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.

View full abstract

CsPbBr₃ nanocrystal (NC), which is a perovskite quantum dot, has attracted much attention as excellent phosphor; however, its deterioration by excitation light is a significant problem. The authors founded self-recovery of CsPbBr₃ NC during dark storage after photodegradation without ambient air. In this work, the photodegradation and self-recovery were investigated. Synthesized CsPbBr₃ NC was packed in a solid-sample cell. The sample color changed from yellow to black by 468nm blue LED irradiation for 72h, accompanied with decrease in photoluminescence (PL) intensity. The color returned to yellow during subsequent dark storage, and the PL intensity recovered completely after 2400h. Infrared spectroscopy for surface ligand on the NC surface revealed change in adsorption state of oleic acid. The photodegradation might be explained by desorption of the surface ligand due to diffused excitons generated by the excitation irradiation. The self-recovery should be resulted from readsorption of the desorbed ligand.

Color change of CsPbBr₃ NC during the irradiation and subsequent dark storage.

View full abstract

The formation of naringenin (NRG) coamorphous using coformer candidates of nine selected flavonoids was investigated. The screening test showed that hesperetin (HPT) is an excellent potential coformer. The melt-quenched particles (MQPs) of NRG/HPT (molar ratio of 3/1 to 1/3) were prepared by melt-quenching method. MQPs of NRG/HPT showed the hallow-pattern in any combination ratio in powder X-ray diffraction. MQPs of NRG/HPT (1/1) showed the highest physical stability without recrystallization of NRG and HPT upon storage. Conversely, other MQPs showed recrystallization from the compound with a higher molar ratio, implying the stoichiometric relationship between NRG and HPT at a molar ratio of 1/1. The MQPs of NRG/HPT (1/1) showed significantly improved dissolution properties of both NRG and HPT in simulated intestinal fluid. In addition, the MQPs of NRG/HPT (1/1) enhanced the solubility of both NRG and HPT even in oil components. Their solubility from the MQPs of NRG/HPT (1/1) increased 5-times compared to untreated compound powder in oil components. These results showed that a coamorphous of NRG/HPT (1/1) enhances the physical stability and solubility of both NRG and HPT.

Dissolution profile of (a) NRG and (b) HPT in simulated intestinal fluid. Data are presented as mean ± SD, (n = 3).

View full abstract

Dry powder inhalation (DPI) has attracted much attention as a treatment for respiratory diseases. Understanding the drug particle motion in the respiratory system and the deposition behavior is necessary to improve the efficiency of DPI. We conducted computer simulations using a model coupling a discrete element method and a computational fluid dynamics method (DEM–CFD) to evaluate the particle deposition in human respiratory system. A simple respiratory model was developed, which numerically investigated the effect of particle properties on the particle deposition behavior. The DEM–CFD simulations demonstrated that the smaller and lower-density particles showed higher reachability into the simple respiratory model, and the particle arrival ratio to the deep region depended on the aerodynamic diameter. Furthermore, the exponential relationship between the particle reachability into the depth of the simple respiratory model and the aerodynamic diameter predicted the particle aerodynamic diameter based on the required reachability. The particle shape also had an impact on the particle deposition behavior. The rod-like particles with a larger aspect ratio indicated higher reachability into the depth of the simple respiratory model. This was attributed to the high velocity motion of the particles whose long axis was in the direction of the deep region.

View full abstract

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.

(a) Digital photographs of the magnetically responsive behavior of colored magnetic nanoparticles. (b) International Commission on Illumination (CIE) 1931 chromaticity plot of colors prepared by particle mixing. Adapted with permission from Ref. (Kohaku et al., 2020). Copyright: (2020) American Chemical Society.

View full abstract

Typical pigments are composed of organic dyes that absorb a certain region of the visible light spectrum. Because excited organic dyes are not chemically stable, their colors fade over time under exposure to light. Structural color generated by optical interactions of light with nano- and micro-structures have attracted considerable research and industrial attention because the color never diminishes as long as the structure is preserved. Color pixels with highly saturated scattering colors have been produced by nanostructures, and high-resolution color printing has been achieved by using these color pixels. However, the printing is limited to a very small area (<1mm²) owing to the restriction of the nanofabrication processes. In this work, we develop a high-quality color ink composed of crystalline silicon (Si) nanoparticles for the structural coloration of an arbitrary substrate. By reducing the size distribution of colloidal Si nanoparticles, we succeeded in coloring solutions of Si nanoparticles in the blue-to-orange range. We demonstrate the structural coloration of a flexible substrate by Si nanoparticle color inks.

