solid targets made from boron and boron nitride (BN) materials are ablated by a nanosecond pulsed laser at sub-atmospheric pressures of nitrogen and helium gases. The excited species in the ablation plume from the target are probed by spatiotemporally resolved optical emission spectroscopy (OES). The evaluation of the chemical composition of the plasma plume revealed that for both boron-rich targets, emission from BN molecules is always observed in nitrogen-rich environments. In addition, BN molecules are also present when ablating a boron nitride target in a helium gas environment, an indication that BN molecules in the plume may originate from the solid target. Furthermore, the ablation of the BN target features emission of B2N molecules, regardless of the pressure and surrounding gas. These results suggest that the ablation of the BN target is more favorable for the generation of complex molecules containing boron and nitrogen species and possibly hint that BN is also more favorable feedstock for high-yield BN nanomaterial synthesis. Plasma parameters such as the electron temperature (peak value of 1.3 eV) and density (peak value of 2 × 1018 cm-3) were also investigated in this work in order to discuss the chemical dynamics in the plume.

Lattice Dynamics and Contraction of Energy Bandgap in Photoexcited Semiconducting Boron Nitride Nanotubes

Structural dynamics and changes in electronic structures driven by photoexcited carriers are critical issues in both semiconducting and optoelectronic nanodevices. Herein, a phase diagram for the transient states and relevant dynamic processes in multiwalled boron nitride nanotubes (BNNTs) has been extensively studied for a full reversible cycle after a fs-laser excitation in ultrafast TEMs, and the significant structural features and evolution of electronic natures have been investigated using pulsed electron diffraction and femtosecond-resolved electron energy-loss spectroscopy (EELS). It is revealed that nonthermal anisotropic alterations of the lattice apparently precede the phonon-driven thermal transients along the radial and axial directions. Ab initio calculations support these findings and show that electrons excited from the π to π* orbitals in the BN nanotubes weaken the intralayer bonds while strengthening the interlayer bonds along the radial direction. Importantly, time-resolved EELS measurements show contraction of the energy bandgap after fs-laser excitation associated with nonthermal structural transients. This fact verifies that laser-induced bandgap renormalization in semiconductors can essentially be correlated with both the rapid processes of excited carriers and nonthermal lattice evolution.

Atmosphere-Mediated Superhydrophobicity of Rationally Designed Micro/Nanostructured Surfaces

Superhydrophobicity has received significant attention over the past three decades owing to its significant potential in self-cleaning, anti-icing and drag reduction surfaces, energy-harvesting devices, antibacterial coatings, and enhanced heat transfer applications. Superhydrophobicity can be obtained via the roughening of an intrinsically hydrophobic surface, the creation of a re-entrant geometry, or by the roughening of a hydrophilic surface followed by a conformal coating of a hydrophobic material. Intrinsically hydrophobic surfaces have poor thermophysical properties, such as thermal conductivity, and thus are not suitable for heat transfer applications. Re-entrant geometries, although versatile in applications where droplets are deposited, break down during spatially random nucleation and flood the surface. Chemical functionalization of rough metallic substrates, although promising, is not utilized because of the poor durability of conformal hydrophobic coatings. Here we develop a radically different approach to achieve stable superhydrophobicity. By utilizing laser processing and thermal oxidation of copper (Cu) to create a high surface energy hierarchical copper oxide (CuO), followed by repeatable and passive atmospheric adsorption of hydrophobic volatile organic compounds (VOCs), we show that stable superhydrophobicity with apparent advancing contact angles ≈160° and contact angle hysteresis as low as ≈20° can be achieved. We exploit the structure length scale and structure geometry-dependent VOC adsorption dynamics to rationally design CuO nanowires with enhanced superhydrophobicity. To gain an understanding of the VOC adsorption physics, we utilized X-ray photoelectron and ion mass spectroscopy to identify the chemical species deposited on our surfaces in two distinct locations: Urbana, IL, United States and Beijing, China. To test the stability of the atmosphere-mediated superhydrophobic surfaces during heterogeneous nucleation, we used high-speed optical microscopy to demonstrate the occurrence of dropwise condensation and stable coalescence-induced droplet jumping. Our work not only provides rational design guidelines for developing passively durable superhydrophobic surfaces with excellent flooding-resistance and self-healing capability but also sheds light on the key role played by the atmosphere in governing wetting.

