Packing Behavior Research Articles

Packing of cylindrical particles: DEM simulations and experimental measurements

In order to achieve efficient particle packing, minimizing the space of occupation and maximizing the strength of packing, it is important to understand the best methods of fill and the effects of various particle properties, including particle shape. In this study, the packing behavior of cylindrical particles is studied via both Discrete Element Method (DEM) simulations and complementary experiments. The effects of coefficient of friction, coefficient of restitution, drop height, fill height, packing method, deposition intensity (number of particles deposited per second), container size, surface roughness, and Young's modulus are investigated. In addition, two methods of packing density analysis from DEM simulations - a center of particle method and a top grid analysis method - are introduced. It is found that the packing density increases with fill height, container diameter, coefficient of restitution and drop height and decreases with coefficient of friction, surface roughness and Young's modulus. Different packing methods are explored, and it is found that the most efficient packing scheme is to pouring particles over the whole cross-section with low deposition intensity and at a variable drop height. Finally, DEM simulation predictions for particle packing of cylinders show good agreement with experimental measurements.

Packing Efficiency Characterization of SiC Abrasive Machining Particles for Photovoltaic Silicon Wafer Slicing

Silicon Carbide (SiC) abrasive machining solid particulates is one of the key engineering materials in the continuous development of wafer technology. Analysis of its packing behaviour is important to ensure the highest quality in the ingot cutting process to produce silicon PV wafers. One of the parameters that is monitored is the amount of fine particles present during the cutting operation and the subsequent separation technologies to recycle the material to reduce cost and allow environmental sustainability. This study presents results showing that with increasing circularity, less fines remain in the slurry suspension which is expressed as the percentage of total volume of particles in the slurry mixture. Furthermore, the work has gathered that there is a strong relationship between the % fines removed and the average diameter of the particles. An analysis of the relationship between the actual % fines remaining as a function of particle diameter reveals that the % fines remaining decreases as the particle diameter increases and this behavior correlates well with a power law equation. This agrees with a model of the fishhook effect during particle separation in a mini-hydrocyclone expressed as an equation raised to the fourth power.

The PCPDTBT Family: Correlations between Chemical Structure, Polymorphism, and Device Performance

We highlight the influence of processing conditions on polymorphism and structure formation on the mesoscale for the family of PCPDTBT polymers with branched alkyl side chains. Direct correlations of morphology to the chemical structure and to transistor device performance are established. We found that up to four different packing motifs could be realized depending on the polymer derivative and the processing conditions: amorphous, π-stacked, cross-hatched and dimer-containing polymorphs. While C- and F-PCPDTBT display similar packing behavior organizing in π-stacked and dimer-like structures, Si-PCPDTBT gives rise to cross-hatched structures upon simple deposition from solution. The observed differences in chain packing for C-/F-PCPDTBT versus Si-PCPDTBT are attributed to differences in backbone conformations and aggregation behavior in solution. The effect of polymorphism on charge transport is probed using field-effect transistors, in which both π-stacked and cross-hatched polymer chain arrangements y...

Supramolecular layers and versatile packing modes: The solid state behavior of ortho, ortho-linked bisphenols

A series of ortho-ortho-linked bisphenols featuring electron-withdrawing groups (EWGs) attached to the phenolic rings is reported. Their respective molecular structures and packing behaviors have been studied by X-ray diffraction, comparatively discussed and put into relation with the unsubstituted mother compound. Except for the mother compound, the molecular structures of all bisphenols studied here exhibit distorted aromatic moieties. Hence, the substituents studied here prevent proximal positioning of phenolic units and the formation of strong OH⋯O hydrogen bonds. In the packing of the underivatized bisphenol we found a strand-like molecular arrangement featuring strong OH⋯O hydrogen bonds and extensive edge-to-face contacts (CH⋯π) between the bisphenol molecules. The introduction of EWGs to the aromatic moieties changes these intermolecular interactions into face-to-face contacts resulting either in bisphenol stacks or handshake-like motifs between two bisphenol molecules. In both cases, the CH⋯π interactions are more or less replaced by CH⋯O contacts as the prevalent non-covalent interaction. In the packing of two nitro bisphenols in their DMSO inclusion compounds an exciting layered arrangement is observed, which also matches with the pronounced foliated habitus of their crystals. Additionally, proton NMR was used to establish the binding coefficients between the respective bisphenols and DMSO in solution.