(a) Schematic of Si nanoparticle -PVP composite film. (b–e) Reflectance spectra of Si nanoparticle ink and films. (f, g) Photos of Si nanoparticle-PVP composite film on PET substrate. Reprinted with permission from Ref. (Sugimoto et al., 2020) under the terms of the CC-BY 4.0 license. Copyright: (2020) The Authors, published by Willey-VCH.

View full abstract

Most of the polymeric materials used in industry are multicomponent systems, and structural reinforcement and new functions are added to them by adding fillers with various properties and shapes. When fibers or rod-like particles are added to a polymeric material, their density and orientation distribution have a significant effect on the physical properties. Therefore, it is particularly important to predict and control the phase separation and aggregation/orientation behavior of polymeric and particulate dispersions. In this study, flexible fibrous particles dispersed in one- and two-component fluids were modeled and numerically simulated using the Smoothed Profile Method (SPM) (Nakayama Y., 2008). The time evolution of the relative viscosity in the start-up shear flow was calculated for fibers dispersed in a single component fluid, and the relation between their orientation and the viscosity was made clear. The calculation results agreed well with the experimental results. It was also found that the orientation of the fibrous particles dispersed in a two-component fluid depends not only on the fluid flow but also on the affinity of the particles to each fluid. In addition, depending on the affinity of the particles to the fluid components, the size and the shape of the phase separated domain are found to be quite different from those in the absence of the fibrous particles.

Time dependent relative viscosities η_r⁺ for various volume fractions ϕ_v(r_f=9).

View full abstract

The mechanical characteristics of soft particle systems, such as hydrogels, are expected to be very complex due to the additional degree of freedom of deformation within each particle and its details have not been well understood. In this study, we attempt to develop a numerical model based on the boundary element method (BEM) toward the elucidation of mechanical behaviors of soft particle systems in detail. As a first step, the deformation behavior of a single soft particle is studied using the proposed model. The results of a compression test show that, within the small deformation, the strain-force relation is generally consistent with experiments using hydrogel particles while the force becomes much smaller than the experiments when the deformation becomes large.

Deformation of a soft particle.

View full abstract

Due to the increase of unstable electric power production from renewable energy sources such as solar and wind powers, thermal power plants are becoming more important to adjust the balance of supply and demand of electricity. In addition to that, the reduction of CO₂ is required at the same time. From the background of the possibility of introducing hydrogen to coal-fired power plant as a fuel in the future, in this study, the experiments of hydrogen/pulverized coal particle clouds co-combustion were conducted to clarify the flame propagation characteristics of hydrogen/pulverized coal particle clouds co-combustion and to obtain the validation data for future development of the co-combustion models for the numerical simulation. As results, the flame propagation velocity of hydrogen/pulverized coal particle clouds co-combustion is lower than that of pure hydrogen flame, even in the condition that the equivalence ratio of hydrogen/air is less than unity (fuel lean condition). This result is different from the previous research for the co-combustion of ammonia/pulverized coal particle clouds conducted by authors, and is a new finding from this study.

Typical images of Schlieren photograph, direct imaging, and OH radical imaging, and the methods to obtain the flame radius.

View full abstract

The liposome-protamine-DNA complex (LPD) is an effective cationic carrier of various nucleic acid constructs such as plasmid DNA and small interfering RNA (siRNA). Hyaluronic acid coated on LPD (LPDH) reduces cytotoxicity and maintains the silencing effect of LPD-encapsulated siRNA. Herein, we aim to develop LPD- or LPDH-containing spray-freeze-dried particles (SFDPs) for therapeutic delivery of siRNA to the lungs. LPD- or LPDH-containing SFDPs (LPD- or LPDH-SFDPs) were synthesized and their structure and function as gene carriers were evaluated using physical and biological methods. The particle size of LPDH, but not of LPD, was constant after re-dispersal from the SFDPs and the amount of siRNA encapsulated in LPDH was larger than that in LPD after re-dispersal from the SFDPs. The in vitro pulmonary inhalation properties of LPDH-SFDPs and LPD-SFDPs were almost the same. The cytotoxicity of LPDH-SFDPs in human umbilical vein endothelial cells (HUVEC) was greatly decreased compared with that of LPD-SFDPs. In addition, Bcl-2 siRNA in LPDH-SFDPs had a significant gene silencing effect in human lung cancer cells (A549), whereas Bcl-2 siRNA in LPD-SFDPs had little effect. These results indicate that compared with LPD, LPDH is more useful for developing SFDPs for siRNA pulmonary inhalation.

