In this study, a numerical simulation model was developed in conjunction with X-ray CT (computed tomography) images of actual facemasks in order to clarify the behavior of submicron-sized particles in the facemask microstructure. It was found that the presence of large pores inside the microstructure caused streamlines to curve near the facemask domain, and particles accompanying the streamlines were more likely to be collected on the pore surface. Although the presence of pores results in a decrease in a pressure drop and the collection efficiency, the above effect suppresses the decrease in the collection efficiency and thus improves the performance (quality factor) of the facemask.

The mechanical reliability of products must be assured for scaling up and production of complex-shaped components by spark plasma sintering (SPS) of spray-dried granules. The evolution of morphologies of pores and defects, which control the mechanical strength, is investigated by using synchrotron X-ray multiscale tomography during SPS of alumina granules at 1300°C. While large defects arising from the hierarchical granule packing structure cannot be removed by pressureless sintering, crack-like defects and branched rodlike defects are almost eliminated by SPS at stresses higher than 30 and 50 MPa, respectively. But, small ellipsoidal porous regions, which may arise from aggregates or dimples of granules, cannot be removed even at a pressure of 50 MPa. A very large defect is also found by using micro-CT. It is supposed that this defect is formed from a large void in loosely packed granules. The shrinkage of large voids and the elimination of crack-like defects are explained by the theoretical prediction based on the continuum theory of sintering.

All-solid-state lithium-ion batteries are promising next-generation secondary batteries, primarily because of their superior safety. In their production process, it is necessary to achieve large contact interfaces between the particles and improve particle fluidity. The particle shape of the solid electrolyte plays a key role in addressing these requirements. Li₃PS₄ (LPS) is synthesized in the liquid phase and offers the advantages of cost-effectiveness and production scalability. However, the mechanisms controlling particle size and shape have not yet been revealed. In this study, we synthesized LPS particles in the liquid phase using a hot stirrer and an ultrasonic homogenizer to investigate the effects of reaction temperature and impact force on the reaction time and particle shape. We successfully synthesized shape-controlled particles with high ionic conductivity by combining different synthesis methods. This study provides valuable data for optimizing the synthesis conditions to attain specific particle shapes and sizes.

Porous structures are increasingly getting attentions in developing environmental catalysts, such as three-way catalysts (TWC), due to their ability to improve catalyst performance without changing their composition. This study explored various template-to-TWC mass ratios to create an optimal interconnected nanoporous structure while maintaining the catalyst morphology. This optimized sample was then investigated to compare CO oxidation performance with nanoparticles and aggregate structures. The results demonstrated that the nanoporous structure improved CO oxidation efficiency by 50% compared with other structures. This improvement is attributed to the better diffusion of reactants within the interconnected porous structures of the nanoporous sample. These findings highlight the critical role of nanoporous structures in enhancing the effectiveness of environmental catalysts.

Several types of metal–organic frameworks (MOFs) exhibit S-shaped adsorption isotherms due to their structural expansions. These materials are obtained as powder samples and require molding for industrial use; however, molding the samples with polymer binders reportedly made the S-shape less distinct. Our previous study elucidated this mechanism: the polymers inhibited the volume expansion of MOFs in the pellets. In this study, we molded two types of flexible MOFs exhibiting different volume expansion ratios and compared their adsorption behaviors. We concluded that a flexible MOF with a smaller volume expansion suppresses the smeared effect when in pellet form.

Ag particles supported on a metal oxide support have been used for various catalytic reactions (e.g. selective oxidation of ethylene). To improve the catalytic activity, size reduction of Ag particles is desired. However, it is challenging to obtain small Ag particles due to the low Tammann temperature of Ag. In this study, we successfully deposited 20 wt% of Ag clusters (~2 nm) onto TiO₂ using flame spray pyrolysis. The Ag clusters were stabilized by strong metal-support interaction (SMSI) between Ag and TiO₂ which was induced in the combustion reaction zone. SMSI formed TiOx as confirmed by X-ray diffraction. The amount of TiOx depended on the flame conditions and Ag content (10–40 wt%). The surface area of Ag clusters was estimated by H₂ pulse titration. The Ag surface area increased with Ag content up to 20 wt%, and by further increasing the Ag content to 40 wt%, the surface area did not change. The stability of Ag clusters depended on the Ag content, the flame conditions, and the specific surface area of the titanium oxide support. In the future, we will explore catalytic activity of FSP-made Ag clusters for some reactions.

Hemolysis assay using red blood cells has been widely used as the simplest cytotoxicity test for nanoparticles. Nevertheless, the hemolytic action mechanism of nanoparticles is still poorly understood. In this study, the hemolytic action of silica nanoparticles with different particle diameters (5–120 nm) and surface functional groups (none, amino group, and carboxyl group) was investigated under different exposure environments: temperatures (4–43°C) and phosphatic buffered saline solutions (additive-free, serum added, and serum albumin added). Adding to the hemolysis assay, the adhesion number of nanoparticles to red blood cells and the aggregation/dispersibility of red blood cells were measured, whereby the overall picture of the hemolytic action mechanism of nanoparticles was given.