Surface-Induced Heterogeneity Analysis of an Alkanethiol Monolayer on Microcrystalline Copper Surface Using Sum Frequency Generation Imaging Microscopy

An octadecanethiol (ODT) self-assembled monolayer on microcrystalline copper is investigated by sum frequency generation (SFG) imaging microscopy and electron backscattering diffraction (EBSD). The strong SFG signal contrast across the domain boundary indicates the existence of grain structures on copper surface, which is further verified by EBSD measurements. The nonresonant contribution of SFG response shows anisotropy with respect to the in-plane rotation of the sample relative to the surface normal and varies in each crystal domain area. The resonant contribution of the monolayer, such as the amplitude ratio of CH3-sym/CH3-asym, is azimuthally nearly isotropic. Since the zzz tensor component of nonlinear susceptibility dominates, the resonant part of SFG spectra on the metal surface does not show any anisotropy. Further, a strong correlation between the local metal structures with the top monolayer packing behaviors is identified based on the statistical distribution analysis. Using the methyl group a...

Field Synergy Analysis and Optimization of the Thermal Behavior of Lithium Ion Battery Packs

In this study, a three dimensional (3D) modeling has been built for a lithium ion battery pack using the field synergy principle to obtain a better thermal distribution. In the model, the thermal behavior of the battery pack was studied by reducing the maximum temperature, improving the temperature uniformity and considering the difference between the maximum and maximum temperature of the battery pack. The method is further verified by simulation results based on different environmental temperatures and discharge rates. The thermal behavior model demonstrates that the design and cooling policy of the battery pack is crucial for optimizing the air-outlet patterns of electric vehicle power cabins.

Morphology orientation of comb-like polymers with rigid backbones under the influence of shear fields

The influence of shear fields on the packing behavior and morphology orientation are studied for two comb-like polymers viz. poly(1,4-phenylene-2,5-didecyloxy terephthalate) (PPDOT) and poly(2,5-didecyloxy-1,4-phenylenevinylene) (DOPPV) with different rigid backbones having C = 10 alkyl carbons per side chain. Crystallographic analysis based on X-ray diffractometry measurements shows that both PPDOT and DOPPV exhibit a long-range ordered layered structure with alternating main chains and alkyl nanodomains and can be characterized by an orthorhombic and monoclinic unit cell respectively. No measurable influence of processing on the unit cell of the individual polymers is observed comparing diffraction data on isotropic (powder) samples and extruded fibers. The main difference between the PPDOT and DOPPV is in the molecular orientation of the backbones in shear aligned fibers as observed from the 2D diffraction patterns. While, for PPDOT the polymer backbones align along the direction of extrusion (fiber axis), for DOPPV the backbones align perpendicular to the extrusion direction. A possible relation between differences in backbone orientation under influence of shear fields for DOPPV and PPDOT and differences in the packing state of the side chains, which are in a crystalline state for DOPPV but in a disordered state for PPDOT, is considered.

Systematic description of the effect of particle shape on the strength properties of granular media

In this paper, we explore numerically the effect of particle shape on the mechanical behavior of sheared granular packings. In the framework of the Contact Dynamic (CD) Method, we model angular shape as irregular polyhedral particles, non-convex shape as regular aggregates of four overlapping spheres, elongated shape as rounded cap rectangles and platy shape as square-plates. Binary granular mixture consisting of disks and elongated particles are also considered. For each above situations, the number of face of polyhedral particles , the overlap of spheres, the aspect ratio of elongated and platy particles, are systematically varied from spheres to very angular, non-convex, elongated and platy shapes. The level of homogeneity of binary mixture varies from homogenous packing to fully segregated packings. Our numerical results suggest that the effects of shape parameters are nonlinear and counterintuitive. We show that the shear strength increases as shape deviate from spherical shape. But, for angular shapes it first increases up to a maximum value and then saturates to a constant value as the particles become more angular. For mixture of two shapes, the strength increases with respect of the increase of the proportion of elongated particles, but surprisingly it is independent with the level of homogeneity of the mixture. A detailed analysis of the contact network topology, evidence that various contact types contribute differently to stress transmission at the micro-scale.

