Cohesive Forces Research Articles

Effects of Polyethylene Glycol/Porous Silica Form-Stabilized Phase Change Materials on the Performance of Asphalt Binders.

The road performance and temperature-regulating properties of asphalt binders modified with novel polyethylene glycol (PEG)/porous silica (PS) form-stabilized phase-change materials (PEG/PS-fs-PCMs) were studied. PS and PEG were used as the supporting substance and PCMs. The results showed that PEG/PS-fs-PCMs could maintain a maximum weight percentage of 70% without leakage, at temperatures as high as 90 °C. The PEG/PS-fs-PCMs exhibited stable chemical structures, excellent thermal stability, high heat storage density, and suitable phase-change temperature. Based on conventional physical tests, the addition of PEG/PS-fs-PCMs can increase the viscosity and the degree of hardness of asphalt binders; thus, achieving an excellent comprehensive performance of the modified asphalt binder depends on determining the optimal dosage of PEG/PS-fs-PCMs. Additionally, incorporating PEG/PS-fs-PCM particles into the asphalt binder can enhance its ability to withstand permanent deformation at elevated temperatures, while PEG/PS-fs-PCMs mainly act as a filler, weakening the cohesive force of the asphalt molecules, and preventing the ductility of asphalt from expansion, according to DSR and BBR tests. Moreover, the use of PEG/PS-fs-PCMs can enhance the heat transfer properties of the asphalt binders, resulting in an improved temperature regulation performance. However, the accumulation of PEG/PS-fs-PCM particles on asphalt binders can negatively impact the storage stability of the modified asphalt binders, because of the difference in density between the two materials.

Overcoming the yield challenge of mussel foot proteins: Enhancing adhesion through metal ion-incorporated nanoparticles

Mussel foot proteins (MFPs) hold tremendous potential for various fields, but their low natural production yield presents a significant challenge for practical use. This study aims to explore possible solutions to overcome this limitation. While advanced recombinant technology can improve production efficiency, the resulting proteins lack the crucial chemical signature of mussel adhesion, 3,4-Dihydroxyphenylalanine (DOPA). Recent studies have shown that adhesives in nanoparticle form offer higher adhesion on solid surfaces, making them a promising alternative. Moreover, metal ions can enhance the cohesive forces between MFPs, leading to improved adhesion. In this study, we prepared MFP nanoparticles via spray-drying and tested their adhesion performance on surfaces with varying hydrophobicity using a universal testing machine. Our findings confirmed that MFP nanoparticles exhibit stronger adhesive performance than native MFPs, with metal ions contributing to even more robust adhesion. This study offers valuable insights into the adhesive behavior of MFPs in nanoparticle form with metal ions, presenting a potential solution to the challenge of low natural production yield of MFPs and the possibility of enhancing their adhesion properties in bio-adhesive materials.

Mixing sub-micron particles in a ProCell type spouted bed

Mixing sub-micron particles of two different materials produce hetero-aggregates, which can exhibit innovative and superior properties over homo-aggregates of a single material. The present study investigates the hetero-aggregate formation from sub-micron particles in ProCell type spouted bed equipment. Sub-micron particles can exist in the form of homo-aggregates, clusters of particles of the same material that are held together by cohesive forces such as van der Waals forces. In the special spouted bed used, the inlet air velocities are significantly higher than in conventional fluidized beds and can be expected to exert an influence that promotes aggregate breakage and rearrangement. Indeed, by use of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), it is shown that mixing is achieved at sub-agglomerate level. Region of interest with a size of 2.5 μm (which is more than double the size of the bigger primary particle) is found to be a reasonable scale to investigate the mixing of sub-micron sized particles in compressed wafers and also in single agglomerates (by a new method of quantification).

