Search

Cooperative behavior displayed by five steel disks falling in a low-density particle bed involves the formation of upward and downward convex configurations, which resembles the flying pattern of a flock of birds. In this study, we focused on overtaking behavior in two falling disks, which causes the cooperative behavior, and we investigated the effects of differences in the disk release time and the initial disk separation distance on the falling behavior of the disks experimentally. Expanded polystyrene (EPS) particles (diameter 5.08 mm, mass 1.45 mg) were used as the bed particles and steel disks (diameter 25.4 mm, thickness 5.22 mm, mass 20.2 g) were used as the falling disks. We released one to five disks with various disk release time differences (0–0.154 s) and initial separation distances (0–100 mm). We recorded the disk falling behavior in the particle bed with a high-speed video camera (500 fps) and analyzed the behavior with image analysis software. Five-disk cooperative behavior similar to that reported in the literature occurred in our experimental setup. In the two-disk experiments, we observed overtaking behavior for an initial separation distance of 10 mm and release time difference of ≤ 0.076 s, and for an initial separation distance of ≤ 60 mm and release time difference of 0.02–0.03 s. The overtaking behavior arose from the decrease in the falling velocity of the first disk released. The EPS particle packing fraction in the area above the disk one disk diameter wide and a quarter of the disk diameter high determined the disk falling velocity. This mechanism was explained by the displacement behavior of EPS particles around the disks as the disks fell.

A new model for estimating macroscopic permittivity was proposed to predict filler particles' dispersion states in a particulate composite material. In the model, the estimation targets are randomly packed composite materials. The composite materials were represented as a cluster of unit cells. A proposed layer structure model connected the unit cells. The macroscopic permittivity was estimated by calculating the synthetic capacity of the cluster. The proposed model was validated by comparisons between estimated and measured macroscopic permittivity of several particulate composite materials. It was also identified that the proposed model could estimate the permittivity more accurately 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.

Particle flowability can be improved by admixing particles smaller than the original particles (main particles). However, the effects of coating structures on the improvement of flowability are not yet fully understood. In this study, we focused on vibrating discharge particle flowability and investigated the effect of discharging vibration conditions and coating structures on improving the flowability. Main and admixed particles of 60.8 μm and 8 nm in diameter, respectively, were mixed in various mass ratios, and the discharge particle flow rates of the mixed particles were measured. Scanning electron microscopy and scanning probe microscopy images were used to analyze the coverage diameter, surface coverage ratio, and coverage height of the admixed particles on the main particle surfaces. As a result, the admixing mass ratio that gave maximum flowability was found to depend on the maximum value of the vibration acceleration. This could be explained by the relationship between the coating structures of admixed particles and the coated average surface distances due to the vibration acceleration.

To improve particle flowability, a technique is used in which fine particles are admixed with the main particles. However, the effects of coating structure on the improvement in flowability are not yet fully understood. Thus, predicting the improvement resulting from this technique is difficult. In this study, we focused on the effects of the particle diameter distribution of the admixed particles on coating structures and improvement of flowability in terms of the compacted packing fraction in a particle bed. Main particles of size 397 nm with admixed particles of sizes 8 and 104 nm were used. Bimodal particle diameter distributions were adjusted by changing the mixing ratios of the two admixed particles. Furthermore, the main and admixed particles were mixed in various orders. We examined the compacted packing fractions for these different mixing ratios and orders. Scanning electron microscopy images were obtained in order to analyze the coating structures on the main particle surfaces. The results show that the main particle packing fraction was most greatly improved by pre-mixing the two admixed particles. This can be explained by a linked rigid-3-bodies model with leverage based on increasing the apparent diameter of the main particles.