How cube-like must magnetic nanoparticles be to modify their self-assembly?

Systems whose magnetic response can be finely tuned using control parameters, such as temperature and external magnetic field strength, are extremely desirable, functional materials. Magnetic nanoparticles, in particular suspensions thereof, offer opportunities for this controllability to be realised. Cube-like particles are particularly mono-disperse examples that, together with their favourable packing behaviour, make them of significant interest for study. Using a combination of analytical calculations and molecular dynamics we have studied the self-assembly of permanently magnetised dipolar superballs. The superball shape parameter was varied in order to interpolate the region between the already well-studied sphere system and that of the recently investigated cube. Our findings show that as a superball particle becomes more cubic the chain to ring transition, observed in the ground state of spherical particles, occurs at an increasingly larger cluster size. This effect is mitigated, however, by the appearance of a competing configuration; asymmetric rings, a conformation that we show superballs can readily adopt.

Intermolecular contacts in the crystal structures of specifically varied halogen and protonic group substituted azines

A series of azines featuring differently halogen and protic group substituted pyridine, pyrimidine and pyridazine compounds have been synthesized and studied in terms of their crystal structures in order to develop a better understanding of the links between structural conditions and molecular packing behavior. Complemented by the structure results of related compounds known from the literature, intermolecular contact relationships connected to the present substance types were found, having potential use in future crystal engineering of similar compounds. This primarily involves the formation of N⋯I contacts aside from specific halogen⋯halogen and hydrogen bond type interactions.

Photoresponsive amphiphilic block macrocycles bearing azobenzene side chains

The cyclic architecture has an impact on the photoisomerization and packing behavior of micellar aggregates of amphiphilic block copolymers bearing pendant azobenzene and carboxyl groups as compared to their linear counterparts.

Effects of Matrix Densification Based on Particle Packing on Lightweight Al<sub>2</sub>O<sub>3</sub>-MgO Castables

The property of refractory matrix was dominated by both the maineral composition and particle packing behaviors. In this study, the theoretical packing density of refractory castables was calculated to design the particle size distribution (PSD) of its matrix. Four lightweight Al2O3-MgO castables with different matrix PSD (represented by q-value) were prepared and examined. Results show that a suitable q-value was needed to ensure acceptable properties including sintering characteristics, strength and slag resistance, which deteriorated distinctly at high q ( > 0.31). For the sample with q = 0.28, the matrix showed dense and uniform mirostructure, and the properties of castable reached a favorable compromise among sintering characteristics (apparent porosity = 14.8%, bulk density = 3.02g∙cm-3, permanent linear change < 0.6%), strength (cold modulus of rapture = 12.4MPa, cold crashing strength=155.5MPa), and resistance against both slag corrosion (Ic = 22.4%) and penetration (Ip = 11.5%). The sample with q = 0.25 showed the highest strength and resistance against slag corrosion, but its slag penetration resistance was lower due to the existence of cracks between aggregates and matrix.

Real-Time Packing Behavior of Core-Shell Silica@Poly(N-isopropylacrylamide) Microspheres as Photonic Crystals for Visualizing in Thermal Sensing.

We grafted thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) brushes from monodisperse SiO2 microspheres through surface-initiated atom transfer radical polymerization (SI ATRP) to generate core-shell structured SiO2@PNIPAM microspheres (SPMs). Regular-sized SPMs dispersed in aqueous solution and packed as photonic crystals (PCs) in dry state. Because of the microscale of the SPMs, the packing behavior of the PCs in water can be observed by optical microscopy. By increasing the temperature above the lower critical solution temperature (LCST) of PNIPAM, the reversible swelling and shrinking of the PNIPAM shell resulted in dispersion and precipitation (three-dimensional aggregation) of the SPM in aqueous solution. The SPMs were microdispersed in a water layer to accommodate the aggregation along two dimensions. In the microdispersion, the SPMs are packed as PCs with microscale spacing between SPMs below the LCST. When the temperature is increased above the LCST, the microdispersed PCs exhibited a close-packed arrangement along two dimensions with decreased spacing between SPMs. The change in spacing with increasing temperature above the LCST resulted in a color change from red to blue, which could be observed by the naked eye at an incident angle. Thus, the SPM array could be applied as a visual temperature sensor.