Theoretical Investigation of Capture, Collection, and Targeted Transfer of Underwater Gas Bubbles Using Janus‐Faced Carbon Cloth

Recently, a straightforward method for the preparation of a Janus carbon cloth (Janus‐CC) is reported. The method relies on polydimethylsiloxane (PDMS) coating, followed by flame exposure of one face of the PDMS‐coated CC. The nonexposed to the flame face of the Janus‐CC is superhydrophobic, while the exposed to the flame face is superhydrophilic. Underwater, the superhydrophobic face shows superaerophilicity, while the supherhydophilic face shows superaerophobicity. A tethered gas bubble onto the superhydrophobic face has a paraboloid of revolution shape due to the cohesion force between the bubble and the gaseous film. Herein, the geometrical parameters of underwater tethered gas bubbles onto the Janus‐CC are obtained, and the tendency of Janus‐CC for capturing of bubbles is interpreted based on the derived Gibbs free‐energy change equation. It is experimentally observed that a small sited bubble moves toward the bigger one through the formed gaseous film, but this observation cannot be interpreted based on the classical Young–Laplace equation because here the smaller bubble has bigger curvature radius. Herein, a modified Young–Laplace equation is derived and applied for interpretation of the movement of a small bubble toward the bigger one. Also, the buoyancy force for a sited bubble on the gaseous film is discussed.

Research on key influencing factors of scrap tire-soil retaining wall

The emergence of STSW can reduce the amount of materials such as sand and gravel and improve its performance compared to conventional retaining walls. In order to investigate the key influencing factors of STSW, the compression modulus of Scrap tire-soil module (STSM) was obtained by designing a full-scale compression strength test. The shear strength was obtained through a scale-test of shear strength. On this basis, the gravity STSW was established by the finite element numerical simulation software, and the bearing capacity of STSW was analyzed. Further, the key influencing factors of the bearing capacity of STSW were analyzed by designing orthogonal tests, and suggestions for parameter selection for designing STSW were given. The results show that: the friction angle of STSW increases and becomes larger with the increase of area ratio, and the cohesion decreases and decreases with the increase of area ratio; with the increase of compression modulus and internal friction angle, the maximum shear stress inside the retaining wall increases, while the cohesive force has almost no effect on the maximum value of shear stress inside the retaining wall; when constructing retaining walls, it is recommended to use Internal filling material with large compression modulus, small area ratio and its in the range of [0.3–0.5] of STSM.

Electrostatic Adsorption Behaviors of Polymer Plates to a Droplet.

Electrostatic transfer and adsorption of electrically conductive polymer-coated poly(ethylene terephthalate) plates from a particle bed to a water droplet were studied, with the influence of plate thickness and shape observed. After synthesis and confirmation of the particles' properties using stereo and scanning electron microscopies, elemental microanalysis, and water contact angle measurement, the electric field strength and droplet-bed separation distance required for transfer were measured. An electrometer and high-speed video footage were used to measure the charge transferred by each particle, and its orientation and adsorption behavior during transfer and at the droplet interface. The use of plates of consistent square cross section allowed the impact of contact-area-dependent particle cohesion and gravity on the electrostatic transfer of particles to be decoupled for the first time. The electrostatic force required to extract a plate was directly proportional to the plate mass (thickness), a trend very different from that previously observed for spherical particles of varied diameter (mass). This reflected the different relationship between mass, surface area, and cohesive forces for spherical and plate-shaped particles of different sizes. Thicker plates transferred more charge to the droplet, probably due to their remaining at the bed at higher field strengths. The impact of plate cross-sectional geometry was also assessed. Differences in the ease of transfer of square, hexagonal, and circular plates seemed to depend only on their mass, while other aspects of their comparative behavior are attributed to the more concentrated charge distribution present on particles with sharper vertices.

Infiltration and shear strength characteristics of gully heads soil of typical vegetation on the gullied Loess Plateau, Northwest China.

Gully head is the main active part of gully erosion, which seriously affects the occurrence of gully headcut erosion. To investigate root distribution and soil physical and mechanical characteristics of typical vegetation gully head, we analyzed the infiltration, root distribution, physical and mechanical properties of soil-root complex of soil in different layers (0-1 m) in natural restoration gully head and artificial restoration gully head. The results showed that the variability of soil bulk and total porosity among different vegetation gully heads was low, with bulk density ranging from 1.10 to 1.37 g·cm-3 and total porosity ranging from 48.3% to 58.4%. Infiltration index of different vegetation gully heads generally decreased with increasing soil depth. The infiltration rate of different soil layers in natural restoration gully head tended to stabilize in 20-30 min, while that of artificial restoration gully head tended to stabilize in 40 min. The infiltration capacity and average infiltration rate of artificial restoration gully head were generally higher than those of natural restoration gully head in all soil layers. Root length density, root surface area density, and average diameter all tended to decrease with increasing soil depth. Except for the 20-40 cm soil layer, root length density, root surface area density and average diameter of natural restoration gully head were all lower than those of artificial restoration gully head. Root system of both vegetation gully heads mainly consisted of 0-0.5 mm roots, accounting for 84.2%-93.6% of the total root length. In the vertical depth, with the increases of water content, the cohesion force decreased linearly with the deepening of soil layer, ranging from 0.42 to 22.67 kPa. The average cohesion force of artificial restoration gully head was higher than natural restoration gully head at each level of water content. The study revealed the effects of vegetation on the gully head cut erosion, which could provide scientific basis for the effective prevention and control of soil erosion in the region.

