Formation Of Particle Chains Research Articles

A novel “S” chain structure mechanism model of magneto-rheological elastomer

Mechanism models based on chain-like structures are often used to characterize the morphology of magneto-rheological elastomer (MRE) and provide theoretical guidance for MRE preparation. However, widely used shear and tension mechanism models based on oblique straight chain or bent-chain structures have the limitation of insufficient accuracy in characterization, mainly because the internal particle chains of anisotropic MRE are not simple oblique straight or bent from scanning electron microscope (SEM) results. Therefore, the particle chain formation and particle interaction mechanism within MRE are revealed firstly. The theoretical results shows that particles tend to form S-like chain structures due to complex attraction and extrusion. On this basis, a novel “S” chain mechanism model is proposed, which is confirmed to have higher accuracy than the ideal shear model and tension model by comparing with the experimental results. The main reason is that the “S” chain mechanism model has realized the unification of shear, compressive, or tension mode, and integrates the fully coupled magnetic field, distribution parameters and interface stretching. The “S” chain mechanism model also takes into account the radius and volume fraction of the particles in MRE preparation, which makes it a more accurate guide to subsequent preparation.

Magnetic coagulation and flocculation of kaolin suspension using Fe3O4 with plant polyphenol self-assembled flocculants

In this work, magnetic flocculant (Fe3O4@PP) was synthesized using plant polyphenol (PP) as a shaping ligand via in situ self-assembly. Characterization results revealed that Fe3O4@PP exhibited uniform particle size and excellent dispersibility with PP coating amount of 16.4 %. Experimental results suggested that Fe3O4@PP showed excellent turbidity removal efficiency in a wide pH range (3.0–10) and initial turbidity range (50–2000 NTU). Under the optimal conditions, Fe3O4@PP achieved 95.2 % of turbidity removal for simulated kaolin suspension and 96.9 % for actual wastewater. Fe3O4@PP exhibited excellent recycling and reusability properties, with high recycling efficiency of 93.3 % even after the fifth cycle. Microscopic observation revealed the formation process of magnetic flocs, involving particle aggregation, chain and cluster formation, and dense network aggregate formation. The structural characteristics and size of magnetic flocs were found to be significantly influenced by the combined effects of magnetic force, electric charge, van der Waals force, and functional groups on the surface of PP. The extended Deryaguin-Landau-Verwey-Overbeek models indicated that magnetic interactions were the primary mechanism for magnetic flocculation, accompanied by charge neutralization, adsorption bridging, sweeping, and net trapping.

Tools for the quantification of the dynamic assembly of colloidal chains of ellipsoidal particles

The assemblies of colloidal particles and their characterization are becoming more complex as new particle shapes, materials, and assembly methods are being introduced. Consequentially, there is a need for tools that can analyze videos and extract quantitative data from qualitative media to elucidate the dynamic processes of assembly formations. This contribution presents an algorithm that analyzes videos of the 2D assembly process of ellipsoidal particles. Particles are both classified using abstracted interparticle properties and tracked over time. Our algorithm is customized to quantiatively analyze the dynamic assembly of the ellipsoidal colloidal particles into chains, which break and reform over time. By analyzing the yielded data from our algorithm, we better elucidate the dynamic nature of particle chain formation. We foresee our algorithm being capable of analyzing videos in real time to study the dynamic assembly behavior of diverse matter such as biological samples and nanoparticles of various shapes.

Gap Distance Between Pearl Chains in Acoustic Manipulation

We present a theory to compute the stable gap (interparticle) distance between particle chains collected in the pressure node of an acoustic standing wave. The primary and secondary acoustic radiation forces are the two competing forces that act on the particles during the particle chain formation. The stable equilibrium distance between two chains is reached when both forces are in balance. Most interestingly, the density scattering coefficient appears to the second power in the theoretical prediction of the gap distance, indicating that the particle-chain formation occurs for both particles heavier than the surrounding medium and, notably, also for buoyant particles. Experimentally, the gap distance is evaluated for several different media and particle material combinations and the particle-chain formation is observed for both buoyant particles and particles heavier than the surrounding medium. The theory agrees well with experiments in the cases where the material properties of the medium and the particles are well known.

