Uniform Packing Research Articles

Studying of Surfactant Excess Separation from Non-aqueous Quantum Dots Solution on its Monolayer Formation Process

Controlled purification of non-aqueous solution of CdSe/CdS/ZnS quantum dots (QD) (dispersed in toluene or chloroform) from an excess of surfactant (oleic acid) was studied. The separation of unbound oleic acid from QD solution was carried out by using high-density polyethylene (HDPE) membrane. The secondary solution with a separated surfactant as well as initial QD solution was spread over the water surface to obtain a monolayer with its compression isotherms studied using Langmuir-Blodgett (LB) technique. This approach allowed us to determine the concentration of surfactant at a level of 10−5 mol/l or less for CdSe/CdS/ZnS QD. For better understanding of the influence of purification on the properties of QD, the monolayer of QD was transferred onto solid substrate and its morphology was studied. Atomic force microscopy showed that removal of oleic acid excess results in a more uniform and dense packing of quantum dots.

Study of Elastic-Strength Properties of Basalt-, Glass-Filled Plastics with Different Winding Schemes

Samples of models of OHL supports based on basaltic and glass roving in the form of tubes with five different winding schemes were fabricated: longitudinal-transverse, spiral-longitudinal, spiral-longitudinal-transverse, and spiral with angle 30 and 60° with respect to the axis of the mandrel. The elastic-strength properties were investigated in tests by transverse bending and it was shown that the largest values of the elastic modulus obtain with the longitudinal-transverse winding scheme and the smallest values with spiral winding at angle 60° with respect to the axis. The elastic modulus of the basalt-plastic tubes is someone smaller than that of glass-plastic tubes, which can be explained by the lower linear density and more uniform packing of the used glass roving.

Defect-mediated polarization switching in ferroelectric films for low-power-consuming and ultra-high-density memories

Ferroelectric poly(vinylidene fluoride) (PVDF) based polymers are attracting tremendous interest because of their potential applications in flexible non-volatile memories. Current research suggests that the existence of a large hysteresis loop results in high-voltage operation and low writing/erasing speed, which is originated from uniform chain packing and coherent ferroelectric sequences in the crystalline regions. Here, we demonstrate the novel approach to understand the defect-mediated switching mechanisms in ferroelectric polymers by PFM-probe based technology. The single-point and linear polarization reversal is well controlled by defect-mediated ferroelectric phases that determine activation energy, switching rate, and the thermal stability. By the regulation of VDF/TrFE ratio and varying processing conditions, the coherent ferroelectric phase with all-trans sequence in the P(VDF-TrFE) has been disrupted by defects. Specially, the crystallites formed at high temperature in the copolymer P(VDF-TrFE) 50:50 mol% exhibit less ordered ferroelectric crystalline sequences, thus attaining the excellent features of the low operation voltage of about 4 V with a switching time of 100 ms, ultra-high memory density of 43.9 Gbit∙in−2 (by a 7 V, 1 ms pulse) and a high usage temperature of 60 °C. Compared with P(VDF-TrFE) 68:32 mol%, normal ferroelectric, it saves approximate 50% ratio of energy cost, and realizes four times higher resolution. Understanding and controlling defect functionality in ferroelectric materials is as critical for realizing their reliable applications in ferroelectric memories.

Revisiting the confined comminution of granular materials with the consideration of the initial particle size distributions and repetitive loadings

The initial particle size distributions (PSDs) and cyclic loading effects for the confined comminution tests are studied by using discrete element method (DEM). Three typical PSDs, i.e. the uniform, bimodal and fractal, respectively, are used to explore the general correlations from microscopic quantities to macroscopic quantities during the loading-unloading-reloading procedure. For the initial bimodal packing, it cannot easily generate an ultimate fractal packing. And for the initial uniform and fractal packings, the ultimate fractal dimension of PSD would gradually increase during the reloading procedure. Moreover, the coordination distribution of particles (CNP) is insensitive with the initial PSDs and cyclic loadings. Furthermore, the fractal analysis of the network of force chains is also studied by the box method to evaluate the fractal features of force chains from the general, strong and weak perspectives. Additionally, a new descriptor for interpreting the relationship between the force chains and the composed particles (CFC) is proposed to evaluate the packing geometrical topologies and force chains. It can be used to evaluate the inter-particle structure feature of the granular assemblies. It is interesting to find that CFC is gradually increased with the increasing loading stress, and reaches a peak value in the unloading stage for the same stress state and decreases with the increasing number intensity of force chains.