Pacheco-Vazquez and Ruiz-Suarez reported an interesting cooperative behavior for disks falling in a particle bed. This behavior involved the formation of upward and downward convex configurations during the falling of five steel disks into a bed of polystyrene particles. We used discrete element method simulations to investigate the generation mechanism for this cooperative behavior. Particles with a diameter of 5.0 mm and a density of 14.0 kg/m3 were placed randomly in a container with a width of 900 mm or 2700 mm and a height of 2700 mm. Model spheres with the same mass and diameter as the steel disks with a diameter of 25.4 mm and a thickness of 5.0 mm were then dropped into the particle bed, and we investigated the cooperative behavior of the model spheres. Similar cooperative behaviors were observed for the containers with widths of 900 mm and 2700 mm, indicating that the container side walls do not affect the occurrence of this behavior when the width is larger than 900 mm. The falling velocity of each disk was strongly dependent on the packing fractions over the disk and the flow velocity of the bed particles around the disks. Based on these results, the generation mechanism of the upward and downward convex configurations is discussed.

The anti-solvent crystallization behavior of the glycine aqueous and ethanol system was addressed through molecular dynamics simulation of a non-equilibrium state. A rectangular simulation cell was assigned to mimic the instant of the first contact state of the aqueous phase (solvent) and ethanol (anti-solvent). Here, glycine zwitterions began to aggregate into clusters with the invasion of ethanol into the aqueous phase, caused by the dehydration and supersaturation of the area. The number and size of clusters gradually increased with the formation and collapse of the clusters with time progression as liquid structures. The cluster structure reacted to the degree of supersaturation and exhibited higher probability of structured interaction modes, especially in ethanol rich areas. Pre-determination of the crystal polymorph during liquid–liquid phase separation was suggested for this water and ethanol anti-solvent system with the glycine zwitterion as the simplest amino acid, which contained multiple interaction sites. These findings agree with the experimental results and support the precursor behavior of nucleation and mechanism in the two-step nucleation theory and liquid–liquid phase separation.

The present study aimed to control the release rate profile of a multivitamin that has hydrophilic and hydrophobic properties and to investigate its diffusion rate from titanium dioxide (TiO2) hollow particles. The TiO2 hollow particles encapsulating the vitamins C and E were prepared via a sol-gel process using an inkjet nozzle. The obtained particles were evaluated by scanning electron microscopy and energy dispersive X-ray spectroscopy. The sustained release rate was estimated by the dialysis bag method. Additionally, a diffusion mechanism for the multivitamin from the TiO2 hollow particles was proposed. TiO2 particles prepared by this method exhibited spherical porous structures. The TiO2 hollow particles were successful in encapsulating both the hydrophilic vitamin C and the hydrophobic vitamin E, resulting in a sustained release profile for these two components from the TiO2 hollow particles. The release behavior of the multivitamin was quite different from that of each single vitamin. This is related to the adsorption state of each vitamin on the TiO2 particle surface. The effective diffusion coefficient of VC derivative (8.403 × 10−13 cm2/s) was faster than that of VE derivative (1.671 × 10−13 cm2/s). This tendency may be attributed to the difference between hydrophilic and hydrophobic properties. Additionally, the value of effective diffusion coefficient in multi-component was always larger than that in single component. The value of Knudsen diffusion coefficient in VC and VE derivative was 2.684 × 10−3 and 2.264 × 10−3 cm2/s, respectively. In all samples, Knudsen diffusion coefficient was larger than molecular diffusion coefficient. The diffusion mechanism of the active ingredients likely depends on the pore size of TiO2 and the molecular size of the active ingredients.

Many oil-encapsulation techniques, in which particles are used to improve the stability of polyunsaturated fatty acids (PUFAs) against oxidation and the handling of oils, have been reported. We developed techniques for encapsulating oil within powders with a liquid–liquid interfacial crystallization by using nozzleless electrostatic atomization. This process was used to prepare fine spherical encapsulated soybean oil particles with a microscale single process. An inexpensive soybean oil containing PUFAs was chosen as the oil phase. W/O emulsion systems were synthesized via the electrostatic atomization process. After the W/O emulsions were prepared, glycine and taurine well provided in supplements were used as the wall material for encapsulation. The soybean oil content of the encapsulated particles and their stability at high temperatures were evaluated. The oxidative stability of the soybean oil during high-temperature storage was improved for the encapsulation.

