Packing State Research Articles

Effect of Mo addition on nanoindentation creep behavior of FeCoBSiNb bulk metallic glasses

Novel Fe52Co20-xB20Si4Nb4Mox (x = 0–5) bulk metallic glasses with a diameter of 2 mm are successfully prepared by vacuum suction casting and the effect of Mo addition on their nanoindentation creep behavior is studied. Through a differential scanning calorimetry and creep compliance spectral analysis, it is found that the addition of a small amount of Mo increases the enthalpies (ΔH) and free volumes of the alloys. These factors stimulate the rearrangement of the atomic structures of the alloys and induce the adjustment of their internal structure, resulting in a relatively loose atomic packing state that allows the alloys to provide a continuous response to stress during creep deformation. By analyzing the unloading and load holding sections on the load-displacement curves, it is shown that the hysteresis of deformation induces the displacement jump phenomenon and the amplitude of the jump is inversely proportional to the equivalent stress. The larger the equivalent stress, the less obvious the displacement pop-out phenomenon. The changes in strain rate sensitivity exponent (m) and hardness are also studied. Combined with a delay spectral analysis, it is found that a 5% Mo addition significantly improves the creep resistance of the alloys.

Effect of Cement and Bitumen Emulsion on the Drying and Film Formation of Bitumen Emulsion Paste

To obtain a bitumen emulsion paste with a good bitumen film structure and rapid drying rate, the effect of cement content, cement type, and emulsion type on the drying and film formation of bitumen emulsion paste was studied. The drying and film formation mechanism of emulsion was employed to study the drying curve of bitumen emulsion paste. Results indicate that the drying and film formation process of bitumen emulsion paste can be divided into three stages. The solid volume fraction of the beginning of the final stage (ϕ2) and the maximum particle volume fraction (ϕm) are proposed to evaluate the drying and film formation quality of bitumen emulsion paste. Higher values of ϕ2 and ϕm indicate a denser particle packing state and lower residual water content of the final stage, which are beneficial to the drying and film formation quality of bitumen emulsion paste. The ϕ2 and ϕm of bitumen emulsion paste differ slightly with the increasing content of ordinary portland cement. However, these quantitative indexes vary significantly with changing bitumen emulsions with different values of ϕ2 and ϕm. Compared with ordinary portland cement, sulfoaluminate cement can lead to a noticeable decrease in ϕ2 and ϕm; thus, its addition is harmful to the film structure of bitumen emulsion paste. Overall, to obtain a bitumen emulsion paste with a good bitumen film structure and rapid drying rate, a bitumen emulsion with good drying and film formation quality is recommended.

Dispersibility and surface properties of hydrocortisone-incorporated self-assemblies

The ability of lipidic self-assembly systems to solubilize hydrophobic drugs allows for the enhancement of the delivery of poorly water-soluble drugs. Hydrophobic molecules are incorporated into the lipidic part of the self-assemblies, which alters their structure and surface properties, affecting their dispersibility. The effects of the incorporation of hydrophobic molecules on the structure of aqueous dispersions of amphiphiles should be precisely investigated. However little work has been done regarding the effects of drug incorporation on the surface and internal properties of lipidic self-assemblies. Herein, the effects of the incorporation of the hydrophobic drug, hydrocortisone (HC), on dispersions composed of monoolein (MO), oleic acid (OA), and Pluronic F127 (F127) are investigated. Via Raman spectroscopic analysis, HC was shown to be homogeneously distributed in the particles. This revealed that the incorporated HC had minimal effects on the lipid packing state in the self-assemblies. The HC-incorporated particles were dispersive for at least 24 h, although aggregation might happen after long incubation (couple of days). Cryogenic transmission electron microscopy images revealed particles with altered inner structure after HC incorporation. HC increased the size of the particles, suggesting that HC could reorganize the molecules in the dispersions. The absolute zeta potential values of the particles decreased by increasing the HC loading, suggesting an increased hydrophobicity of the HC-loaded particles. Laurdan fluorescence analysis revealed that the localized polarity of the dispersions turned to be more hydrophobic with increased HC concentrations. These results suggest that hydrophobic drugs, like HC, certainly influence the surface properties and inner structure of the self-assemblies, resulting in the changes in the particles’ dispersibility. The characterization method using fluorescent probe-based analysis and Raman spectroscopy is effective in revealing how the physicochemical properties of the self-assemblies contribute to understanding the dispersibility of nanocarriers encapsulating hydrophobic drugs.

