Ellipsoidal Particles Research Articles

Nonreciprocal absorption properties of a magneto-optical microstructure with suppressed photothermal effects

In this work, a magneto-optical microstructure of titanium (Ti)-doped ellipsoidal particles is designed, and an improved equivalent medium theory (EMT) combined with thin-film optics theory are proposed. The doped magneto-optical microstructures obtain strong broadband nonreciprocal absorption spectra in the near-infrared band, and the nonreciprocal absorption spectra remain above 0.9 at 4.5 to 5μm with nonreciprocity up to 0.53. In addition, the effects of dopant layer thickness, filling ratio and incident angle on the nonreciprocal absorption are also discussed in detail. It worth nothing that the photothermal effect of the magneto-optical microstructures are numerically studied. The optical power of the incident light affects the overall temperature rise, which results in nonreciprocal effect due to the unequal forward and reverse incident absorption spectra. It is found that the photothermal effect for our magneto-optical model caused by the plasmon effect does not produce a normal high temperature rise. The highest temperature rise is only 5.45 K for a single cycle irradiated by 50 mW of optical power, which effectively suppresses the photothermal effect, this is important for maintaining optical devices such as solar cells, optical isolators, and infrared camouflagers at optimal operating temperatures. This property provides new ideas for the design of solar cells, infrared camouflage, optical isolators, radiation-cooled films, and other applications.

Effect of aspect ratio of ellipsoidal particles on segregation of a binary mixture in a rotating drum

In this work, the Discrete Element Method (DEM) is used to investigate the evolution of radial segregation and its dependence on the shape by varying the particle’s aspect ratio. A total of 37 different types of binary mixtures are created, where the aspect ratio of particles varies from 0.25 to 4.0. The results shows that in binary mixture the aspect ratio of both coarse and fine particles influence mixing. The initial well-mixed binary mixture of coarse and fine particles evolves into a radial segregated state where the fine particles occupy a central core of the drum surrounded by coarse particles. Spherical shape particles, whether acting as coarse or fine in binary mixture, promote segregation. Two characteristics of particles i.e., Monodisperse random packing density and sphericity are used to explain the segregation trend and its relationship to aspect ratio.

Morphology of impact fragmentation distribution of single spherical and ellipsoidal particles in drop weight experiments

Particle shape is an important factor affecting the fragmentation distribution of the ore particles. To investigate the influence of particle shape on the morphological fragmentation distribution characteristics, the crushable ore particles are defined as prolate, oblate ellipsoid and spherical particles, which have different aspect ratios (AR) and sphericity (S). Based on the drop weight experiment, the influence of the net drop height on the macroscopic mechanical behavior and crushing distribution characteristics of the single spherical and ellipsoidal particles is studied. The results show that different peak-shifting characteristics exist during particle fragmentation. The fragmentation distribution peak shifts left when the increased impact energy is eventually only enough to break medium-sized sub-particles. Conversely, it shifts right when impact energy is increased enough to break largest-sized sub-particles. Besides, regardless of whether the net drop height changes, the maximum continuous fragmentation degree presents “M”-shaped characteristic with the increased AR. Compared with the ellipsoid particles, the single spherical particle is more difficult to be broken by impact, with wider equivalent particle fragmentation distribution. With the increase of particle sphericity, the maximum continuous fragmentation degree of a single ellipsoid particle has an overall trend of initial increase and subsequent decrease. Especially when particle sphericity is 0.9 < S < 0.95, the maximum continuous fragmentation degree of both prolate and oblate ellipsoid particles is much higher.

Eshelby tensors and effective stiffness of one-dimensional orthorhombic quasicrystal composite materials containing ellipsoidal particles

Eshelby tensors and effective stiffness of one-dimensional orthorhombic quasicrystal composite materials containing ellipsoidal particles

Shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids.

We present the diffusiophoresis of ellipsoidal particles induced by ionic solute gradients. Contrary to the common expectation that diffusiophoresis is shape independent, here we show experimentally that this assumption breaks down when the thin Debye layer approximation is relaxed. By tracking the translation and rotation of various ellipsoids, we find that the phoretic mobility of ellipsoids is sensitive to the eccentricity and the orientation of the ellipsoid relative to the imposed solute gradient, and can further lead to nonmonotonic behavior under strong confinement. We show that such a shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids can be easily captured by modifying theories for spheres.