Particle flowability can be improved by admixing with particles smaller than the main particles. However, the mechanism by which this technique improves flowability is not yet fully understood. In this study, we focused on vibrating discharge particle flowability as one type of flowability and investigated the influence of the main particle roughness created by the adhesion of the admixed particles on improving the flowability. The diameters of the main and admixed particles (MPs and APs) were 41.4 or 60.8 μm and 8 or 104 nm, respectively. The main and admixed particles were mixed in various mass ratios, and the discharge particle flow rates of the mixed particles were measured. Scanning electron microscopy images were acquired from two different angles to determine the three-dimensional surface roughness using image analysis software. We then calculated the coating structure parameters from the obtained three-dimensional surface roughness. The observed trends for improving the vibrating discharge particle flowability were found to differ from those reported for compression particle flowability. Furthermore, the main particle roughness conditions that led to the greatest improvement involved the presence of several admixed particle agglomerations between the main particles.

The amorphization of indomethacin (IMC) with cystine (Cys2) was studied by discrete element method (DEM) simulations and principal component analysis (PCA). X-ray powder diffraction (XRPD) analysis suggested that the conversion of crystalline IMC to amorphous state was accelerated by co-grinding with Cys2. XRPD spectra about amorphization of IMC with Cys2 were analyzed by PCA. PCA results suggest that IMC/Cys2 system undergoes two-phase amorphization, as indicated by the 2nd PC score, and that the change in phase depends on the total frictional energy calculated by DEM simulations. Electron spin resonance result revealed that the radical from Cys2 may be related to the amorphized progression of IMC.

The preparation of the titanium dioxide hollow particles encapsulating L-ascorbic acid via sol-gel process using inkjet nozzle has been performed, and the sustained release and the effect protecting against degradation of L-ascorbic acid in the particles were investigated. The morphology of titanium dioxide particles was evaluated by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). The sustained release and the effect protecting against degradation of L-ascorbic acid were estimated by dialysis bag method in phosphate buffer saline (PBS) (pH = 7.4) as release media. The prepared titanium dioxide particles exhibited spherical porous structures. The particle size distribution of the titanium dioxide particles was uniform. The hollow titanium dioxide particles encapsulating L-ascorbic acid showed the sustained release. It was also found that the degradation of L-ascorbic acid could be inhibited by encapsulating L-ascorbic acid in the titanium dioxide hollow particles.

Particle flowability can be improved by admixing particles smaller than the original particles (main particles). However, the mechanisms by which this technique improves flowability are not yet fully understood. In this study, we examined compressed packing in a particle bed, which is affected by particle flowability. To estimate the mechanism of improvement, we investigated the effects of the main particle diameter on the improvement of compressed packing fractions experimentally. The main particles were 397 and 1460 nm in diameter and the admixed particles were 8, 21, 62, and 104 nm in diameter. The main and admixed particles were mixed in various mass ratios, and the compressed packing fractions of the mixtures were measured. SEM images were used to analyze the coverage diameter and the surface coverage ratio of the admixed particles on the main particles. The main particle packing fraction was improved as the diameter ratio (=main particles/admixed particles) increased. This was explained by a linked rigid-3-bodies model with leverage. Furthermore, the actual surface coverage ratio at which the most improved packing fraction was obtained decreased with increasing main particle diameter. This was explained by the difference in the curvature of the main particle surface.

The purpose of this study was to investigate how the size distribution of taurine particles produced by electrostatic atomization in a liquid–liquid two-phase system without using a nozzle was affected by the process parameters. A Taylor cone was observed to be formed at the liquid–liquid interface during the process, with many droplets ejected from the tip of the cone when ring and needle electrodes were used to apply the electric field perpendicularly to the interface. The droplet size was controlled by varying the angle of the Taylor cone between 60° and 75° through adjustment of the process parameters such as the inter-electrode distance, electrical conductivity of the water phase, and ring diameter. The effect of the ring electrode diameter on the electric field and the interface was examined by solving the Poisson equation. The established variability of the mean taurine particle diameter by adjusting the inter-electrode distance and conductivity of the solution phase can be used to achieve continuous production by avoiding clogging and electrical corrosion of the system.

