Control Of Particle Shape Research Articles

Effect of reaction temperature and impact force on formation and particle shape of β-Li3PS4 in liquid phase synthesis

All-solid-state lithium-ion batteries are promising next-generation secondary batteries, primarily due to their superior safety. In their production process, it is necessary to achieve large contact interfaces between the particles and improve particle fluidity. The particle shape of the solid electrolyte plays a key role in addressing these requirements. Li3PS4 (LPS) is synthesized in the liquid phase and offers the advantages of cost-effectiveness and production-scalability. However, the mechanisms controlling the particle size and shape have not yet been revealed. In this study, we synthesized LPS particles in the liquid phase using a hot stirrer and an ultrasonic homogenizer to investigate the effects of reaction temperature and impact force on the reaction rate and particle shape. We successfully synthesized shape-controlled particles with high ionic conductivity by combining different synthesis methods. This study provides valuable data for optimizing the synthesis conditions to attain specific particle shapes and sizes.

Surfactant-assisted combustion synthesis of agglomerated-free, size- and shape-controlled magnetic iron oxide nanoparticles for biomedical applications

An advanced version of the solution combustion synthesis (SCS) method was developed to prepare iron oxide (IO) nanoparticles, through controlling the agglomeration, size and shape of nanoparticles by assisting a cationic surfactant, “cetyltrimethylammonium bromide (CTAB)” and ethanol. Various IO nanoparticles were prepared in the presence of different CTAB:ethanol molar compositions of 0:0, 0.27:0, 0.55:0, 0.27:17.1, 0.55:17.1 and 0.82:17.1. The morphological evolution from agglomerated-shape particles to the well-dispersed as well as the size- and shape-controlled particles depended directly on the CTAB:ethanol molar composition. A shift from ferromagnetic behavior to superparamagnetic was observed by the application of CTAB along with ethanol, where the lowest blocking temperature (Tb, 60 K), highest saturation magnetization (Ms, 83.5 emu g−1), zero coercivity and remanance magnetization were revealed for the particles prepared by CTAB:ethanol molar compositions of 0.55:17.1. These particles showed an acceptable specific absorption rate (SAR) value (320 W g−1) as well as no obvious hemolytic and cytotoxic effects. This work provides new insights into advancing the SCS method and thus controlling the morphology, size and shape of metal oxide nanoparticles.

Facile Fabrication of Oxygen-Defective ZnO Nanoplates for Enhanced Photocatalytic Degradation of Methylene Blue and In Vitro Antibacterial Activity

In this study, we examined whether catalysts with many defects have excellent photoactivity. We prepared ZnO nanoplates with varying degrees of defects in a short time of 4 h by varying the crystal growth temperature at 50, 100, 150, and 200 °C under a strong alkali NaOH atmosphere of 4.0 M. During high-temperature preparation of ZnO, crystal defects were reduced and crystallinity was further increased. In crystallized systems over 100 °C, rhombic nanoplates were used to control particle shape and induce growth in only two axes. The PL, Raman, and XPS analyses confirmed the presence of strong oxygen vacancies in all ZnO nanoplates, and the vacancies decreased with increasing crystallization temperatures. Methylene blue (MB) dye was initially fixed at 50 mg/L with a peak decrease in absorption at 600–700 nm, confirming its decomposition over time. For the 5 h reaction, the MB removal concentration follows the following order: ZnO-50 < ZnO-100 < ZnO-150 < ZnO-200. The study confirms that ZnO-200 nanoplates with fewer oxygen vacancies decompose MB more quickly. ZnO-200 nanoplates synthesized at 200 °C provided the best sterilization performance when tested against gram-positives and gram-negatives, Escherichia coli and Staphylococcus aureus, respectively. ZnO-200 nanoplates after 3 h showed a high sterilization performance of 96.95% (86.67% in a dark room) for staphylococcus aureus and 95.82% (74.66% in a dark room) for Escherichia coli when irradiated with light. Particularly noteworthy in this study is that ·OH and ·O2− radicals are generated more strongly in ZnO-200 than in ZnO-50 nanoplates. These results show that too-strong oxygen vacancies rather inhibit the antibacterial performance, and that the virtue of moderation also exists in the catalytic activity.

