Formation Of Particle Clusters Research Articles

Asymptotic analysis of particle cluster formation in the presence of anchoring sites

The aggregation or clustering of proteins and other macromolecules plays an important role in the formation of large-scale molecular assemblies within cell membranes. Examples of such assemblies include lipid rafts, and postsynaptic domains (PSDs) at excitatory and inhibitory synapses in neurons. PSDs are rich in scaffolding proteins that can transiently trap transmembrane neurotransmitter receptors, thus localizing them at specific spatial positions. Hence, PSDs play a key role in determining the strength of synaptic connections and their regulation during learning and memory. Recently, a two-dimensional (2D) diffusion-mediated aggregation model of PSD formation has been developed in which the spatial locations of the clusters are determined by a set of fixed anchoring sites. The system is kept out of equilibrium by the recycling of particles between the cell membrane and interior. This results in a stationary distribution consisting of multiple clusters, whose average size can be determined using an effective mean-field description of the particle concentration around each anchored cluster. In this paper, we derive corrections to the mean-field approximation by applying the theory of diffusion in singularly perturbed domains. The latter is a powerful analytical method for solving two-dimensional (2D) and three-dimensional (3D) diffusion problems in domains where small holes or perforations have been removed from the interior. Applications range from modeling intracellular diffusion, where interior holes could represent subcellular structures such as organelles or biological condensates, to tracking the spread of chemical pollutants or heat from localized sources. In this paper, we take the bounded domain to be the cell membrane and the holes to represent anchored clusters. The analysis proceeds by partitioning the membrane into a set of inner regions around each cluster, and an outer region where mean-field interactions occur. Asymptotically matching the inner and outer stationary solutions generates an asymptotic expansion of the particle concentration, which includes higher-order corrections to mean-field theory that depend on the positions of the clusters and the boundary of the domain. Motivated by a recent study of light-activated protein oligomerization in cells, we also develop the analogous theory for cluster formation in a three-dimensional (3D) domain. The details of the asymptotic analysis differ from the 2D case due to the contrasting singularity structure of 2D and 3D Green’s functions.Graphical abstract2D model of diffusion-based protein cluster formation in the presence of anchoring cites and particle recycling. a A set of N anchoring sites at positions xj\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ extbf{x}}_j$$\\end{document}, j=1,…,N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$j=1,\\ldots ,N$$\\end{document}, in a bounded domain Ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Omega $$\\end{document}. b Diffusing particles accumulate at the anchoring sites resulting in the formation of particle aggregates or clusters Uj\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal {U}}}_j$$\\end{document}. c The clusters are dynamically maintained by a combination of lateral diffusion outside the clusters and particle recycling

Turbulence Unsteadiness Drives Extreme Clustering.

We show that the unsteadiness of turbulence has a drastic effect on turbulence parameters and in particle cluster formation. To this end we use direct numerical simulations of particle laden flows with a steady forcing that generates an unsteady large-scale flow. Particle clustering correlates with the instantaneous Taylor-based flow Reynolds number, and anticorrelates with its instantaneous turbulent energy dissipation constant. A dimensional argument for these correlations is presented. In natural flows, unsteadiness can result in extreme particle clustering, which is stronger than the clustering expected from averaged inertial turbulence effects.

Comparison of CFD-DEM and MP-PIC in the Simulation of Metal Powder Conveying for Laser Metal Deposition

Pneumatic conveying of fine powders is essential for many industrial processes, including Laser Metal Deposition (LMD), a Direct Metal Additive Manufacturing (DMAM) technology that builds solid objects layer-by-layer using a laser to melt metal powder. To optimize the process, it is necessary to have a correct understanding of the powder’s behaviour under the process condition. The coupled Computational Fluid Dynamics - Discrete Element Modelling (CFD-DEM) and MultiPhase - Particle In Cell (MP-PIC) are two popular Eulerian-Lagrangian models to simulate particle laden flows. This study compares them to analyse powder behaviour in a small channel of LMD machines. Results from the two methods differ significantly, with CFD-DEM offering a more accurate representation of the physical reality, while MP-PIC is more computationally efficient. The study finds that the CFD-DEM method produces higher fluctuations in the solids flow rate due to the formation of particle clusters, while MP-PIC displays a smooth and essentially uniform flow. The results suggest that CFD-DEM should be used for more accurate and detailed studies of solids flow rate in pneumatic conveying systems, while MP-PIC can be used for preliminary studies and design optimization.