Numerical Investigation of Aggregate Segregation of Superpave Gyratory Compaction and Its Influence on Mechanical Properties of Asphalt Mixtures

In the laboratory, there are significant differences in mechanical properties of asphalt mixtures with the same size gradation and asphalt binder, which is not conducive to evaluating and designing the pavement structure accurately. Meanwhile, the influence of aggregate segregation in height on the mechanical properties of asphalt mixtures is unclear. This study developed a new method to generate a three-dimensional (3D) model of the real composition and aggregate shape to characterize the aggregate segregation during Superpave gyratory compaction (SGC). The graphic segregation index (GPSI) is employed to assess the mixing degree of coarse aggregate and asphalt mortar within spatially variable specimens [i.e., Superpave-13, stone mastic asphalt (SMA-13), and open-graded asphalt friction course (OGFC-13) mixtures]. The results reveal that asphalt mixtures with different aggregate gradations have different compaction characteristics. For example, the increase of fine aggregates may reduce the strain energy and the average contact force during compaction. The compaction curves of the three gradation types were very different, which is attributed to different packing states and gyratory numbers. Aggregate segregation has a significant effect on micromechanical behavior. Specifically, the contact number and the proportion of strong contact force change considerably with height. In terms of segregation degree, the GPSI of OGFC-13 specimens was the highest, and the volume change of its fine particles created a leakage zone after the compaction. Additionally, this segregation had an increasing tendency with gyration numbers, and it was influenced by gradation types. Furthermore, the uniaxial compressive strength and cohesion of the Superpave-13 specimen decreased, whereas the friction angle increased with the increase of GPSI.

Long Chain Polyamides: Influence of Methylene Sequence Length and External Forces on Structural Features

AbstractCrystallographic studies on a series of even–even polyamides PA10.n (12, 14, 16, and 18) with variable methylene sequence length (n − 2) are performed. Temperature‐dependent X‐ray diffraction studies show that a triclinic α phase is the preferred polymorph after slow cooling to room temperature like in many other even–even polyamides. For PA10.12 and PA10.14 the pseudo‐hexagonal high temperature phase γ is observed between the Brill transition temperature TB and melting point TM. For both higher members a distinct Brill transition is absent below TM. The influence of temperature on the packing state of the stems during cooling is discussed and compared to related polymers. An analysis of well oriented crystalline states in annealed fibers reveals that the crystalline state achieved under ambient conditions is influenced by external forces due to small energetic differences between different α and β polymorphs. All PA10.n samples show in the fiber‐oriented state a prominent β polymorph which is dominant in PA10.12 and PA10.14 but superimposed with a significant α fraction in both higher members. The consequences of changes in the polymorphic state under the influence of external forces for crystalline states achieved under application relevant processing conditions are considered.

Rheological properties of cemented gangue backfill material based on fractal characteristics of waste coal gangue.

The study herein was intended to evaluate the rheological properties of cemented gangue backfill material (CGBM). For this purpose, the rheological test of CGBM with fractal aggregate particle size distribution was carried out, and variations of static yield stress, dynamic yield stress, and plastic viscosity were investigated as a function of fractal dimension and time. The results reveal that aggregate particle size distribution exerts a significant influence upon the rheological properties of CGBM, and with the escalation of the fractal dimension of the aggregate, the yield stress and plastic viscosity initially decline and then increase. In addition, with elapsing time, the correlation between the static yield stress and the fractal dimension of CGBM specimens increases, while the correlations between the dynamic yield stress and the plastic viscosity and the fractal dimension decrease. The relationships between rheological parameters and fractal dimensions at different times are established based on the experimental results. The influence mechanism of aggregate particle size distribution on CGBM is analyzed from the perspective of the aggregate packing state. This study can provide a basis for the ratio design of CGBM in backfill mining.