Density-dependent drag coefficient for gas-adsorbed particles in free-molecule flows

Gas adsorption by the spherical particles in gas–particle flows has been recently studied by Yu et al. [“Direct simulation Monte Carlo of the gas adsorption of particles in gas–particle flows,” Phys. Fluids 34, 083302 (2022)]. However, the gas-adsorption distribution on the particle surface has heretofore remained unknown. This paper addresses this knowledge gap by introducing a numerical method to calculate the gas-adsorption distribution for ellipsoidal particles in gas–particle flows. We split the particle surface into internal flat plates and calculate the gas adsorption for each internal flat plate in the gas flow. Based on this numerical method, the gas adsorption distribution for the ellipsoidal particles is reconstructed by using the direct simulation Monte Carlo method. The results show that the average adsorption by prolate particles with particle eccentricity reverses as the particle temperature increases. Moreover, we show that the density-dependent drag coefficient for particle motion in the free-molecule flow may evince gas adsorption at the particle surface. Those points could inspire the studies of dust physics in rarefied gas spaces.

The Process-Directed Self-Assembly of Block Copolymer Particles.

The kinetic paths of structural evolution and formation of block copolymer (BCP) particles are explored using dynamic self-consistent field theory (DSCFT). It is shown that the process-directed self-assembly of BCP immersed in a poor solvent leads to the formation of striped ellipsoids, onion-like particles and double-spiral lamellar particles. The theory predicts a reversible path of shape transition between onion-like particles and striped ellipsoidal ones by regulating the temperature (related to the Flory-Huggins parameter between the two components of BCP, χAB ) and the selectivity of solvent toward one of the two BCP components. Furthermore, a kinetic path of shape transition from onion-like particles to double-spiral lamellar particles, and then back to onion-like particles is demonstrated. By investigating the inner-structural evolution of a BCP particle, it is identified that changing the intermediate bi-continuous structure into a layered one is crucial for the formation of striped ellipsoidal particles. Another interesting finding is that the formation of onion-like particles is characterized by a two-stage microphase separation. The first is induced by the solvent preference, and the second is controlled by the thermodynamics. The findings lead to an effective way of tailoring nanostructure of BCP particles for various industrialapplications.

Particles, Microstructures, and Impact Toughness of CGHAZ of Ca Deoxidation Shipbuilding Steel Plates with Different Nb Contents

Herein, the effects of the Nb content on the particles, microstructure evolution, and mechanical properties of base metal (BM) and high‐heat input coarse‐grained heat‐affected zone (CGHAZ) of shipbuilding steel plates with Ca deoxidation are studied. With increasing Nb content, the strength and microhardness of the BM increase without significant loss of impact toughness. However, in CGHAZ, the average grain size increases from 168 to 244 μm, and the brittle phase fraction increases from 0.33% to 11.76%. The high‐angled grain boundary (HAGB) density in microstructures reduces from 0.35 to 0.19 μm−1, and the average effective grain sizes increase from 10.97 to 12.48 μm. The particles in 40 Nb‐BM and 40 Nb‐CGHAZ are mainly cubic TiN particles. In 170 Nb, except for cubic particles, there are approximately ellipsoid particles with high value of Nb content, which tend to dissolve into matrix at the elevated temperature. With increasing Nb content, the average size of particles in CGHAZ increases from 18.33 to 32.29 nm, and the number density decreases from 13.44 to 10.35 μm−2. Therefore, the impact toughness of CGHAZ decreases from 197 to 96 J at −20 °C under the high‐heat input welding of 400 kJ cm−1.

Interfacial interaction between ellipsoidal particle and membrane surface with random topographies

Modeling rough surfaces has received attention as it can facilitate understanding of colloidal systems. This work comprehensively discussed a facile approach for simulating the surface morphologies of ellipsoidal particles and membrane surfaces three-dimensionally. The fractal geometry theory was applied to construct a randomly rough surface. The assessment approach involving the surface element integral (SEI) method based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was proposed to quantify the interfacial interaction between the constructed ellipsoidal particle and membrane surface. The simulated results demonstrated that the total interaction energy created between the particle and membrane surface was intensified by enlarging the particle and elevating the fractal dimension of the surface. The fractal roughness and orientation angle of the particle negatively affected the total interfacial energy between the particle and membrane surface. Moreover, the shape of the particle was found to have a profound effect on the total interaction energy. The new method has a wide range of potential applications in membrane bioreactor design and operation since it can predict the interaction of sludge flocs and membrane surface.