Molding processed multi-layered and multi-functional nanocomposites with high structural ability, electrical conductivity and durable superhydrophobicity

Bioinspired superhydrophobic surfaces are mainly attributed to nano/micro textures and low surface energy materials, and have exciting potential for use in fields such as self-cleaning, water-proofing, anti-icing, anti-fouling, and so forth. However, the natural weakness of such delicate hierarchical surface structures pose great challenges to using artificial superhydrophobic surfaces under harsh mechanical conditions. Completely transforming multi-layered composite materials with good structural ability into superhydrophobic surfaces would greatly extend their durability under continuous mechanical abrasion. Endowing these composites with electrical conductivity could further expand their scope of application, especially in anti-static environments. Here we employ a facile molding process to fabricate a new type of multi-layered and multi-functional nanocomposite (MMNC), with a tensile strength up to ∼226.4 MPa, a modulus of up to ∼24.8 GPa, a surface electric conductivity of ∼1.2 S cm-1, a water contact angle of ∼155.4° and a water sliding angle of ∼2.0°. These multi-layered and multi-functional nanocomposites (MMNCs) demonstrate robust water-repellency under harsh mechanical abrasion (tested using a high tack sticky tape peel, cyclic sand paper abrasion and even file abrasion) and strong chemical corrosion (tested by using hydrochloric acid, sulfuric acid and sodium hydroxide solutions). Additionally, our MMNCs are highly resistant to water impalement (tested by turbulent water jet impact with a velocity of up to ∼29.5 m s-1 and a corresponding Weber number of ∼32 000). The robustness of the superhydrophobicity is multifaceted, and owing to the excellent structural performance and conductivity, these MMNCs could find potential uses in vehicles, containers, wind blades, infrastructures, electronics and so forth, which usually experience comprehensively harsh conditions such as rainfall, abrasion, static electricity, high loads and so forth.

Boron nitride nanotubes: synthesis and applications

Boron nitride nanotube (BNNT) has similar tubular nanostructure as carbon nanotube (CNT) in which boron and nitrogen atoms arranged in a hexagonal network. Owing to the unique atomic structure, BNNT has numerous excellent intrinsic properties such as superior mechanical strength , high thermal conductivity, electrically insulating behavior, piezoelectric property, neutron shielding capability, and oxidation resistance. Since BNNT was first synthesized in 1995, developing efficient BNNT production route has been a significant issue due to low yield and poor quality in comparison with CNT, thus limiting its practical uses. However, many great successes in BNNT synthesis have been achieved in recent years, enabling access to this material and paving the way for the development of promising applications. In this article, we discussed current progress in the production of boron nitride nanotube, focusing on the most common and effective methods that have been well established so far. In addition, we presented various applications of BNNT including polymer composite reinforcement, thermal management packages, piezo actuators, and neutron shielding nanomaterial.

Bimetallic catalytic growth of boron nitride nanotubes

Boron nitride nanotubes (BNNTs) have outstanding properties and potential applications. However, the fundamental issue regarding the growth mechanism remains an open question. Herein, we design a bimetallic catalyst that dissolves B and N simultaneously, which has been proved to be key for BNNT growth.

Advanced Sorbents for Oil-Spill Cleanup: Recent Advances and Future Perspectives

Oil sorbents play a very important part in the remediation processes of oil spills. To enhance the oil-sorption properties and simplify the oil-recovery process, various advanced oil sorbents and oil-collecting devices based on them have been proposed recently. Here, we firstly discuss the design considerations for the fabrication of oil sorbents and describe recently developed oil sorbents based on modification strategy. Then, recent advances regarding oil sorbents mainly based on carbon materials and swellable oleophilic polymers are also presented. Subsequently, some additional properties are emphasized, which are required by oil sorbents to cope with oil spills under extreme conditions or to facilitate the oil-collection processes. Furthermore, some oil-collection devices based on oil sorbents that have been developed recently are shown. Finally, an outlook and challenges for the next generation of oil-spill-remediation technology based on oil-sorbents materials are given.