(Invited) Engineered Electrode Materials Via Dry Processing

Dry bulk processing methods can offer surprising control of particle shape, size, internal composition, and surface morphology. Mechanofusion is a method that can be used to smooth, spheronize, coat, and embed particles [1–4]. Dry particle microgranulation (DPMG) is a newly developed mechanofusion method in which ~50 μm speres are added to the process as "templating" media [5]. Here it will be shown that DPMG and new applications of mechanofusion offer unprecedented control in particle shape, internal porosity, and internal composition variation, enabling the creation of never before possible highly engineered particles, including: consolidating submicron particles into dense and uniform ~10 μm particles that are spherical or tetrahedral in shapespontaneous formation of core/shell particles from a mixture of submicron particles with different compositionscreating spherical graphite particles from fine flake graphiteembedding nanoparticles within the core of ~10 μm host particlesapplying fused dense oxide particle coatingssmoothing the surface of polycrystalline particles to lower their surface area Such methods can produce no waste and operate at 100 % yields, greatly reducing environmental impact and cost compared to other commercial particle production methods. This offers tremendous opportunity for creating sustainable advanced battery materials. Examples of new cathode and anode materials synthesized by these methods and opportunities for new materials will be discussed.

Shaping Block Copolymer Microparticles by Positively Charged Polymeric Nanoparticles.

Shape-transforming block copolymer (BCP) microparticles have attracted extensive attention due to their promising applications in nanotechnology, biomedicines, interfacial science, and other fields. As their performance is highly associated to their shape and structure, it is very important to realize the precise control of particle shape. In this report, a method is proposed to regulate the shape and structure of polystyrene-b-polydimethoxysiloxane (PS-b-PDMS) microparticles by using positively charged core-crosslinked nanoparticles (CNPs) as a cosurfactant, combining with cationic surfactant cetyltrimethylammonium bromide (CTAB). The electrostatic repulsive interactions between CNPs and CTAB dominate the shape of PS-b-PDMS particles. Upon introducing NaCl, the electrostatic repulsion is reduced, resulting in the reshape of PS-b-PDMS particles from striped Janus ellipsoids to onion-like microspheres at a critical concentration of NaCl (cNaCl ). Interestingly, it is found that the critical cNaCl first increases then reaches a plateau, with the increase in the crosslinking degree of the CNPs. The work provides a simple strategy to tailor the morphology of BCPs by manipulating the electrostatic interaction.

A novel method for generation of particle packing model used in numerical simulation for the mechanical behavior of multi-component material

This study presents a novel algorithm to establish a numerical model for the study of mechanical behavior of multi-component material such as particle reinforced metal matrix composites, concrete, particle filled polymers, etc. The algorithm consists of two steps, one is to divide the given region into sub-regions of a specified size distribution, and the other is to fill each sub-region with particles of specified shapes. During the filling process, the contact states between particles can be controlled by the number and positions of reference points. Taking the quasi-static uniaxial tensile simulation of concrete as a verification example, two concrete models with the same particle size distribution but different shapes have been established. Through the comparison of elastoplastic responses of different aggregate shape models in different tensile directions, it is concluded that the models meet the requirements of macroscopic uniformity, meso-scale randomness and statistical rationality. This verifies the feasibility of modeling method and its advantages in precise control of particle shape, distribution and other parameters.

Particle morphology of water atomised iron‑carbon powders

Water atomisation can produce metal powders faster and at lower cost than gas atomisation, but it is well known that the powder particles are irregular and may contain a large number of pores. The current study analyses three iron‑carbon alloys with different superheats, produced as powder by water atomisation and compares the particle shapes and porosity in each. The alloy with the most carbon (4.2 wt%) showed the highest circularity (0.72) for 20–45 μm particles, but the lowest (0.59) for 180-212 μm particles. This is consistent with collisions between droplets affecting particle shape. The lowest-carbon melt (0.22 wt%) solidified fastest, so underwent fewest collisions and showed similar circularity for all particle sizes. The breakdown of water to form hydrogen and the formation of hydrogen bubbles was the most likely cause of porosity. The findings of this study may be used to inform future water atomisation process design to control particle shape and minimise porosity.

Excluded area of superellipse sector particles.

Superellipse sector particles (SeSPs) are segments of superelliptical curves that form a tunable set of hard-particle shapes for granular and colloidal systems. SeSPs allow for continuous parametrization of corner sharpness, aspect ratio, and particle curvature; rods, circles, rectangles, and staples are examples of shapes SeSPs can model. We investigate the space of allowable (nonoverlapping) configurations of two SeSPs, which depends on both the center-of-mass separation and relative orientation. Radial correlation plots of the allowed configurations reveal circular regions centered at each of the particle's two end points that indicate configurations of mutually entangled particle interactions. Simultaneous entanglement with both end points is geometrically impossible; the overlap of these two regions therefore represents an excluded area in which no particles can be placed regardless of orientation. The regions' distinct boundaries indicate a translational frustration with implications for the dynamics of particle rearrangements (e.g., under shear). Representing translational and rotational degrees of freedom as a hypervolume, we find a topological change that suggests geometric frustration arises from a phase transition in this space. The excluded area is a straightforward integration over excluded states; for arbitrary relative orientation this decreases sigmoidally with increasing opening aperture, with sharper SeSP corners resulting in a sharper decrease. Together, this work offers a path towards a unified theory for particle shape control of bulk material properties.