We have developed a phase retrieval holography module for microparticle measurement. The system that this module has comprises two cameras connected to a single-board computer (SBC) with a graphics processing unit (GPU), a diode-pumped solid-state green laser, and a beam splitter. Furthermore, the GPU provides real-time reconstruction. The system can record the shapes and positions of particles falling in a static flow in a three-dimensional volume as two holograms generating an interference pattern. Phase retrieval holography with two holograms solves the twin image problem that arises due to the lack of phase information. We also present the requirement of this module for experimentally recording and numerically reconstructing holograms of particles. Finally, we conclude that holographic measurement, limited to use in a laboratory, can be used for in-line/ on-line measurement of powder production processes.

In order to functionalize the powders, it is important to understand the relationship between the powders’ structure and their functionalities. As one of the techniques, the Mahalanobis-Taguchi system (MTS) has been utilized because that effective variables which improve accuracy of classification can be visualized. The surface-roughness-related variables were the effective powder structure which improve accuracy of classification into male/female of Japanese beetles larval droppings as the model powders. Considering that binder concentration in the females’ dropping was higher than in the males’ dropping, the females’ droppings could be deformed during molding process through the larval gut. The MTS can be expected as the effective way to improve the accuracy of the classification by visualization of the relationship between powder structure and functionalities without individual differences.

Si-Si σ bonds exhibit reactivity and physical properties similar to those of C=C π bonds. The research group is utilizing the flexibility of the Si–Si σ bond and the σ–π conjugation with aromatic substituents to investigate the synthesis, structure, and physical properties of various disilane-bridged macrocycles. We have already studied the synthesis and temperature-dependent behavior of a dimer (tetrasilacyclophane). Here we report on the synthesis of trimeric and tetrameric macrocycles and their crystal structures at different temperatures.

In the production of pharmaceutical solid formulations such as tablet, the spherical crystallization method, in which crystallization and granulation are carried out simultaneously in the same system, can integrate the downstream in the pharmaceutical production process, thus enabling high efficiency in pharmaceutical manufacturing. On the other hand, process enhancement such as filtration, drying, and formulation after crystallization has been an issue. To solve this problem, we developed a one-pot processing system with hybridized powder processing operations in addition to filtration and drying functions. This desktop-sized device has a highly functional rotating spherical chamber that can handle all the processes of filtration, drying, powder mixing, and wet granulation at once. In this study, we confirmed that the suspension of fenofibrate granules prepared by the spherical crystallization method can be processed by the one-pot powder processing equipment. It was also found that the wet granulation of acetaminophen granules was possible by spraying binder from the spray nozzle in this apparatus.

In Discrete Element Method (DEM), it is common to reduce the particle stiffness artificially from the original material property to employ a large time step and reduce the computational cost. When simulating cohesive particles, however, the reduction of the particle stiffness can cause excessive energy dissipation due to the prolonged contact duration, which can make the particles become more cohesive than the original ones. Recently, several scaling laws for attraction force are proposed to overcome this problem. Although these scaling laws are effective for dynamic systems where particles are fully fluidized as a bulk body, they are not applicable to relatively static systems since the instantaneous force balance is not maintained. In the present work, a new approach to reduce the viscous damping coefficient instead of the attraction force is proposed. The proposed model is applied to simulate cohesive particles in a rotary drum, and it is confirmed that the static phenomena such as the particles sticking on the drum wall as well as the dynamic phenomena such as the dynamic angle of repose are well replicated at the same time, which is difficult to achieve with the conventional method.

Surface-enhanced Raman scattering (SERS) is a phenomenon in which Raman scattered light of molecules adsorbed on noble metal nanoparticles with a diameter of about 50 to 100 nm is greatly amplified by surface plasmon resonance on the metal surface. Since it is possible to detect trace components, it is expected to be applied to ultra-sensitive analysis in a wide range of fields such as the medical field and the biological field. In SERS, it is known that when particles form a dimer or a further aggregate, an extremely strong electromagnetic field called a hot spot is formed between these particles. Since the target molecule is selectively adsorbed between such particles, the SERS effect is expected to be further amplified in the aggregated particles due to the synergistic effect of these two. However, the relationship between the aggregation state of such particles and the surface enhancement effect has not been completely elucidated. In this study, we fabricated a nanoparticle multilayer film by atomizer and verified the SERS effect due to the aggregate structure of the particles. The SERS effect was obtained with the nanoparticle accumulated film that prepared by 70-nm Ag nanoparticles with colloid concentration of 4.3 × 10¹² particles mL^–1.

This study was conducted to reveal the relationship between properties of porous membrane and process conditions, when membrane is manufactured via wetting process. Membrane in this study was manufactured using two kind of carbon black (XC-72r and Li-100) which have different specific surface area. Time of ultrasonic dispersion to disperse carbon black and heating temperature to evaporate medium were process conditions to be changed. The thickness, permeability and surface roughness were measured for obtained membrane. As a result, permeability increased to the thickness in the case used Li-100. On the contrast, it was almost constant to the thickness for the case of XC-72r. Although the surface roughness did not depend on the thickness obviously, it became larger for the membrane used the slurry of bi-modal particle distribution for carbon black than used the slurry mono-modal. Consequently, it was revealed that the tendency of permeability and surface roughness to the membrane was understood by the morphology and particle distribution in slurry of carbon black.

