Packing Of Layers Research Articles

Multi-Level Structural Design Strategy toward Low-Sensitivity Energetic Materials: From Planar Molecule to Layered Packing Crystal

Layered packing structures have been of great interest in the field of energetic materials (EMs) due to their excellent balances between energy and safety. Nevertheless, the present advanced layered EMs and rational design approaches are still lacking. In this work, we proposed a multi-level structural design strategy for layered EMs, from molecular to crystal level. Inspired by the experimentally known energetic crystals with the specific NH2···NO2 intermolecular motifs, we established a set of guidelines for designing and screening potential target molecules based on the H2N–C–C–NO2 moiety via a systematic analysis of structure/composition–performance relationships. Subsequently, the possible crystal packing structures were searched accurately by the evolutionary algorithm USPEX coupled with a recently developed energetic molecule-specific polarizable force field. The theoretical results show that B1 (4,4′-diamino-3,3′-dinitro-[5,5′-biisoxazole] 2,2′-dioxide) and C2 [(E)-3,3′-(diazene-1,2-diyl) bis (4-amino-5-nitroisoxazole 2-oxide)] are promising candidates of advanced layered EMs with good mechanical sensitivities (better than TNT) and detonation performances (superior to FOX-7). Hopefully, our multi-level design procedure can accelerate the discovery of novel layered EMs with advanced properties.

Carbon Erosion of a Bulk Nickel\u2013Copper Alloy as an Effective Tool to Synthesize Carbon Nanofibers from Hydrocarbons

Carbon erosion of bulk metals and alloys in a carbon-containing atmosphere can be used as an effective tool for the targeted synthesis of carbon nanomaterials. In this study, a set of bulk Ni0.89Cu0.11 (11 at % Cu) alloys has been synthesized by the mechanochemical alloying of metal powders in an Activator 2S planetary mill. The synthesized samples have been studied as precursors of catalyst for the synthesis of carbon nanofibers (CNFs) from ethylene at 550°C. The effect of the activation time on the particle morphology and phase composition of the alloys, the kinetics of growth, and the carbon product yield in C2H4 decomposition has been studied. For the most active samples, the CNF yield has exceeded 100 g/gcat within 30 min of reaction. The early stage of carbon erosion of a bulk Ni0.89Cu0.11 alloy has been studied by electron microscopy methods. It has been found that the nucleation of carbon fiber growth active sites occurs during a short-term contact of the sample with the reaction mixture (less than 1 min); the complete disintegration of the alloy is observed in a few minutes. The carbon product is represented by nanofibers having a submicrometer diameter and characterized by a dense “stacked” and coaxial-conical packing of graphene layers. The material has a developed specific surface area (140–170 m2/g) and a low bulk density (less than 30 g/L).

Nanofiber Architecture Engineering Implemented by Electrophoretic-Induced Self-Assembly Deposition Technology for Flash-Type Memristors.

Electrophoretic deposition (EPD) has been recognized as a promising large-scale film preparation technology for industrial application. Inspired by the conventional EPD method and the crystal diffusion growth strategy, we propose a modified electrophoretic-induced self-assembly deposition (EPAD) technique to control the morphologies of organic functional materials. Here, an ionic-type dye with a conjugated skeleton and strong noncovalent interactions, celestine blue (CB), is chosen as a module molecule for EPAD investigation. As expected, CB molecules can assemble into different nanostructures, dominated by applied voltage, concentration effect, and duration. Compared to a nanopillar layered packing structure formed by the traditional spin-coating method, the EPAD approach can produce a nanofiber structure under a fixed condition of 10 V/10 min. Intriguingly, a memristor device based on a pillar-like nanostructure exhibits WORM-type behavior, while a device based on nanofibers presents Flash memory performance. The assemble process and the memory mechanism are uncovered by molecular dynamics simulations and density-functional theory (DFT) calculations. This work endows the typical EPD technique with a fresh application scenario, where an in-depth study on the growth mechanism of nanofibers and the positive effect of unique morphologies on memristor performance are offered.