X ray diffraction (XRD) analysis and evaluation of antioxidant activity of copper oxide nanoparticles synthesized from leaf extract of Cissus vitiginea

Nanoparticles have a diameter of up to 100 nm and a higher surface-to-volume ratio, enabling more active surface atoms to contribute to implementations and improve material properties. In nanoparticle preparation, the ability to control particle size, shape, and morphology is important. The most important tool for studying nanomaterials is XRD, it is a vital characterization tool in solid-state chemistry and materials science. For any compound, XRD is a simple method for determining the unit cell's size and shape. This study explains how copper oxide nanoparticles are formed in Cissus vitiginea leaves. The antioxidant function and XRD study of the synthesized CuONPs were also investigated. According to the XRD results, the copper oxide nanoparticles formed by reducing Cu2 + ions by Cissus vitiginea leaf extract are crystalline in nature. CuONPs have an average crystalline size of ~32.32 nm, according to the Debye-Scherrer formula. CuONPs have higher antioxidant activity than plant extract and are closest to ascorbic acid in terms of standard.

(Invited) Advances in Pyrolyzed Polymeric Sulfur Cathodes for Low-Cost Lithium Metal Batteries

Sulfur is a highly desirable cathode material for lithium batteries but its complex reaction mechanisms involving soluble species have limited its cycle life. When sulfur exists as a very short chain or substituted function groups on aromatic rings, the dissolution process appears to be mitigated, leading to a long cycle life. A good example is Sulfurized-poly(acrylonitrile) (SPAN), which is synthesized by pyrolyzing a mixture of PAN and elemental S at 300-500oC. SPAN is essentially a nitrogen doped carbon host for sulfur and has shown exceptional cycling stabilities in common carbonate electrolytes.We have recently launched an intensive effort to advance the Li/SPAN battery technology to an energy density of > 300 Wh/kg. Its exceptional cycle life and low cost will make the technology a promising choice for electric vehicle applications. In this talk, we will review several interrelated efforts to realize this goal: 1) searching for SPAN-like materials with higher S loading and higher capacities by tuning N:C:S ratios with different polymer and sulfur precursors; 2) improving the packing density of SPAN particles in the cathode by controlling particle shape and size using new synthesis approaches. A highlight is a um-sized, platelet-like morphology that greatly increase packing densities; 3) developing a solvent-free homogenous chemical lithiation method for the synthesis of lithium containing SPAN. The lithiated SPAN can greatly reduce the irreversible capacity loss during the first discharge cycle and minimize the volume change associated with the initial lithiation process; and 4) continuing the development of new electrolyte compositions that can further improve the lithium metal anode efficiency without sacrificing SPAN cycle life. These studies hold the promise to enable a practical, low-cost and long-life Li/S battery.

Improvement of Gold Nanorods in Photothermal Therapy: Recent Progress and Perspective.

Cancer is a life-threatening disease, and there is a significant need for novel technologies to treat cancer with an effective outcome and low toxicity. Photothermal therapy (PTT) is a noninvasive therapeutic tool that transports nanomaterials into tumors, absorbing light energy and converting it into heat, thus killing tumor cells. Gold nanorods (GNRs) have attracted widespread attention in recent years due to their unique optical and electronic properties and potential applications in biological imaging, molecular detection, and drug delivery, especially in the PTT of cancer and other diseases. This review summarizes the recent progress in the synthesis methods and surface functionalization of GNRs for PTT. The current major synthetic methods of GNRs and recently improved measures to reduce toxicity, increase yield, and control particle size and shape are first introduced, followed by various surface functionalization approaches to construct a controlled drug release system, increase cell uptake, and improve pharmacokinetics and tumor-targeting effect, thus enhancing the photothermal effect of killing the tumor. Finally, a brief outlook for the future development of GNRs modification and functionalization in PTT is proposed.

Numerical study of the interaction between a pulsating coated microbubble and a rigid wall. I. Translational motion

Coated microbubbles exhibit a complex surface rheology. When accelerated towards a wall subject to an acoustic disturbance they behave like a deformable solid and assume a prolate rather than oblate shape, as is the case with conventional bubbles, due to the dominance of friction over pressure drag. This results from the balance between viscoelastic stresses that develop on the protective shell and pressure and viscous stresses from the surrounding fluid which generate a progressively more prolate shape as the translational Reynolds number increases. Proper coating design can optimally control particle shape and motion in applications, notably in biomedical ones.

