Loose Packing Research Articles

Synthesis and Excited-State Properties of Donor-Acceptor Azahelical Coumarins.

A set of three donor-acceptor azahelical coumarins (DA-AHCs), namely, H-AHC, Me-AHC, and Ph-AHC, were rationally designed and synthesized, and their excited-state properties were comprehensively investigated. All three DA-AHCs are shown to display very high fluorosolvatochromic shifts as a result of significant intramolecular charge transfer in their excited states. The para-quinoidal forms of the latter apparently contribute predominantly to large dipole moments in their excited states. By virtue of the fact that these helical systems structurally incorporate a highly fluorescent coumarin dye, they exhibit high quantum yields in both solution and solid states. Indeed, their emission behaviors in the crystalline media are shown to be remarkably correlated with their respective crystal packings. Incisive analyses demonstrate (i) strengthening of hydrogen bonding in the excited state promotes quenching (H-AHC), (ii) efficient crystal packing promotes high emission (Me-AHC) by precluding deactivations via vibrational motions, and (iii) loose crystal packing contributes to excited-state deactivation to account for low quantum yields of emission (Ph-AHC).

Ultraslow Settling Kinetics of Frictional Cohesive Powders.

Using discrete element method simulations, we show that the settling of frictional cohesive grains under ramped-pressure compression exhibits strong history dependence and slow dynamics that are not present for grains that lack either cohesion or friction. Systems prepared by beginning with a dilute state and then ramping the pressure to a small positive value P_{final} over a time τ_{ramp} settle at packing fractions given by an inverse-logarithmic rate law, ϕ_{settled}(τ_{ramp})=ϕ_{settled}(∞)+A/[1+Bln(1+τ_{ramp}/τ_{slow})]. This law is analogous to the one obtained from classical tapping experiments on noncohesive grains, but crucially different in that τ_{slow} is set by the slow dynamics of structural void stabilization rather than the faster dynamics of bulk densification. We formulate a kinetic free-void-volume theory that predicts this ϕ_{settled}(τ_{ramp}), with ϕ_{settled}(∞)=ϕ_{ALP} and A=ϕ_{settled}(0)-ϕ_{ALP}, where ϕ_{ALP}≡.135 is the "adhesive loose packing" fraction found by Liu etal. [Equation of state for random sphere packings with arbitrary adhesion and friction, Soft Matter 13, 421 (2017)SMOABF1744-683X10.1039/C6SM02216B].

Void fraction for random loose packing of multi-size mixed cylindrical particles

Most particles in industrial applications are mixed cylindrical particles with the same diameter and different aspect ratios (ARs). In this study, the void fraction of packed bed with binary, ternary, quaternary, and quintuple mixtures of cylindrical particles is explored by discrete element method (DEM). The concept of equivalent AR is proposed for predicting void fraction of packing of mixed cylindrical particles based on previous research. Results show that (1) the correlation between equivalent AR and void fraction is higher when ARVave is used, and the prediction error is only −0.57%–6.21%. (2) Better prediction results can be obtained using ARNave in some cases, such as for packing of mixed cylindrical particles with small AR intervals and wide distribution. However, the prediction results are unsatisfactory in the case of larger AR intervals and cylindrical particles with AR = 1. (3) The R2 can be increased to 0.983 when corrected by multiplying by 96.87%.

AIE activity, mechanochromic property and solvent inclusion of two β-diketones with tetraphenylethylene unit

Highly twisted molecular conformation easily leads to the loose molecular packing and big voids, which are desirable for mechanochromism and solvent inclusion. Here, TPE-BF and TPE-BT with highly twisted molecular conformation were designed and synthesized by α-substitution of two β-diketonates. TPE-BF and TPE-BT show similar aggregation-induced emission activity, but different mechanochromism. Subsequently, the corresponding internal mechanism are analyzed and discussed in-depth by XRD, DSC, fluorescence lifetime, crystal analysis and theoretical calculation. Compared with crystal TPE-BF, crystal TPE-BT exhibits more obvious mechanochromism (red shift of 12 nm) before/after grinding, which is attributed to EtOAc inclusion and different intermolecular interactions and stacking. Furthermore, wavelength shifts of TPE-BF and TPE-BT do not exceed 35 nm after phase transition from crystalline state to amorphous state. Obviously, highly twisted molecular conformations fail to bring about high-contrast mechanochromism (wavelength shift above 100 nm), whose reason should be the suppressed intermolecular π-π interactions and overlap before/after grinding. Combined with previous research results of our laboratory, the luminogens forming solvent inclusion generally have twisted molecular conformation, and similar structural fragment with solvent molecule, which will provide a potential design strategy for selective solvent inclusion.