Trapping multiple absorbing particles in air using an optical fiber by photophoretic forces

We demonstrate photophoretic force-based optical trapping of multiple absorbing particles in air by loosely focusing a Gaussian beam emanating from a single mode fiber using convex lenses of different focal lengths, and investigate the dependence of the number of trapped particles and their sizes on the focal length. We observe the formation of particle chains at a particular focal length, and measure the axial dynamic range of optical trapping for each lens system. We then develop a numerical simulation to explain this observed dynamic range by estimating the temperature distribution across a particle surface, and determining the axial photophoretic force. Our simulation results are in reasonable agreement with experimental results. Interestingly, we also observe that the average size of trapped particles reduces as we increase the lens focal lengths. This is somewhat intriguing as each lens produces the same intensity profile, albeit at different axial distances. However, the axial intensity gradient reduces as the lens focal length is increased, which suggests that such gradients may somehow be involved in the mechanism of photophoretic confinement.

On the polydisperse particle migration and formation of chains in a square channel flow of non-Newtonian fluids

The migration of polydisperse particles and the formation of self-organized particle chains in a square channel flow of non-Newtonian fluids is studied. The effects of rheological behaviour of the fluid, solution concentration and flow rate are explored experimentally. The direct forcing/fictitious domain method is adopted to qualitatively verify the experiments and further analyse the mechanisms of particle migration and particle chain self-organization. The results show that only particles in viscoelastic fluids with negligible shear-thinning effect will remain at the channel centreline as the flow rate increases. The monodisperse particles reach the same velocity when migrating to the equilibrium position. However, in polydisperse suspensions, the smaller the particle diameter, the greater the velocity when the particle migrates to the equilibrium position. In a viscoelastic fluid, the polydisperse particles are more likely to self-organize into long particle chains along the channel centreline than the monodisperse particles, where the large and small particles are at the front and end of the chain. The dimensionless alignment factor (Af) is adopted to quantify the formation of particle chains, which is the largest in viscoelastic fluids and rapidly increases before decreasing to a stable value as the flow rate increases. For larger particle diameter ratios and stronger shear-thinning effect, the long particle chain self-organization is less obvious. The self-organizing particle chains at the channel centreline are strongly influenced by the fluid elastic properties and weakly by the inertial effect; however, the shear-thinning effect disperses the particles and prevents the formation of long straight particle chains.

Experimental and Theoretical Study of Electric-Field-Induced Long Particle Chain Formation in Mgo Aerosols

Experimental and Theoretical Study of Electric-Field-Induced Long Particle Chain Formation in Mgo Aerosols

Synthesis of Si nanoparticle chains and nanowhiskers by the monosilane decomposition in an adiabatic process during cyclic compression

A cyclic adiabatic compression reactor is used for the Si powder fabrication by the monosilane decomposition in a gas mixture with argon. Along with arbitrary agglomerations of Si nanoparticles, this method allows synthesizing nanoparticle chains and nanowhiskers, as an outlet gas pressure in the reactor increases from about 2.0 to 5.0 MPa. The increase in pressure corresponds to an increase in temperature from ~450 to 1050 °C, which leads to a change in the particle structure from amorphous to crystalline and reduces the particle size distribution. The particle chain and nanowhisker formation is associated with an increase in the duration of the synthesis process. The optical properties of the synthesized Si powders were determined by Si/SiO2 interfaces appeared by the oxidation in the air. The method is characterized by a relatively high production rate of Si powders of various morphologies, which may be of interest for various applications.

