Packing Behavior Research Articles

Discrete Element Modeling of Irregular-Shaped Particles Using an Automatic Generation Algorithm-Based Multi-Sphere Model

Within the Discrete Element Method (DEM) framework, the multi-sphere model capable of creating irregular-shaped particles by several sub-spheres attracts increasing attention. Traditionally, the creation of irregular-shaped particles using the multi-sphere model requires manual determination of the position and diameter of each sub-sphere, which extremely increases the difficulty and workload of DEM modeling of irregular-shaped particles. To tackle this issue, a new automatic generation algorithm that helps to create arbitrary-shaped multi-sphere particles automatically was developed in this study. The quality of created multi-sphere particles can be easily controlled by adjusting the number of sub-spheres and size factor referred to as the size ratio of the smallest sub-sphere to the largest sub-sphere. To verify the effectiveness of the newly developed automatic generation algorithm, two verification tests were conducted in this study: (i) The packing behavior of irregular-shaped particles in a rectangular container and (ii) the mechanical behavior of irregular-shaped particles under the uniaxial compression. The fill heights of the simulations were in line with those of the experiments with an error of less than 8%. The mechanical behavior of irregular-shaped particles under the uniaxial compression can also be well reproduced. Besides, the influence of important parameters on simulation accuracy was also investigated. The results demonstrated that the newly developed automatic generation algorithm can accurately create complex-shaped particles with a small number of sub-spheres. Increasing the number of sub-spheres will improve the simulation accuracy but at the expense of computational efficiency. A larger size factor leads to higher computational efficiency in DEM simulation but is accompanied by a significant loss of accuracy.

Supramolecular structure, DFT calculation and vibrational characterization of melamin-1-ium oxalurate monohydrate

Crystallization from an aqueous solution of melamine with parabanic acid was taken in a molar ratio of 1:1 leads to the formation of melamin-1-ium oxalurate monohydrate (MOX) crystals. The compound crystallizes in the centrosymmetric space group P21/n of the monoclinic system with four molecules per unit cell. The molecular geometry and vibrational frequencies of MOX in the ground state have been calculated by using the density functional hybrid function B3LYP 6–31+G(d) basis set. The results of optimized molecular structure are presented and compared with the experimental X-ray diffraction data. Furthermore, Fourier Transform Infrared (FT-IR) and Raman Spectra were used to conduct vibrational characterization to study the compound's structural groups. The calculated Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energies show that charge transfer occurs in the molecule and other related electronic properties have also been calculated. Besides, Molecular Electrostatic Potential (MEP) was performed to identify the possible electrophilic and nucleophilic sites. First order hyperpolarizability results establish the nonlinear response of the grown MOX crystal with respect to the electric field. Further, the crystal packing behaviour of MOX was studied quantitatively with the aid of Hirshfeld surface analysis.

Sustainable Heat Generation in Flow from a Molecular Solar Thermal Energy Storage System

As the global deployment of renewable technologies accelerate, finding efficient ways to store energy will aid in responding to shifting energy demands. A prospective option not only in harvesting solar energy but also in emission‐free heating is MOlecular Solar Thermal (MOST) energy storage. A central part of MOST applications is to develop methods to release the stored energy. Herein, the Quadricyclane (QC)‐to‐Norbornadiene catalyzed back reaction is explored in a specially designed packed‐bed reactor. Four distinctly sized and purposely synthesized platinum on activated carbon catalysts are studied to trigger the heat release from the energy‐dense QC isomer. The catalysts are fully characterized using a variety of structural, surface, and spectroscopic techniques. Parameters to optimize catalytic conversion and heat release in flow conditions are explored including particle size and packing behavior, flow rates, and molecular residence times. Moreover, using CO pulse chemisorption technique, site time yield values and a turnover number are reported. Complementary to the flow reactions, computational fluid dynamic simulations applying lattice Boltzmann methods to two catalytic packed beds of different size ranges are done to evaluate fluid‐dynamic behavior within the reactor bed to ascertain the ideal particle size and packing density for catalysis in MOST applications.