Ionic self-assembled derivatives of perylene diimide: Synthesis, aggregated structure and molecular packing behavior

A novel perylene diimide material was prepared by ionic self-assembly (ISA) method. The phase behavior and aggregated structures of the complex were then elucidated via a combination of different experimental techniques such as differential scanning calorimetry, one- and two-dimensional X-ray diffraction, UV/Vis absorption spectra, and Fourier transform infrared spectroscopy. The experimental results reveal that the ISA complex possesses multiple thermally-induced phase structures which are sensitive to peripheral chain motions. At room temperature, it can self-assemble into a monoclinic crystalline structure with dimensions of a = 4.10 nm, b = 3.70 nm, c = 0.34 nm, α = β = 90°, γ = 98.94°. During heating, the complex enters a hexagonal columnar liquid crystalline phase before developing into another monoclinic liquid crystalline phase. Notably, the complex can be well aligned by simple shearing, which shows anisotropic properties in UV/Vis absorption spectra. This property, in combination with the supramolecular structure, makes the complex a promising material for use in polarized optoelectronic devices.

Synthesis, Aggregation-Induced Emission, and Liquid Crystalline Structure of Tetraphenylethylene–Surfactant Complex via Ionic Self-Assembly

A novel tetraphenylethylene material with liquid crystalline (LC) helical structure and aggregation-induced emission (AIE) property was prepared by ionic self-assembly (ISA). The AIE activity, phase behavior, self-assembly structure, and molecular packing behavior of the complex were then elucidated via a combination of different experimental techniques such as UV–vis absorption spectra, photoluminescence spectra, differential scanning calorimetry, polarized optical microscopy, one- and two-dimensional X-ray diffraction, and Fourier transform infrared spectroscopy. The experimental results reveal that the ISA complex possesses high-efficiency luminescent property with quantum yield as high as 46% in solid state. Meanwhile, the complex could self-assemble into different interesting structures which are sensitive to peripheral chain motions. During heating, the complex takes a low-ordered helical supramolecular structure at ambient temperature and then forms another LC phase with high-ordered helical molecu...

Synthesis and characterization of O-acylated-ω-hydroxy fatty acids as skin-protecting barrier lipids

A series of O-acylated-ω-hydroxy fatty acids (Acyl acids) of up to 34 carbons were synthesized and characterized through DSC, FTIR and Langmuir isotherm measurements to identify potential replacements to petrolatum, a highly used occlusive technology that if unrefined, it can potentially be classified as carcinogenic. Fourier transform infrared spectroscopy studies demonstrated that long acyl acids engender orthorhombic packing; packing behavior that is predominant in the lipid matrix of healthy stratum corneum, the outmost layer of the skin. In addition, Differential Scanning Calorimetry (DSC) and Langmuir isotherm studies suggested that the length of the hydrocarbon chain and the position of the ester bond influence the molecular organization of the acyl acids. For instance, 16-(tetradecanoyloxy)hexadecanoic acid (30 carbons) displayed a higher melting point (mp=68°C) than 10-(stearoyloxy)decanoic acid (28 carbons; mp=63°C) and 10-(tetradecanoyloxy)decanoic acid (24 carbons; mp=55°C) according to DSC. Moreover, Langmuir isotherm studies showed that mixtures of acyl acid with distearoylphosphatidylcholine improved packing behavior. Finally, Water Vapor Transmission Rate (WVTR) measurements showed that the compounds in fact decrease WVTR compared to untreated control (P<0.001) which demonstrates the potential of these ingredients as occlusive technologies to combat skin barrier diseases.