Multiple Flexibilities Trigger Luminescent Piezochromism of Closely Packed Cu(I) Coordination Polymers

AbstractThe packing states of luminescent molecules can be affected by external stimuli, leading to changes in the emission energy. Compared with the traditional organics and metal−organic frameworks, closely packed coordination polymers (CPs) have more transition types and better stabilities, respectively. However, little attention is paid to the closely packed CPs in the field of piezochromism, and much less to the corresponding optical mechanism. For studying the effect of molecular structure and the energy transfer on piezochromism, ten [Cu2I2] cluster‐based CPs with bridging aromatic ligands and terminal triphenylphosphine ligands are constructed to explore the pressure‐dependent luminescence, especially the influences of bridging ligand length, supramolecular interactions, and halogen atoms on the wavelength shift for luminescent piezochromism. In these CPs, the conformational and structural flexibilities can be effectively increased by lengthening the bridging ligand and addition of pendent methyl groups in the phosphine ligands, respectively, resulting in more obvious piezochromism. In addition, the XLCT/MLCT ratios are efficiently modulated by adjusting the flexibility of halogen electron cloud, which further affects the piezochromic property. Upon the combined effect of multiple flexibilities, a closely packed CP with a large wavelength shift (77 nm) and reversible piezochromism is found.

Theoretical and Experimental Study of Molecular Interactions of Fluralaner with Lipid Membranes.

Fluralaner is a relatively new insecticide belonging to the isoxazoline group, whose action mechanism involves the blocking of GABAA-receptors in the insect nervous system. Because of its high hydrophobicity, fluralaner could bioaccumulate and reach toxic local concentrations. Since there are no data available about the penetration and persistence of isoxazolines in biological membranes, we intend to evaluate fluralaner permanence as a pollutant by using model membranes. We used experimental and in silico models to characterize the incorporation of fluralaner into the lipid phase at different packing states. We determined its impact in the membrane structure and organization. Our results confirm that fluralaner is capable of penetrating, holding, and accumulating in the lipid membrane and provide details on its precise location and orientation. These properties would allow fluralaner to reach high local concentrations in different membranes and organs, which could be dangerous for vertebrate organisms if its handling is not properly controlled.

Thermal-controlled cellular uptake of "hot" nanoparticles.

Nanoparticles (NPs) have shown immense potential in the field of biomedical applications, particularly in NP-based photothermal therapy, which offers a remote-controlled approach to achieve precise temperature control for site-specific heating and sub-cellular tumor treatment. However, the molecular mechanisms underlying related cellular activities, such as the cellular uptake behavior of irradiated NPs in photothermal effects, remain elusive. In this study, we conducted a thorough investigation of the interaction between an irradiated NP with elevated temperature (ranging from 270 to 360 K) and a model bilayer membrane composed of DPPC or DOPC using nonequilibrium coarse-grained molecular dynamics simulations with the implicit-solvent Dry Martini force field. We observe that the interaction between a "hot" NP and a membrane is thermally regulated. In addition, the wrapping of membranes around NPs exhibits a strong dependence on the temperature of the irradiated NP, demonstrating a step-like change in behavior. This membrane wrapping effect is attributed to the heat conduction between NPs and membrane lipids, which occurs almost simultaneously with the membrane deformation and wrapping of NPs during the NP-membrane interaction process. Especially, during the process of heat conduction, a gel-to-fluid phase transition of the membrane may occur, which plays a crucial role in determining the deformation behavior of the membrane. Moreover, it is found that the membrane lipids in the two leaflets exhibit obvious and asymmetric molecular-level responses to heat flux, characterized by significant changes in packing states (e.g., the order parameter of lipid tails and area per lipid) and possible interdigitation between lipids. Furthermore, the thermal-controlled wrapping effect is tightly linked to the properties of NPs (e.g., size, NP-lipid affinity) and lipid species. Our findings are valuable for comprehending the thermal-regulated cellular internalization of NPs and offer insights into devising strategies to precisely modulate NP endocytosis by exploiting the interplay between heating and NP properties.