Cassie-State Stability of Metallic Superhydrophobic Surfaces with Various Micro/Nanostructures Produced by a Femtosecond Laser

The Cassie-state stability plays a vital role in the applications of metallic superhydrophobic surfaces. Although a large number of papers have reported the superhydrophobic performance of various surface micro/nanostructures, the knowledge of which kind of micro/nanostructure contributes significantly to the Cassie-state stability especially under low temperature and pressure is still very limited. In this article, we fabricated six kinds of typical micro/nanostructures with different topography features on metal surfaces by a femtosecond laser, and these surfaces were modified by fluoroalkylsilane to generate superhydrophobicity. We then systematically studied the Cassie-state stability of these surfaces by means of condensation and evaporation experiments. The results show that some superhydrophobic surfaces, even with high contact angles and low sliding angles under normal conditions, are unstable under low temperature or external pressure. The Cassie state readily transits to a metastable state or even a Wenzel state under these conditions, which deteriorates their superhydrophobicity. Among the six micro/nanostructures, the densely distributed nanoscale structure is important for a stable Cassie state, and the closely packed micrometer-scale structure can further improve the stability. The dependence of the Cassie-state stability on the fabricated micro/nanostructures and the laser-processing parameters is also discussed. This article clarifies optimized micro/nanostructures for stable and thus more practical metallic superhydrophobic surfaces.

PEGylated boron nitride nanotube-reinforced poly(propylene fumarate) nanocomposite biomaterials

Novel PPF/PEG-g-BNNTs nanocomposites were synthesized and characterized. These antibacterial and non-toxic biomaterials are suitable for bone tissue engineering.

Systematic investigation of the ball milling–annealing growth and electrical properties of boron nitride nanotubes

Boron nitride nanotubes (BNNTs) were grown on stainless-steel substrates by ball milling–annealing in an N₂/H₂ atmosphere.

Nanoscale structure and superhydrophobicity of sp(2)-bonded boron nitride aerogels

Aerogels have much potential in both research and industrial applications due to their high surface area, low density, and fine pore size distribution. Here we report a thorough structural study of three-dimensional aerogels composed of highly crystalline sp(2)-bonded boron nitride (BN) layers synthesized by a carbothermic reduction process. The structure, crystallinity and bonding of the as-prepared BN aerogels are elucidated by X-ray diffraction, (11)B nuclear magnetic resonance, transmission electron microscopy, and resonant soft X-ray scattering. The macroscopic roughness of the aerogel's surface causes it to be superhydrophobic with a contact angle of ∼155° and exhibit high oil uptake capacity (up to 1500 wt%). The oil can be removed from the BN aerogel by oxidizing in air without damaging the crystalline porous structure of the aerogel or diminishing its oil absorption capacity.

Synthesis of boron nitride nanotubes and their applications

Boron nitride nanotubes (BNNTs) have been increasingly investigated for use in a wide range of applications due to their unique physicochemical properties including high hydrophobicity, heat and electrical insulation, resistance to oxidation, and hydrogen storage capacity. They are also valued for their possible medical and biomedical applications including drug delivery, use in biomaterials, and neutron capture therapy. In this review, BNNT synthesis methods and the surface modification strategies are first discussed, and then their toxicity and application studies are summarized. Finally, a perspective for the future use of these novel materials is discussed.

High-efficient production of boron nitride nanosheets via an optimized ball milling process for lubrication in oil

Although tailored wet ball milling can be an efficient method to produce a large quantity of two-dimensional nanomaterials, such as boron nitride (BN) nanosheets, milling parameters including milling speed, ball-to-powder ratio, milling ball size and milling agent, are important for optimization of exfoliation efficiency and production yield. In this report, we systematically investigate the effects of different milling parameters on the production of BN nanosheets with benzyl benzoate being used as the milling agent. It is found that small balls of 0.1–0.2 mm in diameter are much more effective in exfoliating BN particles to BN nanosheets. Under the optimum condition, the production yield can be as high as 13.8% and the BN nanosheets are 0.5–1.5 μm in diameter and a few nanometers thick and of relative high crystallinity and chemical purity. The lubrication properties of the BN nanosheets in base oil have also been studied. The tribological tests show that the BN nanosheets can greatly reduce the friction coefficient and wear scar diameter of the base oil.