Thermorheological properties of magnetorheological grease and its thermomagnetic coupling mechanism

A heating phenomenon exists in the service process of magneto-rheological devices. For magnetorheological devices using magnetorheological grease (MRG) as the working medium, changes in the medium’s rheological behaviors caused by temperature increase will generate challenges in the reliable service of the devices. With laboratory-prepared MRG as the research object, MRG rheological property laws under different temperatures and magnetic field intensities are investigated, and the magnetic properties of carbonyl iron (CI) powder under different temperatures are analyzed. The relationship between the evolution of the MRG structural system and changes in rheological properties under the action of thermomagnetic coupling is discussed. The results show that the MRG structural system is composed of base carrier liquid soap fibers and magnetic chains under the action of a magnetic field, and the soap fibers can strengthen the structural intensity of the MRG. A decrease in the entanglement degree of the soap fiber structure caused by temperature increase will obviously weaken the intensity of the entire MRG system and narrow the regulation and control scope of the MRG rheological properties. The structural evolution of soap fibers under thermomagnetic coupling will affect the chain formation of magnetic particles and ultimately their rheological properties. At low temperature and magnetic field intensity, the entanglement degree of soap fibers is relatively high, and the magnetic force on magnetic particles is weak, which cannot completely overcome the binding of soap fibers. The influence of soap fibers is the dominant factor affecting the MRG rheological properties. As temperature and magnetic field intensity increase, the entanglement degree of soap fibers decreases, magnetic particles gradually disperse from the soap fibers under the action of a large magnetic field force, and the magnetic chain structure gradually becomes the dominant factor affecting the MRG rheological properties. Moreover, the weakening degree of the temperature increase effect on the MRG rheological properties decreases, and the rheological law changes gradually.

Chain formation mechanism of magnetic particles in magnetorheological elastomers during pre-structure

Current research on magnetic particles in magnetorheological elastomers (MRE) mainly focuses on the effect of particle distribution and arrangement on the mechanical properties. However, there are few studies on the chain formation mechanism of magnetic particles in MRE. In order to solve the above problems, we proposed a numerical simulation method to study the movement of magnetic particles in MRE. First, the force of the magnetic particles under the magnetic field was analyzed, and the magnetic particle movement model was established. Further, the change of the movement parameters of the particles during the contact process was obtained, including the changes of magnetic force, viscous force, displacement, and velocity. According to the analysis results, the critical angle of attraction and repulsion was determined, and the simulation results were verified by experiments. Finally, the effect of magnetic field strength, volume fraction and particle size on the chain formation of magnetic particles was simulated, it was found that the strength of the external magnetic field affected the efficiency of particle chain formation, and the volume fraction and particle size affected the morphology of the particle chain formation.

Chains of cubic colloids at fluid-fluid interfaces.

Inspired by recent experimental observations of spontaneous chain formation of cubic particles adsorbed at a fluid-fluid interface, we theoretically investigate whether capillary interactions can be responsible for this self-assembly process. We calculate adsorption energies, equilibrium particle orientations, and interfacial deformations, not only for a variety of contact angles but also for single cubes as well as an infinite 2D lattice of cubes at the interface. This allows us to construct a ground-state phase diagram as a function of areal density for several contact angles, and upon combining the capillary energy of a 2D lattice with a simple expression for the entropy of a 2D fluid we also construct temperature-density or size-density phase diagrams that exhibit large two-phase regions and triple points. We identify several regimes with stable chainlike structures, in line with the experimental observations.

Average cluster size inside sediment left after droplet desiccation

In this work, we continue to study the formation of particle chains (clusters) inside the annular sediment during the drying of a colloidal droplet on a substrate. The average value of the cluster size was determined after processing experimental data from other authors. We performed a series of calculations and found the value of the model parameter allowed to get numerical results agreed with the experiment. Also, a modification of the previously proposed algorithm is analyzed here.