Constructing high-efficiency orange-red thermally activated delayed fluorescence emitters by three-dimension molecular engineering

Preparing high-efficiency solution-processable orange-red thermally activated delayed fluorescence (TADF) emitters remains challenging. Herein, we design a series of emitters consisting of trinaphtho[3,3,3]propellane (TNP) core derivatized with different TADF units. Benefiting from the unique hexagonal stacking architecture of TNPs, TADF units are thus kept in the cavities between two TNPs, which decrease concentration quenching and annihilation of long-lived triplet excitons. According to the molecular engineering of TADF and host units, the excited states can further be regulated to effectively enhance spin-orbit coupling (SOC) processes. We observe a high-efficiency orange-red emission at 604 nm in one instance with high SOC value of 0.862 cm−1 and high photoluminescence quantum yield of 70.9%. Solution-processable organic light-emitting diodes exhibit a maximum external quantum efficiency of 24.74%. This study provides a universal strategy for designing high-performance TADF emitters through molecular packing and excited state regulation.

Derivation and verification of multilevel particle packing model for Ultra-High Performance Concrete (UHPC): Modelling and experiments

This paper aims to address the conflict between gap gradation and continuous particle packing for the precise design of ultra-high performance concrete (UHPC). More exactly, a new multilevel particle packing model is proposed by deriving the modified Anderson and Andreasen (MAA) equation. The key parameters of the model are determined by Box-Behnken design method. On this basis, the dense packing states of powder and aggregate segments are achieved, and the accurate ratio of two segments are confirmed. Thus, the optimal mix proportion of UHPC matrix can be calculated. Moreover, some novel viewpoints on the development of dense particle packing theory are presented in this study, including the derivation of multilevel particle packing model with n times of gap gradation and the discussion of general mix design procedure that unifies gap gradation and continuous packing, which could further improve the design theory of UHPC composites.

Properties prediction of discontinuous-fibre reinforced thermoplastic composites with fibre-cell-based fibre distribution description

The fibre distribution inside discontinuous-fibre reinforced polymer matrix composites (DFR PMCs) is usually characterized and analyzed separately by different features such as fibre orientations and fibre lengths. There is no established method to characterize fibre packing states within the DFR PMCs, and the links between different fibre distribution features are rarely addressed. In this study, the concept of fibre cell is proposed to provide an alternative to characterize the fibre distribution within DFR PMCs. The concept involves dividing a fibre domain into smaller cells based on the location of each fibre and characterizing the fibre distribution within the fibre domain based on the fibre cell properties. Compared with traditional characterization methods, the proposed method is able to include fibre packing information, and all fibre distribution features can be characterized in a joint manner instead of separately by different fibre distribution features. The proposed method is merged into a machine learning (ML) framework to deduce the feature-property correlation via an artificial neural network. The ML framework is used as a surrogate model for fast homogenized elastic modulus predictions. Moreover, the concept of fibre cell is also very versatile and can be extended to microstructures with different material properties and inclusion shapes.

Revealed Properties of Various Self-Assemblies in Two Catanionic Surfactant Systems in Relation to Their Polarity and Molecular Packing State.

A catanionic surfactant system is an aqueous solution or dispersion of cationic and anionic surfactants that spontaneously self-assemble into structures such as micelles, vesicles, and coacervates. Their structural diversity varies depending on the ratios of cationic and anionic surfactants (compositions), the chemical structure of the constituent molecules, etc. Herein, two types of catanionic surfactant systems were systematically characterized: (i) cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), both typical ionic surfactants; and (ii) dodecylmethylimidazolium ammonium bromide ([C12mim]Br) and SDS, where the former is an ionic liquid. By observing the sample appearance, turbidity, and particle size, the phase state of each system was analyzed according to the total concentration of surfactants and the molar ratio of cationic surfactants to the total concentration. Especially, for specific compositions of catanionic surfactant vesicles (cataniosome), the closed structure of the vesicles was confirmed through calcein entrapment and release detected with a fluorescence assay. The polarities of the interface of the prepared self-assemblies were evaluated using a fluorescence probe, Laurdan. The packing state of the molecules in the formed self-assembly structure was estimated using Raman spectroscopy. The results clearly indicate consistent phase-transition behavior for the CTAB-SDS (i) and [C12mim]Br-SDS (ii) systems, depending on the total surfactant concentration and composition, while the membrane properties of the two systems differed. The cataniosome formed in the CTAB-SDS system was in a tightly packed membrane state and more hydrophobic than that formed in the [C12mim]Br-SDS system owing to the difference in the structure of the constituting molecule: [C12mim]Br has a larger head group and shorter acyl chain than CTAB. The self-assembly properties evaluated in this study were compared with those of typical lipid membranes, liposomes (lipid vesicles), to determine a possible application of the catanionic systems with various self-assembly formulations.