Plasma-assisted interface engineering of boron nitride nanostructure films

Today many aspects of science and technology are progressing into the nanoscale realm where surfaces and interfaces are intrinsically important in determining properties and performances of materials and devices. One familiar phenomenon in which interfacial interactions play a major role is the wetting of solids. In this work we use a facile one-step plasma method to control the wettability of boron nitride (BN) nanostructure films via covalent chemical functionalization, while their surface morphology remains intact. By tailoring the concentration of grafted hydroxyl groups, superhydrophilic, hydrophilic, and hydrophobic patterns are created on the initially superhydrophobic BN nanosheet and nanotube films. Moreover, by introducing a gradient of the functional groups, directional liquid spreading toward increasing [OH] content is achieved on the films. The resulting insights are meant to illustrate great potentials of this method to tailor wettability of ceramic films, control liquid flow patterns for engineering applications such as microfluidics and biosensing, and improve the interfacial contact and adhesion in nanocomposite materials.

High Purity and Yield of Boron Nitride Nanotubes Using Amorphous Boron and a Nozzle-Type Reactor

Enhancement of the production yield of boron nitride nanotubes (BNNTs) with high purity was achieved using an amorphous boron-based precursor and a nozzle-type reactor. Use of a mixture of amorphous boron and Fe decreases the milling time for the preparation of the precursor for BNNTs synthesis, as well as the Fe impurity contained in the B/Fe interdiffused precursor nanoparticles by using a simple purification process. We also explored a nozzle-type reactor that increased the production yield of BNNTs compared to a conventional flow-through reactor. By using a nozzle-type reactor with amorphous boron-based precursor, the weight of the BNNTs sample after annealing was increased as much as 2.5-times with much less impurities compared to the case for the flow-through reactor with the crystalline boron-based precursor. Under the same experimental conditions, the yield and quantity of BNNTs were estimated as much as ~70% and ~1.15 g/batch for the former, while they are ~54% and 0.78 g/batch for the latter.

Robust Cassie state of wetting in transparent superhydrophobic coatings

This paper investigates the stability of the Cassie state of wetting in transparent superhydrophobic coatings by comparing a single-layer microporous coating with a double-layer micro/nanoporous coating. Increasing pressure resistance of superhydrophobic coatings is of interest for practical use because high external pressures may be exerted on surfaces during operation. The Cassie state stability against the external pressure of coatings was investigated by squeezing droplets sitting on surfaces with a hydrophobic plate. Droplets on the single-layer coating transformed to the Wenzel state and pinned to the surface after squeezing, whereas droplets on the double-layer micro/nanoporous coating preserved the Cassie state and rolled off the surface easily. In addition, the contact angle and contact-line diameter of water droplets during evaporation from surfaces were in situ investigated to further understand the stability of coatings against Wenzel transition. A droplet on a microporous coating gradually transformed to the Wenzel state and lost its spherical shape as the droplet volume decreased (i.e., the internal pressure of the droplet increased). The contact line of the droplet during evaporation remained almost unchanged. In contrast, a water droplet on a double-layer surface preserved its spherical shape even at the last stages of the evaporation process, where pressure differences as high as a few thousand pascals were generated. For this case, the droplet contact line retracted during evaporation and the droplet recovered the initial water contact angle. The demonstrated method for the preparation of robust transparent superhydrophobic coatings is promising for outdoor applications such as self-cleaning cover glasses for solar cells and nonwetting windows.

