Interparticle Adhesion Forces Research Articles

Direct measurement and theoretical prediction model of interparticle adhesion force between irregular planetary regolith particles

Interparticle adhesion force has a controlling effect on the physical and mechanical properties of planetary regolith and rocks. The current research on the adhesion force of planetary regolith and rock particles has been primarily based on the assumption of smooth spherical particles to calculate the intergranular adhesion force; this approach lacks consideration for the adhesion force between irregular shaped particles. In our study, an innovative approach was established to directly measure the adhesion force between the arbitrary irregular shaped particles; the probe was modified using simulated lunar soil particles that were a typical representation of planetary regolith. The experimental results showed that for irregular shaped mineral particles, the particle size and mineral composition had no significant influence on the interparticle adhesion force; however, the complex morphology of the contact surface predominantly controlled the adhesion force. As the contact surface roughness increased, the adhesion force gradually decreased, and the rate of decrease gradually slowed; these results were consistent with the change trend predicted via the theoretical models of quantum electrodynamics. Moreover, a theoretical model to predict the adhesion force between the irregular shaped particles was constructed based on Rabinovich’s theory, and the prediction results were correlated with the experimental measurements.

Interfacial Adhesion Forces of Hydrate Particles in the Presence of Hydrate Inhibitors

Hydrate inhibitors are traditionally utilized to prevent hydrate plugging. In this study, the adhesion forces of cyclopentane (CP) hydrates with thermodynamic inhibitors (ethanol, urea, and NaCl) and anti-agglomerant inhibitors [sorbitan monooleate (Span 80) and lecithin] were measured to understand the effects of hydrate inhibitors on the adhesion forces of hydrates. It was found that the thermodynamic inhibitors increased the early hydrate interparticle adhesion force due to the enhanced liquid bridge force. However, the liquid bridge acted as a lubricant layer to prevent the irreversible agglomeration of hydrate after long-term contact. The hydrate adhesion forces decreased by 90.5-93.0% and 76.6-92.7% with an increase in the concentration of Span 80 and lecithin, respectively, from 0.1 to 1 wt %. Both rough morphology and low interfacial tension contributed to the adhesion force decrease of hydrate after the addition of anti-agglomerant inhibitors. The results may be helpful for understanding the mechanism of influence and quantifying the impact of hydrate inhibitors on hydrate interparticle adhesion force.

Effect of fill level in continuous twin-screw granulator: A combined experimental and simulation study

• Fill level effect in twin-screw granulator on tablet hardness was investigated. • Fill level in twin screw granulator was directly measured in experiments. • Interparticle adhesion force increased with increase in fill level. • DEM simulations demonstrated high compressive force on particles at high fill level. • Combination of experiments and simulations revealed mechanism of fill level effect. Twin-screw granulators for continuous wet granulation have attracted interest in the pharmaceutical industry. The physical properties of granules and tablets prepared through the twin granulation process depend on several factors, such as screw and barrel geometries, operating conditions, and formulations of raw materials. The fill level has been reported to be one of the most important factors in determining granule properties. However, the mechanism of the fill level effect on granule properties has not yet been fully clarified. In this study, the effects of the fill level in the twin-screw granulator on granule and tablet properties were investigated through a combination of experimental and simulation studies. In the experiment, temporal changes in the fill level were directly measured. It was found that a high fill level increased granule strength, resulting in large tablet hardness. The discrete element method simulations demonstrated that the compressive force on the particles in the granulator strongly depends on the fill level. In addition, by combining the experimental and simulation results, it was quantitatively revealed that a high fill level increased the interparticle adhesion, leading to the high hardness of tablets prepared with the granules.