Delicate Regulation of Central Substituents Boosts Organic Photovoltaic Performance of Dimeric Acceptors.

Dimeric acceptors are expected to satisfy both excellent power conversion efficiency (PCE) and operational stability of organic solar cells (OSCs). However, comparing to highly planar and symmetrical monomer-like acceptors, the quite different steric/spatial configurations of dimeric acceptors affect device outcomes greatly. Herein, on basis of the same dimeric molecular platform that constructed by bridging central units of two monomer-like acceptor, diverse substituents (─OCH3 for D1, ─CH3 for D2, and ─CF3 for D3) are grafted on central units to regulate the three dimensions (3D) geometries of dimeric acceptors delicately. A systematic investigation reveals the substituent-dependent variation of energy level, absorption, and molecular packing behavior. Consequently, D2 acceptor, characteristic of more favorable configuration, affords a superior film morphology and charge transfer/transport dynamics in resulting OSCs, thus yielding an excellent PCE of 17.50% along with a good long-term stability. This work manifests the crucially important role of central substituents in constructing high-performance dimeric acceptors.

Enhancing battery pack safety against cone impact using machine learning techniques and Gaussian noise

The increasing prevalence of electric vehicles underscores the need for enhanced battery pack safety, particularly against impacts that can lead to thermal runaway and fires. This study investigates the mechanical and thermal characteristics of battery packs subjected to cone impact on the lower part. Utilizing finite element model (FEM) simulations, we examined the effects of top radius, shell condition, velocity, and angle on the battery pack's response. Five machine learning (ML) techniques were employed to predict the battery pack's behavior under impact, with training data generated from a well-planned Latin hypercube experiment based on FEM dynamic simulations. The accuracy and robustness of the ML models were evaluated under various scenarios, including the introduction of Gaussian noise. Among the models tested, BESA-ELMM (Bald eagle search algorithm-Extreme learning machine model) demonstrated exceptional speed, making it suitable for real-time assessments, while WOA-SVMM (whale optimization algorithm-Support vector machine model) exhibited superior resilience and accuracy, particularly under noisy conditions. Both models, along with the other ML techniques, showed significant effectiveness in predicting the mechanical responses of battery packs to impact. Our findings indicate that ML approaches are highly efficient in evaluating the mechanical effects on battery packs, providing crucial insights for designing safer and more durable battery packs. This study contributes to the advancement of battery safety by demonstrating the potential of integrating ML techniques with FEM simulations to enhance the resilience and impact resistance of battery packs in electric vehicles.

Supramolecular Assembly of Nitrogen-Containing Curved π-Conjugated Molecules to Polar Crystal

The chemistry of curved π-conjugated molecules has been extensively studied because of the development of their synthetic approach. Among the numerous studies, we have been engaged in nitrogen-containing curved π-conjugated molecules. These molecules have extended optical properties, redox-active behaviors, and electron-donating ability due to the electron-rich nature of nitrogen atoms. Recently, we have focused on the supramolecular assembling behavior of these compounds. For example, we have reported buckycatcher consisted of two azabuckybowls, providing two-photon absorbing host-guest complexes with fullerenes. In this presentation, we would like to show the packing behavior using π-extended azahelicenes and azabuckybowls. Our group has developed π-extended aza[5]helicene derivatives, showing brilliant emissive features. Recently, we succeeded in the synthesis of unsymmetrically substituted azahelicenes. We found that their stackings in the crystal were dependent on the substituent. X-ray diffraction analysis for all products showed π-stacked conformation with each other in the crystal (Figure 1b). In particular, azahelicenes with triisopropylsilyl groupswere found to align their dipole moments to form a one-dimensional columnar structure in the crystal. Polar crystals are expected to have applications in ferroelectric, piezoelectric, and nonlinear optical response materials. This is the first example of a polar crystal with helicenes, paving the way for novel piezoelectric organic materials.The second topic is related to azabuckybowl. In the crystal, azabuckybowl forms a face-to-face dimer by concave-convex interaction. In this study, we prepared two types of azabuckybowl perylene bisimide (PBI) dyads connected with alkyne linkages. PBIs have also been reported to show columnar stacking in solution. We anticipated that the segregate stacking should be achieved by recognizing the difference in structures between the bowl and planar geometry. The UV/vis absorption spectra revealed the presence of intramolecular charge-transfer interaction. In addition, the concentration-dependent absorption spectra and 1H NMR spectra indicated PBI and azabuckybowl units stacked with each other independently in solution (Figure 1a). Here, we would like to discuss about the effect of the effect of molecular shape on the supramolecular assembly with the data obtained using these compounds. Figure 1