Towards stochastic discrete element modelling of spherical particles with surface roughness: A normal interaction law

The current work is the first attempt towards establishing a stochastic discrete element modelling framework by developing a normal contact interaction law based on the classic Greenwood and Williamson (GW) model for spheres with rough surfaces. Two non-dimensional forms of the model that have a substantial impact on the computational efficiency are discussed and the theoretical relationship between the GW model and the Hertzian model for smooth spheres is formally established. Due to the inter-dependence between the contact pressure and deformation distributions in the model, a Newton–Raphson based iterative solution procedure is proposed to effectively and accurately obtain the contact force in terms of the overlap and two surface roughness parameters. The related key components of the procedure are addressed in detail. The numerical results obtained are first validated and then curve-fitted to derive an empirical formula as a new normal interaction law for spheres with surface roughness. The explicit nature of the new interaction law makes it readily be incorporated into the current discrete element modelling framework. A simple example is presented to illustrate the effect of surface roughness on the packing behaviour of a particle assembly.

Capturing the non‐spherical shape of granular media and its trickle flow characteristics using fully‐Lagrangian method

We performed a numerical analysis for simulating granular media structures containing non‐spherical elements and the liquid trickle flow characteristics of such structures. Fully‐Lagrangian numerical simulation methods can track all motion information for solid or liquid elements at each point in time. We introduced suitable compressibility to moving particle semi‐implicit (MPS) and performed individual packing behavior calculations for non‐spherical elements, based on discrete element method (DEM) with expanded functions. Rigid bodies‐DEM is a method using a DEM contact force model that is expanded to handle the motion of freely shaped solids. It expresses complex shapes to enable low calculation costs and intuitive mounting. We used the boundary for the granular media configured with non‐spherical elements to implement a trickle flow simulation based on weakly compressible‐MPS. Even for elements of equal volume, different shapes changed the liquid passage velocity and hold‐up amount. The mean downflow velocity of the liquid phase was not always dependent on the void fraction. For the plane of projection, we obtained a good correlation with the mean downflow velocity in each packed structure, and successfully performed arrangements according to the new liquid‐passage shape coefficient. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2257–2271, 2017

Compressive mechanical properties of partially sintered porous alumina of bimodal particle size system

This paper examined theoretically and experimentally packing behavior, sintering behavior and compressive mechanical properties of sintered bodies of the bimodal particle size system of 80vol% large particles (351nm diameter)–20vol% small particles (156nm diameter). The increased packing density as compared with the mono size system was explained by the packing of small particles in 6-coordinated pore spaces among large particles owing to the similar size relation between 6-coordinated spherical pore and small particle. The sintering between adjacent large particles dominated the whole shrinkage of the powder compact of the bimodal particle size system. However, the bimodal particle size system has a high grain growth rate because of the different curvatures of adjacent small and large particles. The derived theoretical equations for the compressive strengths of both mono size system and bimodal particle size system suggest that the increase in the grain boundary area and relative density by sintering dominate the compressive strength of a sintered porous alumina. The experimental compressive strengths were well explained by the proposed theoretical models. The strength of the bimodal particle size system was high at low sintering temperatures but was low at high sintering temperatures as compared with that of mono size system of large particles. This was explained by mainly the change of grain boundary area with grain growth. The stress–strain relationship of the bimodal particle size system showed an unique pseudo-ductile property. This was well explained by the curved inside stress distribution along the sample height. The inside stress decreases toward the bottom layer. The fracture of one layer of sintered grains over the top surface proceeds continuously with compressive time along the sample height when an applied stress reaches the critical fracture strength.

Ultralong Fatty Acyl Derivatives As Occlusive Structure Lipids for Cosmetic Applications: Synthesis and Characterization

Finding sustainable and commercially viable sources of occlusive materials, as an alternative to petroleum, is of great interest. Inspired by the fundamental role of long chain fatty acids in maintaining skin barrier, ultralong fatty acyl derivatives with diverse structures (varied acyl chain length and different polar head; i.e. glycerol, ethylene glycol, and diethylene glycol) were synthesized. These molecules can be feasibly obtained via enzymatic esterification of fatty acids or fractionated from commercial glycerides mixture via short path distillation. The molecular packing behaviors of compounds were characterized via differential scanning calorimetry, Fourier transform infrared, and Langmuir isotherm measurements. The structure–property relationship study reveals that a glycerol molecule monoacylated with an ultralong fatty acyl is the derivative which entails the most occlusive properties of the series of ultralong chain fatty acid derivatives. Fast Fourier transform filtering (FFTF) analysis of ...