Effect of Process Conditions on Particle Size and Shape in Continuous Antisolvent Crystallisation of Lovastatin

Lovastatin crystals often exhibit an undesirable needle-like morphology. Several studies have shown how a needle-like morphology can be modified in antisolvent crystallisation with the use of additives, but there is much less experimental work demonstrating crystal shape modification without the use of additives. In this study, a series of unseeded continuous antisolvent crystallisation experiments were conducted with the process conditions of supersaturation, total flow rate, and ultrasound level being varied to determine their effects on crystal size and shape. This experimental work involved identifying acetone/water as the most suitable solvent/antisolvent system, assessing lovastatin nucleation behaviour by means of induction time measurements, and then designing and implementing the continuous antisolvent crystallisation experiments. It was found that in order to produce the smallest and least needle-like particles, the maximum total flow rate and supersaturation had to be combined with the application of ultrasound. These results should aid development of pharmaceutical manufacturing processes where the ability to control particle size and shape would allow for optimisation of crystal isolation and more efficient downstream processing.

Catalytic Stability Studies Employing Dedicated Model Catalysts.

Long-term stability of heterogeneous catalysts is an omnipresent and pressing concern in industrial processes. Catalysts with high activity and selectivity can be searched for by high-throughput screening methods based maybe on educated guesses provided by ab initio thermodynamics or scaling relations. However, high-throughput screening is not feasible and is hardly able to identify long-term stable catalyst so that a rational and knowledge-driven approach is called for to identify potentially stable and active catalysts. Unfortunately, our current microscopic understanding on stability issues is quite poor. We propose that this gap in knowledge can be at least partly closed by investigating dedicated model catalyst materials with well-defined morphology that allow for a tight link to theory and the application of standard characterization methods. This topic is highly interdisciplinary, combining sophisticated inorganic synthesis with catalysis research, surface chemistry, and powerful theoretical modeling. In this Account, we focus on the stability issues of Deacon catalysts (RuO2 and CeO2-based materials) for recovering Cl2 from HCl by aerobic oxidation and how to deepen our microscopic insight into the underlying processes. The main stability problems under harsh Deacon reaction conditions concomitant with a substantial loss in activity arise from deep chlorination of the catalyst, leaching of volatile chlorides and oxychlorides, and decrease in active surface area by particle sintering. In general, powder materials with undefined particle shape are not well suited for examining catalyst stability, because changes in the morphology are difficult to recognize, for instance, by electron microscopy. Rather, we focus here on model materials with well-defined starting morphologies, including electrospun nanofibers, shape-controlled nanoparticles, and well-defined ultrathin crystalline layers. CeO2 is able to stabilize shape-controlled particles, exposing a single facet orientation so that comparing activity and stability studies can reveal structure sensitive properties. We develop a quasi-steady-state kinetic approach that allows us to model the catalyst chlorination as a function of temperature and gas feed composition. For the case of pure CeO2 nanocubes, this simple approach predicts chlorination to be efficiently suppressed by addition of little amounts of water in the reaction feed or by keeping the catalyst at higher temperature. Both process parameters have great impact on the actual reactor design. Thermal stabilization of CeO2 by intermixing Zr has been known in automotive exhaust catalysis for decades, but this does not necessarily imply also chemical stabilization of CeO2 against bulk-chlorination since Zr can readily form volatile ZrCl4 and may quickly lose its stabilizing effect. Nevertheless, with model experiments the stabilizing effect of Zr in the Deacon process over mixed CexZr1-xO2 nanorods is clearly evidenced. Even higher stability can be accomplished with ultrathin CeO2 coatings on preformed ZrO2 particles, demonstrating the great promise of atomic layer deposition (ALD) in catalysis synthesis.

Particle Shape Control of Zn-Al Composite Oxides by Using Composite Hydroxides as a Precursor

Particle Shape Control of Zn-Al Composite Oxides by Using Composite Hydroxides as a Precursor

Selective shape-change response by anisotropic endoskeletal droplets

Control of particle shape is of increased interest, as it can broaden the versatility of dispersed material applications. The design of targeted and selective response, such as shape-change, in synthetic materials offers an opportunity to mimic and understand biophysical motion, but also enhance commercial active material delivery. Although solids can experience a wide range of shape-change behavior, soft materials like viscoelastic droplets are also quite versatile, exhibiting shape-change and localized wrapping when triggered by external temperature or stress fields. Here we show, with elastocapillary concepts, that viscoelastic droplets can self-trigger shape-change and wrapping behavior in response to physical contact with targets below a threshold curvature. The model is in good agreement with experimental data on interactions between rod-shaped endoskeletal droplets and cylindrical targets of varying curvature. The concept of a pre-programmed physical sensing and response by simple, soft material shapes is explored and used to suggest additional applications and more complex applied modeling, shape designs, and responses.