End Group Nonplanarization Enhances Phototherapy Efficacy of A-D-A Fused-Ring Photosensitizer for Tumor Phototherapy.

Enhancing the phototherapy efficacy of organic photosensitizers through molecular design is a fascinating but challenging task. Herein, we propose a simple design strategy to first realize the generation of superoxide anion radical (O2•-) by A-D-A fused-ring photosensitizers. Through replacing one cyano group of traditional end group with an ester group, we designed a novel nonplanar end group (A unit) to synthesize a novel A-D-A photosensitizer F8CA. In a comparison with its counterpart F8CN with the traditional end group, F8CA displays more loose packing and larger spin-orbit coupling constants. The F8CA nanoparticles showed higher photodynamic activities with the generation capability of singlet oxygen (1O2), hydroxyl radical (•OH), and O2•-, while F8CN nanoparticles could only generate 1O2 and •OH. In addition, F8CA nanoparticles still remain high photothermal conversion efficiency (61%). As a result, F8CA nanoparticles perform well in hypoxia-tolerant tumor phototherapy. This study brings an effective design thought for A-D-A photosensitizers.

Crystal packing and photoelectric property of bis(2-picolyl)amine-functionalized triarylborane and its complexes

Organic crystalline materials are attracting increasing interest due to their promising applications in the fields of nonlinear optics (NLO), organic lasers, optical waveguides, and light-emitting transistors. In this paper, a photoelectric molecule QB was constructed through combining an electron-withdrawing unit, a triarylborane, and a metal-ligand unit of bis(2-picolyl)amine. The crystallization behavior and crystalline photoelectric properties of QB and its complexes were thoroughly studied. This compound exhibited polymorphism, and a green emitting block-like crystal and blue-emission lamellar crystal were obtained, respectively. Their different photoluminescence mechanisms were clarified through X-ray crystallographic analysis and theoretical calculations. Furthermore, the single-crystal structures of the complexes of QB coordinating with KCN and Zn(ClO4)2 were also determined. Crystal QB-KCN emitted strong blue fluorescence at 445 nm, owing to the formation of rigid 2-to-2 adduct, which could effectively suppress non-radiative transitions. Crystal QB-Zn(ClO4)2 showed very weak cyan emission due to its loose molecular packing. The electrochemical results illuminated that the metal coordination can effectively affect the electron-withdrawing ability of conjugated triarylborane, and further affect the monomolecular luminescent properties due to the intramolecular charge transfer. We believe that polymorphism and metal coordination are available means to obtain excellent crystalline photoelectric materials.

Evolution of the structure of meat protein particles at the oil–water interface facilitates the ultra-long storage stability of high internal pickering emulsion

Myosin, a myofibrillar protein, acts as a key meat emulsifying agent. Actin, tropomyosin, and troponin are also myofibrillar proteins, however, the role of these proteins in the emulsification process remains unclear. In this study, we aimed to determine the meat emulsifying capacities of actin, tropomyosin, and troponin. We fabricated meat protein particles (MPs) with actin, tropomyosin and troponin, under different pH conditions. Under acidic conditions, in the bulk phase solution, protein aggregates with block-like characteristics were formed by the hydrophobic interaction, which disassembled and adsorbed on the surface of the oil droplets during the emulsification process. During the emulsion storage process, the meat particle stabilizer was transformed into a structural agent with polygonal network characteristics, which elicited changes in emulsion droplet morphology (to loose, close, and ultra-close packing). This resulted in the following emulsion properties: ultra-long stability and good rheological properties. However, this phenomenon was not observed under neutral and alkaline conditions, in high internal Pickering emulsion (HIPPEs) constructed of aggregates dominated by coarse beaded characteristics. Overall, protein particles with different structural characteristics, in bulk phase solution, influence the structural evolution and properties of HIPPEs. The study findings provide scientific guidance for meat protein hierarchical utilization in the production of emulsion-based food products, under high efficiency and low-cost conditions.

