Plate penetration into dry granular materials is numerically studied using a large-scale discrete element method (DEM). To investigate the effects penetration angle on the interactions between particles and the plate, the simulations with the different angles from 0 (vertical penetration) to 60 degree are compared. The results show that the drag force acting on the plate increases with a decrease in the penetration angle. For all cases, the formation of shear bands from the plate tip to the free surface in the bed is confirmed. The analysis of energy consumption in the bed shows that most of the energy input to the bed by the plate is locally dissipated by sliding frictions between particles in shear bands. As the penetration angle decreases, the amount of energy dissipation due to the friction increases in the shear bands formed near the plate tip.
Controlling flow behavior of micro food powder in the mixer is important for improving the efficiency of premix powder production. Four important factors (particle diameter, particle diameter distribution, particle shape, adhesion force) which could influence the flow behavior in the mixer were examined by several experiments and Distinct Element Method simulations. The experiments and simulations showed that the particle diameter, particle diameter distribution and particle shape had little effect on the flow behavior of the food powder in the rotating drum, while the adhesive force had a very large effect. On the basis of this finding, we proposed a simple adhesion model for representing the behavior of micro food powder in the mixer. It was found that the flow behavior of several kinds of food powder can be represented by the proposed model.
Toward industrial applications of commercialized carbon nanotubes (CNT), fully utilizing the intrinsic CNT properties is challenging due to the quality deterioration and the uncontrolled states through dispersion processes in matrices. Therefore we propose a predispersion step of CNTs prior to distributing them into matrices, clarifying the unravelling effect of CNT powders by various liquids with different viscosities like alcohols, silicone oils, ionic liquid, ketone, hydrocarbons, aprotic polar solvents, and water. Regardless of solvent polarity, liquids with higher viscosities led to more unravelled CNT particles, reaching up to an approximately ten thousand times higher particle number than one before the dispersion.
Herein we report a new grinding method to obtain fine particles having high specific surface area which is difficult to realize a conventional dry grinding. Several inorganic carbonates and metal oxides have been studied. Planetary ball milling under dry conditions and subsequent water addition realize the particles with a crystallite size and equivalent size of the specific surface area in the nanometer range. The equivalent size could be down to 25–136 nm using our method except TiO2. Regarding ground TiO2 sample, 47 nm in the equivalent size was successfully obtained via adding KOH solution and washing process. From the view point of solubility, we proposed the mechanism for the equivalent size down to nanometer range.
In this study, the effect of multivalent ions on ionic crosslinking of polyelectrolytes adsorbed on particle was investigated. Ammonium polycarboxylate, one of the typical polyelectrolytes, was used as a dispersant. Zinc oxide and titanium oxide was used as sample powder. A well-dispersed slurry was prepared by adding polyelectrolytes as the dispersant beforehand. Thereafter, multivalent cations were added to the slurry to convert it from liquid to a gel-like consistency, which was caused by the ionic crosslinking of polyelectrolytes adsorbing on the surface of the particles. It was found that the ionic radius of adding multivalent cation has an influence on the strength of the gel. It was also shown that this method was effective for prevention of density segregation during sedimentation.
Functional nanoparticle syntheses by thermal plasmas are reviewed. The advantages of thermal plasmas, such as high enthalpy, high chemical reactivity, and rapid quenching capability, have brought the advances and demands in plasma processing. Recent researches by DC arc, multiphase AC arc, and induction thermal plasma are summarized. Metal, intermetallic compounds, oxide, nitride, and boride nanoparticles are successfully synthesized by thermal plasma method. In particular, nanomaterial synthesis for the utilization in lithium-ion battery are summarized. Attractive nanomaterials related to cathode, anode, and electrolyte are successfully synthesized by thermal plasmas. High-productivity of the nanoparticles by thermal plasmas for industrial utilization can be achieved by improving energy efficiency and solving electrode erosion issue.
This paper shows the effect of the agglomeration control on the catalytic activity for oxygen evolution reaction (OER). In this study, (Ca0.5Sr0.5)RuO3 (CSRO) catalyst was selected as the bi-functional catalyst for OER and oxygen reduction reaction (ORR). The sol-gel derived CSRO particle was mixed with the carbon nano-particle in the tetrahydrofuran (THF) based solution under the various pH condition to prepare the ink for the air electrode of rechargeable metal-air battery. The microstructure of the air electrode was designed by controlling the electrostatic repulsion force of the CSRO catalyst particles in the ink. As a result, the surface area of the air electrode increased with increasing the electrostatic repulsion force of the CSRO catalyst particle, resulting in the enhancement of the OER activity. From these results, we concluded that the agglomeration control of the catalyst particle in the ink is one of the key factors to enhance the catalytic activities of the electrocatalysts.