Comparison of the Anti-inflammatory Activity and Cellular Interaction of Brush Polymer-N-Acetyl Cysteine Conjugates in Human and Murine Microglial Cell Lines.

Microglia-mediated neuroinflammation is commonly associated with neurodegeneration and has been implicated in several neurological disorders, such as Alzheimer's disease and Parkinson's disease. Therefore, it is crucial to develop a detailed understanding of the interaction of potential nanocarriers with microglial cells to efficiently deliver anti-inflammatory molecules. In this study, we applied brush polymers as a modular platform to systematically investigate their association with murine (BV-2) and human (HMC3) microglial cell lines in the presence and absence of the pro-inflammatory inducer lipopolysaccharide (LPS) using flow cytometry. Brush polymers of different sizes and shapes, ranging from ellipsoid to worm-like cylinders, were prepared through a combination of the two building blocks carboxylated N-acylated poly(aminoester)s (NPAEs)-based polymers and poly(2-ethyl-2-oxazoline)-NH2 (PEtOx-NH2) and characterized by 1H NMR spectroscopy, size exclusion chromatography, and small-angle neutron scattering. Generally, ellipsoidal particles showed the highest cellular association. Moreover, while no significant differences in murine cell association were observed, the brush polymers revealed a significant accumulation in LPS-activated human microglia compared to resting cells, emphasizing their higher affinity to activated HMC3 cells. Brush polymers with the highest cell association were further modified with the anti-inflammatory agent N-acetyl cysteine (NAC) in a reversible manner. The brush polymer-NAC conjugates were found to significantly attenuate the production of interleukin 6 (p < 0.001) in LPS-activated HMC3 cells compared to LPS-activated BV-2 cells. Thus, the presented brush polymer-NAC conjugates showed a high anti-inflammatory activity in human microglia, suggesting their potential for disease-targeted therapy of microglial-mediated neuroinflammation in the future.

CFD-DEM Study of heat and mass transfer of ellipsoidal particles in fluidized bed dryers

In this paper, a 2D computational fluid dynamics (CFD) approach combined with 3D discrete element method (DEM) is extended by incorporating heat, mass transfers, and drying kinetic models to study the drying of ellipsoidal particles with equivalent volumes in fluidized beds. The validity of the proposed model is tested in terms of hydrodynamic and mass transfer behaviors. It is shown that the simulation results are in well-agreement with existing correlation or data. Finally, the effects of aspect ratio on heat and mass transfer behaviors at the same superficial gas velocity are then analyzed to improve the fundamental understanding of the system. It is demonstrated that the spherical particle has the highest drying rate compared to other ellipsoidal particles due to its highest average Reynold number of individual particles. The obtained results should be useful to the development of the fundamental understanding and optimization of fluidized bed dryers.

Three Generations of Surface Nanocomposites Based on Hexagonally Ordered Gold Nanoparticle Layers and Their Application for Surface-Enhanced Raman Spectroscopy

The fabrication technology of surface nanocomposites based on hexagonally ordered gold nanoparticle (AuNP) layers (quasi-arrays) and their possible application as surface-enhanced Raman spectroscopy (SERS) substrates are presented in this paper. The nanoparticle layers are prepared using a nanotextured template formed by porous anodic alumina (PAA) and combined with gold thin-film deposition and subsequent solid-state dewetting. Three types of hexagonal arrangements were prepared with different D/D0 values (where D is the interparticle gap, and D0 is the diameter of the ellipsoidal particles) on a large surface area (~cm2 range), namely, 0.65 ± 0.12, 0.33 ± 0.10 and 0.21 ± 0.09. The transfer of the particle arrangements to transparent substrates was optimized through three generations, and the advantages and disadvantages of each transfer technology are discussed in detail. Such densely packed nanoparticle arrangements with high hot-spot density and tunable interparticle gaps are very beneficial for SERS applications, as demonstrated with two practical examples. The substrate-based enhancement factor of the nanocomposites was determined experimentally using a DNA monolayer and was found to be between 4 × 104 and 2 × 106 for the different particle arrangements. We also determined the sensing characteristics of a small dye molecule, rhodamine 6G (R6G). By optimizing the experimental conditions (e.g., optimizing the laser power and the refractive index of the measurement medium with an ethylene-glycol/water mixture), concentrations as low as 10−16 M could be detected at 633 nm excitation.

