Particle Aspect Ratio Research Articles

Mechanism of magnetite iron ore concentrate morphology affecting the pellet induration process

The effect and mechanism of magnetite concentrate morphology on the quality of indurated pellets were investigated. Concentrates with different morphologies were prepared using high-pressure grinding rolls (HPGR) and ball mill (BM) grinding techniques. Then pelletizing and induration process is done in the temperature range of 800 to 1300 °C. With similar specific surface area for both BM and HPGR concentrates, the morphology of HPGR concentrate had a broad particle size distribution with a high aspect ratio for particles. Results showed that the porosity and FeO content of indurated HPGR and BM pellets decreased with increasing temperature while their cold compressive strength (CCS) increased. However, the porosity and FeO content of HPGR pellets were lower than BM pellets. Also, the CCS of indurated HPGR pellets at temperatures above 1100 °C was significantly higher than BM pellets. Microstructural analysis was performed on concentrate powder, fracture surface, and cross-section of pellets to analyze the mechanism of morphological influences. It was found that the irregular shape and broad particle size distribution of HPGR particles improved the CCS of HPGR pellets due to the improved sintering, increased interlocking force, longer crack propagation path, formation of the uniform liquid phase distribution, and decreased the pellet porosity.

Multifield Coupling of Local Surface Plasmon Resonance‐Assisted Au–TiO2 Photocatalysis Considering Bimodal Resonance and Superposition Effect

This study concerns the improvement of the synergetic catalytic efficiency of Au–TiO2 nanorods considering the local surface plasmon resonance (LSPR) effect of different Au nanoparticles (NPs). The absorption spectrum and selective absorption efficiency for visible light, the local electric field, and the generated thermal effect are specifically analyzed based on the multifield decoupling of LSPR‐assisted Au–TiO2 catalysts. The simulation results show that the extinction spectra of both spherical and ellipsoidal Au particles are consistent with the experimental data. Interestingly, the latter is characterized by significant bimodal resonance modes. Comparatively, the simulation results show that the longitudinal mode, which is sensitive to the aspect ratio, is more favorable for the improvement of the photocatalytic activities. It is found that the resonance peaks are highly controllable, and are linear to the particle size and aspect ratio. Meanwhile, the electric field mode of TiO2 is significantly increased under the resonance wavelength. It is worth mentioning that the superposition effect makes a non‐negligible impact on the actual catalysts, leading to a relative shift of resonance wavelength. The consideration of the hot spots caused by the superposition effect influence the photocatalytic results significantly, providing values in diminishing the inadaptability of the theory in near‐touching regions of plasma particles.

Determination of highly active and selective surface for the oxidative dehydrogenation of ethane over phase-pure M1 MoVNbTeOx catalyst

The original phase-pure M1 MoVNbTeOx catalyst was mechanically treated with stirring water for several days under ambient conditions to obtain particles with different sizes. The catalytic performance was significantly improved and stabilized after about 7 days of treatment. Among all the catalysts, the sample treated in water for 7 days can obtain 57.6 % ethane conversion and 0.79 kgC2H4/kgcat/h ethylene productivity while the original phase-pure M1 catalyst was only 19.2 % and 0.27 kgC2H4/kgcat/h at reaction temperature of 400 °C and contact time of 18.5 gcat·h/molC2H6. Meanwhile, the catalyst was systematically characterized and the results showed that there was essentially no difference in microstructure between the original and treated catalysts. TEM and SEM morphological characterizations presented that the particle size and aspect ratio of the catalysts changed significantly, in which the particle size of the catalyst become smaller and the proportion of basal surface was enhanced. The activity and selectivity of the catalysts exhibited a correlation with the amount and proportion of basal surface. It can be deducted that the basal surface is the most active and selective surface during oxidative dehydrogenation of ethane (ODHE) process, and the intrinsic activity based on the basal (001) plane of the catalyst remains stable after the mechanical treatment. Samples treated in water for 7 days showed excellent long-term stability in a 200 h stability test at reaction temperature of 440 °C and contact time of 9.3 gcat·h/molC2H6. The present work demonstrated that the differences in the catalytic properties of different M1 samples depend mainly on the amount and proportion of exposed basal surface, and the possibility of enhancing the activity of orthorhombic M1 phase by fragmentation method.

