Loose Packing Research Articles

Plastic viscosity of cement mortar with manufactured sand as influenced by geometric features and particle size

This paper investigates the plastic viscosity of cement mortar with manufactured sand (MS) concerning the influences of geometric features and particle size of MS. The geometric features, including overall shape, angularity and roughness, of MS with various particle sizes were evaluated by aspect ratio, convexity area ratio, convexity perimeter ratio and circularity. The plastic viscosity of cement mortar was calculated based on the Bingham model. Results show that the combined effects of overall shape, angularity and roughness provide coarser MS particles with lower circularity. In terms of relative plastic viscosity, Robinson model shows optimal fittings for all mixtures and is thus used to determine the packing fraction of MS under shearing. From the particle packing viewpoint, shear-induced orientation increases the packing fraction of non-spherical MS particles from the random loose packing fraction and the influence is increasingly prominent with the decrease of circularity. The relative volume fraction is an important parameter influencing the relative plastic viscosity of mixtures with MS while the relative paste film thickness (R_PFT), calculated from the real packing fraction and specific surface area (SSA), is found as the dominating factor. The dependence of plastic viscosity of cement mortar on geometric features and particle size of MS can be attributed to their influences on the packing fraction and SSA of particles.

A Eulerian–Lagrangian Coupled Method for the Simulation of Submerged Granular Column Collapse

A two-fluid Eulerian–Lagrangian coupled model is developed to investigate the complex interactions between solid particles and the ambient water during the process of submerged granular column collapse. In this model, the water phase is considered to be a Newtonian fluid, whereas the granular column is modeled as an elastic–perfectly plastic material. The water flow field is calculated by the mesh-based Eulerian Finite Volume Method (FVM), with the free surface captured by the Volume-of-Fluid (VOF) technique. The large deformation of the granular material is simulated by the mesh-free, particle-based Lagrangian Smoothed Particle Hydrodynamics method (SPH). Information transfer between Eulerian nodes and Lagrangian particles is performed by the aid of the SPH interpolation function. Both dry and submerged granular column collapses are simulated with the proposed model. Experiments of the submerged cases are also conducted for comparison. Effects of dilatancy (compaction) of initially dense (loose) packing granular columns on the mixture dynamics are investigated to reveal the mechanisms of different flow regimes. Pore water pressure field and granular velocity field are in good agreement between our numerical results and experimental observations, which demonstrates the capability of the proposed Eulerian–Lagrangian coupled method in dealing with complex submerged water–granular mixture flows.

Role of zinc sulfate on thermal and mechanical properties of borovanadate glasses

Zinc sulfate doped boro-vanadate glasses have been synthesized using melt quenching method. Amorphous character of glasses is verified by X-ray diffraction studies. Scanning electron micrograph reveals good homogeneous glass formation but consists of SO42- nano clusters randomly distributed in the amorphous tissue. Glass transition temperature estimated from differential scanning calorimetric studies vary with glass composition. Ultrasound velocities, elastic moduli and Debye temperature decrease whereas Poisson’s ratio increase with ZnSO4 content. This occurs due to reduced network connectivities and weakening of the glass network. The above studies suggest that ZnSO4 do not participate in network formation but dissolves isotropically which results in volume expansion and loose packing of network structure. FTIR studies reveal presence of [B2V2O9]2− (type I and II), [BO3/2]0 and [VOO3/2]0 structural units which are characteristic of modified boro-vanadate glasses.

Mechanochromic luminescence from N,O-Chelated diphenylborinates

A series of N,O-bidentated BPh2 complexes (B1–B3) have been designed and synthesized through the direct reaction of N,O-chelate ligands and diaryl borate solutions. Their crystal structures, photophysical and mechanochromic properties were systematically studied. As verified by both experimental and calculated results, all these compounds possess inherent D-A structures, and adopt highly distorted molecular conformations. Multiple weak intermolecular interactions and relatively loose packing are prevailing in their crystal structures. These favorable structure features promise high solid-state fluorescence efficiency and high color contrast reversible mechanochromic for the three dyes. Moreover, their photophysical and mechanical responsive properties have been found structurally dependent, which are mainly modulated by electronic and steric effects derived from different substitutions in the ligand and the boron atom. As a result, B2 with the most twisted and loosely packed structure shows a most sensitive and pronounced mechanochromic response. Our study thus shows that selection of a N,O-bidentated BPh2 based emitter enables the development of excellent MCL-active materials. The current design strategy will be beneficial for the facile access to various advanced BPh2 based dyes for promising applications in optical force sensors, optoelectronic devices and so on.