A hybrid simulation was carried out using discrete variational (DV) Xα molecular orbital and molecular dynamics methods to examine the storage of hydrogen in metal nanoparticles. The calculation load was light and therefore could be performed quickly on a generic personal computer. The simulation investigates the electronic states of hydrogen on Pd and Ti nanoparticles. The hydrogen dissociation behavior on the metal surface was reproduced, and the calculated bonding orbitals of Pd and hydrogen are consistent with other reports. The diffusion coefficient of hydrogen inside the metal displays the same temperature dependence as the theoretical results. This simplified calculation, which produces results in agreement with experimental/theoretical values, could lead to improved simulation methods for hydrogen storage materials.

The closed-die compaction behaviour of D-mannitol granules has been simulated by the discrete element method (DEM) to investigate the granule rearrangement and fracture behaviour during compaction which affects the compactibility of the tablet. The D-mannitol granules produced in a fluidized bed were modelled as agglomerates of primary particles connected by linear spring bonds. The validity of the model granule used in the DEM simulation was demonstrated by comparing to the experimental results of a uniaxial compression test. During uniaxial compression, the numerical results of the force-displacement curve corresponded reasonably well to the experimental data. The closed-die compaction of the modelled granules was carried out to investigate the rearrangement and fracture behaviours of the granule at different upper platen velocities. The forces during closed-die compaction calculated by DEM fluctuated in the low-pressure region due to the rearrangement of granules. A Heckel analysis showed that the force fluctuation occurred at the initial bending region of the Heckel plot, which represents the granule rearrangement and fracture. Furthermore, the upper platen velocity affected the trend of compaction forces, which can lead to compaction failure due to capping. These results could contribute to designing the appropriate granules during closed-die compaction.

Liquid-liquid interfacial crystallization requires mutual diffusion between two liquids to drive the crystallization. Understanding mass transfer between two liquids is important for achieving sophisticated morphological control. In this work, the effect of mutual diffusion on crystal morphology was examined by calculating the solute concentration near the interface. NaCl crystals were prepared with various organic solvents. The crystal shape, amount of precipitation, and particle size were evaluated. The diffusion rate in each organic solvent was measured from the time evolution of the surface area and the volume of the droplet. The solute concentration and the supersaturation ratio near the interface were calculated by Fick's law. The change in crystal morphology revealed that either nucleation or crystal growth preferentially occurred depending on the organic solvent. The magnitude of the water diffusion rate affected the crystal morphology. The dependence of the crystal morphology on the organic solvent was also determined by the diffusion coefficient and the mutual solubility. These results provide new insight into our understanding of the mutual diffusion at liquid-liquid interfaces and the development of crystal morphology control.

Amorphization and radical formation from micro- and nano-sized particles of cystine in mechanochemical process were examined. Dry grinding was used to create amorphous cystine particles. Cystine samples after dry grinding were characterized using a scanning electron microscope, the Brunauer-Emmett-Teller method, powder X-ray diffraction, electron spin resonance (ESR), and Fourier transform infrared (FT-IR) spectroscopy. The kinetic characteristics of amorphization from nano-sized particles were assessed from the ball impact energy and force calculated using the distinct element method (DEM) simulations. The results showed that the kinetics of amorphization almost followed the Johnson–Mehl–Avrami equation using DEM simulations without adhesion. In addition, the amorphous progression exceeded the threshold value of the impact force. The radical species of cystine particles were identified by evaluating the substance-specific value from ESR spectra and the absorption intensity of FT-IR spectra. The results demonstrated that the radical produced by grinding was a thiyl radical (RS ) because the peaks at 452 cm − 1 in the spectra resulted from the characteristic absorption frequency of disulfide (S-S). The radical formation was closely related to the amorphization of cystine particles.

Powderization of oils has been used as a method to enhance the stability of polyunsaturated fatty acids. Previously, we successfully powderized soybean oil via nozzleless electrostatic atomization. The process of nozzleless electrostatic atomization process was applied to the one-step process of encapsulating oil in wall materials. The encapsulation of oils in powder is dependent on the wall materials. The present study aimed to resolve the behavior of oil encapsulated in particles using a novel method of electrostatic atomization, and to investigate the effect of wall materials on the oil content in the encapsulated formulations. The size of particles surrounding oil was dependent on the type of wall materials used for encapsulation, and the oil content within the encapsulation decreased with increase in particle size. Furthermore, wall materials with higher hydrophobicity increased the oil content within the encapsulation, as more hydrophobic particles could absorb the oil more effectively. PRACTICAL APPLICATION: Nozzleless electrostatic atomization is a new method for preparing encapsulation of oil using various wall materials.

