Efficient Packing Research Articles

Evaporative Drying: A General and Readily Scalable Route to Spherical Nucleic Acids with Quantitative, Fully Tunable, and Record-High DNA Loading.

Nanoparticles (NPs) grafted with highly dense DNA strands are termed as spherical nucleic acids (SNAs), which have important applications benefiting from various unique properties unpossessed by naturally occurring nucleic acids. To overcome existing challenges toward an ideal SNA synthesis, herein, a very simple, while highly effective evaporative drying strategy featuring various long-desired advantages, is reported. This includes record-high DNA loading, generality for more NP materials, fully and quantitatively tunable DNA density, and readiness toward bulk production. The process requires almost zero care and the solid products are especially suitable for a long-time storage without quality degradation. The research reveals a quick and highly efficient packing of thiol-tagged DNA on the NP surface at the critical moment of drying, which refreshes previous knowledge on DNA conjugation chemistry. Based on this advancement, practical applications of SNAs in various fields may become possible.

Limestone calcined clay cement: mechanical properties, crystallography, and microstructure development

Limestone calcined clay cement (LC3) holds promise as a new type of sustainable cement-based material, but the mechanisms underpinning its engineering performance are still poorly understood. Here, a metal intrusion-enhanced imaging approach was employed to quantitatively analyze and link the pore structure development of LC3 to its hydration process, i.e. solid-phase development, and mechanical performance. We found that the early age microstructural development in LC3 is inhomogeneous, with the perimeter of limestone particles displaying higher porosity relative to that surrounding calcined clay and clinker. At later ages, the formation of carboaluminates and calcium-aluminate-silicate-hydrates homogenized the overall microstructure of LC3, thereby delivering improved mechanical performance. Overall, our analysis suggested a more efficient particle packing in LC3 mixes, which decreases the volume/connectivity of micro-pores and can account for LC3’s notable flexural strength. These findings can assist the development of improved LC3 binder formulations alongside other ternary binders with possibly higher limestone additions.

Voxel-Based Solution Approaches to the Three-Dimensional Irregular Packing Problem

Packing Three-Dimensional Irregular Objects Because of its many applications in practice, the cutting and packing literature is extensive and well established. It is mostly concerned with problems in one and two dimensions or with problems where some regularity of the pieces is assumed (e.g., packing boxes). However, the rise of applications in the realm of three-dimensional printing and additive manufacturing has created a demand for efficient packing of three-dimensional irregular objects. In “Voxel-Based Solution Approaches to the Three-Dimensional Irregular Packing Problem,” Lamas-Fernandez, Martinez-Sykora, and Bennell propose a series of tools to tackle this problem using voxels. These include geometric tools, a mathematical model, local search neighborhoods, and details on implementation of metaheuristic algorithms. These tools are tested extensively, and computational results provided show their effectiveness compared with state-of-the-art literature.

Effect of tethered sheet-like motif and asymmetric topology on hydrogelation of star-shaped block copolypeptides

To study the hydrogelation and self-assembly ability of the star-shaped diblock copolypeptides, 6-armed and 12-armed block copolypeptides comprised of poly- l -Lysine (PLL) as the first block and separately tethered with different hydrophobic, sheet-like oligopeptides (β-motifs) were synthesized using polyglycerol dendritic initiators. The hydrogelation of these samples was driven by the various interactions and amphiphilic balances in the polypeptide assemblies, showing a strong dependence on arm number and β-motif. The incorporation of β-motifs could facilitate hydrogelation and the hydrogel mechanical properties could be tuned by varying the tethered β-motif. Moreover, the star-shaped block copolypeptides with a symmetric topology demonstrated a better hydrogelation ability than those asymmetric counterparts possibly due to their more efficient packing. The tethered β-motif strongly influenced both the molecular assembly and micro-/macroscopic structures. This study illustrated the tunability of polypeptide hydrogels by varying the arm number and tethered β-motif as well as the polypeptide chain symmetry. • Hydrogelation was driven by the various interactions and amphiphilic balances in the polypeptide assemblies. • Hydrogelation of these block copolypeptides showed a strong dependence on arm number and β-motif. • Polypeptides using asymmetric PGD G1 and G2 initiators exhibited lower efficiency in packing and hydrogelation. • Hydrogel molecular packing and mechanical properties depended on the arm number, chain symmetry and tethered β-motif.