Void fraction for random loose packing of the cylindrical particles considering filling rate, material and shape

Particle packing is widely applied in organic pollutant adsorption, catalytic reaction, biomass combustion, nuclear cooling, and other scenarios. Due to the complexity of the shape, the studies on the void fraction of the cylindrical particles are not as thorough as the spherical particles. This study investigated the influence of the filling rate, material properties and sphericity on the void fraction of cylinders through experiments and simulation. DEM (discrete element method) was validated by the internal structures of the packing obtained by CT (computed tomography). Based on the logarithmic correlation between the void fraction and filling rate, an ingenious framework for predicting the void fraction of cylindrical particles was presented with two intermediate coefficients. By correlating the coefficients with the material property and sphericity, a novel void-fraction prediction model was established with R-squared of 0.996. The mechanism of void fraction under random loose packing for cylinders was eventually found in this study.

Structural modification of carbon nanotube film toward multifunctional composites via a wet-compression method

Carbon nanotube film (CNTF) assembled by floating catalyst chemical vapor deposition (FFCVD) is a promising material for smart textile, multifunctional composites and soft robotics due to their lightweight, flexibility and electromechanical properties. However, bulk CNTF exhibit unsatisfactory properties, due to the loose and porous packing structures. In this study, an innovative and effective strategy was proposed to densify CNTF by a compression in acetone (wet compression). Due to low surface tension, acetone is easy to penetrate the CNTF and act as a lubricant thus decrease the interactions between the neighboring carbon nanotubes (CNT) under load. Therefore, the CNTF was condensed in thickness from 11.3 to 8.4 µm (34.5% decrease) with a CNT volume fraction increment (~ 11% to ~ 14.7%) under wet-compression treatment. Consequently, the wet-compressed CNTF tensile strength, electrical conductivity and gauge factor enhanced by 97%, 34% and 43% along the direction of CNT alignment and by 213%, 42% and 101% towards the CNT transverse direction. As a potential application, modified CNTF/epoxy composites were fabricated as strong de-icing parts of an airplane. The tensile strength increased to 742 MPa (by 21%) and effectively melted ice by 250 times weight ratio within 1 min; performing as strengthened lightweight multifunctional materials. To summarize, our work provides a universal approach to enhance the overall mechanical properties of the CNTF for several applications.

Fully biodegradable polylactide foams with ultrahigh expansion ratio and heat resistance for green packaging

Long chain branching (LCB) structures are efficiently introduced into polylactide (PLA) by employing sustainable soybean oil (SO) under the initiation of trace amount of cyclic peroxide, which displays robust foamability and heat resistance. It is discovered that with the introduction of 0.6 wt% SO, the expansion ratio and Vicat softening temperature of LCB PLA are sharply raised to 75.2-fold and 155.8 °C, respectively, which is about 17.9 and 2.6 times those of linear PLA. This is because that the amounts of LCB structures are significantly increased in LCB PLA by the addition of SO with low reactivity of internal CC bonds, which can avoid the oligomerization reaction, resulting in more dramatically improved melting strength and crystallization performance of LCB PLA. Moreover, the hydrolytic degradation of LCB PLA is largely expedited as compared to linear PLA, owing to the more rapid water permeation caused by the loose packing of LCB structures. Finally, the PLA foam tray with light weight and good heat resistance is successfully developed by using LCB PLA with 0.6 wt% SO through extrusion foaming with supercritical carbon oxide and thermoforming techniques. Hence, this research offers a green route to produce eco-friendly light-weight and high-heat-resistance LCB-PLA foam with full biodegradability, which is an ideal alternative to the non-degradable oil-based plastics in the field of disposable packaging products.