Large area hexagonal boron nitride monolayer as efficient atomically thick insulating coating against friction and oxidation

Coating is the most widely applied technology to improve surface properties of substrates, and nanotechnology has been playing an important role in enhancing the coating performance. However, the tunability of surface properties by a single atomic layer remains poorly understood. Here we demonstrate that a chemical vapor deposited hexagonal boron nitride (h-BN) monolayer of large area and high quality can serve as a perfect coating to significantly improve friction, oxidation and electric resistance of the substrates. The exceptional low friction and insulation of h-BN monolayer coating facilitate the characterization of the h-BN film vividly by atomic force microscopy, showing the h-BN monolayer consists of domains with size within a few micrometers. This excellent coating performance together with the exceptional high thermal and chemical stability make the h-BN monolayer a promising coating material.

Morphology-driven nonwettability of nanostructured BN surfaces

Designing geometrical structures is an effective route to tailoring the wettability of a surface. BN-based hierarchical nano- and microstructures, in particular, vertically aligned and randomly distributed tubes and cones, were synthesized and employed as a platform for studying the influence of surface morphology on their static and dynamic interactions with water droplets. The variation of the contact angle in different hierarchical BN films is attributed to the combined effects of surface roughness and partial liquid-solid contact at the interface. Moreover, the impact response of water droplets impinging on BN arrays with different wetting properties is distinct. In the case of superhydrophobic films, the water droplet bounces off the surface several times whereas in less hydrophobic films it does not rebound and remains pinned to the surface. These results provide a facile route for the selective preparation of hierarchical BN nanostructure array films and a better understanding of their tunable water-repelling behavior, for which a number of promising applications in microelectronics and optics can be envisaged.

Origins of thermodynamically stable superhydrophobicity of boron nitride nanotubes coatings

Superhydrophobic surfaces are attractive as self-cleaning protective coatings in harsh environments with extreme temperatures and pH levels. Hexagonal phase boron nitride (h-BN) films are promising protective coatings due to their extraordinary chemical and thermal stability. However, their high surface energy makes them hydrophilic and thus not applicable as water repelling coatings. Our recent discovery on the superhydrophobicity of boron nitride nanotubes (BNNTs) is thus contradicting with the fact that BN materials would not be hydrophobic. To resolve this contradiction, we have investigated BNNT coatings by time-dependent contact angle measurement, thermogravimetry, IR spectroscopy, and electron microscopy. We found that the wettability of BNNTs is determined by the packing density, orientation, length of nanotubes, and the environmental condition. The origins of superhydrophobicity of these BNNT coatings are identified as (1) surface morphology and (2) hydrocarbon adsorbates on BNNTs. Hydrocarbon molecules adsorb spontaneously on the curved surfaces of nanotubes more intensively than on flat surfaces of BN films. This means the surface energy of BNNTs was enhanced by their large curvatures and thus increased the affinity of BNNTs to adsorb airborne molecules, which in turn would reduce the surface energy of BNNTs and make them hydrophobic. Our study revealed that both high-temperature and UV-ozone treatments can remove these adsorbates and lead to restitution of hydrophilic BN surface. However, nanotubes have a unique capability in building a hydrophobic layer of adsorbates after a few hours of exposure to ambient air.

Evaporation of pure liquid sessile and spherical suspended drops: a review

A sessile drop is an isolated drop which has been deposited on a solid substrate where the wetted area is limited by a contact line and characterized by contact angle, contact radius and drop height. Diffusion-controlled evaporation of a sessile drop in an ambient gas is an important topic of interest because it plays a crucial role in many scientific applications such as controlling the deposition of particles on solid surfaces, in ink-jet printing, spraying of pesticides, micro/nano material fabrication, thin film coatings, biochemical assays, drop wise cooling, deposition of DNA/RNA micro-arrays, and manufacture of novel optical and electronic materials in the last decades. This paper presents a review of the published articles for a period of approximately 120 years related to the evaporation of both sessile drops and nearly spherical droplets suspended from thin fibers. After presenting a brief history of the subject, we discuss the basic theory comprising evaporation of micrometer and millimeter sized spherical drops, self cooling on the drop surface and evaporation rate of sessile drops on solids. The effects of drop cooling, resultant lateral evaporative flux and Marangoni flows on evaporation rate are also discussed. This review also has some special topics such as drop evaporation on superhydrophobic surfaces, determination of the receding contact angle from drop evaporation, substrate thermal conductivity effect on drop evaporation and the rate evaporation of water in liquid marbles.