Chemically-adhesive particles form stronger and stiffer magnetorheological fluids

Magnetorheological fluids (MRFs) are suspensions of magnetic particles that solidify in the presence of a magnetic field due to the particles forming chains along field lines. The magnetic forces between particles dominate the solidification process and determine the yield stress of the resulting solid. Here, we investigate how reversible chemical links between particles influence MRF behavior in terms of their yield stress and stiffness through rheological testing in flow and oscillation mode. Initially, we functionalize particles with phosphonate groups that are expected to link through hydrogen bonding and find that this MRF exhibits up to 40% higher yield stress and 100% higher stiffness than an MRF composed of unfunctionalized particles. To explain this change, we model the chemical attraction as an adhesion that supplements dipole–dipole interactions between particles. Interestingly, we find that the increase in yield stress is largest for dilute suspensions that are expected to solidify into isolated chains, while the proportional increase in yield stress is less for MRF with higher concentrations. This is explained by the higher concentration MRF forming a body-centered tetragonal lattice in which interparticle adhesion forces are no longer aligned with the applied field. To explore the possibility of dynamically tuning interparticle interactions, we functionalize particles with polystyrene polymers with thymine terminal groups that will only exhibit interparticle hydrogen bonding in the presence of a small linking molecule, namely melamine. We find that MRF formed with these particles also exhibit up to a 40% increase in yield stress and ∼100% increase in stiffness for the polymer grafted particles in the presence of melamine, due to the formation of hydrogen bonding linkages between the thymine and melamine groups. In addition to confirming the role of hydrogen bonding in increasing MRF stiffness and yield stress, these results highlight the possibility of dynamically tuning MRF performance using magnetic fields and chemical modifications.

High-Speed Imaging of the Ultrasonic Deagglomeration of Carbon Nanotubes in Water

Ultrasonic treatment is effective in deagglomerating and dispersing nanoparticles in various liquids. However, the exact deagglomeration mechanisms vary for different nanoparticle clusters, owing to different particle geometries and inter-particle adhesion forces. Here, the deagglomeration mechanisms and the influence of sonotrode amplitude during ultrasonication of multiwall carbon nanotubes in de-ionized water were studied by a combination of high-speed imaging and numerical modeling. Particle image velocimetry was applied to images with a higher field of view to calculate the average streaming speeds distribution. These data allowed direct comparison with modeling results. For images captured at higher frame rates and magnification, different patterns of deagglomeration were identified and categorized based on different stages of cavitation zone development and for regions inside or outside the cavitation zone. The results obtained and discussed in this paper can also be relevant to a wide range of carbonaceous and other high aspect ratio nanomaterials.

Interparticle Adhesion Regulates the Surface Roughness of Growing Dense Three-Dimensional Active Particle Aggregates.

Activity and self-generated motion are fundamental features observed in many living and nonliving systems. Given that interparticle adhesive forces can regulate particle dynamics, we investigate how interparticle adhesion strength controls the boundary growth and roughness of active particle aggregates. Using particle based simulations incorporating both activity (birth, death, and growth) and systematic physical interactions (elasticity and adhesion), we establish that interparticle adhesion strength (fad) controls the surface roughness of a densely packed three-dimensional(3D) active particle aggregate expanding into a highly viscous medium. We discover that the surface roughness of a 3D active particle aggregate increases in proportion to the interparticle adhesion strength (fad) and show that asymmetry in the radial and transverse active particle mean-squared displacement (MSD) suppresses 3D surface roughness at lower adhesion strengths. By analyzing the statistical properties of particle displacements at the aggregate periphery, we determine that the 3D surface roughness is driven by the movement of active particle toward the core at high interparticle adhesion strengths. Our results elucidate the physics controlling the expansion of adhesive 3D active particle collectives into a highly viscous medium, with implications into understanding stochastic interface growth in active matter systems characterized by self-generation of particles.

Viscosity of cohesive granular flows.

Cohesive granular materials such as wet sand, snow, and powders can flow like a viscous liquid. However, the elementary mechanisms of momentum transport in such athermal particulate fluids are elusive. As a result, existing models for cohesive granular viscosity remain phenomenological and debated. Here we use discrete element simulations of plane shear flows to measure the viscosity of cohesive granular materials, while tuning the intensity of inter-particle adhesion. We establish that two adhesion-related, dimensionless numbers control their viscosity. These numbers compare the force and energy required to break a bond to the characteristic stress and kinetic energy in the flow. This progresses the commonly accepted view that only one dimensionless number could control the effect of adhesion. The resulting scaling law captures strong, non-Newtonian variations in viscosity, unifying several existing viscosity models. We then directly link these variations in viscosity to adhesion-induced modifications in the flow micro-structure and contact network. This analysis reveals the existence of two modes of momentum transport, involving either grain micro-acceleration or balanced contact forces, and shows that adhesion only affects the latter. This advances our understanding of rheological models for granular materials and other soft materials such as emulsions and suspensions, which may also involve inter-particle adhesive forces.