The features of the crystal structure of the layered series hydrates of uridine-5'-monophosphate salts (UMPNa x ·yH2O).

Almost all reported salts of nucleotides crystallized from solutions are in the form of hydrate. Layered hydrates often occur in crystals with more than five water molecules per host molecule. In the present report, five single-crystal structures of uridine-5′-monophosphate (UMP) series hydrates of acid or salts (UMPNax·yH2O, x = 0–2) were determined and analysed. It was found that all crystal hydrates were orthorhombic with a C2221 space group but with mere variation in the plane angle of adjacent bases and the distance between phosphate arms. The packing arrangements of UMPNax·yH2O hydrates present typical layered sandwich structures and show that the UMP molecular layers alternate with water molecular layers parallel to the ac plane, linked by hydrogen bonds or coupled with coordinate bonds besides ionic electrostatic interaction. Metal ions were located in water molecular layers as a form of hydration. In addition, we tried to deduce and give insights into the formation of UMPNax·yH2O hydrates. The effect of water molecules and metal ions on the crystal structure and stability was investigated. It was found that the coexistence of relatively rigid architectures constructed by host molecules and flexible interlayer regions was a key factor to the formation of these hydrates. Excessive loss of lattice water would give rise to the irreversible collapse of the host structure and loss of ability to recover to the initial state under humidity. Approximately seven crystal-water molecules were the balance point of sodium salt hydrates at room temperature under 43–76% RH conditions. The number of sodium ions in the crystal lattice is positively correlated with their thermal stability.

Highly stable and isomorphic donor–acceptor stacking in a family of n-type organic semiconductors of BTBT–TCNQ derivatives

Unsymmetrically substituted donor–acceptor type compounds exhibit an isomorphous layered packing structure, which is discussed in terms of DFT-based quantum chemical calculations.

Oil/Water Microreactor with a Core–Shell Wetting State on a SOB/OL-SHB/HL Multilevel Patterned Surface

Droplet-based microfluidics, which manipulate mini-discrete droplets on surfaces to accomplish various chromogenic/fluorescence reaction-based detections, are promising for microminiaturization of analysis systems. However, rapid droplet evaporation in unsaturated surroundings is a complex problem. In this study, we proposed an ingenious concept of generating an oil/water microreactor on a superoleophobic/oleophilic-superhydrophobic/hydrophilic (SOB/OL-SHB/HL) multilevel patterned surface. A dual droplet with a nonvolatile liquid packing layer and a volatile droplet core was formed on the surface, achieving overt evaporation attenuation of the droplet core. The wettabilities of the SOB/OL-SHB/HL surface were first investigated. In addition, due to their outstanding configurability, oil/water microreactors with different pattern shapes, diverse compositions, and scale-up array configurations were obtained in a simple way. Due to the overt evaporation attenuation, the storage times of the reactants and products were markedly prolonged. Finally, as proofs of concept, oil/water microreactors were successfully applied to detect the target ion and to construct a droplet-based pH detector. The proposed oil/water microreactor on the SOB/OL-SHB/HL surface with distinct precision, flexibility, and high throughput is important to the development of high-performance microfluidic chips used in diagnosis, environment monitoring, chemical analysis, and particle synthesis.

Filtering efficiency model that includes the statistical randomness of non-woven fiber layers in facemasks.

Facemasks have become important tools to fight virus spread during the recent COVID-19 pandemic, but their effectiveness is still under debate. We present a computational model to predict the filtering efficiency of an N95-facemask, consisting of three non-woven fiber layers with different particle capturing mechanisms. Parameters such as fiber layer thickness, diameter distribution, and packing density are used to construct two-dimensional cross-sectional geometries. An essential and novel element is that the polydisperse fibers are positioned randomly within a simulation domain, and that the simulation is repeated with different random configurations. This strategy is thought to give a more realistic view of practical facemasks compared to existing analytical models that mostly assume homogeneous fiber beds of monodisperse fibers. The incompressible Navier-Stokes and continuity equations are used to solve the velocity field for various droplet-laden air inflow velocities. Droplet diameters are ranging from 10nm to 1.0µm, which covers the size range from the SARS-CoV-2 virus to the large virus-laden airborne droplets. Air inflow velocities varying between 0.1m·s-1 to 10m·s-1 are considered, which are typically encountered during expiratory events like breathing, talking, and coughing. The presented model elucidates the different capturing efficiencies (i.e., mechanical and electrostatic filtering) of droplets as a function of their diameter and air inflow velocity. Simulation results are compared to analytical models and particularly compare well with experimental results from literature. Our numerical approach will be helpful in finding new directions for anti-viral facemask optimization.