Simulation of Creep Damage of Asphalt Mixture Based on Discrete Element Method

This paper proposes a creative approach for conducting discrete element simulation of creep tests to simulate the mechanical behavior of asphalt mixture and analyze the mechanism of creep damage by virtual tests. Based on the discrete element method (DEM), the creative approach named the aggregate template method was presented to generate the irregular polyhedron of coarse aggregate by 3DsMax and PFC3D. The asphalt mortar was then replaced by spherical particles and by PFC3D. Based on the above preparation, the uniaxial creep tests were simulated by PFC3D and verified by actual tests to illuminate the micromechanical behavior and the creep damage of asphalt mixtures. The test results indicate that the fracture of force chains is consistent with the damage of real samples. The load is used to damage the sample by breaking the bond between the particles and the temperature is used to soften the asphalt mortar particles to damage the sample. The attenuation rate of the cohesive force of particles at the boundary of the sample is obviously larger than that at the center in the process of loading. It was verified that the aggregate template method in DEM is a reasonable approach for studying the creep test of asphalt mixtures by error analysis.

Development of an Empirical Model of the Force between Paramagnetic Particles in Uniform Magnetic Field on M-type Asteroids

M-type asteroids may have remanent magnetic fields. Regolith particles on M-type asteroids are likely to have metallic components, causing them to be paramagnetic and respond to an external magnetic field. Paramagnetic particles placed in an external magnetic field are influenced by induced magnetic moments of neighboring particles. Therefore, the magnetic force between regolith particles on an M-type asteroid can change the net cohesion of the regolith. Previous works have shown the influence of cohesive forces in the evolution of rubble-pile asteroids. This work characterizes the magnetic force between regolith particles on M-type asteroids. We implement existing models of the magnetic force between paramagnetic particles placed in an external magnetic field and then present an empirical model of this force for two magnetic field orientations as an essential step toward a general semiempirical model that the wider planetary science community can more easily use to investigate the significance of this force.

An Experimental Study on the Determination of Minimum Fluidization Velocity

Pneumatic conveying systems are widely used in a variety of industrial settings since different types of materials can be conveyed. There are some classifications of flow modes for conveying of powders and bulk solid particles based on mean particle size, density, and inter particle cohesion forces. In this paper, three different cases which are vertical (test case 1), horizontal (test case 2) and continuous conveying test case are constructed and considered in order to determine the flow modes in pneumatic conveying systems. Seven solid particles are used with the range of 200 kg/m3 < ρblp < 2400 kg/ m3 and 150 μm < dp < 2750 μm in these three cases. In vertical test set-up unstable zone and fluidized dense phase is occurred, then in the horizontal test set-up slug flow and plug flow is observed and lastly plug flow and dilute phase is occurred visually in continuous conveying test case. Finally, all obtained data are considered for the classification according to flow modes in pneumatic conveying systems. The observed flow modes are considered and tabulated with respect to all test cases.

Study of guiding vehicle by railway track

The analysis of scientific publications related to the guiding of wheelsets of railway rolling stock along the rail track has been carried out. It is stated that for a valid simulation of the guiding of wheelsets by a rail track, an accurate description of the contact forces of adhesion is necessary. It was found that the flange wheel-rail contact exists only in combination with the angle of attack and in the presence of a lateral cohesive force. A scheme of power interaction of a wheelset with rails with a ridge contact of one of the wheels has been developed. The force contact interaction of a wheel and a rail is a process that is difficult to describe and, at the same time, very important for studying the dynamics of the frictional interaction of vehicles and track and the guiding of vehicles by the rail track. In the general case, the contact of the wheel with the rail occurs in two contact zones: on the rolling surface and on the flange. Simplified, the contact is considered as a two-point contact. The considered force factors cannot be unambiguously attributed to guiding factors or factors of resistance to movement. Specific values and guiding of forces and moments depend on the position of the wheelset relative to the rail track. It is argued that the longitudinal and transverse slips of the wheelsets cause resistance to movement and are overcome by guiding forces.