Noncontact measurement of density and thermal properties of SS 316L powder bed through flash thermography

PurposePowder bed density is a key parameter in powder bed additive manufacturing (AM) processes but is not easily monitored. This research evaluates the possibility of non-invasively estimating the density of an AM powder bed via its thermal properties measured using flash thermography (FT).Design/methodology/approachThe thermal diffusivity and conductivity of the samples were found by fitting an analytical model to the measured surface temperature after flash of the powder on a polymer substrate, enabling the estimation of the powder bed density.FindingsFT estimated powder bed was within 8% of weight-based density measurements and the inferred thermal properties are consistent with literature findings. However, multiple flashes were necessary to ensure precise measurements due to noise in the experimental data and the similarity of thermal properties between the powder and substrate.Originality/valueThis paper emphasizes the capability of Flash Thermography (FT) for non-contact measurement of SS 316 L powder bed density, offering a pathway to in-situ monitoring for powder bed AM methods including binder jetting (BJ) and powder bed fusion. Despite the limitations of the current approach, the density knowledge and thermal properties measurements have the potential to enhance process development and thermal modeling powder bed AM processes, aiding in understanding the powder packing and thermal behavior.

Effect of a fluorinated surfactant on Langmuir monolayer properties of minimal-linker gemini surfactants

A new class of carboxylic acid-terminated gemini surfactants which contain the smallest possible headgroup linker (a single bond) has recently been reported in the literature. In this current work, we have explored how Langmuir monolayers of two different alkyl tail chain length variants (n = 12, n = 16) of these surfactants, dubbed Cn-0-Cn, are impacted by mixing with a benchmark perfluorinated surfactant, perfluorotetradecanoic acid (PF). Pure PF and C16-0-C16 monolayers share similar general characteristics, yielding compact, incompressible, solid-like films at the air-water interface. In contrast, the shorter tail chain variant, C12-0-C12 forms expanded, compressible liquid-like films. While both tail chain variants formed mixed films with PF that were generally expanded in comparison with their pure components, and were also phase-separated, the extent of interactions between film components and the resulting micron-scale morphology of the mixed films were different for the two alkyl chain lengths. Overall, PF induces different packing behavior in both the systems and the observations are attributed to the difference in the dispersion forces originating from the tail chain length differences.

Deformation, shape transformations, and stability of elastic rod loops within spherical confinement

Mechanical insight into the packing of slender objects within confinement is essential for understanding how polymers, filaments, or wires organize and rearrange in limited space. Here we combine theoretical modeling, numerical optimization, and experimental studies to reveal spherical packing behavior of thin elastic rod loops of homogeneous or inhomogeneous stiffness. Across varying loop lengths, a rich array of configurations including circle, saddle, figure-eight, and more intricate patterns are identified. A theoretical framework rooted in the local equilibrium of force and moment is proposed for the rod loop deformation, facilitating the determination of internal and contact forces experienced by the rods during deformation. For the confined homogeneous rod loops, their stable and metastable configurations are well described using proposed Euler rotation curves, which offer a concise and effective approach for configuration prediction. Moreover, formulated analysis on the stability and critical force for homogeneous rod loops on great circles of the spherical confinement are performed. For inhomogeneous rod loops with two segments of differing stiffness, the stiffer segment exhibits less deviation from the great circle, while the softer segment undergoes more pronounced deformation. These findings not only enhance our understanding of buckling and post-buckling phenomena but also offer insights into filament patterning within confining environments.