High-speed fabrication of colloidal crystal films composed of polystyrene particles was attempted by electrophoretic deposition. Flat, uniform colloidal crystal films were fabricated on ITO-coated glass or PET sheet substrates in several minutes by using an optimum ratio of a mixed solvent of water and ethanol. The obtained colloidal crystal films exhibited structural color predicted from the particle size. The structural color of the colloidal crystals immobilized by immersing silicone elastomer changed to different colors when the interlayer spacing was changed due to the swelling/shrinkage by dropping organic solvents or applying tensile stress on the films. Such structural color changes were applicable for a simple sensor to visualize strain.
Vat photopolymerization is an additive manufacturing process that is used to fabricate highly accurate three-dimensional (3D) ceramics. However, with this process, it is difficult to mold powders, such as carbides and TiO2, which absorb light of a certain wavelength from the light source used. In this study, we investigated the fabrication of low conductivity Al2O3-ZrO2-TiO2 ceramics, a kind of electro-static discharge countermeasure ceramics, by digital light processing type vat photopolymerization. Slurries having a solid concentration of 35 vol%, in which Al2O3, ZrO2, and TiO2 ceramic powders were dispersed in a photocurable resin, were prepared. The influence of TiO2 concentration on the photocurability and laminate properties were investigated. The results showed that as the TiO2 concentration increased, the light irradiation energy required for molding increased. By carefully investigating the molding conditions at a laminating pitch of 25 μm, we could prepare dense and low conductivity Al2O3-ZrO2-TiO2 3D complex shape ceramics.
It is important to reveal fault structures and stress states in accretionary prisms for understanding the building and releasing of seismic energy as they control the generation of great earthquakes and tsunami. Here we show the evolution process of three-dimensional fault structures on sandbox simulations using a discrete element method (DEM). To realize the real-scale sandbox simulation, we developed state-of-the-art techniques in high performance parallel computing methods for the DEM, and then performed the largest DEM simulation in the world using up to 1.9 billion particles with similar grain size of real sand for identifying the three-dimensional fault structure. The DEM simulations reproduced the undulation of fault structures similar to those found commonly in nature. In addition, the characteristic grain motion was found near the frontal fault before beginning the uplift event of sand bed, which could be a precursor of tectonic events behind accretionary prism formation.
For large scale use of renewable energy, hydrogen society is necessary to overcome supply and demand mismatch in time and space. Polymer-electrolyte fuel cells (PEFCs) represent a superior system that exhibits high-efficiency, offering better power generation, meeting the desired levels of demand. However, in order to facilitate widespread use of fuel cells, cost and lifetime problems must be resolved. We are systematically designing and developing new materials from the molecular level to the device level. In the fuel cell systems, different components such as membrane, catalysts, and catalyst layer share significant functions and work in a well-coordinated manner, and hence, the total cell system must be optimized for the best performance. The systematic design and developing approaches concerning electrocatalysts for PEFCs are proposing.
A new simulation model to deal with metal powders was developed. The feature of the proposed model is to express plastic deformation behavior of metal powders. The model is based on Advanced Distinct Element Method (ADEM), which can represent deformation behaviors of elastic materials. The change of the proposed model from ADEM is interaction force of primary particles. In order to confirm the validity of the new model, compression tests and drop tests have been carried out in experiment and simulation. In compression tests, test tablets were thinly stretched and the deformation was maintained. In drop tests, a dimple was formed on the tablet when an iron ball collides. Characteristic behaviors of metal material such as stretching the tablets and forming a dimple were also confirmed in simulation. Therefore, it is identified that the proposed model could express the behavior of metal material.
A new model for estimating macroscopic permittivity was proposed to predict dispersion states of filler particles in a particulate composite material. In the model, the estimation targets are random packed composite materials. The composite materials were represented as a cluster of unit cells. The unit cells were connected by a proposed layer structure model. The macroscopic permittivity was estimated by calculating a synthetic capacity of the cluster.
The proposed model was validated by comparisons between estimated and measured macroscopic permittivity of several particulate composite materials. In addition, it was identified that the proposed model could estimate the permittivity more accuracy than an existing theoretical equation’s one due to considering the effects for the dispersion states of filler particles. Furthermore, it was indicated that the proposed model could also estimate the dispersion states of filler particles by the measured permittivity. The applicability of the method was confirmed by comparisons between estimated and experimental dispersion states of filler particles.