Spatial heterogeneity of biochar (segregation) in biochar-amended media: An overlooked phenomenon, and its impact on saturated hydraulic conductivity

While the use of biochar as a soil amendment is gaining popularity for environmental and agricultural purposes, spatial heterogeneity of biochar (segregation) in biochar-amended media and its underlying causes have been overlooked. In this study, for the first time particle segregation in biochar-amended media and its impact on the media's saturated hydraulic conductivity (Ksat) were investigated. Two uniformly graded media were amended with different sizes of a wood-based biochar under dry and wet conditions. While the intended biochar volume fraction (bf) was 17.5%, in dry-packed columns biochar was often segregated and the measured bf ranged from 7.5 ± 0.8 SE% (SE = standard error) to 23.6 ± 1.8 SE% across all spatial locations. If, however, 20% water (volume of water/bulk volume of packed media) was added to the mixtures during mixing, homogeneous packings were achieved. In dry-packing, segregation was governed by the difference in the physical properties of the media and the biochar: particle size, density, and shape. In wet-packing, segregation was prevented due to the inter-particle adhesion forces associated with water. Although X-ray computed tomography images showed that the presence of segregation altered particle distributions and pore morphologies, the Ksat for wet-packed and dry-packed columns were statistically identical. The results of this study suggest that laboratory methods for packing biochar-amended media should include moisturizing the mixture to inhibit particle segregation. Mixing under wet conditions is recommended for any type of soil and biochar and for any scale of application, in both the laboratory and field.

Using Different Powdered Carbon Forms for Reinforcing Aluminum Composite Materials with Carbon and Titanium Carbide: A Review

The use of both traditional powdered carbon materials (graphite, soot, charcoal, and shungite) and novel carbon nanomaterials (nanodiamonds, fullerene, nanotubes, and graphene) as a dispersed reinforcing phase in aluminum matrix composites (AMCs) and as reagents for the synthesis of reinforcing particles of titanium carbide (TiC) in AMCs is considered. It is noted that the main direction of AMC development to significantly improve the mechanical properties consists of the transition from micron-sized reinforcing particles to nanoparticles, and that the use of novel carbon nanomaterials could play a decisive role in this case. It is necessary that the technologies for producing such AMCs provide the appropriate parameters of the nanoparticles, their uniform distribution throughout the matrix, and a strong adhesive interfacial bond with the matrix. However, the implementation of these technological requirements is a great problem, since carbon and titanium carbide nanoparticles cannot be wetted by aluminum at a temperature below 1000°C and are prone to the formation of agglomerates from nanoparticles owing to interparticle adhesive forces, the magnitude of which increases to the greatest extent with a decreasing particle size. An overview of the achievements and unresolved issues in the use of powdered carbon forms in different solid-phase and liquid-phase methods for manufacturing AMCs based on various techniques is presented. It is shown that the potentialities of using traditional carbon materials are not still exhausted. Considerable attention is paid to the use of self-propagating high-temperature synthesis (SHS) for obtaining reinforcing titanium carbide particles with the use of different carbon materials to produce AMCs.

Application of different powdered forms of carbon for reinforcement of aluminum matrix composite materials by carbon and titanium carbide. А review

The paper considers the use of both traditional powdered carbon materials (graphite, soot, charcoal, shungite) and new carbon nanomaterials (nanodiamonds, fullerene, nanotubes, graphene) as a dispersed reinforcing phase in aluminum matrix composites (AMCs), and as reagents for the synthesis of titanium carbide (TiC) reinforcing particles in AMCs. It is observed that the key area of AMC development for significant improvement of their mechanical properties is the transition from micron-sized reinforcing particles to nanoparticles, and that the use of new carbon nanomaterials can play a decisive role in this. The technologies for producing such AMCs must provide the appropriate parameters of nanoparticles, their uniform distribution in the matrix and a strong adhesive interfacial bond with the matrix. However, it is highly difficult to meet these process requirements since carbon and titanium carbide nanoparticles are not wetted with aluminum at temperatures below 1000 °C and are prone to nanoparticle agglomeration due to interparticle adhesive forces that increase dramatically with the decreasing particle size. The paper provides an overview of advancements and unresolved issues in the use of powdered carbon forms in various solid-phase and liquid-phase methods of AMC production using various techniques to address these process challenges. It is shown that there is still a potential for using traditional carbon materials as well. Considerable attention is paid to the self-propagating high-temperature synthesis (SHS) of titanium carbide reinforcing particles with various carbon materials used to obtain aluminum matrix composites.