Highly cross-linked polymeric nanoparticles with aggregation-induced emission for sensitive and recyclable explosive detection

Aggregation-induced emission (AIE) polymeric nanoparticles (PNPs) are promising candidates for detection of nitroaromatic explosives. However, the major limitation of these AIE PNPs is the complicated synthesis and deteriorated detection accuracy because of the poor colloidal and morphological stability. This study provided a facile method to construct AIE PNPs with highly cross-linked polymer matrix for sensitive and accurate detection of nitroaromatic explosives. The highly cross-linked AIE PNPs with a ~50 nm particle size were prepared through copolymerization of divinylbenzene (DVB) and a tetraphenylethene (TPE)-based AIE luminogen, (4′-tetraphenyletheyl)pheny-3-butenylether (TPE-PBE), in a water-borne miniemulsion system. Due to the good aqueous dispersibility and highly cross-linked polymer matrix, the poly(DVB-co-TPE-PBE) NPs showed excellent solvent resistance, and sensitive and accurate detection of nitroaromatic explosives in aqueous systems, especially picric acid (PA). Moreover, a rigid poly(DVB-co-TPE-PBE) film could preserve spherical morphology after coating poly(DVB-co-TPE-PBE) NPs onto various substrates (such as filter paper and glass slide). The high surface area and loose packing of poly(DVB-co-TPE-PBE) NPs offered convenience for 2,4-dinitrotoluene to diffuse and interact with TPE-PBE units. Therefore, cost-efficient and portable poly(DVB-co-TPE-PBE)-coated test strips and film on glass slides exhibited fast response, strong quenching ability, and reusability in visual detection of liquid and volatile explosives, respectively.

Nanoaggregates Derived from Amyloid-beta and Alpha-synuclein Characterized by Sequential Quadruple Force Mapping.

Overlapping of Alzheimer's disease and Parkinson's disease is associated with the formation of hetero-oligomers derived from amyloid-beta and alpha-synuclein. However, the structural identity of the hetero-oligomer has yet to be elucidated, particularly at high resolution. Here, with atomic force microscopy, the surface structure of hetero-oligomer was examined with four AFM tips tethering one of the selected antibodies recognizing N-terminus or C-terminus of each peptide. All aggregates were found to be hetero-oligomers, and probability of recognizing the termini is higher than that for the homo-oligomers, suggesting that the termini of the former have a greater tendency to be located at the surface or the termini have more freedom to be recognized, probably through loose packing. The methodology in this study provides us with a new approach to elucidate the structure of such aggregates at the single-molecule level, allowing the exploration of other intrinsically disordered proteins frequently found in nature.

Identification of Osinsky horizon organogenic structures by 2D and 3D seismic survey data in the north-eastern part of the Nepa-Botuoba anteclise

The fields of Eastern Siberia belong to the one of the main centers of hydrocarbon production in the eastern part of Russia. The main part of hydrocarbon reserves is located in the area within the Nepa-Botuoba anteclise, where the Lower Cambrian deposits are major production objects. The main purpose of this research is to provide a detailed study of the inner space and features of organogenic structures of the Cambrian period, as well as to determine the procedures for detecting reef structures by seismic research methods. Statistical processing of the available factual material on reservoir properties has shown a very uneven distribution of cavernosity (porosity). It is found that pores were formed as a result of leaching of shaped formations in loose packing locations of epigenetic dolomite grains, along the cementing substance in the intergranular spaces, along cracks and stylolite seams. To identify organogenic structures in the Osinsky horizon of the Nepa-Botuoba anteclise on the basis of seismic studies some additional methodologies have been selected. Identification of single reef structures in the Osinsky horizon of the Lower Cambrian based on the analysis of seismic amplitudes was carried out by means of a 2D and 3D seismic survey. According to the data of seismic studies, the Nepa-Botuoba anteclise features the development zones of both linear and single carbonate structures. It is also revealed that there is an increase in effective thicknesses in wells located in the annular anomaly. Summing up the results and analyzing the compared materials, it can be concluded that the main identification method of ring zones in wells is the method of longitudinal wave slowness measurement. A comprehensive analysis of 2D and 3D seismic survey data by the common depth point method as well as by a number of other methods using a specific algorithm allowed us to identify individual formations of organogenic (riphogenic) structures in the carbonate section of the north-eastern part of the Nepa-Botuoba anteclise.