Effect of chemical composition and microstructure on the crack growth and machinability of GG20 gray cast iron for brake drum application

The objective of the present study is to investigate the effect of chemical composition and microstructure on machinability, mechanical properties, and crack growth of GG-20 gray cast iron for brake drum application. The effects of a reduction in C and Si on microstructural parameters such as type, size, and aspect ratio of graphite particles, interlamellar spacing of pearlite, and the presence of MnS were investigated. In the following, the effect of different microstructures on mechanical properties and machinability of cast iron were studied. The fracture surface, crack growth, worn surface, chip formation and wear on cutting tools have been studied as well. The results showed that both tensile strength and hardness increased, and the machinability reduced by decreasing C and Si. By reducing the C content from 3.4% to 3.2%, the maximum hardness value and tensile strength were obtained to be 207HB and 286 MPa, respectively. Moreover, the Ra and Rz values were increased to 4.3 μm and 25.8 μm, respectively. With an increase in the length of graphite flakes, the distance between microcracks on the machined chips decreased. In the sample with the lower hardness value, delamination occurred extensively and led to the disappearance of cracks and pores on the worn surface.

Evolution of mesoscale structure in fluidized beds with non-spherical dry and wet particles

Instantaneous force distributions at bubble boundaries in non-spherical dry and wet particle systems. • The force distributions at bubble boundaries are analyzed to explain the influence mechanism of different shapes of bubbles in non-spherical dry and wet particle systems. • The effects of particle aspect ratio and liquid viscosities are investigated through the force analysis and factorial analysis. • With the increase of the particle aspect ratio, the bubble equivalent diameter gradually increases. • As the liquid viscosity increases, the bubble frequency gradually decreases. Fluidized beds with non-spherical dry and wet particles are widely used in industrial processes, and the mesoscale structure in the bed has an important influence. In this study, CFD-DEM simulations are performed to evaluate the flow behaviors and mesoscale structure in fluidized beds with non-spherical dry and wet particles. The accuracy of the model is validated by comparison with the results of the particle image velocimetry experiment. The force distributions at bubble boundaries are analyzed to explain the influence mechanism of different shapes of bubbles in non-spherical dry and wet particle systems. The factor analysis indicates the interaction of particle shape and viscous liquid on the translational and rotational kinetic energy of particles. When the bed height is low, as the particle aspect ratio increases, the bubble equivalent diameter gradually increases. In addition, as the liquid viscosity increases, the particle and bubble granular temperature gradually decrease, indicating the reduction of particle velocity fluctuate and the decrease of turbulent kinetic energy of bubble. These findings have guiding significance for the fluidization of non-spherical dry and wet particles and can be used to optimize related industrial processes.

Quasi-steady-state modelling and characterization of diffusion-controlled dissolution from monodisperse prolate and oblate spheroidal particles

A quasi-steady-state model of the dissolution of a single prolate or oblate spheroidal particle has been developed based on the exact solution of the steady-state diffusion equation for mass transfer in an unconfined media. With appropriate treatment of bulk concentration, the model can predict the detailed dissolution process of a single particle in a container of finite size. The dimensionless governing equations suggest that the dissolution process is determined by three dimensionless control parameters, initial solid particle concentration, particle aspect ratio and the product of specific volume of solid particles and saturation concentration of the dissolved substance. Using this model, the dissolution processes of felodipine particles are analysed in a broad range of space of the three control parameters and some characteristics are identified. The effects of material properties indicated by the product of specific volume and saturation concentration are also analysed. The model and the analysis are applicable to the system of monodisperse spheroidal particles of the same shape.