Study on the dense structure and properties of cement-stabilized coral aggregates

The performance of cement stabilized coral aggregates semi-rigid base of pavement with coral reef limestone fragments and biological debris as the main materials is essential in the current reef engineering constructions. The performance of inorganic mixtures such as cement-stabilized coral aggregates mainly depends on the packing state of aggregates and the interfacial bonding among each component. Via digital image analysis theory, a simulation model of the dense packing of particles method was established, considering the influence of arbitrary particles shape distribution, upper limit of particles size, and aggregates gradation. The influencing mechanism of different factors on the packing state was revealed. It was found that the dense packing of coral aggregates is a strong suspension dense structure which did not form the skeleton structure. The strengthening mechanism of the coral particle-coated cement slurry was studied through the experimental analysis of the pore structure of coral rocks and debris particles and the crushing strength of particle-coated cement slurry, combined with the microhardness test of the cement- coral particle interface and the analysis of hydration products. The physicochemical excitation mechanism of hydration products densification，“physical interlocking” and “micro pump” effect at the interface of the cement-coral particle was revealed. Furthermore, based on the macroscopic mechanical properties of cement stabilized coral aggregates, the optimal design ratio of coral aggregates with upper limit particle size of 53mm, fine aggregates content of 45% and cement content of 8% was proposed. The findings of this study can provide a reference for the design and application of cement stabilized coral aggregates semi-rigid pavement base.

Ti-6Al-4V powder reuse in laser powder bed fusion (L-PBF): The effect on porosity, microstructure, and mechanical behavior

This work investigated the effects of powder reuse, and location dependency on the mechanical properties of plasma atomized Ti-6Al-4V Grade 5 parts manufactured via laser powder bed fusion (L-PBF). Reusing the powder enhanced powder flowability and packing state while increasing the oxygen. Fatigue performance improved with limited reuse for the specimens upstream of the shield gas and decreased at downstream locations due to large critical defects. Powder reuse increased tensile strength and the critical energy release rate under high strain-rate loading. The specimens in downstream locations suffered more from spattering, resulting in lower fatigue performance and tensile ductility.

Effect of surface modifier and solvent on the affinity between the surface-modified solid and organic solvent: A molecular dynamics study

To control the dispersibility of surface-modified nanoparticles in fluid, it is important to evaluate the affinity between surface-modified nanoparticles and solvents and elucidate the effect of surface modification on the affinity at the molecular level. In this study, the effect of the chain length of the surface modifier and solvent on the work of adhesion Wadh was investigated for the carboxylic acid-modified Al2O3/n-alkane interface by molecular dynamics simulations using the phantom-wall method. Here, we adopted hexanoic acid, decanoic acid, and octadecanoic acid as the surface modifiers and n-hexane, n-decane, and n-dodecane as the solvents. At a surface coverage of 100%, the effect of the modifier length on Wadh was small because the solvent did not penetrate any modifier layers with a dense packing state. At a surface coverage of 50%, the solvent penetration was good except for the octadecanoic acid modifier, and Wadh for the decanoic acid modifier was higher than that for the hexanoic acid and octadecanoic acid modifiers. For the decanoic acid modifier with a surface coverage of 50%, the effect of the solvent length on Wadh was small because the density distributions of the modifier and solvent near the interface were almost the same in all solvent systems. Solvent penetration was evaluated using the overlap parameter, which is the degree of overlap of the density distribution. A large penetration resulted in high Wadh. We demonstrated that the affinity between surface-modified nanoparticles and solvents can be increased by ensuring high modifier-solvent penetration via adjusting the surface coverage and surface modifier.