Pair correlation functions and stability of nematic in a system of Gay-Berne ellipsoids doped with spherical colloids

Pair-structure of a binary mixture of soft-ellipsoids and spheres interacting via generalized Gay-Berne intermolecular potential using Percus–Yevick (PY) integral equation theory. The generalized Gay-Berne interaction model allows us to vary the diameter of the spheres in comparison to the width of the Gay-Berne ellipsoids. Three different cases of sphere size namely diameter of the spheres being smaller, equal and larger than the minor axis of the ellipsoids have been considered. We have analyzed the radial distribution functions and static structure factors of the mixtures and found that addition of spherical particles to a system of ellipsoids results in stronger pair-correlations between ellipsoidal particles. We observe that smaller spherical additives are more effective in enhancing the ellipsoidal pair-correlations in comparison to the bigger spheres at similar density.The static structure factors are not found to diverge in the low wavelength limit indicating a stable mixture for the set of parameters studied in this work. We have also used classical density functional theory of freezing to investigate the effect of spherical additives and their size on the isotropic-nematic phase transition. We found a stable nematic phase whose order parameter is found to increase with the increase in not only the density of spherical additives but also with increase in their size.

Effects of ellipsoidal and regular hexahedral particles on the performance of the waste heat recovery equipment in a methanol reforming hydrogen production system

Hydrogen production from methanol has attracted attention due to its wide range of raw material sources and mature technology. Using waste heat of industrial high temperature solid particles like blast slag and steel slag etc. To provide vaporization heat and reaction heat for the reaction between methanol and water is an emerging technology for hydrogen production from methanol, which can save additional thermal energy resources. Herein, the performances of equipment that uses the waste heat of ellipsoidal and regular hexahedral particles to provide a heat source for methanol to hydrogen were explored by the DEM-CFD method. Compared with spherical particles of the same equivalent diameter, ellipsoidal and regular hexahedral particles have poor fluidity in the stagnant area, and the empty area is enlarged and irregular in shape. The average velocity peaks of the ellipsoidal and regular hexahedron particles are larger than those of spherical particles, and the overall mean velocity fluctuation of ellipsoidal particles is similar to that of spherical particles while the regular hexahedron particles' is larger. The average temperature drop rate of the ellipsoidal and regular hexahedral particles is slower than that of spherical particles, the uniformity of temperature distribution is worse than that of spherical particles. The ellipsoidal and regular hexahedral particles’ average effective heat transfer coefficient is smaller than that of spherical particles, and the heat transfer effect is weaker than that of spherical particles. The effective heat transfer coefficient of ellipsoidal particles is 2.95 W/(m−2∙K−1) lower than that of spherical particles and the effective heat transfer coefficient of hexahedral particles is 6.09 W/(m−2∙K−1) lower than that of spherical particles. Therefore, compared with the spherical particles of the same equivalent diameter, ellipsoidal and regular hexahedral particles produce less hydrogen.

Size-induced axial segregation of ellipsoids in a rotating drum

Granular materials of different sizes and shapes in a rotating drum tend to segregate in the axial direction. In the past, extensive numerical studies have been conducted for spherical particles, showing the phenomenon of band formation. However, the axial size-induced segregation of non-spherical particles receives limited attention. In this work, we report an interesting finding of band formation for ellipsoidal particles with aspect ratio varying from 0.5 to 2.0. The results show that for ellipsoids, two weak bands appear in the vicinity of endwalls, indicating that low flowability of ellipsoids reduces the tendency of band formation. Moreover, for different shaped particles, small particles in the bands come from different regions. The results also illustrate that the radial size-induced segregation pattern develops quickly, with small particles located at the centre and then the small particles tend to migrate along the drum to form bands.

Polarized light transmission characteristics in a smoky ellipsoidal particle medium.

True natural environments are more complex, and light travels through non-spherical particle media, which can affect the transmission of light. The medium environment of non-spherical particles is more common than that of spherical particles, and some studies have shown that there are differences between spherical and non-spherical particles in polarized light transmission. Therefore, the use of spherical particles instead of non-spherical particles will result in great error. In view of this feature, this paper samples the scattering angle based on the Monte Carlo method, and then constructs a simulation model of a random sampling fitting phase function suitable for ellipsoidal particles. In this study, yeast spheroids and Ganoderma lucidum spores were prepared. The effects of different polarization states and optical thicknesses on the transmission of polarized light at three wavelengths were investigated using ellipsoidal particles with a ratio of 1.5 transverse to vertical axes. The results show that when the concentration of the medium environment increases, the polarized lights of different states all show obvious depolarization, but circularly polarized light has better polarization-preserving characteristics than linearly polarized light, and polarized light with larger wavelengths also shows more stable optical properties. When yeast and Ganoderma lucidum spores were used as the transport medium, the degree of polarization of polarized light had the same trend. However, the equal volume radius of yeast particles is smaller than that of Ganoderma lucidum spores, so when the laser is in the yeast particle medium, the polarization-maintaining property of polarized light is superior. This study provides an effective reference for the variation of polarized light transmission in an atmospheric transmission environment with heavy smoke.