Effects of ZnO/water nanofluid on the thermal performance of wet cooling towers

This article deals with an experimental investigation on the thermal performance of a mechanical draft wet cooling tower when using Zinc Oxide (ZnO) nanoparticles and three packing types with different densities. Stable nanofluids with different weight concentrations of ZnO/water were prepared through a two-step procedure using distilled water. First of all, the influence of three packing types including 7,9 and 18 layers are investigated on the thermal performance of the wet cooling tower using ZnO/water nanofluid with a weight concentration of 0.1%. Secondly, five ZnO/water nanofluids with weight concentrations of 0.02, 0.04, 0.06, 0.08, and 0.1% are utilized to examine the effects of nanoparticle concentration on the performance. The results indicate that water temperature difference, cooling efficiency, and tower characteristic could enhance by increasing layers of packing and weight concentrations of nanofluid. Moreover, the nanofluid effects are more notable when the denser packing is used.

Computational fluid dynamics simulation of multi‐phase flow characteristics in an industrial‐scale randomly packed tower

AbstractA three‐dimensional (3‐D) two‐phase Eulerian–Eulerian‐based computational fluid dynamics (CFD) simulation method coupled with a porous media model was developed in this study to simulate the air–water two‐phase flow in an industrial‐scale randomly packed air cooling tower (RPACT). The authors discussed the effects of gas kinetic energy factor, liquid load, packing materials, and packed bed height on the hydrodynamic performances of the gas–liquid counter‐current flow in the proposed RPACT. The simulation results show that the pressure drop increases with the gas or liquid load increases. Liquid load influences the pressure drop, liquid holdup, and wall film flow rate sensitively. A smaller liquid load, a middle range of gas kinetic energy factor, a relatively greater porous resistance coefficient of packing material, and a higher packed bed height can achieve a more uniform liquid flow distribution in an RPACT. The optimum operating conditions for the present RPACT are determined as gas kinetic energy factor is from 1.76 to 2.11 [(m/s) (kg/m3)0.5], liquid load is in the range of 32.40–67.73 m3/h, and the plastic Cascade ring (filled in the second packing layer) with a height of 10 m. The presented CFD models are useful for engineers to design and optimize the structure and operation conditions of industrial‐scale RPACTs.

A two-dimensional calcium (II) coordination polymer constructed from 2,2'-[terephthaloylbis(azanediyl)]diacetate: synthesis, structure and properties.

A new two-dimensional (2D) coordination polymer, namely, poly[[diaqua-[μ4-2,2'-[terephthaloylbis(azanediyl)]diacetato]calcium(II)] monohydrate], {[Ca(C12H10N2O6)(H2O)2]·H2O}n, (I), has been synthesized by the reaction of CaCl2 with 2,2'-[terephthaloylbis(azanediyl)]diacetic acid (H2L). The title compound was structurally characterized by single-crystal X-ray diffraction analysis, elemental analysis and IR spectroscopy. In the crystal structure of (I), each CaII cation binds to six carboxylate groups from four symmetry-related L2- dianions. The hexadentate L2- ligand links four symmetry-related calcium cations into a 2D layer-like structure, which can be simplified as a uninodal SP 2-periodic (3,6)III net with the point symbol (43·63). In the lattice, all layers pack in parallel arrays through weak interlayer hydrogen bonding and π-π interactions. The thermal stability and photoluminescence properties of (I) have been investigated. Thermogravimetric analysis reveals the different thermal stabilities of the two coordinated water molecules due to their different hydrogen-bonding interactions. The title coordination polymer exhibits an excitation-wavelength-dependent fluorescence in the solid state.

