Particle Aspect Ratio Research Articles

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 semiaxes ratio a/b = 1.25, 1.5, 2.0 and 3.0 as a function of the distance between the particle centers. It is shown that the spherical approximation for MD interaction matrix is incorrect already 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 corresponding small parameter 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.

Dynamics of Brownian Janus rods at a liquid–liquid interface

Amphiphilic Janus nanoparticles exhibit higher interfacial activity and adsorb more strongly to fluid interfaces than homogeneous nanoparticles of similar sizes. Taking advantage of both shape and chemical anisotropy on the same particle, Janus particles offer rich self-assembly possibilities for nanotechnology. By using dissipative particle dynamics simulation, the translational diffusion of Janus nanoparticles at the interface between two immiscible fluids is investigated. The particle aspect ratio affects both particle's translational thermal motion and the average orientation of the particle with respect to the interface at equilibrium. This behavior is also linked to the interfacial tension of the system. Our findings provide fundamental insights into the dynamics and self-assembly of anisotropic Brownian particles at interfaces.

Rheological response of granular materials under dynamic conditions

The rheological behaviour of a dense granular bed under dynamic conditions is investigated by simulating granular flow in the FT4 powder rheometer using the Discrete Element Method. The distribution of the prevailing stresses and strain rates in the granular bed, and their dependence on material properties and blade operational conditions, are analysed. The shear stress was found to be approximately constant in the radial direction along the blade but dissipates in the circumferential direction away from the blade. Analogously, the strain rate decreases with increasing angular distance away from the blade as the bed becomes less dynamic. An increase in the blade tip speed, particle aspect ratio and interfacial energy results in an increase in the average shear stress in the granular bed. A predictive model is proposed to compute the average shear stress in the granular bed based on the blade torque by considering the effects of blade tip speed, particle aspect ratio and interfacial energy.

Engineered Hydroxyapatite Nanoadjuvants with Controlled Shape and Aspect Ratios Reveal Their Immunomodulatory Potentials.

Hydroxyapatite (HAP) has been formulated as adjuvants in vaccines for human use. However, the optimal properties required for HAP nanoparticles to elicit adjuvanticity and the underlying immunopotentiation mechanisms have not been fully elucidated. Herein, a library of HAP nanorods and nanospheres was synthesized to explore the effect of the particle shape and aspect ratio on the immune responses in vitro and adjuvanticity in vivo. It was demonstrated that long aspect ratio HAP nanorods induced a higher degree of cell membrane depolarization and subsequent uptake, and the internalized particles elicited cathepsin B release and mitochondrial reactive oxygen species generation, which further led to pro-inflammatory responses. Furthermore, the physicochemical property-dependent immunostimulation capacities were correlated with their humoral responses in a murine hepatitis B surface antigen immunization model, with long aspect ratio HAP nanorods inducing higher antigen-specific antibody productions. Importantly, HAP nanorods significantly up-regulated the IFN-γ secretion and CD107α expression on CD8+ T cells in immunized mice. Further mechanistic studies demonstrated that HAP nanorods with defined properties exerted immunomodulatory effects by enhanced antigen persistence and immune cell recruitments. Our study provides a rational design strategy for engineered nanomaterial-based vaccine adjuvants.

Flow-Particle Coupling in a Channel Flow Laden with Elongated Particles: The Role of Aspect Ratio

A turbulent channel flow laden with elongated, fiber-like particles is investigated experimentally by optical techniques. The flow-particle inter-coupling is analyzed in the case of particles with an aspect ratio of 40 and 80, at two volume fractions, 10−5 and 10−4. An image processing technique is presented, which is employed to simultaneously obtain carrier flow velocimetry data and distribution and orientation data of dispersed particles. Turbulence enhancement is reported in the near-wall region, with a higher level of increase associated with higher aspect ratio particles. Comparison to fiber data suggests that this mechanism of turbulence modulation stems from a particles orientational behavior. The preferential particle distribution is reported to be dependent on the aspect ratio in the region close to the wall. The probability density function of the fibers’ orientation angle appears to be independent of the particle aspect ratio once it is conditioned to the fibers’ characteristic size.