Orthogonalization of Polyaryl Linkers as a Route to More Porous Phosphonate Metal-Organic Frameworks.

The coordinative pliancy of the phosphonate functional group means that metal-phosphonate materials often self-assemble as well-packed structures with minimal porosity, as efficient inter-ligand packing is enabled. Here, we report a multistep synthesis of a novel aryl-phosphonate linker with an orthogonalized ligand core, 1,3,5-tris(4'-phosphonophenyl)-2,4,6-trimethylbenzene (H6 L2) designed to form more open structures. A series of crystalline metal-phosphonate frameworks (CALF-35 to -39) have been assembled by coordinating to divalent metals (Ba, Sr, Ca, Mg, Zn). H6 L2 is unable to pack efficiently and, as a consequence, yields several distinct microporous structures. The resulting structures are discussed in detail, with a focus on the solid-state packing of the sterically rigidified linker. Combined with larger cations (Sr, and Ba), H6 L2 packs in a parallel-offset manner, yielding isomorphous and microporous metal-organic frameworks (CALF-35 (Sr), and (Ba)). When coordinated to smaller metals (Ca, Mg, Zn), H6 L2 forms four new structures. Two Ca MOFs of different stoichiometry, (CALF-36 and 37) and a Mg MOF CALF-38 show narrow pores and have high selectivities for CO2 over N2 and CH4 . Finally, in CALF-39 (Zn), H6 L2 linkers pack in a herringbone fashion, resulting in a material with 10.9×10.1 Å2 square channels. The stability of all structures was tested, and the most porous structure, CALF-39 (Zn), was found to retain its structure and gas adsorption after immersion in water over pH 3-11.

A Ternary Model for Particle Packing Optimization

Powder packing in metal powders is an important aspect of additive manufacturing (otherwise known as 3-D printing), as it directly impacts the physical and mechanical properties of materials. Improving the packing density of powder directly impacts the microstructure of the finished 3D-printed part and ultimately enhances the surface finish. To obtain the most efficient packing of a given powder, different powder blends of that material must be mixed to minimize the number of voids, irrespective of the irregularities in the particle morphology and flowability, thereby increasing the density of the powder. To achieve this, a methodology for mixing powder must be developed, for each powder type, to obtain the maximum packing density. This paper presents a model that adequately predicts the volumetric fraction of the powder grades necessary for obtaining the maximum packing density for a given powder sample. The model factors in the disparity between theoretical assumptions and the experimental outcome by introducing a volume reduction factor. We outline the model development steps in this paper, testing it with a real-world powder system.

Experimental and numerical investigation of dry pressure drop of 3D-printed structured packings for gas/liquid contactors

Separation units, such as distillation and absorption columns, are used widely in the chemical industry. Their efficiency depends on the performance of their packing, determined by their pressure drop, capacity, and mass transfer efficiency. Combining CFD and additive manufacturing allows the design/production of efficient and high capacity packing. In this paper, the dry pressure drops of newly developed wire-based structured packings are evaluated numerically via a single-phase CFD model. The k-ω-SST turbulence model in Ansys Fluent was used. The experimental and numerical dry pressure drops of three Tetraspline (TS) packings are compared. The numerical model is validated with average errors of 13% and 20% compared with experimental data for TS made in stainless steel and polyamide, respectively, over a capacity factor range of 0.9 to 3.1 Pa0.5. A Kelvin-cell-based packing is also studied to confirm the robustness of the model. This study allows the rapid optimisation of the different TS with different geometric parameters, such as wire diameter and length, based on the pressure drop. Indeed, the experimental values of the dry pressure drop of a column of packing that measures 16,500 cm3 have been reproduced numerically with only a small deviation using a periodic domain of 42 cm3.

Effects of Particle Size Distribution with Efficient Packing on Powder Flowability and Selective Laser Melting Process.

