3D Particles Research Articles

2D particle-in-cell/Monte Carlo collisional simulation of the plasma initiation in the vacuum breakdown stage

In this paper, the plasma formation in the vacuum breakdown stage is simulated with a 2D particle-in-cell/Monte Carlo collisional model. In this model, the field is solved in a 2D cylindrical coordinate system and particles including electrons, atoms, singly, doubly, triply and fourfold charged ions are traced as super particles, each of which represents many real particles. The plasma quickly builds up from the field emission and evaporation near the field emitter with a local field of about 10 GV m−1. The plasma expands in a hemispherical shape with a high-density gradient in the vicinity of the field emitter. During the discharge, a typical structure including an ion sheath, a quasi-neutral region and an acceleration layer is obtained. The well-pronounced potential hump near the cathode, the high ion velocity in the acceleration layer and ion charge state agree well with results in previous research works. Investigation of the effects of the field enhancement factor and emitter surface temperature shows that more highly charged ions can be obtained in simulations with higher field emission current, while the plasma initiates faster and has higher density with stronger evaporation of neutral atoms.

Efficient sizing of single layer graphene oxide with optical microscopy under ambient conditions

Graphene oxide (GO) nanosheets are 2D particles with many advantageous properties including high gas barrier and mechanical strength, and can also be used as precursors to electronically conductive graphene-like structures. Characterizing the size of GO nanosheets is challenging because of the heterogeneous nature and ultra-thin 2D structure (∼1 nm). Current approaches for GO size measurements include atomic force microscopy (AFM) and scanning electronic microscopy (SEM), which both require significant time and environmental or financial resources. In response to these challenges, we herein report a facile method to size GO nanosheets using optical microscopy. As directly visualizing GO nanosheets is difficult due to poor contrast, we utilized the oil-water interfacial co-assembly of GO and charged particles to image single layer GO in situ. Contrast is generated between the ‘dark’ particles that occupy interstitial regions between ‘light’ GO nanosheets. The method allows GO to be imaged in a large area, in contrast to SEM and AFM, covering >200 nanosheets in one image. The size distribution of the nanosheets can be easily determined, giving results consistent to multiple SEM images. The novel method described herein is low cost and efficient, can be applicable to other 2D materials, and is amenable to manufacturing environments.

High internal phase Pickering emulsions stabilized with graphene oxide in supercritical CO2 system

With aid of ultrasonication, water-in-supercritical CO2 (scCO2) Pickering-type emulsions were successfully prepared by using graphene oxide as stabilizer. The phenomenon was observed from observation window that after the termination of ultrasonication, the darkness of the emulsion declined rapidly in a short period, and then kept relatively stable for a relatively long duration. The addition of graphene oxide (GO) greatly increases the proportion of dispersed phase (water) in the scCO2 continuous phase. Under optimized conditions, GO emulsifies up to 23% water in scCO2 with droplets around 0.5 μm–3 μm. The stabilization time of these emulsions exceeded 10 h and increased with system pressure and GO concentration. The superiority of GO as a Pickering stabilizer was theoretically analyzed in this study: by taking advantage of 2D morphology, GO sheets are more likely to irreversibly attach to the scCO2-water interface to form a stabilized emulsion than the conventional 3D particles.

Modeling and mechanical influence of meso-scale concrete considering actual aggregate shapes

Aggregate shape modeling is critical to concrete failure in mesoscale numerical simulation, However, most studies replaced actual aggregate with basic geometry, which caused the imprecise results. Combined with laser scanning technique and spatial random cutting, an actual aggregate database containing 1568 2D particles was formed. To realize rapid placement of particles with complex boundary, an indirect overlapping detection method based on rectangular fitting of aggregate is proposed, and the corresponding modeling method is also established. Uniaxial compression simulations of 30 cubes with different particle size groups were carried out, and parameter statistics of aggregate shape (elongation ratio, circularity and roughness) in the models were calculated. The results show that the effect of large size aggregate on the crack and strength is more obvious, and the difference in elongation ratio and roundness distribution of aggregate cause the fluctuation of concrete strength.