Study the effect of cohesion on fine particle transportation through a pore doublet model: A CFD-DEM study

This research delves into the transportation of micro-sized particles within a doublet pore model featuring two distinct pore throat sizes. To simulate a two-phase particle-fluid suspension, the CFD-DEM method is employed, combining the Navier-Stokes equation with Newton's second law of particle motion. Cohesion forces between particles and pore throats are characterized using the Simplified Johnson-Kendall-Roberts (SJKR) contact model, which is applied in our simulation to identify locations of agglomerations. Results reveal that altering cohesive energy density, from 10,000 Jm3 to 100,000 Jm3, significantly increases the likelihood of agglomeration in the smaller pore throat. It becomes evident that areas in close proximity to the throats are the most prone to particle agglomerations, leading to pressure drops over time. The formation of particle clusters within the pore throats intensifies with both an increase in the number of particles and fluid velocity from 0.001ms to 0.01ms. Nevertheless, low flow rates (0.001ms) are insufficient to mitigate blockages.

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.

Heterogeneous Dynamics of Sheared Particle-Laden Fluid Interfaces with Janus Particle Doping.

The formation of particle clusters can substantially modify the dynamics and mechanical properties of suspensions in both two and three dimensions. While it has been well established that large network-spanning clusters increase the rigidity of particle systems, it is still unclear how the presence of localized nonpercolating clusters affects the dynamics and mechanical properties of particle suspensions. Here, we introduce self-assembled localized particle clusters at a fluid-fluid interface by mixing a fraction of Janus particles in a monolayer of homogeneous colloids. Each Janus particle binds to a few nearby homogeneous colloids, resulting in numerous small clusters uniformly distributed across the interface. Using a custom magnetic rod interfacial stress rheometer, we apply linear oscillatory shear to the particle-laden fluid interface. By analyzing the local affine deformation of particles from optical microscopy, we show that particles in localized clusters experience substantially lower shear-induced stretching than their neighbors outside clusters. We hypothesize that such heterogeneous dynamics induced by particle clusters increase the effective surface coverage of particles, which in turn enhances the shear moduli of the interface, as confirmed by direct interfacial rheological measurements. Our study illustrates the microscopic dynamics of small clusters in a shear flow and reveals their profound effects on the macroscopic rheology of particle-laden fluid interfaces. Our findings open an avenue for designing interfacial materials with improved mechanical properties via the control of formation of localized particle clusters.

Talc concentration effect on shelf life of acetaminophen tablets

Excipients in pharmaceutical formulations are inactive ingredient from the biological point of view, but they have a key role in the preparation, and they can alter the stability of the active principle. In this work, we prepared acetaminophen tablets with different amounts of talc as excipient and the thermal stability was deeply investigated by thermogravimetric studies. Isoconversional analysis by Kissinger–Akahira–Sunose method and “Master plot” analysis have been successfully employed to describe the kinetics of degradation under inert atmosphere, and the shelf lives have been calculated as a function of the talc content. The shelf-life values as well as the activation energy, which is the dominant factor, evidenced that the inorganic filler enhances the drug degradation to a certain extend and that the composition dependence has a peculiar trend reflecting the particle cluster formation at a critical concentration value. An effort of physico-chemical explanation for this behaviour is put forward by a simple geometrical model from the microparticle-size analysis to predict the critical talc concentration.

Spectroscopic investigation of phase transformation of calcium oxalate dehydrates (renal calculi) using acidic Bryophyllum pinnatom powder

Urolithiasis is one of most common renal disorders, characterized by the formation of kidney stones (renal calculi) through the crystallization process within the urinary system. The frequently observed renal calculi are calcium oxalate renal calculi and treatment is done by shock wave method or lithotripsy which is harmful for other cells of the internal system. The objective of this work was to evaluate in vitro diagnosis of calcium oxalate kidney stones in the aqueous solution of Bryophyllum pinnatum. The B. pinnatum powder was mixed in apple cider vinegar and lemon juice separately to make solution 1 and 2 respectively. Apple cider vinegar and lemon juice were used as solvents due to their acidic and body compatible nature. Two surgically removed stones was dipped in solution 1 and 2. After two weeks, kidney stone of weight 2.7 g is completely dissolved in solution 2 while a considerable weight reduction of other kidney stone has been observed in solution 1. Fourier transform infrared (FTIR) spectroscopy results show the presence of two strong absorption peaks at 610 and 912 (cm−1) in both solutions after dissolution of urinary stones are related to calcium oxalate dehydrate (COD). Raman spectra further confirm the dissolution of COD in solution having Raman shifts at 504 and 910 (cm−1). Cluster formation and aggregation of particles has been observed in scanning electron microscopy images. This in vitro study proves that a mixture of Bryophyllum pinnatum powder and lemon juice is a best remedy to remove kidney stones.