Suspension rheology of adhesive particles at high shear-rates

An experimentally verification of a novel theoretical relationship between the suspension viscosity and the interparticle adhesion force $F$ is presented.

CFD-DEM study of gas-solid flow regimes in a Wurster type fluidized bed with experimental validation by electrical capacitance tomography

Wurster type fluidized bed is widely used for particle coating in many industrial sectors, the gas-solid flow regimes within the fluidized bed is an important issue but rarely discussed in the literature, either numerically or experimentally. In this work, a numerical method that couples computational fluid dynamics with the discrete element method (CFD-DEM) was proposed to investigate the gas-solid flow dynamics in a Wurster type fluidized bed, with a focus on the existing gas-solid flow regimes. Two types of simulation cases, i.e., cold flow cases and the cases accounting for adhesion forces, were carried out. Experimental data by electrical capacitance tomography (ECT) imaging was employed to validate the simulation results. In cold flow cases, two fluidization regimes, including plug, and multi-bubbling were observed in the annulus region of the fluidized bed. It was found that the multi-bubbling regime can further be classified into bottom, localized and global fluidization under different air velocities, and more than 83% of the total particle mass is kept within annulus region. With increase in the inter-particle adhesion force, the flow regime in the annulus region changed from multi-bubbling to single-bubbling, followed by plug flow and eventually defluidization. The multi-bubbling, single-bubbling, and plug flows can be discriminated by cycle time ranges of 0–4, 4–15 and more than 15, respectively. Finally, it was discovered that the particle circulation times was within the ranges of 3–9 s, and the gas-solid flow regimes can be used as an indicator of the circulation time distribution. The methodology and new findings in this study complement the existing techniques and knowledge for the optimization of coating process in a Wurster type fluidized bed.

The adhesion of homogenized fat globules to proteins is increased by milk heat treatment and acidic pH: Quantitative insights provided by AFM force spectroscopy

The rheological properties and microstructure of dairy gels involve the connectivity between milk fat globules (MFG) and casein micelles that is affected by technological processes such as milk homogenization and heat treatment. The underlying mechanisms require further quantification of the interactions at the nanoscale level to be fully understood and controlled. In this study, we examined the adhesion of homogenized MFG to milk proteins and evaluated the role of ultra-high temperature (UHT) heat treatment and pH. The combination of physico-chemical analysis, rheology and microscopy observations at different scale levels associated to atomic force microscopy (AFM) force spectroscopy were used. AFM experiments performed at the particle scale level showed that adhesion of individual homogenized MFG to milk proteins (1) is increased upon acidification at pH 4.5: 1.4 fold for unheated samples and 3.5 fold for UHT samples, and (2) is enhanced by about 1.7 fold at pH 4.5 after UHT heat treatment of milk, from 176 pN to 296 pN, thanks to highly-reactive heat-denatured whey proteins located at the surface of MFG and caseins. The increased inter-particle adhesion forces accounted for more connected structures and stiffer UHT milk acid gels, compared to unheated-milk gels. Using a multiscale approach, this study showed that heat treatment of milk markedly affected the interactions occurring at the particle's surface level with consequences on the bulk structural and rheological properties of acid gels. Such findings will be useful for manufacturers to modulate the texture of fermented dairy products through the tailoring of heat-induced complexation of proteins and the connectivity of homogenized MFG with the protein network. This work will also contribute in a better understanding of the impact of process-induced changes on the digestibility and metabolic fate of proteins and lipids.