Advances in granular flow modeling: GPU-based multi-sphere DEM approach and tumbling mill dynamics

Modeling irregular-shaped particulate flow systems poses challenges, especially in mineral processing where accurate representation of particle shape is crucial for capturing macroscopic behavior. The multi-sphere approach, employing DEM, addresses this by approximating particles as overlapping spheres within GPU computing. This study validates particle flow dynamics using literature-based data, showcasing the model’s fidelity and GPU advantages. However, calibration and shape approximation limitations require careful consideration. A quaternion-based orientation method enhances DEM and validates experimental data from packing, hoppers, and tumbling mills. Simulations reveal how particle shape influences granular dynamics, affecting lift-off tendencies, responses to lifter face angles, and power draw trends with mill speed changes. Cubical and spherical particles exhibit orderly packing behavior, contrasting with irregular shapes. This investigation underscores the significant role of particle shape in granular dynamics and its implications for industrial processes.

Comparative study on the compression characteristics of coal and biomass powder bed

Biomass substitution for fossil energy is desirable to achieve carbon emission reductions, and the storage and transportation process of biomass is governed by its compressibility. The compression characteristics of pulverized coal, rice husk and lignocellulose were compared under mechanical and gas pressurization, respectively. The experimental results showed that the descending order of relative packing density (RPD) was lignocellulose > rice husk > pulverized coal under mechanical pressurization, while an opposite trend was observed under gas pressurization. The cohesion properties were rationally correlated with the packing behavior of powder bed, and the differences in RPD order were discussed as the higher cohesion corresponding to a larger void fraction. For mechanical pressurization, biomass had higher void fraction, which was directly linked to larger RPD. On the contrary, gas permeated easily into the biomass powder bed, and the lower pressure drop decreased the compression capacity of gas pressurization. In addition, a model for predicting the RPD was proposed with an error of ± 5 %.

Temper wolf hunt optimization enabled GAN for robust image encryption

In today’s digital era, the security of sensitive data, particularly in the realm of multimedia, is of paramount importance. Image encryption serves as a vital shield against unauthorized access and ensures the confidentiality and integrity of visual information. As such, the continuous pursuit of robust and efficient encryption techniques remains a pressing concern. This research introduces a Temper Wolf Hunt Optimization enabled Generative Adversarial Network Encryption model (TWHO-GAN), designed to address the challenges of image encryption in the modern digital landscape. TWHO, inspired by the collective hunting behavior of wolf and coyote packs, is employed to generate highly secure encryption keys. This algorithm excels in exploring complex solution spaces, creating robust, attack-resistant keys. In TWHO-GAN model, GANs are employed to create encrypted images that are virtually indistinguishable from their original counterparts, adding a layer of security by generating complex encryption keys and ensuring robust protection against attacks. The GAN component reconstructs the encrypted images to their original form when decrypted with the correct keys, ensuring data integrity while maintaining confidentiality. Further, the significance of the proposed model relies on the TWHO algorithm formulated by the integration of the adaptability and coordinated hunting strategies to optimize the chaotic map generation in image encryption protecting the sensitive visual information from unauthorized access as well as potential threats. Through extensive experimentation and comparative analysis, TWHO-GAN demonstrates superior performance in image encryption, surpassing former methods in terms of Cs, 𝐻𝑖𝑠C, MSE, PSNR, RMSE, and SSIM attaining values of 0.93, 94.19, 3.274, 59.70 dB, 1.8095, and 0.940 respectively for 5 numbers of images. Moreover, the TWHO-GAN approach attained the values of 0.91,92.22, 2.03, 49.74 dB, 1.42, and 0.88 for Cs, HisC, MSE, PSNR, RMSE, and SSIM respectively utilizing the Airplanes dataset. The model exhibits robust resistance to various attacks, making it a compelling choice for secure image transmission and storage.