Aqueous debinding of polyvinyl butyral based binder system for titanium metal injection moulding

Titanium is biocompatible, has high specific strength and high corrosion resistance compared to other materials. Producing near-net shape parts by metal injection moulding (MIM) minimizes the need for secondary operations required for other metal-working processes such as casting, forging, and investment casting. Removing binder (debinding) from the MIM moulded part without disturbing the powder particles is a crucial stage. Titanium-MIM parts were manufactured from hydride-dehydride (HDH) titanium alloy powder Ti-6Al-4V (d10, d50 and d90 of 12.8, 51.8 and 117.7μm respectively) and various polyethylene glycol-polyvinyl butyral (PEG-PVB) based binder systems. The effect of binder composition, powder loading (55 and 60vol%), debinding time and temperature on the debinding rate for removing PEG with water, and porosity and microstructure of moulded parts was investigated. Solvent debinding had dissolution-controlled and diffusion-controlled stages; increasing debinding temperature shortened the dissolution-controlled stage. The amount of PEG removed increased with initial PEG content, temperature and debinding time. Porosity of solvent debound Ti-MIM parts increased with debinding time and PEG content. Good quality parts were produced using larger particles than normally recommended for MIM. The best debinding characteristics and uniform particle packing were obtained by making parts with 60vol% Ti-6Al-4V and 80:15:5vol% PEG:PVB:SA binder then solvent debinding for 4h at 35°C or 3h at 45°C. These conditions are very cost-effective compared to conditions published (2001–2016) for other bio-compatible metals-based MIM systems.

Synthesis, fabrication of self-assembled film and ambipolar chemical sensing properties of triple-decker (phthalocyaninato) (porphyrinato) europium complex

A mixed (phthalocyaninato) (porphyrinato) europium triple-decker complex, named (TPyP)Eu[Formula: see text][Pc(OC[Formula: see text]H[Formula: see text]][Formula: see text][TPyP [Formula: see text] dianion of 5,10,15,20-tetra(4-tert-pyridyl) porphyrin, Pc(OC[Formula: see text]H[Formula: see text] 2,3,9,10,16,17,23,24-octabutoxyphthalocyaninate] is synthesized and characterized by MALDI-TOF, 1HNMR, UV-visible spectra and differential pulse voltammetry techniques. Introduction of electron-donating butoxy groups at the periphery of the phthalocyanine ligands and electron-withdrawing pyridyl substituents onto the meso-positions of the porphyrin ring not only increases the solubility of the triple decker but successfully tunes the HOMO and LUMO energy levels into a soluble ambipolar organic semiconductor. A simple quasi-Langmuir–Shäfer (QLS) method is used to fabricate self-assembled film of (TPyP)Eu[Formula: see text][Pc(OC[Formula: see text]H[Formula: see text]][Formula: see text]. Excellent sensitivity, reproducible [Formula: see text]-type and [Formula: see text]-type responses to electron-accepting gas NO[Formula: see text] and electron-donating gas NH[Formula: see text] are found for the films of (TPyP)Eu[Formula: see text][Pc(OC[Formula: see text]H[Formula: see text]][Formula: see text]complex at room temperature. The detection limit towards NO[Formula: see text] and NH[Formula: see text] is as low as 0.4 ppm and 1 ppm, respectively, with percentage current change of 4.2% and 1.6%, depending on the uniform molecular packing and intermolecular interactions among the triple decker molecules. The present results represent not only the excellent example of ambipolar triple-decker phthalocyanine-based sensors obtained by a solution-based method, but more importantly provide a new strategy for the molecular design to obtain soluble ambipolar organic semiconductors in sensing device fabrication.

Direct Writing and Aligning of Small-Molecule Organic Semiconductor Crystals via "Dragging Mode" Electrohydrodynamic Jet Printing for Flexible Organic Field-Effect Transistor Arrays.