Simulation and verification of particle flow with an elastic collision by the immersed edge-based smoothed finite element method

The immersed edge-based smoothed finite element method (IES-FEM) is proposed for the study of elastic collision particulate flow. Particle collision becomes more realistic by using the penalty function and the hyperelastic constitutive model. The effects of grid resolution and Reynolds numbers on particle terminal velocity and drag coefficient are discussed to verify the calculation accuracy and stability. Single-particle collisions with the bottom and side walls are analyzed and experimentally verified. Results show that the calculation error of IES-FEM is less than 0.6% when the fluid grid size is 0.5 times the particle mesh size and the time step is 10–4 s. Particle drag coefficient and flow characteristics agree well with the published models and experiment results. To demonstrate the capabilities of IES-FEM in complex elastic particle systems, the collision and rebound of multiple particles are determined, including the drafting–kissing–tumbling of two circular particles; the chase, collision, and deformation of rectangular particles; and the repeated formation and separation of particle clusters. This work extends the application of IES-FEM in particle-resolved direct numerical simulation methods, which will provide an optional tool for future elastic blood cell flow and collision.

Effect of Pressure on Burning and Soot Characteristics of RP-3 Kerosene Droplets under Sub-Atmospheric Pressure.

The burning and soot characteristics of RP-3 kerosene droplets under sub-atmospheric pressure were experimentally investigated in a pressure chamber. The droplet size during combustion was continuously recorded using a high-speed camera, and the burning rate based on the d 2-law was determined. The flame temperature was calculated from ICCD camera spectral data using two-color pyrometry, and the carbon soot volume fraction was measured by the calibrated laser-induced incandescence (LII) technique. Soot particles were also sampled using a thermophoretic deposition probe and characterized using a transmission electron microscope (TEM) for particle size and morphology. The results showed that the droplet burning rate increased monotonically with increasing pressure under sub-atmospheric pressure, and the flame temperature slightly decreased with increasing pressure. Sub-atmospheric pressure environment significantly inhibits the formation of soot particle clusters during the ignition of droplets. The average soot volume fraction in the flame increases approximately with increasing pressure at 0.2-1.0 bar with a power of 2.044 ± 0.066. As the pressure decreases from 1.0 to 0.2 bar, the average soot volume fraction decreases significantly from 11.801 to 0.437 ppm. This is mainly due to the fact that the sub-atmospheric environment not only inhibits the collision growth of soot particles but also promotes the oxidation process of soot particles. The collected soot particles reveal a significant reduction in particle size under sub-atmospheric pressure with average primary soot particles of 48.23, 40.06, 27.096, and 18.718 nm at 1.0, 0.6, 0.4, and 0.3 bar pressures, respectively. The change in the number density of carbon soot particles is not significant, which reveals that the change in the diameter of soot particles under sub-atmospheric pressure plays a key role in the change in the volume fraction of soot.

Experimental Measurement of Enhanced and Hindered Particle Settling in Turbulent Gas‐Particle Suspensions, and Geophysical Implications

AbstractThe dynamics of geophysical dilute turbulent gas‐particles mixtures depends to a large extent on particle concentration, which in turn depends predominantly on the particle settling velocity. We experimentally investigate air‐particle mixtures contained in a vertical pipe in which the velocity of an ascending air flux matches the settling velocity of glass particles. To obtain local particle concentrations in these mixtures, we use acoustic probing and air pressure measurements and show that these independent techniques yield similar results for a range of particle sizes and particle concentrations. Moreover, we find that in suspensions of small particles (78 μm) the settling velocity increases with the local particle concentration due to the formation of particle clusters. These clusters settle with a velocity that is four times faster than the terminal settling velocity of single particles, and they double settling speeds of the suspensions. In contrast, in suspensions of larger particles (467 μm) the settling velocity decreases with increasing particle concentration. Although particle clusters are still present in this case, the settling velocity is decreased by 30%, which is captured by a hindered settling model. These results suggest an interplay between hindered settling and cluster‐induced enhanced settling, which in our experiments occur respectively at Stokes number O(100) and O(1). We discuss implications for volcanic plumes and pyroclastic currents. Our study suggests that clustering and related enhanced or hindered particle settling velocities should be considered in models of volcanic phenomena and that drag law corrections are needed for reliable predictions and hazard assessment.