Role of particle size on the cohesive behavior of limestone powders at high temperature

Thermal Energy Storage (TES) using granular solids is gaining momentum in the last years. With no degradation up to very high temperatures and very low price the use of some granular materials such as sand or SiC would be feasible for storing sensible heat at large scale. A further step beyond TES is thermochemical energy storage (TCES) wherein the granular solids undergo a highly endothermic reaction at high temperature. Energy can be in this way more efficiently stored in the long term and released on demand by means of the reverse exothermic reaction. The Calcium Looping process, based on the calcination/carbonation of CaCO3, is being actively investigated for this purpose. However, a caveat of using granular solids for energy storage is the possible increase of interparticle adhesive forces with temperature which would severely hamper the flowability of the solids in the process. The cohesiveness of granular materials is essentially determined by particle size. In this paper we investigate the dependence of the tensile yield strength and compressibility of CaCO3 powders on temperature and consolidation stress using samples of narrow particle size distribution in the relevant range between ∼30 and ∼80μm particle size and temperatures up to 500°C. Our experimental results show that powder cohesiveness is greatly increased with temperature especially in the case of the finest powders whose tensile yield strength can be increased by up 2 orders of magnitude. The increase of cohesiveness with temperature is further enhanced with a previously applied consolidation stress, which is particularly relevant for applications wherein large amounts of solids are to be stored at high temperature. Experimental data are consistent with the predictions by a contact mechanics model assuming that the solids deform plastically at interparticle contacts. A main conclusion from our work is that some mechanical properties of the solids, specially the mechanical hardness, and how they change with temperature, play a critical role on the flowability of the solids as affected by an increase of temperature.

A revised methodology for the determination of bulk material cohesion and adhesion

The determination of the wall liner properties and more importantly the flow properties of a bulk material is critical for the design of any bulk materials handling system. The design of such materials handling systems will be most effective when handling bulk materials at the physical properties they were designed to handle. Due to the fast-paced nature of expansion in the mining industry and demand of mineral resources, it is quite common for materials handling systems to handle bulk materials that were not intended for the system. Wet and Sticky Materials (WSM) within the materials handling stream can cause significant downtime, due to events such as blockages of bins, hoppers and transfer chutes, remains left in train wagons and dump trucks as well as conveyor belt carry back (Roberts, 2005; Connelly, 2011 [2]).WSM are problematic within the materials handling stream due to the inter-particle and boundary cohesion and adhesion forces. The current measurement techniques for WSM have limitations and new methods must be considered. The development of new testers that can measure the wall adhesion and inter-particle adhesion of a bulk material can give a quantitative value for the adhesion present in a bulk material sample. The following paper will present a revised methodology for the estimation of the adhesion of bulk materials determined from the extrapolation of the Instantaneous Yield Locus (IYL). The predicted adhesion values from this methodology will be compared to experimental measurements using an inter-particle adhesion tester.

Effects of sample preparation on the microstructural signatures of faulting in clay-bearing fault gouge

Clay-rich fault gouge in the principal slip zones of faults stores abundant water within pores and between clay interlayers. During the preparation of thin-sections and rock chips for microstructural observations, fault-gouge samples are commonly air-dried at room temperature or in an oven. However, during the drying process, remnant liquid water between gouge grains produces an inter-particle adhesion force (liquid-bridge force), which rearranges the grain-to-grain structure, likely resulting in a disturbance of the original fabric. For this study, we prepared gouge samples from the Itozawa fault, northeastern Japan, using a t-butyl alcohol freeze-drying method that mitigates drying-induced fabric disturbance. We then compared the microstructure of our samples with those prepared using the conventional air-drying method. The freeze-dried samples preserve a smooth fault plane, clearly defined nanoparticles, and well-developed shear-sense indicators, including slickenlines and Riedel shear planes. In contrast, the air-dried samples underwent shrinkage during drying, which distorted the geometry of the fault plane. These air-dried samples lack nanoparticles and display only a weak shear fabric. We conclude that microstructural observations on samples prepared using the t-butyl alcohol freeze-drying method, compared with conventional air-drying, could preserve more evidence for the retrieval of fault information, including the kinematics, slip stability, and dynamic weakening mechanism of a fault.