Near-Infrared Piezochromism from an o-Carborane Dyad: Boron Clusters Facilitating a Wide-Range Redshift and High Sensitivity.

Piezochromic materials, which exhibit a fluorescence response with large emission spectral shifts and high sensitivity, may be useful in important applications, but there have been few reports of such organic luminophores. Herein, we report a new high-sensitivity piezochromic material based on the incorporation of an o-carborane unit, which exhibits aggregation-induced emission properties. In a high-pressure experiment, compared to carborane-free MTY, which exhibits an emission spectral shift of 75 nm and a sensitivity of 19.1 nm ⋅ GPa-1 , the o-carborane dyad MTCb shows a larger emission wavelength difference of 131 nm and a higher sensitivity of 32.8 nm ⋅ GPa-1 , demonstrating a performance that ranks among the best of organic piezochromic materials reported thus far. MTCb molecules adopt a J-aggregated pattern and have relatively loose molecular packing in the crystalline state. Interestingly, nonconjugated spherical carborane can disrupt the π-π interactions between adjacent molecules during compression, which results in excellent piezochromic performance.

Evolution of Protein Assemblies Driven by the Switching of Interplay Mode.

A protein assembly with the ability to switch interplay modes of multiple driving forces has been achieved. Although biomolecular systems driven by multiple driving forces have been exploited, work on such a protein assembly capable of switching the interplay modes at nanoscale has been rarely reported so far as a result of their great fabrication challenge. In this work, two sets of driving forces such as ligand-ligand interaction and protein-protein interaction were leveraged to antagonistically underpin the multilayered stackings and trigger the hollow evolution to afford the well-defined hollow rectangular frame of proteins. While these protein frames further collapsed into aggregates, the ligand-ligand interactions were weakened, and the interplay of two sets of driving forces thereby tended to switch into synergistic mode, converting the protein packing mode from porously loose packing to axially dense packing and thus giving rise to a morphological evolution toward a nanosized protein tube. This strategy not only provides a nanoscale understanding on the mechanism underlying the switch of interplay modes in the context of biomacromolecules but also may provide access for diverse sophisticated biomacromolecular nanostructures that are historically inaccessible for conventional self-assembly strategies.

A geometric probabilistic approach to random packing of hard disks in a plane.

In this paper, the random packing fraction of hard disks in a plane is analyzed, following a geometric probabilistic approach. First, the random close packing (RCP) of equally sized disks is modelled. Subsequently, following the same methodology, a simple, statistical geometric model is proposed for the random loose packing (RLP) of monodisperse disks. This very basic derivation of RLP leads to a packing value (≈0.66) that is in very good agreement with values that have been obtained previously for 2D disk packings. The present geometrical model also enables a closed-form expression for the contact (coordination) number as a function of the packing density at different states of compaction. These predictions are thoroughly compared with empirical and simulation results, among others the Rényi parking model, yielding good agreement.

Multifunctional Fluorescent Materials with Reversible Mechanochromism and Distinct Photochromism

AbstractIt is extremely significant and desirable to integrate the fascinating mechanochromism and photochromism in one simple molecule. Herein, two intriguing cyanostilbene‐containing triphenylamine (TPA)/tetraphenylethylene (TPE) derivatives (Z‐TPA‐MB and Z‐TPE‐MB) are elaborately designed, which not only display excellent aggregation‐induced emission (AIE) properties with high solid‐state fluorescence quantum yields (60.9% and 63.8%) but also exhibit reversible and high contrast mechanochromism and distinct photochromism. The powders of Z‐TPA‐MB and Z‐TPE‐MB both exhibit large red‐shift under mechanical stimulation based on the highly twisted conformation and the resulting loose packing mode, accompanied by significant changes in apparent and fluorescent colors. Meanwhile, their solid‐state fluorescence can be reversibly switched between crystalline and amorphous structures through alternating grinding and solvent fuming, exhibiting good fatigue resistance. In addition, the molecules also exhibit distinct dual‐mode photochromic behaviors owing to the presence of cyanostilbene moieties: under 420/365 nm light irradiation, the fluorescence of which decreases in solution owing to the photo‐isomerization, while decreases and blue‐shifts in the aggregated state owing to the photodimerization reactions. The reversible, tractable, and high‐contrast mechanochromism and distinct photochromism of the cyanostilbene‐containing molecules endow them with excellent application prospects in the field of rewritable papers and photo‐patterning.