Achieving high strength and superior ductility in Al–Si alloy by cold rolling and friction stir processing

In the current work, the influence of heat treatment, rolling, and friction stir processing (FSP) on the microstructure, hardness, tensile behavior, and fracture mechanism of hypoeutectic Al–Si alloy were investigated. The FSP led to a reduction in the aspect ratio and increased the size and sphericity of particles. Also, fine silicon and Fe-rich particles were uniformly distributed in the matrix. With increasing the rotational speed, the size and aspect ratio of particles was decreased, and their sphericity was increased. The best morphology of Si particles (size of 2.23 µm, aspect ratio of 1.91, and sphericity of 0.682) had been obtained at the rotational speed of 800 rpm. The microhardness profiles of the FSPed samples were roughly homogeneous. After the cold rolling, the yield strength (YS), ultimate tensile strength (UTS), and energy absorption (EA) were enhanced to 288.7 MPa, 296.0 MPa, and 18.5 J/cm3, however, the total elongation (TE) was reduced to 6%. Interestingly, the YS, UTS, TE, and EA of all FSPed samples were much higher than that of the initial material. The 800–120 sample had the best tensile properties with YS, UTS, TE, and EA of 116.7 MPa, 235 MPa, 27.2%, and 57.9 J/cm3, representing 162%, 43%, 263%, and 395% improvement, respectively. The results of the fractography exhibited that the preferential cracks propagated perpendicularly to the loading direction along the Al/Si and Al/Fe-rich interfaces in the initial and heat-treated samples. In contrast, the crack planes of the rolled and FSPed samples were oriented around 45° with respect to the loading direction. The fracture of the initial, heat-treated, and rolled samples was dominated by cleavage mode. In contrast, the FSPed samples revealed a full ductile fracture.

Determining a representative element volume for DEM simulations of samples with non-circular particles

Numerical studies on the number of particles or system size required to attain a representative element volume (REV) for discrete element method (DEM) simulations of granular materials have almost always considered samples with spherical or circular particles. This study considers how many particles are needed to attain a REV for 2D samples of 2-disc cluster particles where the particle aspect ratio (AR) was systematically varied. Dense and loose assemblies of particles were simulated. The minimum REV was assessed both by considering the repeatability of static packing characteristics and the shearing behaviour in biaxial compression tests, and by investigating the effect of sample size on the measured characteristics and observed shearing behaviour. The repeatability of the data considered generally improved with increasing sample size. The packing characteristics of the dense samples were more repeatable suggesting that the minimum REV reduces with increasing packing density. The minimum REV was observed to be sensitive to the characteristic measured. Although the overall responses of the samples during shear deformation were similar irrespective of the sample sizes, the smaller the sample size, the higher the fluctuations observed in the responses. Analysis of the coefficient of variation of the fluctuations around the critical state stress ratio can provide insight as to whether a REV is attained. The particle AR influences the effect of sample size on shearing characteristics and thus the minimum number of particles required to attain a REV; this can be explained by the influence of AR on the number of contacts within the samples.

Gain-Assisted Optical Pulling Force on Plasmonic Graded Nano-Shell with Equivalent Medium Theory

The tunable optical pulling force on a graded plasmonic core-shell nanoparticle consisting of a gain dielectric core and graded plasmonic shell is investigated in the illumination of a plane wave. In this paper, the electrostatic polarizability and the equivalent permittivity of the core-shell sphere are derived and the plasmonic enhanced optical pulling force in the antibonding and bonding dipole modes of the graded nanoparticle are demonstrated. Additionally, the resonant pulling force occurring on the dipole mode is shown to be dependent on the aspect ratio of the core-shell particle, which is illustrated by the obtained equivalent permittivity. This shows that the gradation of the graded shell will influence the plasmonic feature of the particle, thus further shifting the resonant optical force peaks and strengthening the pulling force. The obtained results provide an additional degree of freedom to manipulate nanoparticles and give a deep insight into light–matter interaction.

Experimental and theoretical investigations of the rheological and electrical behavior of nanocomposites with universal percolation networks