The powder bed-based additive manufacturing (AM) process contains uncertainties in the powder spreading process and powder bed quality, leading to problems in repeatability and quality of the additively manufactured parts. This work focuses on identifying the uncertainty induced by particle size distribution (PSD) on powder flowability and the laser melting process, using Ti6Al4V as a model material. The flowability test results show that the effect of PSDs on flowability is not linear, rather the PSDs near dense packing ratios cause significant reductions in flowability (indicated by the increase in the avalanche angle and break energy of the powders measured by a revolution powder analyzer). The effects of PSDs on the selective laser melting (SLM) process are identified by using in-situ high-speed X-ray imaging to observe the melt pool dynamics during the melting process. The results show that the powder beds made of powders with dense packing ratios exhibit larger build height during laser melting. The effects of PSD with efficient packing on powder flowability and selective laser melting process revealed in this work are important for understanding process uncertainties induced by feedstock powders and for designing mitigation approaches.

Random trilobe packing using rigid body approach and local Gas-Liquid hydrodynamics simulation through CFD with experimental validation

It is quite difficult to measure the local information of the gas/liquid flow inside random packed extrudate catalyst beds in a large scale. Obtaining the local information through computational fluid dynamic (CFD) simulations in such system is also difficult due to the complexity of random particle packing and two-phase flow simulation. An efficient packing scheme was implemented to randomly pack 2917 trilobe particles (10 cm in height) in a 2-inch column to represent the trickle bed reactor (TBR) based on the rigid body approach. The generated geometry was used to define the computational domain for the two-phase hydrodynamics simulation based on the volume of fluids (VOF) approach. This hydrodynamics modelling study is paired with an experimental study using our in-house developed advanced measurement techniques based on optical fiber probes, which allowed to determine local liquid velocity and saturation profiles. The experimental measurements were used for local validation of the implemented model.

A novel all-nitrogen molecular crystal N16 as a promising high-energy-density material.

All-nitrogen solids, if successfully synthesized, are ideal high-energy-density materials because they store a great amount of energy and produce only harmless N2 gas upon decomposition. Currently, the only method to obtain all-nitrogen solids is to apply high pressure to N2 crystals. However, products such as cg-N tend to decompose upon releasing the pressure. Compared to covalent solids, molecular crystals are more likely to remain stable during decompression because they can relax the strain by increasing the intermolecular distances. The challenge of such a route is to find a molecular crystal that can attain a favorable phase under elevated pressure. In this work, we show, by designing a novel N16 molecule (tripentazolylamine) and examining its crystal structures under a series of pressures, that the aromatic units and high molecular symmetry are the key factors to achieving an all-nitrogen molecular crystal. Density functional calculations and structural studies reveal that this new all-nitrogen molecular crystal exhibits a particularly slow enthalpy increase with pressure due to the highly efficient crystal packing of its highly symmetric molecules. Vibration mode calculations and molecular dynamics (MD) simulations show that N16 crystals are metastable at ambient pressure and could remain inactive up to 400 K. The initial reaction steps of the decomposition are calculated by following the pathway of the concerted excision of N2 from the N5 group as revealed by the MD simulations.

Connecting Packing Efficiency of Binary Hard Sphere Systems to Their Intermediate Range Structure.

Using computed x-ray tomography we determine the three dimensional (3D) structure of binary hard sphere mixtures as a function of composition and size ratio of the particles q. Using a recently introduced four-point correlation function we reveal that this 3D structure has on intermediate and large length scales a surprisingly regular order, the symmetry of which depends on q. The related structural correlation length has a minimum at the composition at which the packing fraction is highest. At this composition also the number of different local particle arrangements has a maximum, indicating that efficient packing of particles is associated with a structure that is locally maximally disordered.

Cation-fluorinated ionic liquids: Synthesis, physicochemical properties and comparison with non-fluorinated analogues