An optimization-based approach for modeling of complex particles

Producing of granular media with irregular shapes is one of the significant challenges in different fields related to granular particles. Representing inaccurate and simplified particles can result in wrong predictions. In this paper, a new statistical and optimization-based algorithm is presented by which 3D particles with complex shapes are generated on a random container. Stochastic conditional sampling along with an optimization method are combined such that particle with realistically and controllable shapes are generated. Depending on the initial shape of the container, a pack of spheres is generated. Then, an iterative optimization-based conditional sampling is proposed by which other complex shape descriptors are considered and can help to avoid artifacts and unrealistic shapes. The proposed method is applied to two examples wherein the particles reproduction and controllability of algorithm is demonstrated. The performance of the algorithm, in terms of shape reproduction, is also quantified using various utilized statistical measures.

Phase field modeling of chemomechanical fracture of intercalation electrodes: Role of charging rate and dimensionality

We investigate the fracture of Li-ion battery cathodic particles using a thermodynamically consistent phase-field approach that can describe arbitrarily complex crack paths and captures the full coupling between Li-ion diffusion, stress, and fracture. Building on earlier studies that introduced the concept of electrochemical shock, we use this approach to quantify the relationships between stable or unstable crack propagation, flaw size, and C-rate for 2D disks and 3D spherical particles. We find that over an intermediate range of flaw sizes, the critical flaw size for the onset of crack propagation depends on charging rate as an approximate power-law that we derive analytically. This scaling law is quantified in 2D by exhaustive simulations and is also supported by 3D simulations. In addition, our results reveal a significant difference between 2D and 3D geometries. In 2D, cracks propagate deep inside the particle in a rectilinear manner while in 3D they propagate peripherally on the surface and bifurcate into daughter cracks, thereby limiting inward penetration and giving rise to complex crack geometries.

Morphology Change Study of Molybdenum Oxide from 3D to 2D Particles

Morphology Change Study of Molybdenum Oxide from 3D to 2D Particles

Generation of 3D Microparticles in Microchannels with Non-rectangular Cross Sections

Flow lithography in a conventional rectangular microchannel is limited to fabrication of particles for which only the shapes of top perimeters are controlled. We present a flow lithography technique for fabrication of microparticles of diverse 3D shapes and multiple layers using non-rectangular microchannels with designed cross sections that allow the creation of complex shapes and diverse cross-sectional shapes. Variations in cross-sectional shape allow high-throughput, on-demand production of microparticles in unconventional shapes such as tetrahedrons and pyramids. Multilayered 3D particles were generated in an enlarging triangular channel combined with on-chip PDMS valves, which allow particle alignment and fluid exchange. These 3D microparticles are expected to further expand the wide variety of applications of microparticles, especially in drug delivery and tissue engineering fields.

Porous Cupric Oxide: Efficient Photocathode for Photoelectrochemical Water Splitting

AbstractPhotoelectrochemical (PEC) water splitting is considered as an effective approach to generate hydrogen at the cathode, and can be used as a means to generate green energy. A simple electrochemical deposition technique is developed for the synthesis of CuO nanostructures. CuO with different morphologies like porous 2D sheets, porous bipyramids, particles, and spheres are developed after oxidation of the electrodeposited Cu nanostructure. Among them, CuO porous 2D nanosheets show the best activity as photocathode towards PEC water splitting due to the high light absorbance and high electrochemically active surface area (ECSA). CuO porous 2D sheets contains three times higher ECSA compared to CuO particles, indicating their higher electrochemical activity. CuO porous 2D sheets can generate a current density of 3.09 mA cm−2 at an applied potential of −0.1 V vs RHE in 0.5 M Na2SO4 solution. Furthermore, Mott‐Schottky measurements demonstrate that CuO porous 2D sheets possess high carrier density, 8.18×1020 cm−3, and a high flat band potential of 1.215 V vs. RHE. Thus, CuO porous 2D sheets have excellent conductivity and a high degree of band bending. After PEC water splitting, XRD analysis was carried out to reconfirm the photostability of the CuO porous 2D sheets. It may be due to the higher charge transportation in the porous structures.