Cohesive sediment: intermediate shear produces maximum aggregate size

We interpret the Taylor–Green cellular vortex model in terms of the Kolmogorov length and velocity scales, in order to study the balance between aggregation and breakup of cohesive sediment in fine-scale turbulence. One-way coupled numerical simulations, which capture the effects of cohesive, lubrication and direct contact forces on the flocculation process, reproduce the non-monotonic relationship between the equilibrium floc size and shear rate observed in previous experiments. The one-way coupled results are confirmed by select two-way coupled simulations. Intermediate shear gives rise to the largest flocs, as it promotes preferential concentration of the primary particles without generating sufficiently strong turbulent stresses to break up the emerging aggregates. We find that the optimal intermediate shear rate increases for stronger cohesion and smaller particle-to-fluid density ratios, and we propose a simple model for the equilibrium floc size that agrees well with experimental data reported in the literature.

Experimental investigation to elucidate the hydrate Anti-Agglomerating characteristics of 2-Butoxyethanol

To alleviate the severity of hydrate formation in subsea oil and gas pipelines, the injection of anti-agglomerants (AAs) is one of the promising approaches. In this work, we investigate the hydrate anti-agglomerating characteristics of 2-butoxyethanol, also called butyl glycol ether (BGE), which has been reported in the literature as an effective synergist for kinetic hydrate inhibitors (KHIs), and a solvent for low dosage hydrate inhibitors (LDHIs). In view of its hydrophobic and hydrophilic moieties, we evaluate the adsorption affinity of BGE for the oil–water interface employing the interfacial tensiometer (IFT) apparatus. Moreover, a micromechanical force (MMF) apparatus was used to probe the interfacial behavior of hydrate particles, wherein we measured the cohesive forces between cyclopentane hydrate particles in the presence of BGE at atmospheric pressure and 274.2 K. The kinetics of methane hydrate formation and resistance-to-flow were assessed while measuring the dynamic pressure–temperature data and motor torque signals alongside with visual observations, respectively, employing a high-pressure visual autoclave (HPVA). IFT results reveal the strong surface active properties of BGE with a substantial reduction in oil–water interfacial tension at ambient conditions. However, no considerable change in the cohesive forces between cyclopentane hydrate particles was observed through MMF measurements. In contrast, HPVA results reveal that the addition of BGE enhanced the kinetics of methane hydrate formation; however, the corresponding torque pattern/visual interpretations indicated an anti-agglomerating action of BGE. While synergistically combining the BGE with under-inhibited dosages of mono-ethylene glycol, we further demonstrated a significant improvement in the hydrate transportability, wherein this synergism led to a non-plugging scenario (flowable hydrate slurry). Our findings will offer new insights into the development of new anti-agglomerant chemistries.

Study on the Surface Settlement of an Overlying Soft Soil Layer under the Action of an Earthquake at a Subway Tunnel Engineering Site