Patterning and aligning of organic small-molecule semiconductor crystals over large areas is an important issue for their commercialization and practical device applications. This Letter reports "dragging mode" electrohydrodynamic jet printing that can simultaneously achieve direct writing and aligning of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) crystals. Dragging mode provides favorable conditions for crystal growth with efficient controls over supply voltages and nozzle-to-substrate distances. Optimal printing speed produces millimeter-long TIPS-PEN crystals with unidirectional alignment along the printing direction. These crystals are highly crystalline with a uniform packing structure that favors lateral charge transport. Organic field-effect transistors (OFETs) based on the optimally printed TIPS-PEN crystals exhibit high field-effect mobilities up to 1.65 cm2/(V·s). We also demonstrate the feasibility of controlling pattern shapes of the crystals as well as the fabrication of printed flexible OFET arrays.

Efficient Solid-State Electrochemiluminescence from High-Quality Perovskite Quantum Dot Films.

Halide perovskite materials have emerged as a new class of revolutionary photovoltaic and optoelectronic nanomaterials. However, the study on electrochemiluminescence (ECL) from halide perovskite nanomaterials is still in its infancy due to their instability, sensitivity, and difficulties in purification and film formation. Here, we propose a scraping coating method for the fabrication of high-quality halide perovskite quantum dot (QD) film on electrode, which shows dense and uniform packing with minimum grain size. When CsPbBr3 QDs are taken as model materials, highly efficient ECL can be obtained from such perovskite QD film with anhydrous ethyl acetate as both electrolyte and coreactant. The CsPbBr3 QD film displays intense and stable ECL with ultranarrow emission spectrum bandwidth (24 nm). The CsPbBr3 QD film shows an extremely high ECL efficiency which is up to 5 times relative to the standard Ru(bpy)32+/tri-n-propylamine system. This approach is universal and also applies to hybrid organic-inorganic halide perovskite QDs. This work not only extends the properties and applications of halide perovskite materials but also provides a new method for the in-depth study on the structure and properties of these kinds of materials.

Additive manufacturing and characterization of complex Al2O3 parts based on a novel stereolithography method

AbstractIn this work, we prepared Al2O3 ceramic green parts with complex geometry and architecture using an additive manufacturing process based on stereolithography. The rheological and thermal behavior of Al2O3 slurry was firstly examined and used to establish the conditions for molding and debinding. As opposed to previous researches that only focused on manufacture techniques, the sintering behavior and densification process were systematically investigated. In addition, special attentions were paid to the evolution of microstructure between green bodies and sintered parts. The results showed that debound parts were equipped with uniform particle packing and narrow pore size distribution. The dimensions of the Al2O3 parts changed anisotropically with the different processing steps. The densification process was greatly accelerated by the decrease in pore size and annihilating of interconnected pores in which significant grain growth was observed above 1450°C. The sintered part also had a homogeneous microstructure and no interface between adjacent layers. High densification (relative density of 99.1%) and much desirable Vickers hardness (17.9 GPa) of Al2O3 parts were achieved at the sintering temperature of 1650°C.

TiO2 Nanobelts Decorated with In2S3 Nanoparticles as Photocatalysts with Enhanced Full‐Solar‐Spectrum (UV–vis–NIR) Photocatalytic Activity toward the Degradation of Tetracycline

Herein, ultradispersed In2S3 nanoparticle (NP)/TiO2 nanobelt (NB) heterostructures with an intimate interfacial coupling effect are synthesized from the consideration of combining the visible/near‐infrared photoabsorption property of In2S3 with the excellent UV photocatalytic property of TiO2. In this process, the 1D TiO2 NBs not only perform as the support to form the heterostructure, but are also employed as a dispersant to confine the aggregation of In2S3 NPs. As expected, the obtained In2S3 NP/TiO2 NB heterostructure gives rise to a prominently strong optical absorption in the full solar region of 300–1800 nm, and thus displays a desired photocatalytic degradation of tetracycline in full utilization of all solar energy, compared with that of pristine In2S3 and TiO2. Besides, the In2S3 NP/TiO2 NB heterostructure photocatalysts have no selectivity and can effectively degrade other different kinds of organic pollutants, including cationic dyes (methyl blue and rhodamine B) and colorless chemical pollutants (phenol and salicylic acid). The exceptional photocatalytic enhancement is due to the synergistic interactions of heterojunction with the strong interfacial coupling effect, the In2S3 extended light absorption, efficient photogenerated e−/h+ pair separation, and fully exposed reactive sites induced by uniform packing of the ultrasmall In2S3.