Surface Structure Characterization of Shape and Size Controlled Pd Nanoparticles by Cu UPD: A Quantitative Approach.

The search for new surface sensitive probes that characterize the surface structure of shape and size-controlled nanoparticles is an interesting topic to properly understand the correlations between electrocatalytic properties and surface structure at the nanoscale. Herein, we report the use of Cu UPD to characterize, not only qualitatively but also quantitatively, the surface structure of different Pd nanoparticles with controlled particle shape and size. Thus, Pd nanoparticles with cubic, octahedral and rhombic dodecahedral shapes, that is, with preferential {100}, {111}, and {110} surface structures, respectively, were prepared. In addition, cubic Pd nanoparticles with different particles sizes and spherical (2–3 nm) Pd nanoparticles were also synthesized. Based on the Cu UPD results on Pd single crystals, a new approach is proposed to qualitatively and quantitatively determine the percentages of {100}, {111}, and {110} surface domains present at the surface of the different shape and size controlled Pd nanoparticles. The results reported clearly show the benefits of this Cu UPD to get detailed information of the surface structure of the nanoparticles according to their particle shape and size.

Characterization of additive manufactured particles for DEM validation studies

Discrete element method (DEM) simulations are often validated using physical laboratory tests on analogue soils to confirm the macro-scale response. These analogue soils have typically consisted of steel ball bearings or glass beads, thus limiting the shapes to spherical particles. Additive Manufacturing (AM) technologies can be used to create 3D objects of any shape layer-by-layer. Using these AM particles as analogue soils allows for DEM validations to be performed using a wide range of shapes, more realistically replicating natural sands and gravels. In order to use these AM particles, however, characterization of the AM material is essential to ensure its suitability for laboratory testing and to determine the intrinsic material properties input into the DEM models. This paper describes a study in which material properties and surface characteristics of two different additively manufactured materials are determined. A gypsum-epoxy composite material and a photopolymer material were tested to determine properties such as Young’s modulus, Poisson’s ratio, shape, surface roughness, and inter-particle friction angle. In comparison to the commonly used steel ball bearings and alkaline glass beads, the AM particles exhibited improved circularity. The hardness and Young’s modulus values were measured directly and then a fitting procedure was used to assess the Hertzian behavior of the spheres under uniaxial compression. While the inter-particle friction angle and the surface roughness were higher for the AM particles in comparison to the steel ball bearings and glass beads, the ability to control particle shape for the AM particles proves advantageous for manipulation of shape parameters for DEM validation.

Modeling method of concrete material at mesoscale with refined aggregate shapes based on image recognition

Numerical simulation of concrete materials has become widely accepted, and modeling the aggregate based on the actual material is critical. However, the particle shape control still needs to be improved. In this paper, a refined aggregate modeling method is proposed using statistical rules based on image recognition. The geometrical data of 4407 real particles are extracted from the specimen cross-sections, and the joint probability distributions of particle size and aspect ratio are investigated. The statistical rules are remarkable and stable. The recommended distribution functions for geometrical parameters are provided to guide the simulation. The aggregate model is refined to a three-level framework based on the particle size, aspect ratio, and surface texture, and a corresponding concrete modeling method is also proposed. To investigate the method effect, numerical experiments on 800 models are conducted. The results show that it is necessary to precisely control the particle aspect ratio for accurate simulation.

Shape-directed rotation of homogeneous micromotors via catalytic self-electrophoresis

The pursuit of chemically-powered colloidal machines requires individual components that perform different motions within a common environment. Such motions can be tailored by controlling the shape and/or composition of catalytic microparticles; however, the ability to design particle motions remains limited by incomplete understanding of the relevant propulsion mechanism(s). Here, we demonstrate that platinum microparticles move spontaneously in solutions of hydrogen peroxide and that their motions can be rationally designed by controlling particle shape. Nanofabricated particles with n-fold rotational symmetry rotate steadily with speed and direction specified by the type and extent of shape asymmetry. The observed relationships between particle shape and motion provide evidence for a self-electrophoretic propulsion mechanism, whereby anodic oxidation and cathodic reduction occur at different rates at different locations on the particle surface. We develop a mathematical model that explains how particle shape impacts the relevant electrocatalytic reactions and the resulting electrokinetic flows that drive particle motion.