Discrete element method (DEM) combined with response surface methodology (RSM) was carried out for investigating the segregation behaviour of binary particles during die filling of the pharmaceutical tableting machine, which comprised a horizontally moving die equipped with a vertically moving bottom punch. To achieve accurate particle flow simulations, parameters of the pharmaceutical spherical granules were calibrated using experimental bounced height, rolling distance and angle of repose. These parameters were implemented in the DEM simulations and compared with experimental high-speed camera observations and measurements of the filling ratio. Simulations and experimental results showed reasonable qualitative and quantitative agreement, validating the simulation model. The validated model was employed to evaluate the segregation of binary particle mixtures and RSM was used for analysing the DEM results of the segregation. The RSM revealed that, unlike the die velocity, small particle size, horizontal position and vertical position affected the segregation index significantly. The segregation resulted from percolation of small particles between large particles in the feed shoe and bottom back corner of the die. DEM combined with RSM approach will become significantly efficient method to understand the process for implementing the quality by design approach.

The purpose of the present study is to prepare palladium-supporting porous titania particles via a sol–gel process using an inkjet nozzle and to improve the photocatalytic activity of the particles. The morphology of titania particles produced by the sol–gel process using an inkjet nozzle was evaluated by scanning electron microscopy and nitrogen physisorption measurements. The photocatalytic activity of the obtained titania particles was evaluated using the changes in the concentration of a methylene blue solution under UVC light irradiation and the effect of palladium supported on the inner and outer surfaces of the titania particles on the photocatalytic activity was investigated. The titania particles prepared by inkjet processing exhibited spherical porous structures. The particle and pore size distributions of the obtained titania particles were more uniform than those of the titania particles prepared using the non-inkjet nozzle. The titania particles supporting palladium on the inner and outer surfaces exhibited a faster rate of photocatalytic degradation than the titania particles supporting palladium on only the outer surface, with anatase titania particles exhibiting the highest rate of photocatalytic degradation. Thus, we have successfully improved the photocatalytic activity of titania particles by supporting palladium on the inner and outer titania surfaces. This sol–gel process using an inkjet nozzle is an effective method for the preparation of porous titania particles supporting palladium on their inner and outer surfaces.

The purpose of this study was to produce composite particles, consisting of core starch particles coated with glycine, by liquid–liquid interfacial crystallization with an ultrasonic spray nozzle and to investigate the effect of operating conditions on glycine particle morphology. We confirmed that ultrasonic irradiation could improve the coating efficiency of the core starch particles during the crystallization process. We also investigated the transformation between different polymorphs of glycine crystals that covered the starch surface. The coating efficiency of the fine glycine crystals on the starch particles was improved by using an ultrasonic spray nozzle rather than anti-solvent crystallization without an ultrasonic spray nozzle. The glycine crystals on the surface of starch particles transformed from unstable to stable forms according to the solution-mediated mechanism and Ostwald rule of stages. The interaction between the core particles and guest particles was found to be a key factor in producing the composite particles. The results indicate that this crystallization process using the ultrasonic spray nozzle is promising for efficiently producing composite particles.

Quantitative evaluation of heterogeneous nucleation is important in order to control crystal form or particle morphology. In the present work, heterogeneous nucleation was quantitatively estimated from induction time, which was defined as the period required for nucleation. The induction time of heterogeneous nucleation was thermodynamically measured with a differential scanning calorimeter. As a result, the free energy change of glycine nucleation in the supersaturated solution was calculated from the heterogeneous nucleation rate. The free energy change decreased with an increase in the occurrence frequency of heterogeneous nucleation. This method suggested that there was a possibility of making the distinction between homogeneous nucleation and heterogeneous nucleation from quiet supersaturated solution. Characteristic parameters of critical nucleus of homogeneous nucleation gave a good agreement with the experimental results. We could quantitatively predict the characteristic properties of heterogeneous nucleation introducing substance-specific parameters.

