SPH fluids for viscous jet buckling

We present a novel meshfree technique for animating\ud free surface viscous liquids with jet buckling effects, such as\ud coiling and folding. Our technique is based on Smoothed Particle\ud Hydrodynamics (SPH) fluids and allows more realistic and\ud complex viscous behaviors than the preceding SPH frameworks\ud in computer animation literature. The viscous liquid is modeled\ud by a non-Newtonian fluid flow and the variable viscosity under\ud shear stress is achieved using a viscosity model known as Cross\ud model. The proposed technique is efficient and stable, and our\ud framework can animate scenarios with high resolution of SPH\ud particles in which the simulation speed is significantly accelerated\ud by using Computer Unified Device Architecture (CUDA)\ud computing platform. This work also includes several examples\ud that demonstrate the ability of our technique.FAPESP - processos nos. 2013/19760-5 e 2014/11981-5FAPES - processos no. 53600100/11CNP

Superparamagnetic Microspheres with Controlled Macroporosity Generated in Microfluidic Devices

A microfluidic approach to preparing superparamagnetic microspheres with tunable porosity is described. In this method, droplets consisting of iron oxide nanoparticles, a functional polymer and solvent are formed in a microfluidic channel. The droplets are subsequently collected in solutions of sodium dodecyl sulfate (SDS) where the solvent is left to diffuse out of the droplet phase. By adjusting the concentration of the SDS and the polarity of the solvent of the dispersed phase, the porosity of the microparticles is controlled from non porous to porous structure. The formation of the pores is shown to depend on the rate at which solvent diffuses out of the droplet phase and the availability of SDS to adsorb at the droplet interface

Fabrication of High Content Carbon Nanotube–Polyurethane Sheets with Tailorable Properties

We have fabricated carbon nanotube (CNT)–polyurethane (TPU) sheets via a one-step filtration method that uses a TPU solvent/nonsolvent combination. This solution method allows for control of the composition and processing conditions, significantly reducing both the filtration time and the need for large volumes of solvent to debundle the CNTs. Through an appropriate selection of the solvents and tuning the solvent/nonsolvent ratio, it is possible to enhance the interaction between the CNTs and the polymer chains in solution and improve the CNT exfoliation in the nanocomposites. The composition of the nanocomposites, which defines the characteristics of the material and its mechanical properties, can be precisely controlled. The highest improvements in tensile properties were achieved at a CNT:TPU weight ratio around 35:65 with a Young’s modulus of 1270 MPa, stress at 50% strain of 35 MPa, and strength of 41 MPa, corresponding to ∼10-fold improvement in modulus and ∼7-fold improvement in stress at 50% strain, while maintaining a high failure strain. At the same composition, CNTs with higher aspect ratio produce nanocomposites with greater improvements (e.g., strength of 99 MPa). Electrical conductivity also shows a maximum near the same composition, where it can exceed the values achieved for the pristine nanotube buckypaper. The trend in mechanical and electrical properties was understood in terms of the CNT–TPU interfacial interactions and morphological changes occurring in the nanocomposite sheets as a function of increasing the TPU content. The availability of such a simple method and the understanding of the structure–property relationships are expected to be broadly applicable in the nanocomposites field

Enhanced Shear Performance of Hybrid Glass Fiber–Epoxy Laminates Modified with Boron Nitride Nanotubes

Matrix enhancement using nanotubes is one method to produce hybrid, multiscale fiber reinforced polymer (FRP) composites with improved interlaminar performance and added functional properties. Carbon nanotubes (CNTs) have been shown to be promising, and recent advances in the manufacturing of boron nitride nanotubes (BNNTs), which are largely unexplored for structural reinforcement of hybrid composites with microscale fibers, offer new opportunities to employ BNNTs in reinforced hybrid composite structures. This study investigates the shear and impact properties of BNNT hybrid composites, specifically glass fiber–epoxy/BNNT composite laminates. Two manufacturing techniques were used to fabricate the specimens: wet layup and vacuum-assisted resin transfer molding (VARTM). Shear punch, short beam shear, and modified Charpy tests were selected for their relevance to complex loading systems that involve shear, such as ballistic or other impact loading. The addition of 1 wt % BNNTs to the epoxy resin was found to improve the performance of the laminates: 8% increase in specific shear punch strength, 15% increase in the specific short beam shear strength, and an average of 22% increase in the specific fracture energy per area in modified Charpy tests. Improvements were lower in test cases approaching pure shear, which led to the conclusion that BNNT reinforcement most effectively improves laminate performance in more complex loading situations in which an element of normal stress, such as bending, is present. As such, BNNT reinforcement, which offers different functional properties than CNTs, is also promising to improve the impact performance in multiscale hybrid composites