Ionization waves in the PK-4 direct current neon discharge

The PK-4 system is a micro-gravity dusty plasma experiment currently in operation on-board the International Space Station. The experiment utilizes a long DC discharge in neon or argon gases. We apply our 2D particle-in-cell with Monte Carlo collisions discharge simulation to compute local plasma parameters that serve as input data for future dust dynamics models. The simulation includes electrons, Ne+ ions, and Ne m metastable atoms in neon gas and their collisions at solid surfaces including secondary electron emission and glass wall charging. On the time scale of the on-board optical imaging, the positive column appears stable and homogeneous. On the other hand, our simulations show that on microsecond time scales the positive column is highly inhomogeneous: ionization waves with phase velocities in the range between 500 m s−1 and 1200 m s−1 dominate the structure. In these waves, the electric field and charged particle densities can reach amplitudes up to 10 times of their average value. Our experiments on ground-based PK-4 replica systems fully support the numerical findings. In the experiment, the direction of the DC current can be alternated, which has been found to favor dust particle chain formation. We discuss possible mechanisms for how the highly oscillatory plasma environment contributes to the dust particle chain formation.

Efficient Chain Formation of Magnetic Particles in Elastomers with Limited Space

The magnetic response of the storage modulus for bimodal magnetic elastomers containing magnetic particles with a diameter of 7.0 μm and plastic beads with a diameter of 200 μm were investigated by varying the volume fraction of plastic beads up to 0.60 while keeping the volume fraction of the magnetic particles at 0.10. The storage modulus at 0 mT for monomodal magnetic elastomers was 1.4 × 104 Pa, and it slightly increased with the volume fraction of plastic beads up to 0.6. The storage modulus at 500 mT for bimodal magnetic elastomers at volume fractions below 0.25 was constant, which was equal to that for the monomodal one (=7.9 × 104 Pa). At volume fractions of 0.25–0.40, the storage modulus significantly increased with the volume fraction, showing a percolation behavior. At volume fractions of 0.40-0.60, the storage modulus was constant at 2.0 × 105 Pa, independently of the volume fraction. These results indicate that the enhanced increase in the storage modulus was caused by the chain formation of the magnetic particles in vacancies made of plastic beads.

Complex dynamical interplay between solid particles and flow in driven granular suspensions

Granular materials immersed in a fluid are ubiquitous in daily life, industry, and nature. They include food processing, pastes, cosmetics, paints, concretes, cements, muds, wet sands, snows, landslides, and lava flow. They are known to exhibit a rich variety of complex rheological behavior, but the role of a fluid component in such behavior has remained poorly understood due to the nonlocal and many-body nature of hydrodynamic interactions between solid particles mediated by the fluid. We address this fundamental problem by comparing the microrheological response of athermal granular suspensions with and without hydrodynamic interactions to an externally driven probe particle by numerical simulations. We find that the presence of the fluid drastically increases the drag coefficient of the probe particle by more than one order of magnitude near the jamming transition. We reveal that this is a consequence of the nontrivial long-range nature of hydrodynamic interactions, which originates from unlimited cumulative transmission of near-field hydrodynamic interactions due to the incompressibility of both fluid and solid particles. Force chain formation of solid particles is dynamically coupled with hydrodynamic flow, leading to strong spatiotemporal fluctuations of flow pattern and nonlinear rheological response. Our study reveals essential roles of hydrodynamic interactions in complex rheological behavior of dense granular suspensions under an external drive.

Simulation Study on the Motion of Magnetic Particles in Silicone Rubber-Based Magnetorheological Elastomers

Magnetorheological elastomer (MRE) is an intelligent composite material and has been widely used in various fields such as vibration reduction and sensing. MRE has an excellent magnetorheological effect through the chaining of its internal magnetic particles. Current studies on MREs mainly focus on the preparation of materials and characterization of mechanical properties. However, very few studies have been conducted on the mechanism of magnetic particle motion during MRE curing. Based on the silicone rubber-based MRE, the motion mechanism of magnetic particles during curing was explored through numerical simulation. First, we analyzed the magnetic force and viscous force of magnetic particles in MRE and discussed the equations of motion of magnetic particles under applied magnetic field. Further, we established a uniform magnetic field model through the finite element method and simulated the motion of two magnetic particles under the magnetic field. Finally, we discussed the effects of particle distribution angles, particle radii, applied magnetic field strength, and distance between particles on particle velocity and displacement. The results show that the distance between particles has the greatest influence on the motion of magnetic particles, and the size of the distance between particles will affect the contact time of the particles, thus affecting the chain formation of magnetic particles in the MRE.