Dielectric Characterization of Confined Water in Chiral Cellulose Nanocrystal Films.

A known deterrent to the large-scale development and use of cellulose nanocrystals (CNCs) in composite materials is their affinity for moisture, which has a profound effect on dispersion, wetting, interfacial adhesion, matrix crystallization, water uptake, and hydrothermal stability. To quantify and control the hydration and confinement of absorbed water in CNCs, we studied sulfated-CNCs neutralized with sodium cations and CNCs functionalized with less hydrophilic methyl(triphenyl)phosphonium cations. Films were cast from water suspensions at 20 °C under controlled humidity and drying rate, yielding CNC materials with distinguishably different dielectric properties and cholesteric structures. By controlling the evaporation rate, we obtained self-assembled chiral CNC films with extended uniformity, having helical modulation length (nominal pitch) tunable from 1300 to 600 nm. SEM imaging and UV-vis-NIR total reflectance spectra revealed tighter and more uniform CNC packing in films cast at slow evaporation rates or having lower surface energy when modified with phosphonium. The dielectric constant was measured by a noncontact microwave cavity perturbation method and fitted to a classical mixing model employing randomly oriented ellipsoidal water inclusions. The dielectric constant of absorbed water was found to be significantly smaller than that for free liquid indicating a limited mobility due to binding with the CNC "matrix". In the case of hydrophilic Na-modified CNCs, a decreasing pitch led to greater anisotropy in the shape of moisture inclusions (ellipsoidal to platelet-like) and greater confinement. In contrast, the structure of hydrophobic phosphonium-modified CNC films was found to have reduced pitch, yet the shape of confined water remained predominantly spherical. These results provide a useful perspective on the current state of understanding of CNC-water interactions as well as on CNC self-assembly mechanisms. More broadly, we believe that our results are beneficial for the realization of CNC-based functional materials and composites.

Numerical investigation of the random arrangement effect of coated fuel particles on the criticality of HTTR fuel compact using MCNP6

This study investigated the random arrangement effect of coated fuel particles (CFPs) on the criticality of the fuel compact of the high-temperature engineering test reactor (HTTR). A utility program coupled with MCNP6, namely the realized random packing (RRP) model, was developed to explicitly model the random arrangement of CFPs in a specified fuel compact of the HTTR. The criticality and neutronic calculations for a pin cell model were performed using the Monte Carlo MCNP6 code with ENDF/B-VII.1 neutron library data. The reliability of the RRP model was confirmed by the insignificant variance of the infinite multiplication factor (kinf) among 10 different random arrangements of the CFPs. Next, the criticality of the RRP model was compared with those of a non-truncated uniform packing (NUP) model and an on-the-fly random packing (ORP) model, which is a stochastic geometry capability in MCNP6. The results indicated that there was no substantial difference between the NUP and ORP models. However, the RRP model presented a lower kinf (by about 0.32–0.52%Δk/k) than the NUP model. In addition, the difference in kinf was increased as uranium enrichment decreased. Investigation of the 4-factor formula showed that the difference in kinf was predominantly a result of the resonance escape probability, with the RRP model showing the smallest value.

Filtration Properties of Nanofiber/Microfiber Mixed Filter and Prediction of its Performance

ABSTRACTThere is an increasing demand of air filters with a high collection performance, i.e., high collection efficiency and low pressure drop, for the application to indoor air cleaning. Air filters consisting of nanofibers have attracted great interests since they may have a low pressure drop because of slip flow effect and high collection efficiency due to interception. Although various nanofiber filters are available on the market, their collection performance is not as high as expected by the conventional filtration theory because non-uniform packing of fibers plays a significant role. In the present work, the collection performance of nanofiber (780 nm) and microfiber (11.2 µm) mixed filters with various mixing fractions was studied in order to maximize the quality factor of filter, qF, as a function of mixing fraction of nanofibers. The collection performance of mixed fiber filters was predicted by using theoretical equations reported by Bao et al. (1998) for bimodal distribution of fibers. As a result, it was found that the mixed fiber filters had a uniform fiber packing compared to laminated filters and that the collection efficiency was well predicted by introducing the inhomogeneity factor calculated for the filter consisting of two distinct fiber sizes. Furthermore, we found that the mixed fiber filter with the nanofiber mixing fraction of 5% in mass had the highest quality factor.