Stress anisotropy in confined populations of growing rods.

A central feature of living matter is its ability to grow and multiply. The mechanical activity associated with growth produces both macroscopic flows shaped by confinement, and striking self-organization phenomena, such as orientational order and alignment, which are particularly prominent in populations of rod-shaped bacteria due to their nematic properties. However, how active stresses, passive mechanical interactions and flow-induced effects interact to give rise to the observed global alignment patterns remains elusive. Here, we study in silico colonies of growing rod-shaped particles of different aspect ratios confined in channel-like geometries. A spatially resolved analysis of the stress tensor reveals a strong relationship between near-perfect alignment and an inversion of stress anisotropy for particles with large length-to-width ratios. We show that, in quantitative agreement with an asymptotic theory, strong alignment can lead to a decoupling of active and passive stresses parallel and perpendicular to the direction of growth, respectively. We demonstrate the robustness of these effects in a geometry that provides less restrictive confinement and introduces natural perturbations in alignment. Our results illustrate the complexity arising from the inherent coupling between nematic order and active stresses in growing active matter, which is modulated by geometric and configurational constraints due to confinement.

Radar Retrieval Evaluation and Investigation of Dendritic Growth Layer Polarimetric Signatures in a Winter Storm

Abstract This study evaluates ice particle size distribution and aspect ratio φ Multi-Radar Multi-Sensor (MRMS) dual-polarization radar retrievals through a direct comparison with two legs of observational aircraft data obtained during a winter storm case from the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) campaign. In situ cloud probes, satellite, and MRMS observations illustrate that the often-observed Kdp and ZDR enhancement regions in the dendritic growth layer can either indicate a local number concentration increase of dry ice particles or the presence of ice particles mixed with a significant number of supercooled liquid droplets. Relative to in situ measurements, MRMS retrievals on average underestimated mean volume diameters by 50% and overestimated number concentrations by over 100%. IWC retrievals using ZDR and Kdp within the dendritic growth layer were minimally biased relative to in situ calculations where retrievals yielded −2% median relative error for the entire aircraft leg. Incorporating φ retrievals decreased both the magnitude and spread of polarimetric retrievals below the dendritic growth layer. While φ radar retrievals suggest that observed dendritic growth layer particles were nonspherical (0.1 ≤ φ ≤ 0.2), in situ projected aspect ratios, idealized numerical simulations, and habit classifications from cloud probe images suggest that the population mean φ was generally much higher. Coordinated aircraft radar reflectivity with in situ observations suggests that the MRMS systematically underestimated reflectivity and could not resolve local peaks in mean volume diameter sizes. These results highlight the need to consider particle assumptions and radar limitations when performing retrievals. significance statement Developing snow is often detectable using weather radars. Meteorologists combine these radar measurements with mathematical equations to study how snow forms in order to determine how much snow will fall. This study evaluates current methods for estimating the total number and mass, sizes, and shapes of snowflakes from radar using images of individual snowflakes taken during two aircraft legs. Radar estimates of snowflake properties were most consistent with aircraft data inside regions with prominent radar signatures. However, radar estimates of snowflake shapes were not consistent with observed shapes estimated from the snowflake images. Although additional research is needed, these results bolster understanding of snow-growth physics and uncertainties between radar measurements and snow production that can improve future snowfall forecasting.

Crystal Shape Control on the Repacking and Jamming of Crystal‐Rich Mushes

AbstractThe rheology of crustal mushes is a crucial parameter controlling melt segregation and magma flow. However, the relations between mush dynamics and crystal size and shape distribution remain poorly understood because of the complexity of melt‐crystal and crystal‐crystal interactions. We performed analog experiments to characterize the mechanisms that control pore space reduction associated with repacking. Three suspensions of monodisperse particles with different geometries and aspect ratios (1:1, 2:1, 4:1) in a viscous fluid were tested. Our results show that particle aspect ratios strongly control the melt extraction processes. We identify two competing mechanisms that enable melt extraction at grain scale. The first mechanism leads to continuous deformation and melt extraction and is associated with “diffuse” frictional dissipation between neighboring particles. The second is stochastic, localized, and nearly instantaneous and is associated with the development and destruction of force chains percolating through the granular assembly.