The uptake of nanoparticles (NPs) into biological cells with rigid cell walls is poorly understood. Interestingly, the authors demonstrated that positively charged polystyrene NPs were taken into yeast cells in the physiological saline. However, the polystyrene NPs are not suitable for carrier NPs due to their low biodegradability. In this study, we evaluated the uptake of biodegradable poly(lactic-co-glycolic) acids (PLGA) NPs into the yeast cells. As a result, PLGA NPs were taken into yeast cells regardless of their surface potentials. The yeast cells were alive after the uptake of negatively charged NPs, whereas the cell viability for the positively charged NPs was low. In addition, the experiments using endocytosis inhibitors suggested that the uptake of PLGA NPs was different from the conventional endocytosis. These experimental results strongly suggested that the negatively charged PLGA NPs are suitable for the delivery of useful substances to eukaryotic cells with cell walls.
Monolayer films composed of ordered particle arrays exhibit unique optical properties, which lead to various potential applications like sensors and antireflective coatings. In this study, we investigated particle deposition processes by using a drag coating technique based on convective self-assembly. Unlike micron-sized particles, 300-nm particles formed submonolayers instead of monolayers. Hence, we modified the technique and demonstrated that reversed dragging, introduction of a film blade, and periodic change in deposition speed dramatically improved the particle deposition process to cover the entire substrate surface uniformly with a monolayer of ordered particle arrays. Furthermore, our modified drag coating process produced monolayers of particles with different sizes of 570, 120, 45, and 27 nm. Thus, our technique is simple and versatile, and is applicable to a wide particle size ranging from microns to tens of nanometers.
Computational fluid dynamics has been increasingly adopted as a promising tool to understand the essential dynamics of particulate flow. The present review gives a brief description of numerical methods to describe the boundary condition of moving solid surface at lattice Boltzmann method (LBM), including bounce-back (BB) method (and improved BB method), immersed boundary (IB) method, and smoothed profile (SP) method. It is essential to choose an appropriate numerical method according to the target system. Among these methods, the author and coworkers have used the SP method to efficiently simulate flows including a number of particles. Here, typical results obtained by the SP-LBM simulations are presented.
Preparation of boehmite-silica composite particles using heterocoagulation was studied to improve the packing ratio and flowability of the particles used as fillers and flame retardants in resins. By measuring the zeta potential of each particle, silica showed a negative charge at pH > 2, and boehmite showed a positive charge at pH < 9. Therefore, mixing of each suspension of silica and boehmite prepared at pH 4 successfully produced boehmite-silica composite particles by heterocoagulation. We used two different silica particle sizes. Using smaller silica particles, composite particles uniformly coated with silica were obtained. The composite particles showed excellent fluidity in liquid paraffin, which suggested improved packing ratio.
Magnetorheological Fluids (MRF) whose apparent viscosity is controllable by applying magnetic fields are known as a kind of functional fluids. It is generally considered that such viscosity changes are caused by the formation of chain-like clusters of magnetic particles dispersed in the fluid. Many researches have been conducted to understand the mechanism of the viscosity change of MRF but there are few report which directly indicate the relation between the cluster formation and the viscosity change because of the difficulty of the observation such phenomena simultaneously. In this study, the relation between particle clustering and viscosity change has been investigated using DEM-DNS simulation. The simulations are conducted just a few chain-like clusters of magnetic particles in simple shear flow and the simulation results indicate that the apparent viscosity corresponds to both of the chain length and the angle between magnetic field direction and chain axis which depend on the Mason number.
Surface modification of functional polymers onto liposomes is effective strategy to obtain functional liposomes that release drugs at target site or intracellular compartments. Here, design of pH-sensitive liposomes for cell-specific intracellular drug delivery was summarized. Liposomes modified with hyaluronic acid derivatives exhibited selective anticancer drug delivery to CD44-expressing cancer cells. Furthermore, liposomes modified with curdlan derivatives were efficiently recognized by dendritic cells, leading to efficient antigen delivery, activation of dendritic cell and induction of antitumor immunity on tumor-bearing mice. Therefore, functional polymer-modified liposomes are promising for cell-selective cancer chemotherapeutic system or immunotherapeutic systems.
Thermally conductive polymer composites offer new possibilities for the thermal management in electronic devices. An approach of current interest to improve the thermal conductivity of polymer composites is the addition of high thermally conductive fillers with different shape and size. This paper described an overview of the microstructural design techniques for polymer composites with high thermal conductivity, and recent progress and advances that have been made on the enhancement of thermal conductivity of the polymer composites.