Tuned drop-shape magnetophoretic conductors for controlled single-particle transport in microfluidic chips

In recent years, lab-on-a-chip devices have attracted many researchers due to their numerous advantages, making them suitable for important bioapplications. One of the key challenges in this field is manipulating a group of particles and cells at single-particle resolution. Different techniques have been proposed to tackle this challenge; however, none of them offer the controllability and scalability required in most bioapplications. Recently, drop-shape magnetophoretic circuits have been introduced as an advanced technique for the precise transport of a great number of particles simultaneously. However, in moving along the magnetic track, the particles experience a sudden jump from one magnet to the next one, which may not be in a highly controlled fashion and can be problematic. To overcome this issue, in the current work, we introduce a new design equipped with a tuning gate electrode added to the blind spots of the magnetophoretic conductor. This design transports the particles in a tri-axial magnetic field, with a vertical bias field that reduces the attraction force between particles and inhibits the particle cluster formation. We study the effect of straight and curved current-carrying gates and show that they positively affect the resulting magnetic energy. Based on our finite element method, we found the curved gate offers controlled smooth particle transport at lower electrical currents. We fabricate the proposed chip based on this design and show that the experimental results agree well with the simulation predictions. The introduced design enhances the reliability of the magnetophoretic circuits operating in a tri-axial magnetic field and makes them good candidates for fundamental applications in single-cell biology and medicine.

Agglomeration behavior of the dense medium in a gas–solid separation fluidized bed

In this study, the atomic force microscopy (AFM) was used to measure the micro-forces between different particles and study the influence of different operating parameters on the formation of particle clusters in the gas–solid fluidized bed separation process. In this way, the mechanism of liquid bridge formation and fracture can be elucidated, thereby providing a theoretical basis for inhibiting the formation of particle clusters. The results indicated that for relative humidity (RH) < 40%, the extrusion liquid bridge is the dominant factor for the formation of the particle liquid bridge, and the liquid film thickness, h, and liquid film volume, Vsq, vary linearly with RH; however, once the RH is > 40%, these relationships become nonlinear. The adhesion force between magnetite powder particles was found to be the largest and that between pulverized coal particles was found to be the smallest, with the mixture of the two particle types being in between. Further, the adhesion between particles increased monotonically with RH, while showing a maximum value with increasing particle separation. A theoretical analysis of the critical fracture distance, Drupture*, of the particle liquid bridge showed that, as the liquid bridge volume, V*, and contact angle, θ, increase, Drupture* gradually increases, but its rate of increase rate. The theoretical analysis was found to be largely consistent with the experimental data, only deviating at low RH.

Sedimentation and rheological behavior of reactive and non-reactive magnesium hydroxide pulps for industrial spray dryer processing

Two different reactive concentrated magnesium hydroxide (HM) pulps, produced in a lab reactor mill, and a synthetic and non-reactive HM-pulp, for comparative analyses, have been prepared and studied. Sodium polyacrylate was selected as a dispersant for improving the HM pulp fluidity, with concentrations varying from 0.42% to 2.0% on a dry basis. The two reactive pulps differed from each other mainly by the impurity level and for both, a residual MgO amount was detected, implying that the hydration reaction could proceed. Results (with and without dispersant) confirmed the formation of particle clusters as HM concentration rose until a critical value, above which the pulp behaved as a solid. Reactive HM-pulps with high impurities may represent a limiting factor in the drying operation. Among all HM-pulps studied, the purest reactive pulp with 1% dispersant presented the best flow behavior making this reactive pulp the most suitable to be tested in a pilot spray dryer.

Rheology and microstructure of thermoresponsive composite gels of hematite pseudocubes and Pluronic F127.