View full abstract

There are plenty of adhesive supra-structures in nature. For instance, geckos have a number of submicron-sized fibers on their feet, which allow it to stick and adhere strongly along the contour of the surface. This structure makes it possible for geckos to show strong adhesiveness to various surfaces. Inspired by such adhesion mechanism derived from micro- and nano-structures, I aimed to create a multi-layered gel membrane possessing surface adhesiveness and followability. The layer-by-layer deposition of gel particles via a polymer complex was carried out onto the gel base to create 3D gel structures. By tuning the type and the number of the layer-by-layer deposition, I could modulate elasticity and surface followability of the gel membrane to improve its adhesiveness.

View full abstract

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.

Schematic illustration of the iLiNP device.

View full abstract

This work aimed at obtaining high heat-insulating (low thermal conductivity) focusing on thermal transport at a nanoparticle interface based on transparent oxide semiconductors (In₂O₃:Sn, ITO). In particular, thermal conductance processes were investigated using thermo-reflectance based on pulsed light heating from experimental and theoretical approaches. ITO nanoparticle films (ITO NP films) showed low thermal conductivity of 0.3 [W/m·K], which were caused by reduction of thermal conductance (phonon propagation) at nanoparticle interfaces. In addition, ITO NP films had low film density, which were also considered as a cause of low thermal conductivity. Therefore, thermal transport of ITO NP film played an important role in controlling surface structures of nanoparticles and a stacking method for fabricating three-dimensionally assembled films. These results contribute to development of functional materials with both “visible transmittance” and “heat-insulating”. This assignment provided new insight for control of thermal transport based on nanoparticle interfaces.

(a) Schematic picture of a RF-type thermoreflectance measurement method. (b) Time domain thermoreflectance measurement of an ITO nanoparticle thin film. Theoretical and experimental results are shown by the straight lines (-) and black circles (○), respectively. (c) Cross-sectional SEM image of a three-layer structure consisting of Pt, ITO nanoparticle thin film, and Pt. (d) Interfacial SEM image at a Pt-ITO interface.

View full abstract

Monodisperse particles of cathode active material for Li-ion secondary batteries were obtained by membrane emulsification using highly ordered anodic porous alumina. The membrane emulsification was carried out by injecting a dispersed phase containing monomer and metal salts into a continuous phase through the uniform-sized holes in the anodic porous alumina membrane. The obtained emulsion droplets were solidified and heat-treated for the preparation of monodisperse particles of cathode active material. From electrochemical measurements, it was confirmed that the obtained particles acted as cathode active material for Li-ion secondary batteries. It was also observed that the properties of the batteries depended on the particle size.

SEM image of LiCoO₂ particles obtained by membrane emulsification.

View full abstract

In this study, activated carbon was prepared using bagasse and carbon fiber (RCF) recycled from carbon fiber reinforced plastic (CFRP), and its specific surface area was measured to evaluate its properties.

RCF with a critical fiber length of less than 700μm was obtained from CFRP using a cutter mill. In the hydrolysis reaction of cellulose in bagasse, the amount of functional groups, such as the carboxyl group and hydroxyl group, on the RCF surface was enough to function as a catalyst for the hydrolysis reaction of cellulose. The fabrication method for composite of RCF and bagasse was performed by ultrasonic irradiation in water.

Hydrolysis of cellulose in the process of activated carbon from bagasse using sulfuric acid as an activator proved to be essential for making micropores. It was also found that sulfuric acid impregnated the pores of cellulose decomposed and removed in bagasse at high temperature and contributed to making micropores by acting as a mold for the pores. It was found that the addition of RCF could increase the specific surface area by up to 20% when the heat treatment was performed at a temperature higher than the temperature at which bagasse was sufficiently carbonized.

Scheme of synthesis of activated carbon using bagasse and carbon fiber recycled from CFRP.

View full abstract

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.

View full abstract

We attempted to prepare the sulfur-impregnated carbonaceous adsorbent from bamboo using mechanochemical treatment under hydrogen sulfide atmosphere. Bamboo was pyrolyzed at 400°C under N₂ atmosphere to obtain the carbonaceous bomboo, and was treated with planetary ball mill under 10% H₂S atmosphere for mechanochemical treatment. As a result, sulfur-impregnated carbonaceous adsorbent with high nickel removal ability can be prepared from carbonaceous bamboo using mechanochemical treatment under H₂S atmosphere, while the bamboo without pyrolysis cannot be converted into the sulfur-impregnated bomboo with high nickel removal. The adsorption isotherm for nickel ion was found to be applicable to Langmuir model rather than Freundlich model, and the calculated maximum adsorption amount was 0.186mmol/g.

View full abstract

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.