Study on the geometry characteristics of soil primary mineral particles under cryogenic action

Repeated freeze–thaw causes the fragmentation and aggregation of soil particles, which affect particle shape (aspect ratio, roundness, etc.), and this process is a cryogenic weathering process. Changes in soil particle morphology record information about freeze–thaw processes and have the unique characteristics of freeze–thaw traces. To prove this conjecture, four soil specimens were selected in the experiment, and each specimen was studied after 0, 5, 10, 50 and 100 freeze–thaw cycles. The test results show that: Freeze–thaw will change the aspect ratio of particles, and the aspect ratio of particles is mainly distributed between 1 and 4. The particles with aspect ratio of 1.26 are stable and not easy to fragment, and the particles with aspect ratio more than 4 are easy to fragment. The freeze–thaw effect leads to changes in particle roundness, with different manners of change for the four specimens, but all undergo repeated freeze–thaw fragmenting and rounding process. Repeated freezing and thawing can not only lead to fragmentation particle edges and increased particle roundness, but also to fragmentation large-size particles and reduced particle roundness. Compared with the roundness before freeze–thaw and after 100 cycles of freeze–thaw, the coarse sand grains increased the most in roundness, indicating that the large grain size grains showed the most rounding. This study helps to understand the geometric characteristics of soil primary mineral particles under the action of cryogenic environments, and also helps to discern whether the particles have experienced the action of cryogenic environments, which is important for the study of cryogenic soil in cold environments.

The role of the particle aspect ratio in the discharge of a narrow silo

The time evolution of silo discharge is investigated for different granular materials made of spherical or elongated grains in laboratory experiments and with discrete element model (DEM) calculations. For spherical grains, we confirm the widely known typical behavior with constant discharge rate (except for initial and final transients). For elongated particles with aspect ratios between 2 ⩽ L/d ⩽ 6.1, we find a peculiar flow rate increase for larger orifices before the end of the discharge process. While the flow field is practically homogeneous for spherical grains, it has strong gradients for elongated particles with a fast-flowing region in the middle of the silo surrounded by a stagnant zone. For large enough orifice sizes, the flow rate increase is connected with a suppression of the stagnant zone, resulting in an increase in both the packing fraction and flow velocity near the silo outlet within a certain parameter range.

Shape dynamics and rheology of dilute suspensions of elastic and viscoelastic particles

This paper examines the shape dynamics of deformable elastic and viscoelastic particles in an ambient Newtonian fluid subjected to simple shear. The particles are allowed to undergo large deformation, with the elastic stress determined using the neo-Hookean constitutive relation. We first present a method to determine the shape dynamics of initially ellipsoidal particles that is an extension of the method of Roscoe (J. Fluid Mech., vol. 28, issue 2, 1967, pp. 273–293), originally used to determine the shape at steady state of an initially spherical particle. We show that our method recovers earlier results for the in-plane trembling and tumbling dynamics of initially prolate spheroids in simple shear flow, obtained by a different approach. We then examine the in-plane dynamics of oblate spheroids and triaxial ellipsoids in simple shear flow, and show that they too, like prolate spheroids, exhibit time-periodic tumbling or trembling dynamics, depending on the initial aspect ratios of the particle and the elastic capillary number $G \equiv \mu \dot {\gamma }/\eta$ , where $\mu$ is the viscosity of the fluid, $\eta$ is the elastic shear modulus of the particle and $\dot {\gamma }$ is the shear rate. In addition, we find a novel state wherein the particle extends indefinitely in time and asymptotically aligns with the flow axis. We demarcate all the dynamical regimes in the parameter space comprising $G$ and the initial particle aspect ratios. When the particles are viscoelastic, damped oscillatory dynamics is observed for initially spherical particles, and the tumbling–trembling boundary is altered for initially prolate spheroids so as to favour tumbling.

