Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Due to their extraordinary properties, boron nitride nanosheets (BNNSs) have great promise for many applications. However, the difficulty of their efficient preparation and their poor dispersibility in liquids are the current factors that limit this. A simple yet efficient sugar-assisted mechanochemical exfoliation (SAMCE) method is developed here to simultaneously achieve their exfoliation and functionalization. This method has a high actual exfoliation yield of 87.3%, and the resultant BNNSs are covalently grafted with sugar (sucrose) molecules, and are well dispersed in both water and organic liquids. A new mechanical force-induced exfoliation and chemical grafting mechanism is proposed based on experimental and density functional theory investigations. Thanks to the good dispersibility of the nanosheets, flexible and transparent BNNS/poly(vinyl alcohol) (PVA) composite films with multifunctionality is fabricated. Compared to pure PVA films, the composite films have a remarkably improved tensile strength and thermal dissipation capability. Noteworthy, they are flame retardant and can effectively block light from the deep blue to the UV region. This SAMCE production method has proven to be highly efficient, green, low cost, and scalable, and is extended to the exfoliation and functionalization of other two-dimensional (2D) materials including MoS2 , WS2 , and graphite.

Simultaneous Production and Functionalization of Boron Nitride Nanosheets by Sugar-Assisted Mechanochemical Exfoliation.

Boron nitride nanotube (BNNT)/polyvinyl alcohol (PVA) composite fibers (<5 vol % BNNTs) were fabricated via electrospinning so that all BNNTs became aligned in the fiber casting direction. A several-fibers-thick ensemble of parallel-arranged contacting fibers made a single polymer sheet. Numerous sheets were then stacked in different ways with respect to the BNNT orientation (all fibers in adjacent sheets were either parallel or alternately rotated 90°) to make multilayer films that were finally hot-pressed. Various BNNT textures were reflected by the corresponding differences in the measured thermal conductivities of the resultant films due to anisotropy of thermal transport in the nanotubes. The highest values (0.54 W/mK) were obtained along the long axes of aligned BNNTs. Somewhat lower values (0.38 W/mK) were documented in films with alternately stacked fibers/tubes. The theoretical thermal conductivity values were estimated using the Nielsen’s model. These show good match with the experimental data. ...

Alignment of Boron Nitride Nanotubes in Polymeric Composite Films for Thermal Conductivity Improvement

A novel class of carbon nanotube (CNT)-based nanomaterials has been surging since 1991 due to their noticeable mechanical and electrical properties, as well as their good electron transport properties. This is evidence that the development of CNT-reinforced polymer composites could contribute in expanding many areas of use, from energy-related devices to structural components. As a promising material with a wide range of applications, their poor solubility in aqueous and organic solvents has hindered the utilizations of CNTs. The current state of research in CNTs—both single-wall carbon nanotubes (SWCNT) and multiwalled carbon nanotube (MWCNT)-reinforced polymer composites—was reviewed in the context of the presently employed covalent and non-covalent functionalization. As such, this overview intends to provide a critical assessment of a surging class of composite materials and unveil the successful development associated with CNT-incorporated polymer composites. The mechanisms related to the mechanical, thermal, and electrical performance of CNT-reinforced polymer composites is also discussed. It is vital to understand how the addition of CNTs in a polymer composite alters the microstructure at the micro- and nano-scale, as well as how these modifications influence overall structural behavior, not only in its as fabricated form but also its functionalization techniques. The technological superiority gained with CNT addition to polymer composites may be advantageous, but scientific values are here to be critically explored for reliable, sustainable, and structural reliability in different industrial needs.

Fabrication, Functionalization, and Application of Carbon Nanotube-Reinforced Polymer Composite: An Overview.

Closed-shell BO(2)(-) and BO(-) anions are proposed as high-efficiency luminescence centres in boron-nitrogen systems, which makes the anions localized and leads to a radiation transition.

Boron-oxygen luminescence centres in boron-nitrogen systems

Electric field and current assisted alignment of CNT inside polymer matrix and its effects on electrical and mechanical properties

In the paper, free vibration analysis of tapered Functionally Graded Material (FGM) plate with the inclusion of porosity has been performed. The tapered porous FGM plate is considered resting on a two-parameter (Winkler and Pasternak) elastic foundation. The displacement model of the kinematic equation for the plates in the present formulation is based on the First-order shear deformation theory (FSDT). The governing equation for free vibration analysis of FGM plates is obtained using Hamilton's principle. Simple power-law, Exponential Law, and Sigmoid law are used for tailored the material properties in the thickness direction of FGM plates. The solution of the resulting partial differential equation is obtained by using Galerkin-Vlasov's method with different boundary conditions. The solutions for uniform and uniform varying thick plates are investigated, and a comparative study is examined by comparing the results obtained with FSDT and Higher-order shear deformation theory (HSDT). The findings of the comparative study with the present approach provide pertinent outcomes for the vibration analysis of tapered FGM plates. The analytical solution for vibration analysis is presented to reveal the effects of porosity parameter, volume exponent, span ratio, aspect ratio, porosity distribution, and boundary conditions. Also, the elastic foundation parameter on tapered FGM plate increases the non-dimensional frequency, and the Pasternak foundation effect always dominates over the Winkler foundation.