Platinum nanoparticle modified polyaniline-functionalized boron nitride nanotubes for amperometric glucose enzyme biosensor

A novel amperometric biosensor based on the BNNTs-Pani-Pt hybrids with Pt nanoparticle homogeneously decorated on polyaniline (Pani)-wrapped boron nitride nanotubes (BNNTs), was developed. It is shown that π interactions take place between BNNTs and polyaniline (Pani) located at N atoms from BNNTs and C atoms from Pani, resulting in the water solubility for the Pani wrapped BNNTs hybrids. The developed glucose biosensor displayed high sensitivity and stability, good reproducibility, anti-interference ability, especially excellent acid stability and heat resistance. The resulted BNNTs-Pani-Pt hybrid amperometric glucose biosensor exhibited a fast response time (within 3 s) and a linear calibration range from 0.01 to 5.5 mM with a high sensitivity and low detection limit of 19.02 mA M(-1) cm(-2) and 0.18 μM glucose (S/N = 3). Surprisedly, the relative activity of the GC/BNNTs-Pani-Pt-GOD electrode keeps almost no change in a range from pH 3 to 7. Futhermore, the BNNTs-Pani-Pt hybrid biosensor maintains a high GOD enzymatic activity even at a relatively high temperature of 60 °C. This might be attributed to the effect of electrostatic field and hydrophobia of BNNTs. The unique acid stability and heat resistance of this sensor indicate great promising application in numerous industrial and biotechnological operations involving harsh conditions.

Boron nitride nanosheet coatings with controllable water repellency

The growth, structure, and properties of two-dimensional boron nitride (BN) nanostructures synthesized by a thermal chemical vapor deposition method have been systematically investigated. Most of the BN nanosheets (BNNSs) were less than 5 nm in thickness, and their purity was confirmed by X-ray energy dispersive spectroscopy, X-ray photoelectron spectroscopy, electron energy loss spectroscopy, and Raman spectroscopy. The effects of the process variables on the morphology and roughness of the coatings were studied using atomic force microscopy and scanning electron microscopy. A smooth BN coating was obtained at 900 °C, while compact BNNS coatings composed of partially vertically aligned nanosheets could be achieved at 1000 °C and higher temperatures. These nanosheets were mostly separated and exhibited high surface area especially at higher synthesis temperatures. The nonwetting properties of the BNNS coatings were independent of the water pH and were examined by contact angle goniometry. The present results enable a convenient growth of pure BNNS coatings with controllable levels of water repellency, ranging from partial hydrophilicity to superhydrophobicity with contact angles exceeding 150°.

Controlled surface modification of boron nitride nanotubes

Controlled surface modification of boron nitride nanotubes has been achieved by gentle plasma treatment. Firstly, it was shown that an amorphous surface layer found on the outside of the nanotubes can be removed without damaging the nanotube structure. Secondly, it was shown that an oxygen plasma creates nitrogen vacancies that then allow oxygen atoms to be successfully substituted onto the surface of BNNTs. The percentage of oxygen atoms can be controlled by changing the input plasma energy and by the Ar plasma pre-treatment time. Finally, it has been demonstrated that nitrogen functional groups can be introduced onto the surface of BNNTs using an N(2) + H(2) plasma. The N(2) + H(2) plasma also created nitrogen vacancies, some of which led to surface functionalization while some underwent oxygen healing.

Recent advancements in boron nitride nanotubes

This article provides a concise review of the recent research advancements in boron nitride nanotubes (BNNTs) with a comprehensive list of references. As the motivation of the field, we first summarize some of the attractive properties and potential applications of BNNTs. Then, latest discoveries on the properties, applications, and synthesis of BNNTs are discussed. In particular, we focus on low-temperature and patterned growth, and mass production of BNNTs, since these are the major challenges that have hindered investigation of the properties and application of BNNTs for the past decade. Finally, perspectives of future research on BNNTs are discussed.