Zinc-Acetate-Amine Complexes as Precursors to ZnO and the Effect of the Amine on Nanoparticle Morphology, Size, and Photocatalytic Activity.

Zinc oxide is an environmentally friendly and readily synthesized semiconductor with many industrial applications. ZnO powders were prepared by alkali precipitation using different [Zn(acetate)2(amine)x] compounds to alter the particle size and aspect ratio. Slow precipitations from 95 °C solutions produced micron-scale particles with morphologies of hexagonal plates, rods, and needles, depending on the precursor used. Powders prepared at 65 °C with rapid precipitation yielded particles with minimal morphology differences, but particle size was dependent on the precursor used. The smallest particles were produced using precursors that yielded crystals with low aspect ratios during high-temperature synthesis. Particles produced during rapid synthesis had sizes ranging from 21-45 nm. The materials were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, BET, and diffuse reflectance. The materials prepared using precursors with less-volatile amines were found to retain more organic material than ZnO produced using precursors with more volatile amines. The amount of organic material associated with the nanoparticles influenced the photocatalytic activity of the ZnO, with powders containing less organic material producing faster rate constants for the decolorizing of malachite green solutions under ultraviolet illumination, independent of particle size. [Zn(acetate)2(hydrazine)2] produced ZnO with the fastest rate constant and was recycled five times for dye degradation studies that revealed minimal to no reduction in catalytic efficiency.

Effect of neutrally buoyant oblate spheroid's aspect ratio on its equilibrium position in a square duct

The inertial migration of a neutrally buoyant oblate spheroid in a square duct is numerically simulated via the multiple-relaxation-time lattice Boltzmann method. This study aims to investigate the effect of a particle's aspect ratio $(AR)$ on its equilibrium position at different initial positions, orientations, and Reynolds numbers $(Re)$. The spheroid's equatorial radius remains unchanged here, and its $AR$ is adjusted by changing its polar radius, which is distinct from previous studies. Therefore, the particle's volume and mass increase with the $AR$. At a low $Re$ $(Re~=~80)$, the particle's initial position and orientation affect its final motion. There are three possible motion modes, tumbling, log-rolling and inclined log-rolling. Although the oblate spheroids with different $ARs$ may experience different motion modes at their final equilibrium states, their rotational diameters are constant. For the tumbling mode, the $AR$ affects the equilibrium position, and the particle gradually approaches the duct center as the $AR$ increases. For the inclined log-rolling mode, the $AR$ partially affects the equilibrium position, where the corresponding equilibrium positions remain unchanged for the spheroids with $AR~=~0.5$ and $0.75$, approaching closer to the duct center for the spherical particle with $AR~=~1$. Finally, for the log-rolling mode, $AR$ has a negligible effect on the equilibrium positions. Furthermore, in the same motion mode, the particle's equilibrium position approaches the wall as the $Re$ increases from 40 to 160.

Lattice Boltzmann Simulation of Non-Steady-State Particulate Matter Filtration Process in Woven Fiber