Random loose packing of cylindrical particles considering filling rate

Void fraction of cylindrical particles greatly influences heat and mass transfer and resistance characteristics involved in the processes. The effect of the filling rate of cylindrical particles on the void fraction of the random loose packing (RLP) was studied through the experiments. Then, the discrete element method (DEM) was used to reproduce the RLP process of the cylindrical particles, and the effect of the filling rate on the void fraction of the packing was revealed by the internal packing structure. The following conclusions can be drawn: the void fraction increased with the logarithm of the filling rate and did not change after reaching the maximum value; a void fraction prediction model of cylindrical particles, considering filling rate, was established; a larger filling rate would cause the particles to interact to form “bridge” structures, forming larger particle inclination angles and resulting in a larger void fraction of the packing.

DEM simulation of vibrated packing densification of mono-sized regular octahedral particles

The densification of mono-sized regular octahedral particles under vibration is simulated by a DEM model. The model is validated by physical experiments. The effects of operating parameters including vibration amplitude and frequency are investigated. The obtained packing structures are characterized, and corresponding densification mechanisms are identified. The results indicate that vibration amplitude is more critical for densification compared to frequency, where a wide range of suitable amplitudes exists to realize the dense packing structures. Ordered packing structure exists in boundary region. The central region possesses good particle position randomness and orientation randomness, and the packing density for poured packing (initial loose packing) and vibrated packing (dense packing) in the central region are 0.670 and 0.684, respectively. During densification, contacts and constraints between particles decrease, and the stress within the structure becomes larger. The typical arrangement of neighboring particles is close to but not perfect face to face (F–F) contact. Particles in the boundary region experience more rotations and can form local ordered structures. These structures prevent the relative movement of individual particles but favor their movement as a whole. Particles in the central region have relatively little movement and rotation. The ordered structures formed at boundary is difficult to extend to the central region due to the restricted change of particle contact conditions.

Molecular dynamics simulations of Piezo1 channel opening by increases in membrane tension

Piezo1 is a mechanosensitive channel involved in many cellular functions and responsible for sensing shear stress and pressure forces in cells. Piezo1 has a unique trilobed topology with a curved membrane region in the closed state. It has been suggested that upon activation Piezo1 adopts a flattened conformation, but the molecular and structural changes underpinning the Piezo1 gating and opening mechanisms and how the channel senses forces in the membrane remain elusive. Here, we used molecular dynamics simulations to reveal the structural rearrangements that occur when Piezo1 moves from a closed to an open state in response to increased mechanical tension applied to a model membrane. We find that membrane stretching causes Piezo1 to flatten and expand its blade region, resulting in tilting and lateral movement of the pore-lining transmembrane helices 37 and 38. This is associated with the opening of the channel and movement of lipids out of the pore region. Our results reveal that because of the rather loose packing of Piezo1 pore region, movement of the lipids outside the pore region is critical for the opening of the pore. Our simulations also suggest synchronous flattening of the Piezo1 blades during Piezo1 activation. The flattened structure lifts the C-terminal extracellular domain up, exposing it more to the extracellular space. Our studies support the idea that it is the blade region of Piezo1 that senses tension in the membrane because pore opening failed in the absence of the blades. Additionally, our simulations reveal that upon opening, water molecules occupy lateral fenestrations in the cytosolic region of Piezo1, which might be likely paths for ion permeation. Our results provide a model for how mechanical force opens the Piezo1 channel and thus how it might couple mechanical force to biological response.