An ultrasonic feeding mechanism for continuous aerosol generation from cohesive powders

The dispersion of dry, cohesive micro- and nanosized powders has wide applications ranging from medical and environmental science to manufacturing technology. Being able to disperse the dry powder at a stable concentration over periods of time (∼hour to several hours) is challenging to achieve, which we attempt to address with a novel dry powder dispersion technology. A portable, cost effective and simple dry powder dispersion device that uses ultrasonic energy for continuous feeding of aerosol particles to a de-agglomeration device is developed and tested with commercially available powders. The study is performed using 5 µm polyamide powder and rutile TiO2 powders of 500, 100, and 30 nm mean size of primary particles. The ultrasonic dispersion device proved to be able to disperse all of these powders, which represent low-density material to high-density metal oxides, with stable concentration over periods that extend to an hour. From aerosol measurements to obtain the size distribution of various size particles, it is seen that the highly agglomerated powder particles are not easy to de-agglomerate as we go to the lower (nominal) sized powders because of the stronger inter-particle adhesion forces between nanoparticles compared to microparticles. The scanning electron microscopy (SEM) images of particles in their native powder state and those collected after the dispersion showed significant difference in the agglomeration of the powder particles, which suggests partial success of the turbulent jet de-agglomeration employed.Copyright © 2019 American Association for Aerosol Research

Clickable PEG hydrogel microspheres as building blocks for 3D bioprinting.

Three-dimensional (3D) bioprinting is important in the development of complex tissue structures for tissue engineering and regenerative medicine. However, the materials used for bioprinting, referred to as bioinks, must have a balance between a high viscosity for rapid solidification after extrusion and low shear force for cytocompatibility, which is difficult to achieve. Here, a novel bioink consisting of poly(ethylene glycol) (PEG) microgels prepared via off-stoichiometry thiol-ene click chemistry is introduced. Importantly, the microgel bioink is easily extruded, exhibits excellent stability after printing due to interparticle adhesion forces, and can be photochemically annealed with a second thiol-ene click reaction to confer long-term stability to printed constructs. The modularity of the bioink is also an advantage, as the PEG microgels have highly tunable physicochemical properties. The low force required for extrusion and cytocompatibility of the thiol-ene annealing reaction also permit cell incorporation during printing with high viability, and cells are able to spread and proliferate in the interstitial spaces between the microgels after the constructs have been annealed. Overall, these results indicate that our microgel bioink is a promising and versatile platform that could be leveraged for bioprinting and regenerative manufacturing.

Experimental simulations of volcanic ash resuspension by wind under the effects of atmospheric humidity

Ash deposited during volcanic eruptions can be resuspended by wind and become hazardous for health and infrastructure hours to decades after an eruption. Accurate resuspension forecasting requires accurate modelling of the threshold friction velocity of the volcanic particles (Uth*), which is the key parameter controlling volcanic ash detachment by wind. Using an environmental wind tunnel facility this study provides much needed experimental data on volcanic particle resuspension, with the first systematic parameterization of Uth* for ash from the regions Campi Flegrei in Italy and also Eyjafjallajökull in Iceland. In this study atmospheric relative humidity (and related ash moisture content) was systematically varied, from <10% to >90%, which in the case of the Eyjafjallajökull fine ash (<63 μm) produced a twofold increase in Uth*. Using the Campi Flegrei fine ash (<63 μm) an increase in Uth* of only around a factor of 1.5 was observed. Reasonable agreement with force balance resuspension models was seen, which implied an increase in interparticle adhesion force of up to a factor of six due to high humidity. Our results imply that, contrary to dry conditions, one single modelling scheme may not satisfy the resuspension of volcanic ash from different eruptions under wet conditions.

A model for predicting transport velocity in gas fluidized-beds

This study improved the model that used the correlation of the particle entrainment rate to determine the transport velocity. It proposed the new absolute value of the local slope as the criterion of the model for locating the transport velocity in the relationship between dimensionless velocity (U/Ut) and the reciprocal of the entrainment rate (1/Ki∗+). It indicated that the criterion depended on properties of fluidized particles and increased with Archemedes number. The Archemedes number was modified by substituting the critical diameter, the maximum particle diameter at which the sum of the interparticle adhesion forces gave a dominant influence to the particle entrainment rate, for the diameter of particles in case that the mean diameter of particles was smaller than the critical diameter. A correlation was suggested to calculate the absolute value of the local slope at the transport velocity. The new model was successful covering the effect of particle properties in predicting the transport velocity.