Superellipsoid-based study on reproducing 3D particle geometry from 2D projections

The potential of reproducing the 3D geometrical features, e.g., sizes, elongation and flatness, of idealized convex granular particles from their 2D random projections was investigated based on a superellipsoid model. Using the random projection method, the relationships between the geometrical features of monosized superellipsoids and the statistical distributions of the corresponding 2D projected counterparts were examined. The 2D size parameters, e.g., r1max, rmean and r2min, obtained from the projected images were well correlated with the semi-axial principal dimensions of the 3D particles, e.g., R1, R2 and R3. Further studies of randomised superellipsoid particles with various aspherical shapes and limited projection numbers were performed to validate the findings. The capability and reliability of predicting 3D sizes and shapes from 2D projections were statistically analysed and verified. The correlation of prediction accuracy with increasing projection number and varied aspherical shapes was investigated. Based on the results, a particle geometry prediction framework was proposed, and the associated performance was examined using realistic cobble particles obtained from 3D laser scanning. The promising results highlight the potential of this approach in future industrial applications.

Prediction of 3D size and shape descriptors of irregular granular particles from projected 2D images

Macroscopic mechanical properties of granular materials are closely related to particle morphology. For practical reasons, the morphological features are commonly examined from projected two-dimensional (2D) images of the three-dimensional (3D) particles. This brings forward the need for quantifying the correlations between the 2D and 3D particle descriptors. This paper addresses these correlations for irregular granular particles. Three-dimensional images of sand particles were acquired through microfocus X-ray computed tomography, based on which 3D surfaces of the particles were reconstructed using spherical harmonic analyses. The 3D particle size and shape descriptors were subsequently evaluated. All-around projection and random projection of the particles onto 2D planes were undertaken numerically to obtain the projected 2D images and thus the corresponding 2D size and shape descriptors. The results indicate that there are close correlations between 3D and 2D size descriptors averaged from the all-around projections. 2D and 3D shape descriptors can be approximately fitted with a linear relationship. The mean value of 2D descriptors of the tested sands obtained from a series of independent random-projection tests is essentially identical to that from the all-around projections; except that the data from the random-projection tests show a larger scatter. In light of the relationships among the descriptors, a novel and promising approach to predict the cumulative distribution of 3D descriptors from that of 2D descriptors evaluated from a random-projection test is proposed.

The 3D CoNi alloy particles embedded in N-doped porous carbon foams for high-performance microwave absorbers

The 3D CoNi alloy particles embedded N-doped porous carbon (CoNi@PRM-NC) foam with open reticular structures and high-performance microwave absorption are prepared by the novel sponge-templated strategy that uses melamine foam as a sacrificial scaffold and supporting template, phenolic resol as a carbon precursor and cobalt nickel nitrate as a magnetic particle precursor. It is worth noting that the surface of the skeleton has a large amount of honeycomb-like pores without add any pore formers and surfactants. After adding cobalt nickel metal particles, all three materials exhibit the enhanced electromagnetic wave absorption. By contrast, 3D CoNi@PRM-NC performs best, with the minimum reflection loss values of −56 dB at 17.8 GHz when the thickness is 1.7 mm. Meanwhile, an ultrabroad bandwidth of 11.9 GHz (6.1–18 GHz) at the thickness range of 1–5 mm is also obtained. The excellent microwave absorption performance of these materials is ascribed to the multiple scatterings caused by 3D conductive foam structure, large attenuation as well as the balanced impedance match between dielectric loss and magnetic loss. This strategy might open an avenue to large-scale synthesization of various porous carbon-magnetic metal composites which can be a promising candidate for high-performance microwave absorber.

Inherent Photodegradability of Polymethacrylate Hydrogels: Straightforward Access to Biocompatible Soft Microstructures