Achieving over 1,000 mW cm−2 Power Density Based on Locally High‐Density Cross‐Linked Polybenzimidazole Membrane Containing Pillar[5]arene Bearing Multiple Alkyl Bromide as a Cross‐Linker

AbstractCross‐linking is widely accepted as an effective method to improve the mechanical strength and durability of phosphoric acid (PA) doped polybenzimidazole (PBI) membranes. However, the cross‐linked membranes generally exhibit compromised overall performance since their compact network structures decrease the free volumes of membranes, leading to poor proton conductivity. In this study, a locally high‐density cross‐linked polybenzimidazole network based on pillar[5]arene bearing multiple alkyl bromide is constructed for the first time to achieve high proton conductivity, desired mechanical properties, and excellent fuel cell performance. The pillar[5]arene‐cross‐linked network considerably enhances the mechanical strength of membrane (14.6 MPa), particularly with high PA uptake, and provides loose PBI chain segment packing to retain PA (315.9%). Surprisingly, the pillar[5]arene‐cross‐linked PBI membrane displays a high‐power density of 1,084.1 mW cm−2 at 180 °C and 0.6 mg cm−2 Pt loading without backpressure and humidification, that is the highest value reported in cross‐linked membranes for high‐temperature proton exchange membrane fuel cells.

Shear transformations in metallic glasses without excessive and predefinable defects

Plastic flow in metallic glasses (MGs) is known to be mediated by shear transformations (STs), which have been hypothesized to preferentially initiate from identifiable local "defect" regions with loose atomic packing. Here we show that the above idea is incorrect, i.e., STs do not arise from signature structural defects that can be recognized a priori. This conclusion is reached via a realistic MG model obtained by combining molecular dynamics (MD) and Monte Carlo simulations, achieving liquid solidification at an effective cooling rate as slow as 500 K/s to approach that typical in experiments for producing bulk MGs. At shear stresses before global yielding, only about 2% of the total atoms participate in STs, each event involving typically ~10 atoms. These observations rectify the excessive content of "liquid-like regions" retained from unrealistically fast quench in MD-produced glass models. Our findings also shed light on the indeterministic aspect of the ST sites/zones, which emerge with varying spatial locations and distribution depending on specific mechanical loading conditions.

Mechanical Force-Induced Blue-Shifted and Enhanced Emission for AIEgens.

Mechanochromic (MC) luminescence of organic molecules has been emerging as a promising smart material for optical recording and memory devices. At the same time, pressure-induced blue-shifted and enhanced luminescence are rarely reported now. Herein, a series of cyanostilbene-based AIEgens with different substituents were synthesized to evaluate the influence of morphology transformation and push-pull electronic effect on the MC luminescence. Among these luminophores, compound 1 with one cyano group and diethylamino group was more susceptible to mechanical stimuli and obtained blue-shifted and enhanced fluorescence in response to anisotropic grinding. Powder X-ray diffraction patterns indicated that the MC behaviors were ascribed to the solid-state morphology transition from crystal-to-crystal. Analysis of crystal structures revealed that loose molecular packing is a key factor for high high-contrast MC luminescence. The smart molecular design, together with the excellent performance, verified that luminophores with twisted structures are ideal candidates for MC luminogens.

Facile Preparation of Macro-Microporous Thorium Oxide via a Colloidal Sol-Gel Route toward Safe MOX Fuel Fabrication.