Spheroid models to elaborate the broken symmetry and equivalent volume of molecules in crystalline phase.

Dense packing of particles has provided powerful models to elaborate the important structural features of matter in various systems such as liquid, glassy, and crystalline phases. The simplest sphere packing models can represent and capture salient properties of the building blocks for covalent, metallic, and ionic crystals; it, however, becomes insufficient to reflect the broken symmetry of the commonly anisotropic molecules in molecular crystals. Here, we develop spheroid models with a minimal degree of anisotropy, which serve as a simple geometrical representation for a rich spectrum of molecules-including both isotropic and anisotropic, convex and concave ones-in crystalline phases. Our models are determined via an inverse packing approach: Given a molecular crystal, an optimal spheroid model is constructed using a contact diagram, which depicts the packing relationship between neighboring molecules within the crystal. The spheroid models are capable of accurately capturing the broken symmetry and characterizing the equivalent volume of molecules in the crystalline phases. Moreover, our model retrieves such molecular information from low-quality x-ray diffraction data with poorly resolved structures, and by using soft spheroids, it can also describe the packing behavior in cocrystals.

High Mobility n‐Type Imide‐Based Semiconductor with Unusual Single‐Crystal Packing Structure in Solution‐Processed Thin Film

AbstractSolid‐state molecular arrangement has been recognized as the most important role in the charge transport properties of organic semiconductors. Although highly ordered molecular stacking is achieved in single crystals, maintaining single‐crystal molecular packing in solution‐processed thin films remains a significant challenge. Herein, a new type of n‐type organic semiconductors based on an asymmetric fluoranthene imide unit is reported, whose intermolecular packing and aggregation behavior in the thin film state can be effectively controlled by regulating the cyano substitution sites and alkyl chain types in the imide group. F10 with cyano groups at 4,9‐sites and branched 2‐ethylhexyl chain encouragingly shows a highly ordered single‐crystal‐like molecular packing in solution‐processed thin film after thermal annealing, and thus the resulting organic field‐effect transistors exhibit impressive charge transport performance, with the electron mobility as high as 0.116 cm2 V−1 s−1. This work opens a new avenue for developing high‐performance solution‐processed n‐type semiconductors.

Self‐Assembled Cyclotriguaiacyclene‐Integrated Supramolecular Systems for Liquid Crystal and Self‐Assembly Behavior

AbstractAn advanced tri‐substituted supramolecular material was synthesized via conversion of cyclotriveratrylene to cyclotriguaiacyclene with further esterification reaction with fluorescein unit embedded with side‐arms. All four luminescent materials exhibited columnar hexagonal type mesophase on both heating and cooling conditions. The materials with hexadecyloxy and octadecyloxy tail group exhibit liquid crystalline behavior at room temperature indicating the presence of a mesophase even under ambient conditions. By combining polarizing optical microscopy, differential scanning calorimetry, and high‐temperature X‐Ray diffraction techniques to understanding the optical, thermal, and molecular packing behavior of the compounds in the liquid crystalline state. The cyclotriguaiacyclene core with high fluorescent nature displayed columnar hexagonal type self‐assembly at room temperature. All four supramolecular mesogens showed higher thermal stability of mesophase. The computational study provides the importance of the electronic nature of the compounds.

Exploring the combined effect of particle shape and friction on cell structures in granular packings via LS-DEM modeling

To comprehensively understand and predict the macroscopic behavior of a granular system, one must consider not only the properties of individual particles but also the local structures. In this study, we prepare mechanically stable granular packings of super disks using the two-dimensional level set discrete element method (LS-DEM). We identify the cells, the irreducible loops enclosed by contacting particles, in the prepared granular packings and then analyze the statistics of these structures. We find the following. (1) The packing fraction or mean coordination number of studied systems exhibits a non-trivial dependency on particle shapes and inter-particle frictions, making it challenging to establish a direct correlation between them. (2) Using the cell-based description as a bridge, we can measure the packing behavior without considering the influence of particle shape and inter-particle friction. Specifically, the mean coordination number can be explicitly represented as a function of the mean cell order according to Euler’s topological relation. Upon the assumption that all cells are regular polygons, we can also approximately estimate the rattlers-free packing fraction via the mean cell order. (3) We have observed a nearly linear relationship between the mean cell order and rattler fraction. This enables us to determine the packing fraction as well.