Electrically conductive ceramic/polymer nanocomposites with universal percolation networks and varying contents of conductive nanoparticles were prepared herein; the effects of the dispersed state of the conductive nanoparticles on the electrical conductivity of the nanocomposites were investigated. The conductive nanocomposites were prepared by coating carbon black (CB) nanoparticles with a silane coupling agent, followed by their subsequent dispersion in the 1,6-hexanediol diacrylate (HDDA) photocurable polymer. The physical properties of the conductive nanocomposites, such as viscosity, photocurability, flowability, dispersibility, and electrical conductivity were investigated with respect to the loaded CB content. A correlation between conductivity and internal dispersibility was established by conducting theoretical analysis based on conditions of particle dispersion, aspect ratio, orientation, and interface. A comparison of the experimental values and theoretically obtained results assisted in identifying the nanoparticle network structure in the polymer matrix as universal percolation networks with imperfect/tunneling interfaces and a percolation threshold (c*) of 0.016. The electrical conductivity, heat deflection temperature (HDT), and tensile strength of 3D-printed conductive nanocomposite products were analyzed; scanning electron microscopy (SEM) was also employed to examine these samples. This study suggests a new development strategy for improving the quality of nano-products based on the quantitative dispersibility analysis of nanocomposite materials.

Effect of Filler Aspect Ratio on Stiffness and Conductivity in Phase‐Changing Particulate Composites

AbstractVariable stiffness in elastomers can be achieved through the introduction of low melting point alloy particles, such as Field's metal (FM), enabling on‐demand switchable elasticity and anisotropy in response to thermal stimulus. Because the FM particles are thermally transitioned between solid and liquid phases, it is beneficial for the composite to be electrically conductive so the stiffness may be controlled via direct Joule heating. While FM is highly conductive, spherical particles contribute to a high percolation threshold. In this paper, it is shown that the percolation threshold of FM particulate composites can be reduced with increasing particles aspect ratio. Increasing the aspect ratio of phase‐changing fillers also increases the rigid‐to‐soft modulus ratio of the composite by raising the elastic modulus in the rigid state while preserving the low modulus in the soft state. The results indicate that lower quantities of high aspect ratio FM particles can be used to achieve both electrical conductivity and stiffness‐switching via a single solution and without introducing additional conductive fillers. This technique is applied to enable a highly stretchable, variable stiffness, and electrically conductive composite, which, when patterned around an inflatable actuator, allows for adaptable trajectories via selective softening of the surface materials.

Investigating the effect of operation points on crystal quality in reactive crystallization using continuous flow with high shear stress

To obtain crystalline particles with favorable quality, the relationship between operation points on the phase diagram during crystallization and the crystal quality in reactive crystallization has attracted significant attention. This study used a continuous flow with high shear stress (Taylor vortex flow) to elucidate the relationship and investigate an operation strategy to improve the crystal quality in reactive crystallization. This is because the continuous flow with high shear stress allows easy evaluation of the crystal quality at the various operation points estimated based on feed solution conditions by keeping the operation condition and suppressing agglomeration during the reactive crystallization. As a result, the crystal quality, such as the aspect ratio and crystal size distribution of crystalline particles, changed with solution pH and supersaturation. Furthermore, we produced crystalline particles with improved quality by designing an operation strategy due to the considering the influence of operation points on the crystal quality. Therefore, it is suggested that we have succeeded in clarifying the relationship between operation points and crystal quality, as well as in finding the operation strategy using the advantages of continuous flow with high shear stress.

Kaolinite and illite colloid transport in saturated porous media

Understanding the transport of naturally abundant clay colloids is critical in colloid associated contaminant transport in porous media. This study was focused on the impact of the median size of sand grains and the ionic strength of solution on the transport and retention behavior of clay colloids. Two clay samples of kaolinite and illite colloids were selected to represent clay samples containing 1:1 and 2:1 clay minerals, respectively. The observed retention profiles and breakthrough curves demonstrated that the impact of ionic strength on the retention behavior of clay was consistent with other colloidal colloids such as latex colloids or graphene oxide. The quantity of the retained clay increased as the median sizes of sand decreased, and the ionic strength increased from 0 to 0.1 M. However, a similar quantity of retained illite at the ionic strength of 0.01 M and 0.1 M indicates the presence of threshold ionic strength in clay colloid retention. The exponential relationship between sand-to-clay size ratio and first-order retention coefficient at given ionic strength implies the chance in long-term prediction of clay colloid transport from the observed retention profiles. • Transport of kaolinite and illite was investigated in saturated sand column. • Quantity of retained clay does not increase for ionic strength greater than 0.01 M. • Porosity of sand can be a critical factor in clay particle transport. • Impact of aggregation and aspect ratio of clay particles should be considered.