Hybrid 0D-2D Nanoheterostructures: In Situ Growth of Amorphous Silver Silicates Dots on g-C3N4 Nanosheets for Full-Spectrum Photocatalysis.

The smaller particle sizes, better dispersion, and more heterojunction interfaces can enhance the photocatalytic performance of photocatalysts. Herein, ultradispersed amorphous silver silicates/ultrathin g-C3N4 nanosheets heterojunction composites (a-AgSiO/CNNS) with intimate interfacial coupling effect were synthesized through the facile in situ precipitation of ultrafine a-AgSiO (∼5.2 nm) uniformly dispersed on the entire surface of hierarchical ultrathin CNNS. In this process, the ultrathin CNNS not only perform as the support to form heterostructures but also are employed as dispersant to confine the aggregation of a-AgSiO nanoparticles. Notably, the optimum photocatalytic activity of a-AgSiO/CNNS-500 composite is ∼36 and 13 times higher than that of CNNS toward the degradation of rhodamine B and tetracycline, respectively. The excellent photocatalytic activity can be attributed to the synergistic interactions of heterojunction with strong interfacial coupling effect, improved visible light absorbance, abundant heterojunction interfaces, and fully exposed reactive sites, which originate from the well-defined nanostructures such as uniform packing of the ultrasmall a-AgSiO, the intimate and maximum coupling interfaces between a-AgSiO and CNNS. We believe that such an easy and scalable synthetic strategy can be further extended to the fabrication of other ultrafine semiconductors coupled with g-C3N4 for increasing its photocatalytic performance.

Synthesis of Nanostructured/Macroscopic Low-Density Copper Foams Based on Metal-Coated Polymer Core-Shell Particles.

A robust, millimeter-sized low-density Cu foam with ∼90% (v/v) porosity, ∼30 nm thick walls, and ∼1 μm diameter spherical pores is prepared by the slip-casting of metal-coated polymer core-shell particles followed by a thermal removal of the polymer. In this paper, we report our key findings that enable the development of the low-density Cu foams. First, we need to synthesize polystyrene (PS) particles coated with a very thin Cu layer (in the range of tens of nanometers). A simple reduction in the amount of Cu deposited onto the PS was not sufficient to form such a low-density Cu foams due to issues related to foam collapse and densification upon the subsequent polymer removal step. Precise control over the morphology of the Cu coating on the particles is essential for the synthesis of a lower density of foams. Second, improving the dispersion of PS-Cu particles in a suspension used for the casting as well as careful optimization of a baking condition minimize the formation of irregular large voids, leading to Cu foams with a more uniform packing and a better connectivity of neighboring Cu hollow shells. Finally, we analyzed mechanical properties of the Cu foams with a depth-sensing indentation test. The uniform Cu foams show a significant improvement in mechanical properties (∼1.5× modulus and ∼3× hardness) compared to those of uncontrolled foam samples with a similar foam density but irregular large voids. Higher surface areas and a good electric conductivity of the Cu foams present a great potential to future applications.

Compressive behaviour of fibre reinforced plastic with random fibre packing and a region of fibre waviness

A critical limitation of fibre reinforced plastic is its large variability on mechanical performance, especially the longitudinal compressive strength. The influence of fibre random packing and waviness on the compressive strength of UD fibre reinforced plastic is studied in this paper. Three-dimensional geometrically non-linear finite element model is constructed to investigate the compressive behaviour, and an improved approach named Latin hypercube sampling based on random sequential expansion is proposed to generate random fibre distribution across the cross-section. Latin hypercube sampling based on random sequential expansion provides high computation efficiency and good distribution characteristics in comparison to previously proposed methods. Fibre waviness defect with different misalignment angles is also incorporated in the finite element model. It is shown that random fibre packing tends to result in a stochastic detriment of fibre reinforced plastic compressive strength in comparison with uniform fibre packing condition, and the stochastic variation of compressive strength tends to follow normal or lognormal distribution.

Br...Br and van der Waals interactions along a homologous series: crystal packing of 1,2-dibromo-4,5-dialkoxybenzenes.