In order to study the surface settlement characteristics of an overlying soft soil layer in a subway tunnel under seismic loading, the ABAQUS finite-element analysis software was utilized. Taking the construction of Dalian Metro Line 5, which is located in seismic intensity zone Ⅶ and has an overlying soft soil layer, as the engineering background, El-Centro and Kobe waves representing class Ⅱ site seismic waves, as well as an artificial seismic wave with an exceedance probability of 10%, were inputted into the analysis. The settlement characteristics of the ground surface at the construction site of the subway tunnel under the three different seismic waves were investigated, and their behaviors were theoretically analyzed. Then, the surface settlement law with respect to the tunnel roof was studied based on El-Centro wave and soft soil parameters, and a sensitivity analysis of soft soil parameters of surface settlement of the tunnel roof was carried out by the orthogonal test method. The results show that under earthquake action, the settlement of the strata within a certain range of the tunnel roof was significantly greater than that of the surrounding strata, forming a settlement trough with a width of about 8 to 20 m. The width of the settlement trough under the El-Centro wave was the largest, about 19.6 m, surpassing that of the artificially synthesized seismic waves with a probability of 10%, which was about 15.6 m, while the width of the settlement trough under the Kobe wave was the smallest, about 8.5 m. The ground surface within a range of about 20 m above the tunnel roof was most strongly affected by the seismic waves and the special lithology of the overlying soft soil layer, and the settlement was the largest. The settlement law of the settlement trough in the overlying strata of the tunnel conformed to the Peck formula. Increasing the elastic modulus of the silty soil can reduce the settlement of the ground surface above the tunnel roof; increasing the Poisson’s ratio of the silty soil will increase the settlement of the ground surface above the tunnel roof; increasing the cohesive force of the silty soil to 20 kPa will basically stabilize the settlement of the ground surface above the tunnel roof; and increasing the internal friction angle of the silty soil will basically not change the settlement of the ground surface above the tunnel roof. The sensitivities of the soft soil parameters to the settlement of the ground surface above the tunnel roof were in the order of the Poisson’s ratio, the elastic modulus, the cohesive force, and the internal friction angle. Therefore, the research findings of this paper provide scientific support for the problem of surface settlement of the overlying soft soil layer in subway tunnel engineering sites under earthquake action. In addition, these research findings have important theoretical value and engineering application significance, especially in the field of sustainability.

Thrust formation using a numerical granular rock box experiment

A numerical granular rock box experiment based on the Discrete Element Method (DEM) was performed in thin 3D geometry to investigate the role of granularity in thrust formation. This rock box experiment is an extension of the numerical sandbox test, which is considered an analog experiment for accretionary prism formation with cohesive contact force. The parameters of contact-based interaction are adjusted to account for the failure envelope of the host rock in the triaxial test. The developed model allows the numerical simulation of the horizontal shortening of a granular layer on geologically relevant scales. The rock box test successfully reproduces the characteristic structures of accretionary wedges developed during sequential thrust formation. In contrast to the non-cohesive case, the cohesive models generated a surface geometry with steeper angles, surface vertical faults, and enhanced bifurcation of the shear bands. The geometric network of fault planes depended on the healing of the cohesive force within the faulted region. The increasing complexity of the network was demonstrated using finer elements until its maximum radius reached 12.5 m. We also evaluated the granular nature of the thrust thickness, which was found to depend on the number of frictional elements rather than physical length. A decrease in the growth rate of the fault damage zone thickness with increasing fault displacement was found to be consistent with observational data. Our results suggest an important role for granularity in thrust evolution.

Biocidal Coatings against Gram-Positive Bacteria from Linear and Branched Polycations: The Decisive Role of the Diffusion Coefficients of Macromolecules

Positively charged polyelectrolytes hold significant potential as materials for creating antibacterial coatings. We examined the physicochemical and mechanical properties of the macromolecules in water solutions and in coatings for the series of branched polyethyleneimine (PEI) and linear polydiallyldimethylammonium chloride (PDADMAC) with different molecular weights. The microbiological study was conducted to analyze the biocidal activity of the polycation solutions and coatings towards foodborne bacteria. While the moisture saturation of the polycationic coatings and biocidal activity did not significantly depend on the chemical nature of charged groups or the molecular weight or architecture of macromolecules, the lowering of the molecular weight of polymers resulted in the loss of cohesive forces in the coatings and to a dramatic loss of stability when being washed off with water. The diffusion coefficient (D0) of macromolecules was identified as a key parameter for the wash-off mechanism. Films formed by molecules with a D0 below 1 × 10−7 cm2/s demonstrated a high resistance to wash-off procedures. We demonstrated that PEI and PDADMAC samples with high molecular weights showed high antimicrobial activity towards L. monocytogenes. Our results highlight the importance of macromolecule characteristics in the development of new biocidal coatings based on polycations.