The identification of new colloidal sol-gel routes for the preparation of actinide oxides, which have a homogeneous and accessible porosity that can easily be impregnated by any concentrated actinide solution, opens new perspectives for the preparation of homogeneous nuclear fuel for minor actinide transmutation. This homogeneity allows us to avoid "hot spot" formation due to the local accumulation of more fissile elements. Here, we report the preparation of macro-microporous ThO2 materials by a colloidal sol-gel route. Using a thorium salt with 6-aminocaproic acid as a complexing agent at a controlled pH, we were able to pilot the condensation of thorium hydroxo species forming colloids of tuned nanometric size and thus the sol stability. After a freeze-drying process to concentrate colloids and a thermal treatment allowing complexing agent removal and macroporosity formation by a brutal gas release during combustion, a loose packing of ThO2 nanoparticles with an ordered distribution of interparticular porosity and a fraction of nanometric crystallites, whose size depends on the initial colloidal size, were obtained. The sols, pastes, and final materials were characterized by small- and wide-angle X-ray scattering to determine the colloidal size and the final structure of the materials, which was also confirmed by transmission electron microscopy. The most promising material was finally successfully impregnated by a simulating minor actinide solution and thermally treated to prepare a mixed actinide oxide material. This safe technology, relying on the colloidal sol-gel process and the formulation of complex fluids forming tunable precursors, opens new perspectives for the reuse of nuclear waste solutions as new fuel.

Controls of crystal shape on degassing mechanisms in crystal-rich magmas with rhyolitic groundmass melts

Understanding the mechanical effects of crystals on degassing kinetics and permeability development in silicic magmas is important for modeling eruptions and examining first order controls on eruption style. We conducted high-pressure-high-temperature isothermal decompression experiments to investigate the role of crystal shape on permeability development and pore pathway geometry. Experiments were performed on hydrous rhyolitic glass (76.3 wt.% SiO2) seeded with variable amounts of equant (aspect ratio ∼1.8 ± 0.6) corundum crystals and elongate (aspect ratio ∼10 ± 5.5) wollastonite crystals to approximate natural phenocryst and microphenocryst/microlite populations, respectively. We measured total porosity, connected pore volume and permeability directly from the experimental charges by applying Archimedes' principle to determine bulk density, helium-pycnometry to measure connected porosity, and a custom-made permeameter to measure permeability. The experimental samples developed permeability at a critical melt porosity (ϕc-melt, above which degassing is enhanced due to bubble coalescence) of ∼55 vol.% vesicles for the corundum experiments and ∼48 vol.% for the wollastonite-bearing experiments; these values are considerably lower than the ϕc-melt>63 vol.% for prior crystal-free experiments (Lindoo et al., 2016; deGraffenried et al., 2019). Critical porosity is reduced when crystals comprise at least ∼20 vol.%, regardless of shape. Connected porosity increases and average bubble size decreases with increasing abundance of elongate wollastonite crystals, explained by the onset of yield strength behavior induced by loosely touching crystal frameworks that form at decreasing crystallinities with increasing elongation of crystals comprising the network. When the population of high-aspect-ratio crystals reaches random loose packing, the resulting reduction in interstitial melt available for unimpeded bubble expansion forces the bubbles to connect at lower total vesicularity. It therefore seems likely that crystal-bearing intermediate magmas experience an abrupt increase in degassing efficiency when crystallinity attains random loose packing. In hydrous magmas, the efficiency of decompression-driven degassing and resulting formation of anisotropic groundmass crystals is controlled by magma composition and decompression rate. Enhanced gas loss in slowly ascending (and crystallizing) magma may aid the development of dense conduit plugs, thus increasing the possibility of violent Vulcanian explosions.

All-in-One Theranostic Platforms: Deep-Red AIE Nanocrystals to Target Dual-Organelles for Efficient Photodynamic Therapy.

Aggregation-induced emission (AIE) nanoparticles have been widely applied in photodynamic therapy (PDT) over the past few years. However, amorphous nanoaggregates usually occur in their preparation, resulting in loose packing with disordered molecular structures. This still allows free intramolecular motions, thus leading to limited brightness and PDT efficiency. Herein, we report deep-red AIE nanocrystals (NCs) of DTPA-BS-F by following the facile method of nanoprecipitation. It is observed that DTPA-BS-F NCs possess not only a high photoluminescence quantum yield value of 8% in the deep-red region (600-850 nm) but also an impressive reactive oxygen species (ROS) generation efficiency of up to 69%. Moreover, DTPA-BS-F NCs targeting dual-organelles of lysosomes and nucleus to generate ROS are also achieved, thus boosting the PDT effect in cancer therapy both in vitro and in vivo. This work provides high-performance AIE NCs to simultaneously target two organelles for efficient photodynamic therapy, indicating their promising application in all-in-one theranostic platforms.