The crystalline structures of four homologues of the 1,2-dibromo-4,5-dialkoxybenzene series [Br2C6H2(OCnH2n + 1)2 for n = 2, 12, 14 and 18] have been solved by means of single-crystal crystallography. Comparison along the series, including the previously reported n = 10 and n = 16 derivatives, shows a clear metric trend (b and c essentially fixed along the series and a growing linearly with n), in spite of some subtle differences in space groups and/or packing modes. A uniform packing pattern for the aliphatic chains has been found for the n = 12 to 18 homologues, which slightly differs from that of the n = 10 derivative. The crystalline structures of all the higher homologues (n = 10-18) seem to arise from van der Waals interchain interactions and, to a lesser extent, type II Br...Br interactions. The dominant role of interchain interactions provides direct structural support for the usual interpretation of melting point trends like that found along this series. Atoms in Molecules (AIM) analysis allows a comparison of the relative magnitude of the interchain and Br...Br interactions, an analysis validated by the measured melting enthalpies.

Numerical modelling for the effective thermal conductivity of lithium meta titanate pebble bed with different packing structures

The effective thermal conductivity (keff) of lithium meta-titanate (Li2TiO3) pebble beds is an important parameter for the design and analysis of IN LLCB TBM (Indian Lead Lithium Ceramic Breeder Test Blanket Module). The keff of Li2TiO3 pebble beds under stagnant helium gas have been determined numerically using different uniform packing structures and random close packing (RCP) structures. The uniform packing structures of Li2TiO3 pebble bed are modelled by using the simple cubic, body centered cubic and face centered cubic arrangement. The packing structure of the RCP bed of Li2TiO3 pebbles is generated with the discrete element method (DEM) code. keff of Li2TiO3 pebble beds with different packing fractions have been reported as function of temperature; keff of the RCP Li2TiO3 pebble bed is compared with reported experimental results from literature. The numerically determined keff of the Li2TiO3 pebble bed agrees reasonably well with the experimental data.

Approximate core allocations and integrality gap for the bin packing game

A cooperative (uniform) bin packing game is an N-person game, where the player set consists of k bins of capacity 1 each and n items of sizes a1,…,an. The value of a coalition of players is defined to be the maximum total size of items in the coalition that can be packed into the bins of the coalition. We aim at finding a multiplicative ϵ-core allocation with ϵ as small as possible, thus approximating the core as closely as possible. Our main result shows that the 1/4-core is nonempty for all instances of the uniform bin packing game.

Computational study of fluid flow and heat transfer in composite packed beds of spheres with low tube to particle diameter ratio

The effect of the tube wall on the fluid flow and heat transfer would be important in the packed bed with low tube to particle diameter ratio, which may lead to flow and temperature maldistributions inside, and the heat transfer performance may be lowered. In the present paper, the flow and heat transfer performances in both the composite and uniform packed beds of spheres with low tube to particle diameter were numerically investigated, where the composite packing means randomly packing with non-uniform spheres and the uniform packing means randomly packing with uniform spheres, including radially layered composite packing (RLM), axially layered composite packing (ALM), randomly composite packing (RCM) and randomly uniform packing (RPM). Both the composite and uniform packings were generated with discrete element method (DEM), and the influence of the wall effect on the flow and heat transfer in the packed beds were carefully studied and compared with each other. Firstly, it is found that, the wall effect on the velocity and temperature distributions in the randomly packed bed of uniform spheres (RPM) with low tube to particle diameter ratio were obvious. The average velocity of the near-tube-wall region is higher than that of the inner-tube region in the bed. When the tube wall is adiabatic, the average temperature of the near-tube-wall region is lower. With radially layered composite packing method (RLM), smaller pores would be formed close to the tube wall and big flow channels would be formed in the inner-tube region of the bed, which would be benefit to restrain the wall effect and improve heat transfer in the bed with low tube to particle diameter ratio. Furthermore, it is also found that, with composite packing method (RLM, ALM and RCM), both the pressure drop and heat flux are higher than those in the uniform packing (RPM). And with radially layered packing method (RLM), the flow resistance would be reduced, and both the heat flux and overall heat transfer efficiency would be further improved for the composite packing with low tube to particle diameter ratio.