Series of homologues of cation-fluorinated ionic liquids (FILs) containing a perfluoro-octyl group attached to either an imidazolium or pyridinium cation and comprising iodide, bis(trifluoromethylsulfonyl)imide ([NTf2]¯), trifluoromethanesulfonate ([OTf]¯) or acetate ([OAc]¯) were prepared in excellent yield and purity. All ionic liquids were characterized by means of nuclear magnetic resonance and Fourier-transform infrared spectroscopies. Systematic studies of their physicochemical properties, including density, viscosity and refractive index were conducted over a range of temperatures, and compared with the non-fluorinated, alkyl-substituted counterparts (AILs). The results allow for the conclusion that the introduction of fluoroalkyl chains increases dispersion forces leading to a dislocation of [NTf2]¯ and [OTf]¯ towards the cation core, enforcing stronger hydrogen bond interactions of these anions with the cation than in ionic liquids with non-fluorinated alkyl chains. Additionally, structural rearrangements occur in the presence of fluoro-alkyl chain, leading to less efficient packing of acetate- and [OTf]¯-based AILs. This study hence provides the first experimental evidence for the occurance of nanosegregation and triphilicity in cation-fluorinated ionic liquids previously demonstrated through computational studies.A group contribution method was employed to show that the properties of FILs and AILs, such as density, can be predicted from their refractive index. An excellent correlation of predicted densities with experimentally obtained densities was obtained with R2 of 0.9628 for FILs. This study presents properties of single ionic liquids, which is the foundation for an extensive follow-up study on their binary mixture properties.

Organic Phase Change Materials for Thermal Energy Storage: Influence of Molecular Structure on Properties.

Materials that change phase (e.g., via melting) can store thermal energy with energy densities comparable to batteries. Phase change materials will play an increasing role in reduction of greenhouse gas emissions, by scavenging thermal energy for later use. Therefore, it is useful to have summaries of phase change properties over a wide range of materials. In the present work, we review the relationship between molecular structure and trends in relevant phase change properties (melting temperature, and gravimetric enthalpy of fusion) for about 200 organic compounds from several chemical families, namely alkanes (paraffins), fatty acids, fatty alcohols, esters, diamines, dinitriles, diols, dioic acids, and diamides. We also review availability and cost, chemical compatibility, and thermal and chemical stabilities, to provide practical information for PCM selection. Compounds with even chain alkyl lengths generally give higher melting temperatures, store more thermal energy per unit mass due to more efficient packing, and are of lower cost than the comparable compounds with odd alkyl chains.

Closely Compacted TiNb2O7-C Assembly for Fast-Charging Battery Anodes

The fast-charging capability of lithium-ion batteries (LIBs) is becoming more important than before to meet the increasing requirements in practical applications. Because of safe working potential (above 1 V) and moderately high specific capacity, titanium niobium oxide (TiNb2O7, TNO) shows great potential as a fast-charging anode. Herein, a TNO-C assembly consisting of active initial TNO nanoparticles with conformal carbon coating is fabricated. The small size of TNO nanoparticles provides a short diffusion distance for lithium ions, and surficial carbon layers enable good electronic conductivity within the entire assembly. Moreover, the compact structure within the TNO assembly and efficient space packing of spheroidal secondary particles are beneficial for close packing, leading to an overall short distance for electron transport and ion diffusion. As expected, the as-designed TNO-C electrode delivers a high capacity of 194 mAh g–1 under 10C, and 71% of capacity was achieved under 0.2C. Moreover, the TNO-C electrode shows stable cycling performance with capacity retention of 92.2% after 100 cycles under 2C. In addition, by pairing with a lithium nickel–cobalt manganate (LiNi0.6Co0.2Mn0.2O2, NCM) cathode, the full cell exhibits a high capacity of 140 mAh g–1 under 3C and a high capacity retention of 97.4% after 100 cycles. The rational design of a TNO-C assembly makes it an excellent anode candidate for fast-charging LIBs.

Abundant Solvatomorphism-Tuned Spin Crossover in a Dinuclear Fe(II) Compound: Computational Insights on Molecular Distortion and Packing Effects