To enhance the design process of high-performance woven fibers, it is vital to clarify the evolution of particle dendrites, the dynamic pressure drop, and the capture efficiency with respect to dust loading during the non-steady-state filtration process. A general element (orthogonal elliptical fibers) of woven filter cloths is numerically simulated using the 3D lattice Boltzmann-cell automation (LB-CA) method, where gas dynamics is solved by the LB method while the solid particle motion is described by the CA probabilistic approach. The dendrite morphologies are evaluated under various particle diameters, aspect ratios, packing densities, and inlet fluid velocities. For submicron particles in the “Greenfield gap” range, it is revealed that the normalized pressure drop is an exponential function of the mass of deposited particles, and the rate of increase is exactly proportional to the perimeter of the elliptical fibers. Moreover, the normalized capture efficiency is a linear function of the deposited mass. It is not advisable to increase the packing density too much, as this might simply increase the pressure drop rather than enhancing the normalized capture efficiency. It is also worth noting that the fitting slope is more likely to grow linearly once the aspect ratio exceeds 1.6, indicating that orthogonal elliptical woven fibers offer higher capture efficiency than normal orthogonal cylindrical woven fibers. The work is beneficial to gain insights into the angular distribution of particle dendrites, as well as the prediction of dynamic growth of pressure drop and capture efficiency of the elliptical fiber. These efforts could help to deepen the understanding and realize assistant designing for the filtration performance of woven fiber in the future.

Ice microphysical processes in the dendritic growth layer: a statistical analysis combining multi-frequency and polarimetric Doppler cloud radar observations

Abstract. The dendritic growth layer (DGL), defined as the temperature region between −20 and −10 ∘C, plays an important role for ice depositional growth, aggregation and potentially secondary ice processes. The DGL has been found in the past to exhibit specific observational signatures in polarimetric and vertically pointing radar observations. However, consistent conclusions about their physical interpretation have often not been reached. In this study, we exploit a unique 3-months dataset of mid-latitude winter clouds observed with vertically pointing triple-frequency (X-, Ka-, W-band) and polarimetric W-band Doppler radars. In addition to standard radar moments, we also analyse the multi-wavelength and polarimetric Doppler spectra. New variables, such as the maximum of the spectral differential reflectivity (ZDR) (sZDRmax), allows us to analyse the ZDR signal of asymmetric ice particles independent of the presence of low ZDR producing aggregates. This unique dataset enables us to investigate correlations between enhanced aggregation and evolution of small ice particles in the DGL. For this, the multi-frequency observations are used to classify all profiles according to their maximum average aggregate size within the DGL. The strong correlation between aggregate class and specific differential phase shift (KDP) confirms the expected link between ice particle concentration and aggregation. Interestingly, no correlation between aggregation class and sZDRmax is visible. This indicates that aggregation is rather independent of the aspect ratio and density of ice crystals. A distinct reduction of mean Doppler velocity in the DGL is found to be strongest for cases with largest aggregate sizes. Analyses of spectral edge velocities suggest that the reduction is the combined result of the formation of new ice particles with low fall velocity and a weak updraft. It appears most likely that this updraft is the result of latent heat released by enhanced depositional growth. Clearly, the strongest correlations of aggregate class with other variables are found inside the DGL. Surprisingly, no correlation between aggregate class and concentration or aspect ratio of particles falling from above into the DGL could be found. Only a weak correlation between the mean particle size falling into the DGL and maximum aggregate size within the DGL is apparent. In addition to the correlation analysis, the dataset also allows study of the evolution of radar variables as a function of temperature. We find the ice particle concentration continuously increasing from −18 ∘C towards the bottom of the DGL. Aggregation increases more rapidly from −15 ∘C towards warmer temperatures. Surprisingly, KDP and sZDRmax are not reduced by the intensifying aggregation below −15 ∘C but rather reach their maximum values in the lower half of the DGL. Also below the DGL, KDP and sZDRmax remain enhanced until −4 ∘C. Only there, additional aggregation appears to deplete ice crystals and therefore reduce KDP and sZDRmax. The simultaneous increase of aggregation and particle concentration inside the DGL necessitates a source mechanism for new ice crystals. As primary ice nucleation is expected to decrease towards warmer temperatures, secondary ice processes are a likely explanation for the increase in ice particle concentration. Previous laboratory experiments strongly point towards ice collisional fragmentation as a possible mechanism for new particle generation. The presence of an updraft in the temperature region of maximum depositional growth might also suggest an important positive feedback mechanism between ice microphysics and dynamics which might further enhance ice particle growth in the DGL.