Recycling of silicon from waste PV diamond wire sawing silicon powders: A strategy of Na2CO3-assisted pressure-less sintering and acid leaching

Recycling diamond wire sawing silicon powders (DWSSP) from photovoltaic (PV) silicon wafers production has become an urgent problem. The challenge of recovery is the surface oxidation and contamination of the ultra-fine powder with impurities during the sawing and collection process. In this study, a clean recovery strategy of Na2CO3-assisted sintering and acid leaching was proposed. Due to the Al contamination from the perlite filter aid, the introduced Na2CO3 sintering aid can react with the SiO2 shell of DWSSP to form a slag phase with accumulated impurity Al during the pressure-less sintering process. Meanwhile, the evaporation of CO2 contributed to the formation of ring-like pores surrounded by a slag phase, which can be easily removed by acid leaching. When 15 % Na2CO3 was added, the content of impurity Al in DWSSP could be reduced to 0.07 ppm with a removal rate of 99.9 % after acid leaching. The mechanism suggested that the addition of Na2CO3 can trigger the liquid phase sintering (LPS) process of the powders, and the cohesive force and liquid pressures difference generated during the process facilitated the transportation of impurity Al from the SiO2 shell of DWSSP to the formed liquid slag phase. The efficient silicon recovery and impurity removal of this strategy demonstrated its potential for solid waste resource utilization in the PV industry.

Coupling CFD-DEM with cohesive force and chemical reaction sub-models for biomass combustion in a fluidized bed

The present study employs the CFD-DEM method coupled with cohesive force and chemical reaction sub-models to investigate the hydrodynamic and thermal behaviors in a biomass-fired fluidized bed combustor containing bed particles with cohesive features resulting from the high levels of inorganic alkalis in the biomass. The CFD-DEM simulations effectively reproduce the characteristic phenomena in a cohesive fluidized bed, such as particle agglomeration, gas bubbles with irregular boundaries, rat-holes, and gas channels. The results indicate that the particle kinetic energy continuously decreases with increasing particle cohesion, and the pressure-drop profile flattens suddenly at the onset of complete de-fluidization. Additionally, larger cohesive forces occur at coarse bed-particle conditions, while the particle-averaged cohesive force at the onset of de-fluidization weakens as the bed-particle size increases at the same superficial gas velocity. The regions near the bed bottom and sidewall are more sensitive to the hydrodynamic and thermal alterations resulting from increasing particle cohesion, making them more favorable for early detection. The convection heat and reaction heat dominate the heat transfer of bed particles and biomass particles, respectively. As the particle cohesion becomes more pronounced, the biomass-particle reaction heat flux decreases because biomass trapped in agglomerates experiences oxygen-deficient conditions due to the hindering effects of large agglomerates on the gas and the occurrence of gas channels. Overall, the present study indicates that the particle mixing and inter-phase heat transfer capacity, along with reaction intensity in the biomass-fired fluidized bed, deteriorates as particle cohesion increases. The extended model provides a particle-scale approach to analyze complex cohesive gas–solid reaction flow systems.

Experimental study on electrostatic migration of different mineral particles composing lunar dust under electron irradiation

Dust electrostatic migration is one of the primary causes of dust events on the surface of airless celestial bodies, which can result in multiple dust phenomena, including lunar horizon glow and dust pools, and also offer crucial insights into the evolution of the surface materials of airless celestial bodies. To date, the characteristics and laws of dust electrostatic migration are still not well understood. Here, we report the electrostatic migration characteristics of pyroxene, olivine, and ilmenite particles measured by the laser Doppler method and compare them with the findings of anorthite particles in previous experiments to recognize the differential migration characteristics of different mineral components in the lunar dust. The results demonstrate that the particle sizes of most moving pyroxene and olivine particles are in the range of 0–10 μm, and their vertical velocities are typically less than 2 m s−1, which are consistent with the previous studies. The cohesive force between the dust particles is probably what causes the difference in the migration rates of various insulating minerals. Note that no moving ilmenite particles were detected probably due to the material’s good conductivity. It can be speculated that the concentration of fugitive dust in the lunar mare is affected by the ilmenite content, but further research is needed to determine how low ilmenite content can cause dust migration.

Modeling atmospheric microplastic cycle by GEOS-Chem: An optimized estimation by a global dataset suggests likely 50 times lower ocean emissions

Modeling atmospheric microplastic cycle by GEOS-Chem: An optimized estimation by a global dataset suggests likely 50 times lower ocean emissions