A series of solvates based on a dinuclear Fe(II) complex [(TPA)2Fe2(μ-DHBQ)][BF4]2·S [S = CH3OH (1·CH3OH), 2CH3OH (2·2CH3OH), 4DMF (3·4DMF), 2Et2O (4·2Et2O), Et2O·MeCN (5·Et2O·MeCN), and 2CH2Cl2 (6·2CH2Cl2)] were synthesized. Upon solvent removal, single-crystal-to-single-crystal (SC-to-SC) transitions could occur for the first four solvates to give 1, 2, 3, and 4·0.5Et2O. Within the temperature range of 400–10 K, these compounds exhibited abundant variations in their spin crossover (SCO) properties. 2,5·Et2O·MeCN and 6·2CH2Cl2 displayed half high-spin (HS) to low-spin (LS) transitions, and 4·2Et2O underwent incomplete LS-to-HS conversion, whereas other solvatomorphs showed complete SCO. As all these solvatomorphs possessed the identical [(TPA)2Fe2(μ-DHBQ)][BF4]2 core, these variations in SCO behavior emphasized the critical role of the crystal lattice contributions. With the aim of deciphering their origin, periodic DFT+U+D3 computations were performed on these solvatomorphs to quantify the importance of all possible intramolecular and intermolecular effects on their spin-state energetics. Computationally, the isolated [(TPA)2Fe2(μ-DHBQ)]2– molecule in the gas phase would undergo SCO around 350 K in one step intrinsically. However, distinctive roles of the crystal-lattice effects in the solid state resulted in varying SCO behaviors. Different reasons were discovered for the incomplete spin transitions of different solvatomorphs. For 2, although serious volume shrinkage of the LS state caused efficient packing of the overall crystal-lattice organization, the originally close-packing SCO cations got loose and thus strongly destabilized its LS state. For 5·Et2O·MeCN and 6·2CH2Cl2, severe molecular distortions kinetically trapped their LS state. These computationally magneto-structural studies on dinuclear solvatomorphs have great importance for designing SCO compounds with selected properties, which is critical for their actual application.

Using Successive Self-Nucleation and Annealing to Detect the Solid–Solid Transitions in Poly(hexamethylene carbonate) and Poly(octamethylene carbonate)

Solid–solid transitions in poly(hexamethylene carbonate) (PC6) and poly(octamethylene carbonate) (PC8), denoted the δ to α transition, have been investigated, using self-nucleation and the successive self-nucleation and annealing (SSA) technique. The SSA protocol was performed in situ for thermal (differential scanning calorimetry (DSC)), structural (wide-angle X-ray scattering (WAXS)), and conformational (Fourier transform infrared spectroscopy (FT-IR)) characterization. The final heating after SSA fractionation displayed an enhanced (compared to a standard second DSC heating scan) endothermic and unfractionated peak signal at low temperatures corresponding to the δ to α transition. The improved (i.e., higher enthalpy and temperature than in other crystallization conditions) δ to α transition signal is produced by annealing the thickest lamellae made up by α and β phase crystals after SSA treatment. As thicker lamellae are annealed, more significant changes are produced in the δ to α transition, demonstrating the transition dependence on crystal stability and, thus, on the crystallization conditions. The ability of SSA to significantly enhance the observed solid–solid transitions makes it an ideal tool to detect and study these types of transitions. In situ WAXS reveals that the δ to α transition corresponds to a change in the unit cell dimensions, evidenced by an increase in the d-spacing. This implies a more efficient chain packing in the crystal, for both samples, in the δ phase (lower d-spacing at low temperatures) than in the α phase (higher d-spacing at high temperatures). The chain packing differences are explained through in situ FT-IR measurements that show the transition from ordered (δ phase) to disordered (α phase) methylene chain conformations.

Assembly of Biomolecular Gigastructures and Visualization with the Vulkan Graphics API.

Building and displaying all-atom models of biomolecular structures with millions or billions of atoms, like virus particles or cells, remain a challenge due to the sheer size of the data, the required levels of automated building, and the visualization limits of today’s graphics hardware. Based on concepts introduced with the CellPack program, we report new algorithms to create such large-scale models using an intermediate coarse-grained “pet representation” of biomolecules with 1/10th the normal size. Pet atoms are placed such that they optimally trace the surface of the original molecule with just ∼1/50th the original atom number and are joined with covalent bonds. Molecular dynamics simulations of pet molecules allow for efficient packing optimization, as well as the generation of realistic DNA/RNA conformations. This pet world can be expanded back to the all-atom representation to be explored and visualized with full details. Essential for the efficient interactive visualization of gigastructures is the use of multiple levels of detail (LODs), where distant molecules are drawn with a heavily reduced polygon count. We present a grid-based algorithm to create such LODs for all common molecular graphics styles (including ball-and-sticks, ribbons, and cartoons) that do not require monochrome molecules to hide LOD transitions. As a practical application, we built all-atom models of SARS-CoV-2, HIV, and an entire presynaptic bouton with 1 μm diameter and 3.6 billion atoms, using modular building blocks to significantly reduce GPU memory requirements through instancing. We employ the Vulkan graphics API to maximize performance on consumer grade hardware and describe how to use the mmCIF format to efficiently store such giant models. An implementation is available as part of the YASARA molecular modeling and simulation program from www.YASARA.org. The free YASARA View program can be used to explore the presented models, which can be downloaded from www.YASARA.org/petworld, a Creative Commons platform for sharing giant biomolecular structures.