Self Assembly of Patchy Anisotropic Particle Forming Free Standing Monolayer Film (Adv. Theory Simul. 3/2023)

The phase diagram of prolate ellipsoidal particles shows the co-existence of two types of HCP crystals with the gas particles. Through thermodynamic calculation it is established that a free-standing monolayer having an HCP arrangement co-exist with the gas particles in a small region of the phase diagram. This is reported by Sujin B. Babu and co-workers in article number 2200666.

Numerical study of blockage and arching behavior of particle with different shapes in packed bed

Blockage has a significant impact on the flow and heat transfer characteristics of particles in discharging process and can affect the system security seriously. In this study, the discrete element method (DEM) was adopted to analyze the discharge flow of pebbles, ellipsoids, and cubes. The mechanism of blockage formation is the mechanical interaction between particles. With the increase of axial force, the frequency of the blockage increases. High probability of blockage formation arises when the local axial velocity difference dvzl is less than 0.075, while a large local difference in axial velocity (dvzl≥ 0.075) can efficiently avoid blockage. With the increase of the bottom cone angle α of the geometric of the packed bed, blockage during particle flow can be avoided. When α increased to 60°, the particles of Rd less than 0.248 can be discharged smoothly. In addition, the coefficient of friction μ between particles, the ratio of particle diameter to discharge orifice diameter Rd and the aspect ratio Ra of non-spherical particles are all factors influencing the formation of blockages. The critical conditions for particle blockage formation were proposed. For actual working condition of engineering, the application of Rd less than 0.24 and μ less than 0.4 can effectively avoid blockage formation and ensure relatively safe operation for spherical particle systems. For ellipsoidal particles, low aspect ratio (Ra≤4) can effectively avoid blockage.

Multi-level DEM study on silo discharge behaviors of non-spherical particles

The silo discharge of non-spherical particles has been widely practiced in engineering processes, yet the understanding of multi-level mechanisms during solid transportation is still lacking. In this study, a high-fidelity super-ellipsoid Discrete Element Method (DEM) model is established to investigate the discharge behaviors of non-spherical particles with different size distributions. After the comprehensive model validations, we investigated the effects of particle shape (aspect ratio and particle sharpness) on the particle level discharge behaviors. The discharge rates of the ellipsoid particles used in the current work are larger than the spherical particles due to the larger solid fraction. The discharge rates of the cuboid-like particles are determined by the combined effect of the solid fraction and the contact force. Parcel level data show that the translational movements of the ellipsoid particles are more ordered, which is supported by the global level data. Strong correlations exist between the particle level and parcel level data, especially the ellipsoid particles and the large particles in the polydispersed cases.

Metaball-Imaging discrete element lattice Boltzmann method for fluid–particle system of complex morphologies with case studies

Fluid–particle systems are highly sensitive to particle morphologies. While many attempts have been made on shape descriptors and coupling schemes, how to simulate particle–particle and particle–fluid interactions with a balance between accuracy and efficiency is still a challenge, especially when complex-shaped particles are considered. This study presents a Metaball-Imaging (MI) based Discrete Element Lattice Boltzmann Method (DELBM) for fluid simulations with irregular shaped particles. The major innovation is the MI algorithm to capture the real grain shape for DELBM simulations, where the Metaball function is utilized as the mathematical representation due to its versatile and efficient expressiveness of complex shapes. The contact detection is tackled robustly by gradient calculation of the closest point with a Newton–Raphson based scheme. The coupling with LBM is accomplished by a classic sharp-interface scheme. As for refiling, a local refiling algorithm based on the bounce back rule is implemented. Validations on the Jeffery orbit of ellipsoidal particles and three settling experiments of irregular-shaped natural cobblestones indicate the proposed model to be effective and powerful in probing micromechanics of irregular-shaped granular media immersed in fluid systems. The potential of this model on studies of shape-induced physical processes is further investigated with numerical examples that consider the drag and lift forces experienced by realistic particles, as well as the “drafting, kissing and tumbling” process of pairs of non-spherical particles.