Role of Hydrogen in High-Yield Growth of Boron Nitride Nanotubes at Atmospheric Pressure by Induction Thermal Plasma

We recently demonstrated scalable manufacturing of boron nitride nanotubes (BNNTs) directly from hexagonal BN (hBN) powder by using induction thermal plasma, with a high-yield rate approaching 20 g/h. The main finding was that the presence of hydrogen is crucial for the high-yield growth of BNNTs. Here we investigate the detailed role of hydrogen by numerical modeling and <i>in situ</i> optical emission spectroscopy (OES) and reveal that both the thermofluidic fields and chemical pathways are significantly altered by hydrogen in favor of rapid growth of BNNTs. The numerical simulation indicated improved particle heating and quenching rates (∼10⁵ K/s) due to the high thermal conductivity of hydrogen over the temperature range of 3500–4000 K. These are crucial for the complete vaporization of the hBN feedstock and rapid formation of nanosized B droplets for the subsequent BNNT growth. Hydrogen is also found to extend the active BNNT growth zone toward the reactor downstream, maintaining the gas temperature above the B solidification limit (∼2300 K) by releasing the recombination heat of H atoms, which starts at 3800 K. The OES study revealed that H radicals also stabilize B or N radicals from dissociation of the feedstock as BH and NH radicals while suppressing the formation of N₂ or N₂⁺ species. Our density functional theory calculations showed that such radicals can provide faster chemical pathways for the formation of BN compared with relatively inert N₂

Hydrogen-Catalyzed, Pilot-Scale Production of Small-Diameter Boron Nitride Nanotubes and Their Macroscopic Assemblies

Boron nitride nanotubes (BNNTs) exhibit a range of properties that are as compelling as those of carbon nanotubes (CNTs); however, very low production volumes have prevented the science and technology of BNNTs from evolving at even a fraction of the pace of CNTs. Here we report the high-yield production of small-diameter BNNTs from pure hexagonal boron nitride powder in an induction thermal plasma process. Few-walled, highly crystalline small-diameter BNNTs (∼5 nm) are produced exclusively and at an unprecedentedly high rate approaching 20 g/h, without the need for metal catalysts. An exceptionally high cooling rate (∼10⁵ K/s) in the induction plasma provides a strong driving force for the abundant nucleation of small-sized B droplets, which are known as effective precursors for small-diameter BNNTs. It is also found that the addition of hydrogen to the reactant gases is crucial for achieving such high-quality, high-yield growth of BNNTs. In the plasma process, hydrogen inhibits the formation of N₂ from N radicals and promotes the creation of B–N–H intermediate species, which provide faster chemical pathways to the re-formation of a h-BN-like phase in comparison to nitridation from N₂. We also demonstrate the fabrication of macroscopic BNNT assemblies such as yarns, sheets, buckypapers, and transparent thin films at large scales. These findings represent a seminal milestone toward the exploitation of BNNTs in real-world applications

Hydrogen-Catalyzed, Pilot-Scale Production of Small-Diameter Boron Nitride Nanotubes and Their Macroscopic Assemblies

Boron nitride nanotubes (BNNTs) exhibit a range of properties that are as compelling as those of carbon nanotubes (CNTs); however, very low production volumes have prevented the science and technology of BNNTs from evolving at even a fraction of the pace of CNTs. Here we report the high-yield production of small-diameter BNNTs from pure hexagonal boron nitride powder in an induction thermal plasma process. Few-walled, highly crystalline small-diameter BNNTs (∼5 nm) are produced exclusively and at an unprecedentedly high rate approaching 20 g/h, without the need for metal catalysts. An exceptionally high cooling rate (∼10⁵ K/s) in the induction plasma provides a strong driving force for the abundant nucleation of small-sized B droplets, which are known as effective precursors for small-diameter BNNTs. It is also found that the addition of hydrogen to the reactant gases is crucial for achieving such high-quality, high-yield growth of BNNTs. In the plasma process, hydrogen inhibits the formation of N₂ from N radicals and promotes the creation of B–N–H intermediate species, which provide faster chemical pathways to the re-formation of a h-BN-like phase in comparison to nitridation from N₂. We also demonstrate the fabrication of macroscopic BNNT assemblies such as yarns, sheets, buckypapers, and transparent thin films at large scales. These findings represent a seminal milestone toward the exploitation of BNNTs in real-world applications