Naphthalimide-Based Hydrazone Derivatives: Synthesis, Mechanochromism in the Solid State and Response to Ions in Dilute Solutions.

Molecules showing mechanochromic luminescence (MCL) are promising for use in the in the fields of sensing and probes. We report the design and synthesis of new naphthalimide-based hydrazone derivatives, NI-TPE and NI-3BA. Both the luminogens are weakly emissive with s Φf =0.3 % and 0.5 % respectively when aggregated in amorphous states as strong π-π stacking and intermolecular interaction prevent luminescence. On the contrary, in the crystalline state, single crystal analysis of two derivatives shows that nonradiative decay is reduced or inhibited by molecular stacking modes and intermolecular interactions. Increases of fluorescence emission intensity to s Φf =5.5 % and 6.0 % upon solvent evaporation are attributed to weak π-π overlapping and hydrogen bonding (N-H ⋅⋅⋅ O, distance 2.99 Å), which are beneficial to the formation of molecules with a loose packing. At the same time, the packing modes that the two derivatives adopt in the crystal lattice are destroyed to result in a low solid-state fluorescence quantum yield and a bathochromic shift of 23-25 nm upon grinding. All these factors cause the two derivatives show an unusual "turn off" MCL phenomenon. The fluorescence emission, its pH reversibility, and selective response to fluoride and acetate ions of up to 91-93 % in dilute solutions were also demonstrated.

An average model for disordered sphere packings

In this paper, an assembly of disordered packings is considered as a suitable set of packing cells of ordered spheres. In consequence, any of its parameters can be obtained by averaging the values of the set. Namely, the density of a packing of ordered spheres is described by two variables: the angle of the base, and the angle of the inclined edge of the associated parallelepiped. Then, the density of a packing of disordered spheres is obtained by averaging the angle of the base, and the subsequent averaging of the other angle, according to the kind of strain induced by the experiment. The average packing yields the density limits of loose sphere assemblies achieved by a process of fluidization and sedimentation in air, in water, and in viscous liquid at zero gravitational force. It also models the close sphere assemblies shaped by gentle tapping, vertical shaking, horizontal and multidirectional vibrations. The theory allows to elucidate the mechanism of each of the limits, as, for example, the metastable columns of spheres in the loosest packing, as well as the random close packing, and crystallization. The limits obtained coincide very well with the published experimental, numerical and theoretical data.

Incorporation of N-phenyl in poly(benzimidazole imide)s and improvement in H2O-absorbtion and transparency.

5-Amine-2-(4-amino-benzene)-1-phenyl-benzimidazole (N-PhPABZ) was successfully synthesized and polymerized with 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) to obtain a novel N-phenyl-poly(benzimidazole imide) (N-Ph-PBII). The successful incorporation of N-phenyl addressed the issue of high H2O-absorption of traditional PBIIs while retained the superheat resistance property. The resulting N-Ph-PBII possessed a high glass-transition temperature (Tg) up to 425 °C and a low affinity for water of 1.4%. Furthermore, the loose molecular packing and noncoplanar structures led to an increase in optical transparency for the modified PBII.

The spirobichroman-based polyimides with different side groups: from structure-property relationships to chain packing and gas transport performance.

Spirobichroman-based polymers with high gas permeability and selectivity are promising for their applications as membranes in gas separation. In this study, three spirobichroman-based polyimides (PIs; 6FDA-FH, 6FDA-DH, and 6FDA-MH) were synthesised by the polyreaction between diamines containing different substituents (benzene ring, pyridine ring, and methyl group) and 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA). The physical properties, gas transport behaviour, d-spacing, dihedral angle of molecules, and fractional free volume of the PIs were investigated through experiments and molecular simulations. The PIs exhibited excellent thermal stability and good solubility in common organic solvents. The gas permeability of the PIs was investigated; the results highlighted the critical role of the substituents in the enhancement of the gas separation performance of polymer membranes. Detailed analysis of the PIs showed that 6FDA-FH exhibits the highest gas permeability. This can be ascribed to the loose packing of the polymer chain owing to the increased dihedral angle between the two planes. However, the methyl substituent in 6FDA-MH disrupts the polymer chain packing rather than changing the dihedral angle between the two planes, thus enhancing the gas permeability of 6FDA-MH. Furthermore, 6FDA-DH exhibited the highest CO2/CH4 selectivity, which is attributed to the CO2 affinity of the polymer containing the pyridine unit.