AbstractHydrogels are important functional materials useful for 3D cell culture, tissue engineering, 3D printing, drug delivery, sensors, or soft robotics. The ability to shape hydrogels into defined 3D structures, patterns, or particles is crucial for biomedical applications. Here, the rapid photodegradability of commonly used polymethacrylate hydrogels is demonstrated without the need to incorporate additional photolabile functionalities. Hydrogel degradation depths are quantified with respect to the irradiation time, light intensity, and chemical composition. It can be shown that these parameters can be utilized to control the photodegradation behavior of polymethacrylate hydrogels. The photodegradation kinetics, the change in mechanical properties of polymethacrylate hydrogels upon UV irradiation, as well as the photodegradation products are investigated. This approach is then exploited for microstructuring and patterning of hydrogels including hydrogel gradients as well as for the formation of hydrogel particles and hydrogel arrays of well‐defined shapes. Cell repellent but biocompatible hydrogel microwells are fabricated using this method and used to form arrays of cell spheroids. As this method is based on readily available and commonly used methacrylates and can be conducted using cheap UV light sources, it has vast potential to be applied by laboratories with various backgrounds and for diverse applications.

Understanding the Photocatalytic Properties of Pt/CeOx /TiO2 : Structural Effects on Electronic and Optical Properties.

Ceria-titania interfaces play a crucial role in different chemical processes but are especially promising for the photocatalytic splitting of water using light in the visible wavelength region when Pt is added to the system. However, the complexity of this hierarchical structure hampers the study of the origin of its outstanding properties. In this article, the structural, electronic and optoelectronic properties of CeO2 /TiO2 systems containing 1D, 2D, and 3D particles of ceria are analyzed by means of density functional calculations. Adsorption sites and vacancy effects have been studied to model Pt adsorption. Density of states calculations and absorption spectra simulations explain the behavior of these systems. Finally, these models are used for the screening of other metals that can be combined with this heterostructure to potentially find more efficient water splitting photocatalysts.

Influence of hot water treatment during laser ablation in liquid on the shape of PbO nanoparticles

The significant role of the unavoidable hot water treatment during laser ablation of lead in water in formation of the nonspherical 2D (plates) and 3D micro- and nanoparticles (octahedra and rods) in suspension and at the target surface has been shown experimentally. The formation of the nonspherical particles has been demonstrated at hot water treatment alone at temperature above 70 °C achieved frequently during laser ablation in water. The simple model was applied for explanation of the obtained formation of 3D particles. The 2D plates formed by seedless growth. The influence of the unavoidable hot water treatment should be considered as an additional mechanism for explanation of the formation of the nonspherical nanoparticles during laser ablation in water.

Photonic nanojets with mesoscale high-index dielectric particles

In this work, we demonstrate the ability of high-index dielectric particles immersed in air to generate photonic nanojets with extreme resolution (∼0.06λ0). Both 2D (cylindrical) and 3D (spherical) particles are analyzed, and their profile is truncated using the Weierstrass formulation for solid immersion lenses to produce a photonic nanojet at the output surface under plane wave illumination. Their focusing capability is evaluated in terms of the spatial resolution achieving subwavelength values of ∼0.14λ0 and ∼0.06λ0 for a truncated cylinder and sphere, respectively. The capability of the truncated sphere to enhance the backscattering produced by two small metallic spherical scatterers placed near the photonic nanojet is evaluated by using a scanning-probe microscopy configuration. The imaging capabilities of this technique are also analyzed by moving the metallic spheres in the transversal plane where the photonic nanojet is produced. The results presented here improve greatly the typical resolution of photonic nanojets generated with dielectric particles with a small index contrast. In addition, the high-index material allows using mesoscale particles, leading to a more compact setup. These results may find applications in areas such as microscopy, imaging, and sensing devices where a subwavelength resolution below the diffraction limit is needed.

The material design and property research of a novel machine tool material

In this paper, a new machine tool material is put forward where PTFE resin is chosen as the matrix material for its properties of good acid and alkali corrosion resistance. High purity quartz and alumina ceramic microsphere are selected as the aggregates; nano-alumina and hollow glass microsphere are selected as the fillers. First, the aggregate gradation is analysed. Then, Young's modulus and sound attenuation coefficient are predicted in theory. Nonlinear regression analysis is conducted by support vector machine (SVM). 2D and 3D irregular polygons aggregate particles packing model is set up by MATLAB and the properties of the packing model are simulated by finite element analysis. Finally, several vibration experiments are conducted. The analysis results show that the chosen filler and aggregate can improve the stiffness and vibration characteristics of the material, which has a guiding significance to the machinery manufacturing industry.