Depositional controls on diagenetic evolution of the Lower Cretaceous Wealden Sandstones (Wessex Basin, southeast England)

Depositional processes hold crucial controls on the diagenetic processes, events and evolution in sedimentary basins. Using the example of non-marine, Lower Cretaceous Wealden Sandstones from Wessex Basin in southeast England, this study reveals the depositional controls on diagenetic evolution in a sedimentary basin. Seventy-four surface samples, from 6 field locations across the Wessex Basin in Dorset and Isle of Wight were subjected to laboratory analyses such as optical petrography, scanning electron microscopy and Quantitative Evaluation of Minerals by Scanning Electron Microscopy analysis. The degree of compaction in the Wessex Basin sandstones includes moderate packing with most grains in a mix of point and long contact, with rare grains displaying concave-convex or non-grain contact and a loose packing dominated by non-grain contacts, with minor point and long contacts. The authigenic mineral phases identified in the sandstones are quartz, kaolinite, calcite and halite in decreasing abundance. The dissolution of felspars observed in the Wessex Basin sandstones possibly provided the main source of silica for the quartz overgrowths, with silica sources adjacent to the site of cementation. The small amount of quartz overgrowths may have formed during shallow burial. The partial dissolution of quartz observed in the Wessex Basin sandstones is considered likely to be the result of flushing of organic-compound rich waters derived from shale interbeds, under low temperature conditions (c. 25–50 °C). The precipitation of authigenic minerals within the Wessex Basin had a limited impact on the porosity and permeability of sandstones. Detrital mineralogy appears to be the main depositional control on diagenesis and may also explain the low abundance of authigenic kaolinite in the Wessex Basin. Similarly, the shallow burial depth of the sandstones is considered to be the main factor inhibiting more pervasive quartz cementation within the basin.

Experimental and numerical investigation of the compression and expansion of a granular bed of repelling magnetic disks

We studied experimentally and numerically the compaction and subsequent expansion dynamics of a granular bed composed of cylindrical repelling magnets contained in a two-dimensional cell. The particles are firstly compressed vertically with a piston at a given strain rate until a maximum force is reached. The piston is then removed at the same strain rate while the bed expands due to the magnetic repulsion of the particles. In the experiments, two different initial configurations were generated, a standard and a loose packing bed. The standard packing bed was simulated, and modelling the dry friction between the magnetic particles and the walls of the cell was crucial for the correct description of the compression and expansion dynamics. We found that the force acting on the piston increases continuously and exponentially with the piston stroke during compression, being very sensitive to the initial packing conditions of the bed. In contrast, a history-independent exponential decrease of this force was found during the expansion phase. The hysteresis in the system was quantified in terms of the average displacement of the particles. The continuous compression contrasts with the sudden force drops observed during the compaction of granular materials with direct particle-particle contacts, where stick-slip motion is induced by friction and force chain breakage. Moreover, we found that the short range of magnetic interaction induces density inversion and crystallization of the system. Our results can be useful to develop a new kind of magnetic granular dampers.Graphical abstract

Effect of aggregate morphology characteristics on the voidage of aggregate loose packing based on 3D discrete element method

• The aggregate model with real morphology was generated by Clump method. • A 3D aggregate database considering real morphology was established. • The void spatial distribution of aggregate loose packing was studied. Reducing the voidage of aggregate loose packing can improve the workability of concrete, and aggregate morphology directly affects the voidage of aggregate loose packing. This paper combined 3D laser scanning and digital image processing (DIP) technology to perform statistical analysis on aggregate morphology characteristics such as sphericity, flatness, elongation and angularity index. A 3D aggregate database was built using the structured query language (SQL). On this basis, the discrete element model of loose packing was established by the gravity falling method (GFM), considering the natural morphology of aggregates; and the effect of aggregate morphology characteristics on the voidage and void spatial distribution of loose packing under different gradations was quantitatively studied. The results show that the voidage of aggregate loose packing decreases as aggregate sphericity increases and increases with the increase in angularity index. The effect of sphericity on the voidage of aggregate loose packing is about five times that of angularity index. In addition, the voidage in aggregate packing is arranged in Z-shape, and the larger the aggregate sphericity or, the smaller the angularity index, the more uniform the voids in the aggregate packing are distributed.