Spatial mapping of powder layer density for metal additive manufacturing via transmission X-ray imaging

Uniform powder spreading is a requisite for creating consistent, high-quality components via powder bed additive manufacturing (AM), wherein layer density and uniformity are complex functions of powder characteristics, spreading kinematics, and mechanical boundary conditions. High spatial variation in particle packing density, driven by the stochastic nature of the spreading process, impedes optical interrogation of these layer attributes. Thus, we present transmission X-ray imaging as a method for directly mapping the effective depth of powder layers at process-relevant scale and resolution. Specifically, we study layers of nominal 50-250 micrometer thickness, created by spreading a selection of commercially obtained Ti-6Al-4V, 316 SS, and Al-10Si-Mg powders into precision-depth templates. We find that powder layer packing fraction may be predicted from a combination of the relative thickness of the layer as compared to mean particle size, and flowability assessed by macroscale powder angle of repose. Power spectral density analysis is introduced as a tool for quantification of defect severity as a function of morphology, and enables separate consideration of layer uniformity and sparsity. Finally, spreading is studied using multi-layer templates, providing insight into how particles interact with both previously deposited material and abrupt changes in boundary condition. Experimental results are additionally compared to a purpose-built discrete element method (DEM) powder spreading simulation framework, clarifying the competing role of adhesive and gravitational forces in layer uniformity and density, as well as particle motion within the powder bed during spreading.

Synthesis, characterization and optoelectronic properties of 2D hybrid RPbX4 semiconductors based on an isomer mixture of hexanediamine-based dications

Abstract Three new hybrid two-dimensional (2D) organic–inorganic semiconductors are presented, which contain lead halides and a mixture of hexanediamine-based isomers in the stoichiometry [2,2,4(2,4,4)-trimethyl-1,6-hexanediamine]PbX4 (X = I, Br, Cl). These hexanediamine derivatives, with attached methyl groups at the carbon backbone of both isomers, determine the packing of the organic layers between the inorganic 2D sheets, while the optical absorption and photoluminescence spectra reveal excitonic peaks at T = 77 K and room temperature. The as-synthesized semiconductors were stored for three years in the dark and under low humidity and were examined again and the results were compared to those of the fresh materials. The chloride analogue, after the three year storage, displays white-like luminescence. The use of non-equivalent isomer and racemic mixtures in the organic component to form hybrid organic–inorganic semiconductors is an efficient method to alter the properties of 2D perovskites by tuning the isomers’ chemical functionalities. Finally, a comparison of the observed excitonic absorption and photoluminescence signals to that of analogous 2D compounds is discussed.

PH effects on the molecular structure and charging state of β-Escin biosurfactants at the air-water interface

Saponins like β-escin exhibit an unusually high surface activity paired with a remarkable surface rheology which makes them as biosurfactants highly interesting for applications in soft matter colloids and at interfaces. We have applied vibrational sum-frequency generation (SFG) to study β-escin adsorption layers at the air-water interface as a function of electrolyte pH and compare the results from SFG spectroscopy to complementary experiments that have addressed the surface tension and the surface dilational rheology. SFG spectra of β-escin modified air-water interfaces demonstrate that the SFG intensity of OH stretching vibrations from interfacial water molecules is a function of pH and dramatically increases when the pH is increased from acidic to basic conditions and reaches a plateau at a solution pH of > 6. These changes are attributable to the interfacial charging state and to the deprotonation of the carboxylic acid group of β-escin. Thus, the change in OH intensity provides qualitative information on the degree of protonation of this group at the air-water interface. At pH < 4 the air-water interface is dominated by the charge neutral form of β-escin, while at pH > 6 its carboxylic acid group is fully deprotonated and, consequently, the interface is highly charged. These observations are corroborated by the change in equilibrium surface tension which is qualitatively similar to the change in OH intensity as seen in the SFG spectra. Further, once the surface layer is charge neutral, the surface elasticity drastically increases. This can be attributed to a change in prevailing intermolecular interactions that change from dominating repulsive electrostatic interactions at high pH, to dominating attractive interactions, such as hydrophobic and dispersive interactions, as well as, hydrogen bonding at low pH values. In addition to the clear changes in OH intensity from interfacial H2O, the SFG spectra exhibit drastic changes in the CH bands from interfacial β-escin which we relate to differences in the net molecular orientation. This orientation change is driven by tighter packing of β-escin adsorption layers when the β-escin moiety is in its charge neutral form (pH < 4).