The fraction of overlapping interphase around 2D and 3D polydisperse non-spherical particles: Theoretical and numerical models

The fraction of interphase is an important microstructure parameter in the prediction of macroscopic properties of particulate composites. Currently, some researchers have presented theoretical and numerical investigations on the interphase fraction for spherical particle systems, and even quantify the influence of interphase fraction on the overall elastic and transport properties of particulate composites. However, the overlapping interphase fraction in polydisperse non-spherical particle systems is still an open issue. In this work, a generic theoretical model is formulated to derive the overlapping interphase fraction for polydisperse 2D non-circular and 3D non-spherical particle systems by means of the statistical geometry of composites. In this model, the morphology of interphase coated onto the surface of non-spherical particles can be characterized by circularity and sphericity of particles that are important parameters to describe the shape of particles. On the other hand, numerical simulations for the one-point probability function of interphase are presented to verify the proposed theoretical framework. In the numerical simulations, a novel algorithm is developed by reducing the problem of identifying the precise location between an arbitrary spatial point and interphase to the basic issue of finding the distance from the point to the surface of particles. If the distance is less than the interphase thickness, the point definitely locates inside interphase. In addition, the algorithm can be further used to detect the overlap between adjacent ellipsoidal particles (2D ellipses). Moreover, a variety of particle shapes (such as regular polygons and ellipses with the same circularity, and regular polyhedrons and ellipsoids with the same sphericity) are taken into account to generate particle packing structures. Then, the fraction of overlapping interphase in each packing structure is statistically obtained. Results show that statistical values are consistent with their theoretical values under the same conditions. This validates the reliability of the theoretical framework. Finally, the effects of particle size distributions and interphase thicknesses on the interphase fraction are investigated. It can be found that the interphase fraction increases with the increase of particle volume fraction, particle fineness and interphase thickness.

Evaluation of three-dimensional particle shape index from projected two-dimensional image

Traditionally, the shape of a three-dimensional (3D) particle is inferred from a single parameter called the aspect ratio (AR) that is evaluated from a collection of projected two-dimensional (2D) images of the 3D particle. While this approach could offer an estimate of the particle shape, it is likely that a single parameter is insufficient to describe the 3D shape characteristics of a particle. Conventionally, the shape of a 3D particle can be described by two parameters: the elongation index (EI) and the flatness index (FI), defined as the length ratios of different principal dimensions. This paper presents a novel approach that can be used to evaluate the EI and FI of 3D particles based on their projected 2D images. The novelty of this proposed method is that the distribution of the AR is considered rather than only the mean value. The performance of the algorithm is examined using numerically generated ellipsoids and real sand particles scanned using microfocus X-ray computed tomography. The results appear promising and the plausible combinations of the EI and FI of the 3D particles can be obtained.

Investigation of thermal stability of 2D and 3D CoAl2O4 particles in core-shell nanostructures by Raman spectroscopy

We are studying the formation of a nanostructured spinel CoAl2O4 layer on α-Al2O3 giving rise to a core-shell composite. In the final product, two mechanisms of CoAl2O4 crystallization onto a α-Al2O3 microparticle surface are observed, depending on the dispersion grade of Co3O4: a 3D nanostructure from the arrangement of Co3O4 agglomerated nanoparticles; 2D nanoparticles from the diffusion mechanism of isolated Co3O4 nanoparticles. As a consequence, two different crystallization pathways may occur during the thermal treatment. In order to understand the formation mechanisms a Raman Confocal Study is performed. The features of the Raman spectra of the samples depend strongly on the morphology of the nanoparticles located in the shell of the microparticle. Average spectra of the samples show a variation in the Raman shift between the different samples. The differences between 3D or 2D structures is associated with the transmission of phonons among the nanoparticles. The high absorbance of the cobalt species could mask the Raman shift displacement by local heating, so both the temperature and the laser source power are considered in the Raman study. The evolution of the Raman spectra with applied temperature indicates a decoupling of the Raman modes. This fact is more relevant for the 3D aggregates in which nanoparticles produced a larger scattering of phonons and a higher sensitivity to temperature variation. These results clearly indicate that extrinsic parameters such as the size of the crystals and their aggregation state affects their Raman properties.