Investigation of Dispersion, Interfacial Adhesion of Isotropic and Anisotropic Filler in Polymer Composite

The movement of isotropic and anisotropic particles of iron and graphite within the polymer matrix was predicted and examined by the COMSOL simulation method. The interfacial adhesion of filler particles within the matrix was investigated under surface features observation. Carbonyl Iron (CI) particles, considered to be regular with a uniform size of (1–5 µm), were mixed with irregular particles of graphite (20–150 µm) with 30 V% in quantity in a silicone rubber matrix. The particle–matrix and particle–particle interactions were analyzed from the inner surface features. The drag of non-spherical particles and particle Reynolds numbers (Rep) were taken into consideration in point force models for both the Stokes (Rep ≪ 1) and Newton regime for particle shape. Newton regime is based on the aspect ratio for particles with regular and irregular shapes. The boundary area of the irregular particles holds like an anchor inside the polymer matrix for strong adhesion; however, regular particles have partial attachment due to the gravitational pull of attraction from the bottom contact points. However, uniform distribution of isotropic particles has been observed in comparison to the anisotropic particles within the polymer matrix.

Does Symmetry Control Photocatalytic Activity of Titania-Based Photocatalysts?

Decahedral anatase particles (DAPs) have been prepared by the gas-phase method, characterized, and analyzed for property-governed photocatalytic activity. It has been found that depending on the reaction systems, different properties control the photocatalytic activity, that is, the particle aspect ratio, the density of electron traps and the morphology seem to be responsible for the efficiency of water oxidation, methanol dehydrogenation and oxidative decomposition of acetic acid, respectively. For the discussion on the dependence of the photocatalytic activity on the morphology and/or the symmetry other titania-based photocatalysts have also been analyzed, that is, octahedral anatase particles (OAP), commercial titania P25, inverse opal titania with and without incorporated gold NPs in void spaces and plasmonic photocatalysts (titania with deposits of gold). It has been concluded that though the morphology governs photocatalytic activity, the symmetry (despite its importance in many cases) rather does not control the photocatalytic performance.

Taylor dispersion of elongated rods

Particles transported in fluid flows, such as cells, polymers, or nanorods, are rarely spherical. In this study, we numerically and theoretically investigate the dispersion of an initially localized patch of passive elongated Brownian particles constrained to one degree of rotational freedom in a two-dimensional Poiseuille flow, demonstrating that elongated particles exhibit an enhanced longitudinal dispersion. In a shear flow, the rods translate due to advection and diffusion and rotate due to rotational diffusion and their classical Jeffery's orbit. The magnitude of the enhanced dispersion depends on the particle's aspect ratio and the relative importance of its shear-induced rotational advection and rotational diffusivity. When rotational diffusion dominates, we recover the classical Taylor dispersion result for the longitudinal spreading rate using an orientationally averaged translational diffusivity for the rods. However, in the high-shear limit, the rods tend to align with the flow and ultimately disperse more due to their anisotropic diffusivities. Results from our Monte Carlo simulations of the particle dispersion are captured remarkably well by a simple theory inspired by Taylor's original work. For long times and large Peclet numbers, an effective one-dimensional transport equation is derived with integral expressions for the particles' longitudinal transport speed and dispersion coefficient. The enhanced dispersion coefficient can be collapsed along a single curve for particles of high aspect ratio, representing a simple correction factor that extends Taylor's original prediction to elongated particles.

A novel Arcs-based discrete element modeling of arbitrary convex and concave 2D particles

This study presents a novel Arcs-based discrete element method (ArcDEM) for efficient simulation of realistic granules with arbitrary convex and concave 2D particle outlines. In the proposed ArcDEM, a series of computational geometry algorithms are first developed to identify the convex corners and concave troughs of an arbitrary-shaped particle outline. Then, the circle-growing technique and the least squares method are combined to establish the Arcs-based particle that can represent the whole particle outline with multi-connected inward and outward arcs. Next, a new algorithm for efficient overlapping detection and precise contact resolution is developed for the Arcs-based particles. Finally, the ArcDEM is developed as a simulation tool with several implemented contact force laws and particle motions solved by an explicit time integration. To validate the feasibility and efficiency of the proposed ArcDEM, several numerical examples are performed, including (1) random allocation of non-overlapping irregular particles, (2) random packing of super-elliptical particles of different aspect ratios and blockiness, and (3) simulation of repose angle and biaxial compression tests of realistic rock particles with various roundness. The developed ArcDEM tool shows a powerful capability of numerically investigating the macro- and micromechanical properties of realistic convex and/or concave granular particles.