Numerical simulation of the flow behavior and powder spreading mechanism in powder bed-based additive manufacturing

The flow behavior of the powder layer significantly affects subsequent dynamic behavior and final quality of the parts fabricated via powder bed-based additive manufacturing. High powder layer quality is the key scientific problem and technical difficulty, however, the dynamic flow behavior of powder particles and its relationship between powder layer quality were not well understood. In this paper, the influences of typical factors including process parameters (relative layer height and blade velocity) and powder properties (particle size and surface energy coefficient) on powder layer quality of polyamide 6 were systematically investigated by discrete element method to understand the mechanism of the powder layer packing behavior at the particle scale. The packing density, structure uniformity, normalized layer thickness, and surface uniformity were introduced to quantitatively characterize the powder layer quality. The mechanisms at the particle scale, including the blocking of particle, force arch, particle velocity distribution, and cohesion effect were discussed in detail. The results showed that a decreasing value particle size/layer height can effectively weaken the blocking effect of particles, improving the continuity and stability of powder flow and inducing a dense and uniform powder layer. The particles with high average velocity in the gap between the blade and baseplate will move forward after the blade leaves, significantly reducing the layer thickness and packing density. Meanwhile, the cohesion force was determined by the particle size and surface energy coefficient, and the cohesion effect dominated the flow behavior of the particles with a small particle size d = 10μm or a large surface energy coefficient γ = 0.2mJ/m2. These findings can provide useful guidance in understanding the flow behavior at the particle scale and improving the powder layer quality.

Slow Magnetic Relaxation in {[CoCxAPy)] 2.15 H2O}n MOF Built from Ladder-Structured 2D Layers with Dimeric SMM Rungs.

We present the magnetic properties of the metal-organic framework {[CoCxAPy]·2.15 H2O}n (Cx = bis(carboxypropyl)tetramethyldisiloxane; APy = 4,4′-azopyridine) (1) that builds up from the stacking of 2D coordination polymers. The 2D-coordination polymer in the bc plane is formed by the adjacent bonding of [CoCxAPy] 1D two-leg ladders with Co dimer rungs, running parallel to the c-axis. The crystal packing of 2D layers shows the presence of infinite channels running along the c crystallographic axis, which accommodate the disordered solvate molecules. The Co(II) is six-coordinated in a distorted octahedral geometry, where the equatorial plane is occupied by four carboxylate oxygen atoms. Two nitrogen atoms from APy ligands are coordinated in apical positions. The single-ion magnetic anisotropy has been determined by low temperature EPR and magnetization measurements on an isostructural compound {[Zn0.8Co0.2CxAPy]·1.5 CH3OH}n (2). The results show that the Co(II) ion has orthorhombic anisotropy with the hard-axis direction in the C2V main axis, lying the easy axis in the distorted octahedron equatorial plane, as predicted by the ab initio calculations of the g-tensor. Magnetic and heat capacity properties at very low temperatures are rationalized within a S* = 1/2 magnetic dimer model with anisotropic antiferromagnetic interaction. The magnetic dimer exhibits slow relaxation of the magnetization (SMM) below 6 K in applied field, with a τlf ≈ 2 s direct process at low frequencies, and an Orbach process at higher frequencies with U/kB = 6.7 ± 0.5 K. This compound represents a singular SMM MOF built-up of Co-dimers with an anisotropic exchange interaction.