Particle adhesion and deposition in dry powder processes can result in low quality and productivity. In this study, to establish a method for controlling the charge and motion of particles and for removing them without using fluid and/or mechanical external forces, dielectric particles deposited on an insulating plate were charged and levitated using ultraviolet (UV) irradiation in an upward electric field. The particles in the top layer irradiated by UV light were positively charged by photoemission and levitated by the Coulomb forces. The flux and motion of the levitated particles and the charge of each levitated particle were experimentally obtained. The results showed that approximately 40% of the levitated particles descended because of the change in particle charge due to negative charge clouds formed by the photoemission from the particle layers and the levitated particles. Furthermore, applying an upward electric field after UV irradiation, all the particles were levitated without descending because the negative charge clouds were not formed. In addition, more particles were levitated due to an increase in particle charge, but the continuous levitation did not occur.

The particle flowability can be improved by admixing particles smaller than the original particles (main particles). However, the details of this improving mechanism are not yet fully understood. In this study, we focused on effects of adhesive force distribution at each of contact points based on admixing particle coating on improving the flowability, and investigated it using discrete element method (DEM) simulation. In this simulation, we used three different surface adhesive force distribution models (non-uniform, random, and uniform models) and calculated discharge flow rates. As a result, non-uniform models had a larger discharge flow rate compared with the other models. This is because non-uniform models had a larger frequency of generating discontinuous layer, which would suppress a formation of particle arching in a bed. Thus, in a smaller particle admixing system, adhesive force distribution at each of contact points would contribute to improving the flowability.

In this study, we demonstrated the precise size control of Poly lactic-co-glycolic acid (PLGA) nanoparticles using our microfluidic device named iLiNP^®. The size of PLGA nanoparticles was able to control ranged from 30 to 120nm by the flow conditions using the iLiNP device. The iLiNP device was also applied to produce the PEG-PLGA nanoparticles and paclitaxel (PTX)-loaded PLGA nanoparticles. We confirmed the physical properties including average-size, size distribution, and encapsulation efficiency of PTX were enough to evaluate for in vivo and in vitro assays.

Various kinds of particle suspensions in organic solvents are used in a wide range of industries. Thus, characterizing interactive forces between solids in organic solvents is significant for handling such suspensions. However, while the DLVO theory well describes the interaction between surfaces in aqueous solution, the interactions between particles in non-aqueous solvents have been much less understood. In this study, we prepared silica surfaces modified with silane coupling reagents with various terminal groups and investigated the interactions between the modified particle and substrate in organic solvents by atomic force microscopy. We also conducted NMR relaxation measurements to evaluate the relationship between the interaction forces and surface-solvent molecule interactions. The repulsive forces acting over a few nanometers were measured between the surfaces when the particles disperse, whereas only van der Waals attraction was observed when the particles aggregate. This repulsive force was suggested to be the solvation force, arising from the steric hindrance of solvent molecules strongly attached to the surfaces, which was produced when the surface-solvent molecule interaction is strong. On the other hand, when van der Waals attraction dominated the interactions between the surfaces the surface-solvent molecule interaction was found out to be weak.

The accumulation of organic pollutants in surface water, groundwater, and even drinking water have raised as a serious issue in recent decades. Semiconductor-based photocatalysis has emerged as a green and sustainable approach to find remediate solutions for environmental and energy issues. However, the fast recombination rate of photogenerated charge carriers reduces the photocatalytic efficiency of photocatalysts. In this study, a hydrothermal synthesis method is proposed for preparing four types of p–n heterojunctions, BiVO₄/BiOX (X=F, Cl, Br, I). BiVO₄ is an n-type semiconductor and BiOX is a p-type semiconductor. Photocatalytic activity tests showed that the BiVO₄/BiOF has the best photocatalytic performance under visible light, and photoluminescence spectra confirmed the lowest recombination rate of photogenerated charge carriers for BiVO₄/BiOF as compared with others. The microstructure of all samples is also investigated by scanning electron microscope and transmission electron microscope.

Magnetic materials that respond to external magnetic fields are used in a wide range of fields such as magnetic resonance imaging (MRI), medical diagnostic materials, electronic materials, and catalyst. Iron oxide magnetic particles such as magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃), which have excellent magnetic properties, are generally used as constituents of magnetic materials, and various functional magnetic materials based on iron oxide magnetic particles are developed in progress. However, iron oxide magnetic particles are difficult to use as coloring materials and optical materials, since they are dark brown to black materials. In this study, we found that colorless magnetic particles can be obtained by using a polymer network in which lanthanoid elements were combined. By applying this technology, we succeeded in producing full-color magnetic particles and fluorescent magnetic particles. The produced material exhibited magnetism in the powder state and in the state of being dispersed in a solvent, and is expected to be applied as a new magnetic material.