Vibration characteristics of porous FGM plate with variable thickness resting on Pasternak's foundation

The effect of rolling and annealing on boron nitride nanotube (BNNTs) reinforced aluminum- composites is investigated in this study. Composites were fabricated via conventional sintering method with 0, 2 & 5 wt% BNNT addition in aluminum matrix. Addition of 2 wt% BNNT improved hardness and elastic modulus by 23% and 18%, respectively. Rolling the same composite at 200 °C with 60% reduction in single pass improved modulus and hardness of the composite by 60% and 31%, respectively, over Al. Addition of 5 wt% BNNT led to reduced properties due to agglomeration, which on rolling developed cracks. Annealing the rolled Al-BNNT composite further led to an improvement in strength and ductility. Annealed Al-2BNNT showed highest improvement in strength of 41% and 110% over rolled and sintered condition, respectively. In addition, the same composition has recorded 157% improvement in toughness in annealed condition, as compared to rolled condition. Uniformly distributed BNNTs restricted grain growth and grain boundary migration due to pinning, leading to presence of additional grain boundaries inside the old grains thus improving the strength further. Uniform distribution of BNNT is the prime reason behind the improved properties of Al-BNNT composites.

Effect of warm rolling and annealing on the mechanical properties of aluminum composite reinforced with boron nitride nanotubes

Hexagonal boron nitride (h-BN) has a layered structure similar to graphite and can be synthesized in the forms of nanotubes and nanosheets. These forms of BN have potential applications in mechanical, structural, optoelectronics and semiconductor devices. The formation of quantum dots of BN has expanded new physical properties such as fluorescent behavior. In the present study, hexagonal boron nitride (h-BN) nanoflakes have been synthesized by reaction of B2O3 and (NH2)2CO under a controlled atmosphere. BN nanoflakes, as observed in transmission electron microscopy (TEM) and scanning electron microscopy (SEM), were found to have wide size ranges of 6–35 nm. HRTEM for a single particle was also performed to confirm the formation and interplanar spacing corresponds to h-BN. Fourier transformation infrared spectroscopy (FTIR) spectra indicate strong B–N absorption at 1410 cm−1 and 799 cm−1. Absorption spectra of the product, investigated by UV-Vis spectrophotometry, reveal the characteristic peak of h-BN at 205 nm. Luminescence was recorded by fluorescence spectrophotometry and strong luminescence peaks at 411 nm and 435 nm, both in the blue region of the visible spectra, were found. Fluorescence properties of BN nanoflakes were used for imaging of cancer cells at different concentrations. BNNFs were found to be biocompatible against breast cancer celline MCF-7.

Emergence of fluorescence in boron nitride nanoflakes and its application in bioimaging

Polymer composites with suitable reinforcement can offer UV-shielding ability and strength simultaneously. Such material systems are being researched for many commercial applications, including window shields and automobiles. However, the inherent challenge is retaining transparency, while using reinforcement for adequate strength and UV-shielding. In this study, boron-nitride nanoflakes (BN) were reinforced in poly(methyl-methacrylate) (PMMA) to synthesize a strong and transparent sheet for structures for UV-shielding purpose. BN nanoflakes were amine functionalized and added for a range of content (0.1–3 wt%). Uniform dispersion and strong interfacial interaction led to efficient load transfer from matrix to reinforcement, thus increasing strength and modulus by 155% and 148%, respectively, with 2 wt% BN. UV-B and UV-C shielding properties improved as compared to PMMA for all composition. Addition of 0.5 wt% BN to PMMA offered improvement in blocking UV-wavelength by 325%, along with high transparency of ~65% to visible light.

Vijayesh Kumar

Papers

Electric field and current assisted alignment of CNT inside polymer matrix and its effects on electrical and mechanical properties

Vibration characteristics of porous FGM plate with variable thickness resting on Pasternak's foundation

Effect of warm rolling and annealing on the mechanical properties of aluminum composite reinforced with boron nitride nanotubes

Emergence of fluorescence in boron nitride nanoflakes and its application in bioimaging

Strong and transparent PMMA sheet reinforced with amine functionalized BN nanoflakes for UV-shielding application