View full abstract

All-solid-state lithium-ion batteries (ASSLIBs) have attracted considerable attention as a solution to the safety issues of LIBs using organic liquid electrolytes. Si is the most promising anode active material for increasing the energy density of such batteries because of its high theoretical capacity. However, the stress relaxation of Si with large structural fluctuations is a major challenge to the practical application. In the present study, nanoporous Si particles and sulfide-based solid electrolyte are composited to accommodate the volumetric expansion. ASSLIBs with nanoporous Si composite anodes exhibit the capacity retention of 80% at 150th cycles.

Cycle performances of half cells.

View full abstract

It is important to understand the mechanism of suspension rheology by considering changes in its microstructure formed by suspended particles. Suspended particles in a tube flow migrate transversal to the streamlines due to inertial effects. However, it is unclear that the relationship between changes in the microstructure and macroscopic suspension rheology. In this study, numerical simulations of pressure-driven suspension flow between parallel plates were conducted, and the distribution of suspended particles and relative viscosity were evaluated. As a result, the suspended particles migrated towards the equilibrium positions, and relative viscosity decreased with time increasing.

View full abstract

Several interesting phenomena of particle behavior have been reported to date. One of them is that the several disks fall while becoming unique configurations under the condition that they are dropped into a particle bed. This behavior is called “cooperative behavior” and can occur due to the state change of particle bed with the disks falling. In this study, we dropped only two disks into the bed with various the disk initial distance and the dropping time differences, and the interaction between the disks was investigated by analyzing the falling behavior.

Snapshots of disks falling behavior (a) one disk, (b) 10 mm, (c) 30 mm and (d) 60 mm initial disk distance at about 0.20 s.

View full abstract

Gate-type adsorbents have many superior adsorption properties due to the structural transition induced by adsorption; however, there are few studies on practical applications. In this study, in order to investigate the effect of the thermal management property, which is one of their many properties, on the adsorption performance, we focused on mixing phase change materials (PCMs) into an adsorption column as a simple system with the similar thermal property. Therefore, we developed a nonisothermal column model including the contribution of the melting of PCMs and confirmed the efficiency of the thermal management.

Temperature distributions in the column when (a) ϕ_PCM = 0 and (b) ϕ_PCM = 0.3.

View full abstract

The Fukushima nuclear accident caused a great deal of damage by releasing a large amount of radioactive material to the outside. From this accident, the applicant is conducting research on the development of materials that remove radioactive element, and has found that the amorphous structure of calcium carbonate has a very high Sr removability. To further improve the performance, in this study, in order to elucidate this Sr removal mechanism, we evaluated it from the viewpoint of atomic and molecular levels and tried to elucidate the mechanism.

View full abstract

Hematite (α-Fe₂O₃) exhibits earth-abundance, non-toxicity, and excellent chemical and thermal stabilities. However, the conventional deposition methods require high temperatures during deposition or post-growth annealing typically above 500°C, thus making it difficult the deposition of α-Fe₂O₃ layers on thermally fragile substrates. To overcome this drawback, we are exploring novel liquid phase-atomic layer deposition (LP-ALD) methods, where the source and oxidizing solutions are employed as the precursors. In this study, we focus on the development of “Solution-Mediated Alternate Reaction Technique (SMART)” for hematite nanofilm deposition at a low temperature (75°C) with extremely simple operations.

Surface and cross-sectional SEM images of the hematite film fabricated with the FeCl₂/NaNO₂ precursors^[4]. DOI: 10.1039/d0na00345j, Copyright: (2020) © The Royal Society of Chemistry 2020.

View full abstract

The purpose of this study was to design the gelatin/enteric polymer colloidal formulation that delayed drug release in an acidic environment simulated gastric conditions. The acetaminophen release ratio from the gelatin/enteric polymer formulation was 40% at 60min under pH1.2, and the release was slower than that from gelatin formulation. The release profile of FITC-dextrans with varying molecular weights at pH1.2 was proportional to the square root of time. Therefore, gelatin/enteric polymer formed the matrix structure under acidic conditions, resulted in delayed drug release. This result can contribute to developing polymer colloidal formulations suitable for drug characteristics.

FITC-dextran release profile from gelatin/HPMCP at pH 1.2.

View full abstract

In this work, we developed a new combustor in which nanostructured particles can be obtained, and we synthesized nanostructured particles for film fabrication. Tubular flames have been studied so far from basic combustion science as flame elements in cylindrical systems. It is highly adiabatic due to its high symmetry of temperature distribution and aerodynamically stable against the rotational motion of its flow. Focusing on the shape of the tubular flame, we attempted to core-shell fine particles using the high-temperature region inside the tubular flame.

View full abstract

Effects of porous structure of TOCN @ silica particles on lysozyme adsorption mechanism behavior.

View full abstract