A Versatile Tetraphenylethene Derivative Bearing Excitation Wavelength Dependent Emission, Multistate Mechanochromism, Reversible Photochromism, and Circularly Polarized Luminescence and Its Applications in Multimodal Anticounterfeiting

A Versatile Tetraphenylethene Derivative Bearing Excitation Wavelength Dependent Emission, Multistate Mechanochromism, Reversible Photochromism, and Circularly Polarized Luminescence and Its Applications in Multimodal Anticounterfeiting

Investigation of flow behaviors in a fluidized bed reactor with binary mixture of Geldart-A and B particles

Flow dynamics in bubbling and turbulent fluidized beds containing both Geldart-A and B particles were investigated in this research. The numerical model was validated against experimental data, with a 6.16% average deviation. Results show that binary mixture segregation is enhanced as superficial gas velocity decreases. A larger flotsam packing ratio promotes homogeneous flotsam distribution; Second, bed density decreases with increasing bed height or superficial gas velocity. As the flotsam packing ratio decreases from 81.10 to 10.70%, bed density reaches the maximum at 41.50%, indicating the most severe volume contraction; Third, when the flotsam packing ratio decreases, the local mixing index's variances between upper and lower sections in dense phase first increases, then decreases, with stronger radial fluctuation detected; Fourth, as superficial gas velocity or flotsam packing ratio increases, the full mixing height ratio improves; Finally, multivariate correlations for dense phase bed expansion are established, yielding a 3.94% average error. • A modified EMMS drag model was adopted to examine flow features in a bidisperse fluidized bed. • The quantified impacts of superficial gas velocity and packing state on flow are obtained. • Multivariate correlations for dense phase bed expansion were fitted with high accuracy.

Experimental and Numerical Study of Pressure Drop Characteristics of Soybean Grain under Vertical Pressure

The vertical pressure lead to increased airflow resistance through the grain bulk, which affected the efficiency of ventilation and drying. The effects of vertical pressures at 50, 150, and 250 kPa on the pressure drop characteristics of soybeans were studied using experiment and numerical simulation. The random packing and different compression states for soybean packed beds were generated by the Discrete Element Method (DEM). The Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) were coupled to investigate the radial velocity and pressure drop of soybean bulk. The simulation results showed that the radial porosity had an oscillating distribution, and the radial average dimensionless velocity was consistent with the distribution trend of porosity. The increase in vertical pressure causes a decrease in porosity and an increase in local velocity. The PathFinder code was used as a supplementary method to calculate the pore path and pore characterization parameters, and the resistance coefficient term in the Forchheimer equation was determined. The compression of soybeans measured by the experiment mainly occurred within two hours after loading. The pressure drop of soybeans increased with the vertical pressure, with the average pressure drop at vertical pressures of 50, 150, and 250 kPa being 36%, 57%, and 92% higher than the uncompressed state (0 kPa). The pressure drop of soybeans calculated by the DEM-CFD method and the Forchheimer equation under different vertical pressures were in close agreement with the experimental results, and an average relative difference was found to be less than 10%. These results provide guidance for estimating the pressure drop of soybeans at different grain depths.

Membrane Protein Activity Induces Specific Molecular Changes in Nanodiscs Monitored by FTIR Difference Spectroscopy.

It is well known that lipids neighboring integral membrane proteins directly influence their function. The opposite effect is true as well, as membrane proteins undergo structural changes after activation and thus perturb the lipidic environment. Here, we studied the interaction between these molecular machines and the lipid bilayer by observing changes in the lipid vibrational bands via FTIR spectroscopy. Membrane proteins with different functionalities have been reconstituted into lipid nanodiscs: Microbial rhodopsins that act as light-activated ion pumps (the proton pumps NsXeR and UmRh1, and the chloride pump NmHR) or as sensors (NpSRII), as well as the electron-driven cytochrome c oxidase RsCcO. The effects of the structural changes on the surrounding lipid phase are compared to mechanically induced lateral tension exerted by the light-activatable lipid analogue AzoPC. With the help of isotopologues, we show that the ν(C = O) ester band of the glycerol backbone reports on changes in the lipids’ collective state induced by mechanical changes in the transmembrane proteins. The perturbation of the nanodisc lipids seems to involve their phase and/or packing state. 13C-labeling of the scaffold protein shows that its structure also responds to the mechanical expansion of the lipid bilayer.