The aim of the present work is to apply the liquid–liquid interfacial crystallization using a piezoelectric inkjet nozzle to the sol–gel processing. The instillation process was compared with the batch process to elucidate the effectiveness of the inkjet technique on the liquid–liquid interfacial sol–gel processing. The effect of frequency and water concentration in titanium tetraisopoxide (TTIP) solution on titania particle properties was investigated for sol–gel processing with a piezoelectric inkjet nozzle. Titania particles produced by each process were calcined at 500 °C. The crystal structure, morphology, pore size distribution and specific surface area of titania particles were evaluated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen physisorption measurement. The photocatalytic activity of titania particles was evaluated by the photodegradation of methylene blue solution under UVC light irradiation. Monodispersed titania particles could be produced by instillation sol–gel processing of hexane using a piezoelectric inkjet nozzle. Titania particles prepared at 1500 Hz were spherical while titania particles prepared at 1000 Hz and 3000 Hz were non-spherical. The number of particulate fracture increased with water concentration in TTIP solution. The inkjet nozzle-mediated instillation processing was found to be a promising way to create porous titania particles with a high photocatalytic activity.

Clarifying the disintegration mechanism of aggregates in multiphase fluid flow coupled with beads and particulates is important for the optimum design of a wet dispersion process using a stirred media mill. Thus, we develop a numerical method for simulating multiphase flow with beads and particulates using a discrete element method and computational fluid dynamics, and we use the four-way coupling simulation to study the fluid-bead-particulate-coupled phenomenon that occurs in a simple shear box. The results show that the dominant force causing aggregate disintegration is the fluid force, rather than the bead contact force, because aggregates rarely collide with beads, contact force of which is too small to disintegrate aggregates. Furthermore, aggregates with strong aggregation force are effectively disintegrated by the fluid flow with a dominant high pure-shear rate induced near the bead surfaces by the expansive force, rather than the compressive force. © 2014 American Institute of Chemical Engineers AIChE J 60: 4076–4085, 2014

Non-equilibrium molecular dynamics simulations were performed for clarifying the mutual diffusion and ionic behavior near the liquid–liquid interface between KCl aqueous solution and organic solvent (1-butanol, 2-butanol, 2-methyl-1-propanol and 2-butanone). The orientation of organic solvents near the interface was analyzed, and the diffusion of solute ions and solvent molecules was calculated using molecular dynamics simulations. Organic molecules showed the orientational motion in the interfacial region with time evolution. The 2-butanone molecules within the aqueous and organic interface of the system were clearly oriented to the aqueous phase among the aqueous and organic interfaces. Configuration of 2-butanone molecules significantly affects mutual diffusion between KCl aqueous solution and 2-butanone. Clusters, which were aggregated ions, were formed by the dehydration of potassium and chloride ions in the interfacial reason between KCl aqueous solution and organic solvent. The number of clusters at interface between KCl solution and 2-butanone was larger than that in other solvent. This indicates that concentration fluctuation of solute ions is enhanced by 2-butanone near the interface.

The aim of this study is to apply the inkjet technique to liquid–liquid interfacial crystallization. Instillation with an inkjet nozzle was compared with the batch process in order to evaluate the effectiveness of the inkjet technique for controlling particle morphology. The effects of amino acid solution concentration and organic solvent type on particle properties were investigated for instillation with an inkjet nozzle. The morphology of alanine and glycine particles was observed by scanning electron microscopy and X-ray powder diffraction. The inner structure of alanine and glycine particles was investigated by cutting particles with an ion milling machine. Controlling particle size by adjusting the droplet size in the instillation with an inkjet nozzle was found to be feasible. Most alanine and glycine particles produced by instillation were spherical, whereas most particles produced by the batch process were non-spherical. A higher concentration of amino acid in the solution may lead to the generation of solute particles at the spherical interface. It was found that the surface structure of alanine particles changed when using two kinds of organic solvents as anti-solvents. In addition, instillation allowed for β-glycine to be identified and the crystal polymorph of the particles to be controlled.