Indenoannulated Tridecacyclene: An All-Carbon Seven-Stage Redox-Amphoter.

We disclose an indenoannulated tridecacyclene comprising a central cyclooctatetraene moiety with multiple adjacent pentagonal rings which is accessible in a concise synthetic sequence. The saddle-shaped geometry of the non-benzenoid polycyclic scaffold and its unique packing behavior in the solid state were characterized by X-ray crystallography. In electrochemical studies, the compound undergoes seven reversible redox events comprising five reductions and two oxidations. The dicationic and dianionic species obtained by chemical oxidation and reduction, respectively, were characterized spectroscopically in solution. Density functional theory calculations were applied to provide insights into aromaticity evolution in the respective charged species, highlighting the beneficial effect of the non-benzenoid moieties on charge stabilization.

Revealing packing structure in benzimidazole-containing polyimides: Anti-parallel offset π-π stacking

Aromatic polyimides (PIs) exhibit excellent mechanical and thermal properties due to the charge transfer (CT) interactions. The introduction of benzimidazole with hydrogen interactions is a notably effective strategy for yielding exceptional superheat resistance and high thermal dimensional stability of PIs. Decoupling the stacking behavior under CT interactions and hydrogen interactions is crucial for elucidating the behavior of PIs macromolecules. Herein, the packing structure of PIs guided by hydrogen interactions was visualized using three plausible model compounds and theoretical simulations. The phthalimide fragment exhibited a preference for anti-parallel offset stack π-π stacking, while the phenylbenzimidazole fragment formed a shoulder-to-shoulder arrangement, resulting in the adoption of a Mixed Layer Packing (MPL) conformation, which is not the common Preferred Layer Packing (PLP) conformation. The CT interactions of phthalimide served as the primary stacking driving force, rather than the hydrogen interaction of benzimidazole. The intrinsic nature of packing behavior was that the minima and maxima parts of the electron density deviated from the midperpendicular of benzene and succinimide, where the LOL-π map, ESP map and SAPT calculations provided insights into the microscopic electronic structure. Finally, experimental PI fibers was prepared and their XRD pattern further confirmed the presence of an anti-parallel offset π-π stack conformation.

Generic Behavior of Ultrastability and Anisotropic Molecular Packing in Codeposited Organic Semiconductor Glass Mixtures

Generic Behavior of Ultrastability and Anisotropic Molecular Packing in Codeposited Organic Semiconductor Glass Mixtures

Effect of vibration conditions on packing structures of trilobed particles

Packing behaviors of non-spherical particles are generally far more complex than those of spherical particles. Trilobes are widely adopted as supports for catalyst in the field of chemical engineering, and thus their packing behaviors subjected to continuous vertical vibration are numerically investigated by discrete element method in this article. Geometrically exact contact detection algorithm between sphero-cylinders and multi-sphere method are coupled to describe the shape and motion of trilobed particles. It is found that there exist two preferential orientations, which are quite different from the phenomenon of sphero-cylinders. Ordered clusters of different orientations co-exist in the heterogeneous granular bed with obvious phase junctures. The initial stage of crystallization process can be explained by the nucleation growth mechanism. With the growth of the nuclei, distances between small ordered clusters decrease gradually and those ones with identical orientation can eventually get coalesced to form a larger cluster. Moreover, novel sunflower-shaped clusters composed of trilobes of different orientations are observed under vibrations of low amplitudes and high frequencies. In the meanwhile, no consistent relationship between packing densities and packing structures can be found for the dense packing of trilobes. Therefore, other packing parameters more sensitive to the local structures should be analyzed together with the overall packing densities to comprehensively understand the packing behaviors of non-spherical particles.