Influence of Shell Thickness on the Colloidal Stability of Magnetic Core-Shell Particle Suspensions.

We present a Discrete Element study of the behavior of magnetic core-shell particles in which the properties of the core and the shell are explicitly defined. Particle cores were considered to be made of pure iron and thus possessed ferromagnetic properties, while particle shells were considered to be made of silica. Core sizes ranged between 0.5 and 4.0 μm with the actual particle size of the core-shell particles in the range between 0.6 and 21 μm. The magnetic cores were considered to have a magnetization of one tenth of the saturation magnetization of iron. This study aimed to understand how the thickness of the shell hinders the formation of particle chains. Chain formation was studied with different shell thicknesses and particle sizes in the presence and absence of an electrical double layer force in order to investigate the effect of surface charge density on the magnetic core-shell particle interactions. For core sizes of 0.5 and 4.0 μm the relative shell thicknesses needed to hinder the aggregation process were approximately 0.4 and 0.6 respectively, indicating that larger core sizes are detrimental to be used in applications in which no flocculation is needed. In addition, the presence of an electrical double layer, for values of surface charge density of less than 20 mC/m2, could stop the contact between particles without hindering their vertical alignment. Only when the shell thickness was considerably larger, was the electrical double layer able to contribute to the full disruption of the magnetic flocculation process.

Chain Formation and Agglomeration Characterization of Magnetic Particles in Magnetorheological Fluids

Chain Formation and Agglomeration Characterization of Magnetic Particles in Magnetorheological Fluids

Molybdenum and tungsten disulfides surface-modified with a conducting polymer, polyaniline, for application in electrorheology

Molybdenum and tungsten sulfides are semiconducting materials with flake-like morphology. Their applicability in electrorheological suspensions was enabled by the coating with a conducting polymer, polyaniline, after its conversion to non-conducting polyaniline base. For instance, the conductivity of tungsten sulfide, 0.056Scm−1, increased to 0.98Scm−1 after coating with polyaniline, and was conveniently reduced to 6.3×10−6Scm−1 after conversion to polyaniline base. Such approach reduces the potential current drifts in electrorheological suspensions and allows for the application of sulfides in electrorheology. The optical microscopy demonstrated the formation of particle chains in silicone-oil suspensions after application of electric field. The electrorheological performance was assessed by the measurement of viscosity on the shear rate in the absence and in the presence of electric field and it is discussed on the bases of dielectric spectra.

Squeeze flow behavior of shear thickening fluid under constant volume

Squeeze flow behavior of shear thickening fluid (STF) consisting of SiO2 particles and ethylene glycol (EG) was investigated. STF was squeezed out radially between the parallel plate accessory of rheometer. Due to formation of particle chains and alignment of clusters, an obvious increase in normal stress was found in the squeeze procedure. When the sample (71 wt% SiO2) thickness was squeezed from 1 mm to 0.2 mm, normal stress rapidly increased from 0 Pa to 38.48 kPa. In comparison to the peak stress under shear mode (6.38 kPa), the squeeze stress of STF was larger. Moreover, it was found that normal stress was significantly enhanced at large squeeze velocity, large mass fraction and appropriate wall roughness. Meanwhile, shear viscosity under moving boundary was studied by applying a constant shear on STF during the squeeze test. Together with the shear effects, squeeze could change the inner particle distributions and affected the rheological property of STF. The related results were helpful for further understanding the shear thickening mechanism and developing new STF-based applications.