Volumetric and compressibility studies on aqueous mixtures of deep eutectic solvents based on choline chloride and carboxylic acids at different temperatures: Experimental, theoretical and computational approach

Deep eutectic solvents (DESs) constitute a new class of green solvents, the studies on which are going at a fast pace. The binary mixtures of DESs with water are attracting a great deal of interest for various industrial applications owing to their unique properties not exhibited by the neat components. Therefore, thermodynamic properties of DESs-water mixtures should be explored to better understand the prevailing intermolecular interactions for enhancing the application arena of such binary mixtures. Herein, the density (ρ) and speed of sound (u) of binary mixtures of DESs (choline chloride: acetic acid; 1: 2; and choline chloride: L-(+)-lactic acid; 1: 2) with water has been measured over whole composition range at different temperatures (T = 298.15 to 313.15 K) and atmospheric pressure. The values of various thermodynamic parameters have been derived and discussed in terms of the varying extent of intermolecular interactions governed by the components of DESs. The negative values of excess molar volumes (VmE) are ascribed to the stronger hydrogen bond interactions and efficient molecular packing in the binary mixtures over repulsive interactions. The VmE values have been analyzed using Prigogine-Flory-Patterson (PFP) theory, which satisfactorily explained the volumetric behaviour of the binary mixtures. Density functional theory (DFT) calculations have been made to support the variation in VmE and the underlying interactions prevailing between the components. Further, isentropic compressibility (ks) and excess isentropic compressibility (ksE) have been evaluated from the speed of sound data. It is expected that such studies will be beneficial from the academic as well as industrial point of view considering the increasing utilization of DESs for various applications.

LaBH8 : Towards high- Tc low-pressure superconductivity in ternary superhydrides

In the last five years a large number of new high-temperature superconductors have been predicted and experimentally discovered among hydrogen-rich crystals, at pressures, which are way too high to meet any practical application. In this paper, we report the computational prediction of a hydride superconductor, $\mathrm{La}{\mathrm{BH}}_{8}$, with a ${T}_{\text{c}}$ of 126 K at a pressure of 50 GPa, thermodynamically stable above 100 GPa, and dynamically stable down to 40 GPa, an unprecedentedly low pressure for high-${T}_{\text{c}}$ hydrides. $\mathrm{La}{\mathrm{BH}}_{8}$ can be seen as a ternary sodalite-like hydride, in which a metallic hydrogen sublattice is stabilized by the chemical pressure exerted by the La-B scaffolding, which achieves a more efficient packing of atoms than in binary sodalite hydrides thanks to the combination of elements with very different sizes. The proposed aufbau principle may be exploited to design high-${T}_{\text{c}}$ hydrides that survive at even lower pressure, through a careful choice of the elements.

Identifying the Optimal Packing and Routing to Improve Last-Mile Delivery Using Cargo Bicycles

Efficient vehicle routing is a major concern for any supply chain, especially when dealing with last-mile deliveries in highly urbanized areas. In this paper problems considering last-mile delivery in areas with the restrictions of motorized traffic are described and different types of cargo bikes are reviewed. The paper describes methods developed in order to solve a combination of problems for cargo bicycle logistics, including efficient packing, routing and load-dependent speed constraints. Proposed models apply mathematical descriptions of problems, including the Knapsack Problem, Traveling Salesman Problem and Traveling Thief Problem. Based on synthetically generated data, we study the efficiency of the proposed algorithms. Models described in this paper are implemented in Python programming language and will be further developed and used for solving the problems of electric cargo bikes’ routing under real-world conditions.