Mechanical Properties of Solution-Blended Graphene Nanoplatelets/Polyether-Ether-Ketone Nanocomposites.

A lightweight composite with outstanding damping effects and impact resistance is significant for the design of functional structures in advanced equipment, such as aircraft and space vehicles. In this paper, the mechanical properties of solution-blended graphene nanoplatelets (GNPs)/polyether-ether-ketone (PEEK) nanocomposites were characterized by both experimental and numerical methods. It can be found that the layer number and packing configuration of graphene layers are critical to the efficiency of energy dissipation in the composite, while a pack of six- layer graphene and the perpendicular arrangement to the shockwave direction provide the most outstanding energy dissipation ability. The reflection of shockwave caused by graphene reinforcements in the nanocomposite was found to be the dominating reason for the enhanced energy dissipation effect. Physical mechanisms of energy dissipation are investigated by a molecular modeling method to provide insights into the cross-scale design of graphene-reinforced nanocomposites as structural materials.

Polyoxometalate Interlayered Zinc-Metallophthalocyanine Molecular Layer Sandwich as Photocoupled Electrocatalytic CO2 Reduction Catalyst.

Developing efficient and robust heterogeneous metallophthalocyanine electrocatalysts for CO2 reduction remains a challenge. Here, a general synthetic method of zinc-metallophthalocyanine (MPc) molecular layer/polyoxometalate (POM) sandwich lamellar material is developed, and thus improved performance of electrocatalytic and photocoupled electrocatalytic CO2 reduction is achieved. The incorporation of POM could prevent the packing of MPc molecular layers from aggregation, which would be favorable to the exposure of active sites. The molecular layer sandwich catalyst presents superior CO2 reduction activity, delivering the highest CO Faradaic efficiency (FECO) of 96.1% at -0.7 V vs RHE in dark field. Under light irradiation, over 93% FECO is achieved in a broad potential range from -0.6 to -0.9 V vs RHE with a maximum of 96.2%, and the carbon monoxide turnover frequency could exceed 2060 h-1. Photoelectrochemical tests and luminescence characterizations reveal the molecular layer is beneficial for carrier separation during light irradiation; density functional theory calculations and electron paramagnetic resonance indicated a 2-fold enhancement of the external light field on the catalytic performance.

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

ЭМПИРИЧЕСКАЯ ЗАВИСИМОСТЬ ГИДРАВЛИЧЕСКОГО СОПРОТИВЛЕНИЯ ОРОШАЕМОГО СЛОЯ РЕГУЛЯРНОЙ НАСАДКИ ОТ КОЭФФИЦИЕНТА СОПРОТИВЛЕНИЯ И ПЛОТНОСТИ ОРОШЕНИЯ

A criterion equation for the coefficient of hydraulic resistance of a layer of regular packing was ob-tained, and a dependence was obtained that connects the hydraulic resistance of a dry and irrigated packing.

Hexagonal Nickel as a Highly Durable and Active Catalyst for Hydrogen Evolution

The development of highly active and stable earth-abundant electrocatalysts is crucial for the large-scale electrocatalytic hydrogen production. We report herein a crystal-phase heterostructured Ni catalyst with an interior backbone of the face-centered cubic phase covered by a thin surface layer of the hexagonal close packing (hcp) phase. Systematic studies reveal that, upon oxidation, the surface hcp Ni is capable of forming a leaky oxidized layer with abundant Ni0 sites buried underneath. Such underneath Ni0 sites could act synergistically with the leaky surface (hydr)oxide layer from hcp Ni to promote H+ electroreductive formation of H2. The unique surface chemical properties of hcp endow the as-prepared Ni catalyst with high hydrogen evolution activity (112 mV @ 100 mA cm–2) and incredible environment stability even under high current densities and high-concentration alkaline conditions (4–6 M KOH), making it a promising alternative to noble metal catalysts for practical applications in commercial alkaline electrolyzers.