Direct Numerical Simulation of pulsating flow effect on the distribution of non-circular particles with increased levels of complexity: IB-LBM

Equilibrium position, as well as dynamic patterns of suspended particles, plays a dominant role in particle manipulation of segregation, transporting, or sorting. The current paper aims to investigate the falling manners of non-circular particles in an enclosure while the pulsatile flow is involved as a counter-flow. The direct-forcing immersed boundary method is coupled with the lattice Boltzmann method to simulate this widespread issue numerically. Corresponding boundary conditions are hired to take into account pulsatile flow. Findings were first successfully verified against the existing literature and the accuracy of the results is well-demonstrated. For the first time, a series of proof-of-principal simulations with an increased level of geometric complexity, particle aspect ratio, as well as the number and initial configuration (release positions), is carried out. The force resulting from the particle acceleration is also considered. It is shown that considering such factors, particle settling manners would markedly differ. The collective behavior of particles is also studied, and it is revealed that the presence of neighboring particles makes the influence of the particle shape less clear; however, pulsatile flow presents considerable differences in the settling manners of particles.

Anisotropic particles focusing effect in complex flows

We experimentally investigate the effect of shape on finite-size particles long term trajectories and observe that particles with an anisotropic shape can be attracted to coherent regions of the flow with a higher rate than spherical particles. We present a simple model that combines finite-size effects with orientation-dependent drag forces, and show that the aggregation rate and final particle concentration depend on both the particle's Stokes number and aspect ratio.

Effect of anisotropy on the formation of active particle films.

Active colloids belong to a class of nonequilibrium systems where energy uptake, conversion, and dissipation occur at the level of individual colloidal particles, which can lead to particles' self-propelled motion and surprising collective behavior. Examples include coexistence of vapor- and liquid-like steady states for active particles with repulsive interactions only, phenomena known as motility-induced phase transitions. Similarly to motile unicellular organisms, active colloids tend to accumulate at confining surfaces forming dense adsorbed films. In this work, we study the structure and dynamics of aggregates of self-propelled particles near confining solid surfaces, focusing on the effects of the particle anisotropic interactions. We performed Langevin dynamics simulations of two complementary models for active particles: ellipsoidal particles interacting through the Gay-Berne potential and rodlike particles composed of several repulsive Lennard-Jones beads. We observe a nonmonotonic behavior of the structure of clusters formed along the confining surface as a function of the particle aspect ratio, with a film spreading when particles are near-spherical, compact clusters with hedgehog-like particle orientation for more elongated active particles, and a complex dynamical behavior for an intermediate aspect ratio. The stabilization time of cluster formation along the confining surface also displays a nonmonotonic dependence on the aspect ratio, with a local minimum at intermediate values. Additionally, we demonstrate that the hedgehog-like aggregates formed by Gay-Berne ellipsoids exhibit higher structural stability as compared to the ones formed by purely repulsive active rods, which are stable due to the particle activity only.

Magnetostatic interaction in oriented assembly of elongated nanoparticles

The elements of the magneto-dipole (MD) interaction matrix are calculated for a pair of oriented spheroidal magnetic nanoparticles with a semiaxis ratio a/b = 1.25, 1.5, 2.0 and 3.0 as functions of the distance between the particle centers. It is shown that the spherical approximation for the MD interaction matrix is already incorrect at aspect ratios a/b > 1.25, if the distance R between the particle centers is of the order of particle sizes. However, for moderate particle aspect ratios, a/b < 1.5, the first order correction to spherical approximation with respect to a small parameter (a2 – b2)/R2 is shown to be in a good agreement with numerical data. Using exact MD interaction matrix, the quasi-static hysteresis loops of dilute assemblies of oriented clusters of spheroidal nanoparticles with different filling densities are calculated, depending on the direction of the external magnetic field with respect to the particle orientation axis.