Effects of mechanical constraint on thermally induced reverse martensitic transformation in granular shape memory ceramic packings

Zirconia-based ceramics exhibit shape memory and superelastic effects based on the reversible martensitic transformation between tetragonal and monoclinic crystal structures. In the form of granular packings, these shape memory ceramics can be scaled up for bulk applications despite their intrinsic brittleness, while displaying drastically different transformation characteristics than the monolithic counterparts. Here, we present a comparative study to understand the thermally induced reverse martensitic transformation in granular packings and the influence of mechanical constraints. This study employs ZrO2–CeO2 shape memory ceramics of the same composition but with different degrees of mechanical constraints. The explored material forms include loose and jammed granular packings, themselves consisting of polycrystalline or single crystal particles, as well as sintered bulk polycrystals. Except for the latter, no endothermic peak is observed in the heat flow measurement of the reverse transformation process. This unusual behavior is shown to stem from the weak inter-particle mechanical constraint and the transformation heterogeneity among individual particles, rather than stress relaxation or particle rearrangement. To compare, conspicuous endothermic peaks only appear in bursting-type transformations under a strong mechanical constraint. For granular packings, the intra-particle mechanical constraint does not affect the presence of any endothermic peaks in thermal reversion but can influence the austenite start temperature.

Heat transfer enhancement by surface vortex generators. New basic mechanisms and industrial technologies

New energy effective surfaces structured by vortex generators – inclined oval-trench dimples (OTDs) – and the controlling physical mechanisms of heat transfer enhancement are explored. The narrow 7 × 1 channel with a package of one-row OTDs at Re=104.is considered. Turbulent heat transfer is studied at the channel length where the flow is steady. The OTD width is 1, its depth is 0.3, its length is 7 0.3, and its dimple step is 6. The rounding radius of the dimple edge is 0.2. The influence of the OTD inclination angle θ on the mechanisms of separated flow intensification and heat transfer enhancement in the dimple is analyzed when θ is varied from 42° to 55.5°. The optimal angle θ of order 53° is revealed, at which the relative thermal performance is close to 70% for the heated wall with a very loose packing of dimples equal to 0.235. The optimal angle θ, at which the highest thermal and hydraulic performance (THP=0.175) has been achieved, appears to be close to 47°. The maximum local value of the 4.5–5-fold relative heat transfer growth coincides with that of static pressure in the separated flow zone on the section, where relative friction grows, after it has reached its minimum value up to -4.5.

A Multi‐Stimuli‐Responsive Molecule with Responses to Light, Oxygen, and Mechanical Stress through Flexible Tuning of Triplet Excitons

AbstractMultifunctional stimuli‐responsive materials have attracted tremendous attention because of their great potential in a variety of applications. However, conventional stimuli‐responsive emitting materials are limited to single‐stimulus response with rare attention paid to triplet excitons controlling. Herein, a multi‐stimuli‐responsive molecule (SPh‐TP) with tuning of triplet excitons is reported. During illumination, the SPh‐TP crystals with unique twisted structure and loose packing have a high probability to contact with neighboring oxygen atoms, followed by the occurrence of triplet–triplet energy transfer, and thus showing a photosensitive property. Meanwhile, the photosensitive property is also observed for the crystalline sample in vacuum, which is associated with oxygens locked in crystal pores. Upon mechanical stress, the crystalline morphology is broken and the molecules become more planar with tighter stacking, revealing its mechanochromism. In comparison to the crystalline sample, the ground sample can respond to light with different rates depending on the ratio of oxygen. This multi‐stimuli‐responsive material shows potential applications in oxygen detection and double‐encryption of information.