A study on damage evolution in Cu-TiO2 composite fabricated at different temperatures and strain rates

Copper/Titanium Dioxide (CuTiO2) samples were fabricated at three temperatures (450 °C, 650 °C, 850 °C) using: a universal testing machine (quasi-statically at the strain rate of 8 × 10–3 s−1), a drop Hammer (dynamically at the strain rate of about 8 × 102 s−1), and a modified Split Hopkinson Pressure Bar (strain rate of about 1.6 × 103 s−1). The effects of reinforcing particle size on relative density and damage parameter of Cu reinforced by 0, 2.5, 5 and 10% volume fractions of nano- and micro-sized TiO2 were investigated. The results indicated that the size of TiO2 particles, loading rate, and temperature had significant effect on relative density and damage parameter. The results also showed that the Quasi-Static method was superior to the other two methods. In addition, by increasing temperature, the mechanical properties of the composites were improved. The results showed that the effect of nano sized reinforcement particles on damage parameter was more profound than micro sized reinforcement particles. In this work, a new damage model considering the effects of strain rate, temperature, volume fraction and the aspect ratio of particles on damage parameter was proposed. The damage parameter was obtained using relative density and elasticity modulus. The results showed significant difference between the two methods. However, the density method yields more accurate and realistic results.

Dry Sliding Wear Behavior of Wrought Al-12.7Si-0.7Mg Alloy

In present paper, the dry sliding wear behaviors of wrought Al-12.7Si-0.7Mg alloy have been investigated using a pin-on-disc machine. The effect of various parameters, such as alloy conditions, sliding speed, and normal pressure, has been investigated. Wear surface was characterized by SEM/EDX microanalysis. The microstructure, hardness and tensile properties of the extruded profile were investigated with the aim of understanding the wear and friction mechanisms. The present results reveal an improvement in the mechanical and tribological properties, obtained due to microstructure characterized by fine Si particles uniformly distributed in the Al matrix of fine equiaxed grains, as promoted by hot extrusion. It was also revealed that higher hardness and the lower aspect ratio of eutectic Si particles contributed to the better wear resistance.

Crystal plasticity simulation of the macroscale and microscale stress–strain relations of additively manufactured AlSi10Mg alloy

Various Al-Mg-Si components produced via additive manufacturing (AM) have many potential applications. Especially for those applications requiring high quality and reliable safety, precise numerical simulations for designing the structures and components are demanded. The particular microstructure of the additively manufactured alloy should be considered to obtain sufficient simulation accuracy. However, crystal plasticity models and simulations for additively manufactured Al-Si-Mg alloys are not well established yet. Here, based on three-dimensional representative volume elements, a crystal plasticity model is applied and solved using the fast Fourier transform method for the AlSi10Mg alloy produced by laser powder bed fusion. We analyzed the effects of the hardening parameters of the Al phase, the effective aspect ratio of Si particles, and the porosity on the mechanical properties at both the macroscale and the microscale systematically and quantitatively. Furthermore, the model parameters were calibrated by the experimental results from in-situ synchrotron X-ray diffraction. The proposed approach provides an effective tool for interpreting the microstructure-property relation of the additively manufactured AlSi10Mg alloy. The resulting macroscopic material properties can be used for optimizing macroscale components and structures. Of course, the methodology can be transferred to other alloys.

Numerical investigation on effect of particle aspect ratio on the dynamical behaviour of ellipsoidal particle flow

Flow of ellipsoidal particles in a modal shear cell was investigated at the microdynamic level based on discrete element method simulations. In a stress-controlled double-shear condition, the flow was studied by varying the aspect ratio of ellipsoidal particles and comparing with the flow of spherical particle assembly in terms of some key properties, including particle alignment, linear velocity, angular velocity, porosity, contact force and contact energy. It was found that particle elongation impacts the rotational displacement around the axis perpendicular to the shear direction, which causes that the ellipsoidal particles with higher elongation are more aligned with the direction of the shear velocity, with more uniform force network. This then affects other particle properties. The fluctuation of linear velocity and the angular velocity decreases with an increase in particle aspect ratio, although the particle elongation does not significantly affect the flow velocity gradient. There is a reduction in both normal and tangential forces per contact with an increase of particle elongation. Due to the variation of the particle alignment with elongation, the standard deviation of the contact energies increases and then reduces when an increase in particle aspect ratio occurs, and on contrary, the porosity has an opposite variation trend.