Stimuli-responsive materials or smart materials are designed materials whose properties can be changed significantly by applying external stimuli, such as stress, electric or magnetic fields, light, temperature, and pH. We report the linear and nonlinear rheological properties of thermoresponsive composite gels based on submicron-sized hematite pseudocube-shaped particles and a triblock copolymer Pluronic F127 (PF127). These novel composites form hard gels at an elevated temperature of 37°C. For certain concentrations (<20 w/v. %) of hematite pseudocubes in 17.5 w/v. % of PF127, the gel strength is enhanced and the brittleness of the gels decreases. Higher concentrations (>20 w/v. %) of hematite pseudocubes in PF127 result in weaker and fragile gels. We develop an extensive rheological fingerprint using linear and nonlinear rheological studies. Adsorption of PF127 copolymer molecules on the hematite cube surfaces would further assist the formation of particle clusters along with magnetic interactions to be held effectively in the PF127 micellar network at elevated temperatures. The microscopic structure of these composite gels is visualized through a confocal microscope. Our experiments show that addition of hematite cubes up to 20 w/v. % does not change the rapid thermal gelation of PF127 solutions; hence, the hematite-PF127 composite, which transforms into a hard gel near human body temperature of 37°C, could be suitable for use in smart drug delivery systems.

Antibacterial Effect of Green Synthesized Silver Nanoparticles using Cineraria maritima

Nanoparticles display entirely novel physicochemical characteristics for specific applications because of their exceptional size and shape. Owing to the present study, we reported biosynthesis, characterization and antibacterial properties of Cineraria maritima (Cm) assisted silver nanoparticles (Ag NPs). The surface plasmon vibration, crystalline structure, surface morphology, elemental composition, and possible functional molecules vibration of prepared Cm-Ag NPs were characterized by different instrumentation techniques. The spectrum of UV-Vis of Cm-Ag NPs showed maximum plasma intensity occurred around 425nm. XRD spectrum showed the face-centred cubic (FCC) nature of Cm-Ag NPs. The SEM image of the Cm-Ag NPs demonstrated a predominantly spherical shape with cluster formation of small particles to large particles with sizes ranging from 21.57 nm to 39.16 nm. EDS spectrum indicated the existence of Ag elements in Cm-Ag NPs. FTIR intense peaks of Cm-Ag NPs showed the different functional molecules such as phenol, alkene, aldehydes, and a carbonyl group. In addition, Cm-Ag NPs coated textile cotton fabric sample showed substantial anti-bacterial properties against a tested bacterial pathogen.

Effect of bed material size on gas-solid flow characteristics in a CFB at low solid recirculation rates

The gas–solid flow characteristics greatly influence the heat transfer, combustion and pollutant formation processes in a circulating fluidized bed (CFB) boiler. The effects of particle size on the gas–solid flow characteristics, including flow structure, axial pressure and bed density profiles were studied in a two-dimensional CFB cold apparatus under low solid circulation rates (Gs’s). At the same time, an optical fiber probe was used to assess the particle size effect on the formation of particle clusters and their properties under different operating conditions. Results revealed that when the averaged size of bed materials decreased from ∼200 μm to ∼100 μm, at the same operating condition, the bottom dense bed became remarkably higher, and the upper dilute zone had stronger pressure fluctuation, more even axial and horizontal particle distributions, and higher solid density. Gs was more sensitive to the variation of the superficial gas velocity than the bed inventory. In addition, the standard deviation and power spectrum density of instantaneous pressure decreased in the dense bed and increased in the dilute zone. The particle velocity was slightly lower in the lower section of the riser but noticeably greater in the upper riser section. In addition, the clusters formed more frequently and lasted significantly longer. The study showed that flow characteristics in the bed qualitatively changed from that of Type B particles to that Type A particles in the Geldart’s classification, even at a small Gs, and previous studies with Type B particles could very likely not apply in the CFB boilers operating with fine bed materials.

Evaporation, Autoignition and Micro-Explosion Characteristics of RP-3 Kerosene Droplets under Sub-Atmospheric Pressure and Elevated Temperature

The evaporation, autoignition and micro-explosion characteristics of RP-3 kerosene droplets under sub-atmospheric pressure (0.2–1.0 bar) and elevated temperature (473–1023 K) were experimentally investigated using high-speed camera technology. The results showed that the droplet evaporation rate increased monotonically with increasing temperature and pressure under 573–873 K and 0.2–1.0 bar. The decrease of temperature and pressure was obviously detrimental to the successful autoignition of droplets and increased the ignition delay time. Autoignitions at 0.2 bar were very difficult and required an ambient temperature of at least 973 K, which was about 150 K higher than the minimum ignition temperature at 1.0 bar. Sub-atmospheric pressure environment significantly inhibits the formation of soot particle clusters during the autoignition of droplet. Reducing pressure was also discovered to reduce the likelihood of micro-explosions at 673, 773 and 823 K but increase the bubble growth rate and droplet breakage intensity. Strong micro-explosions with droplet breakage time close to 1 ms were observed at 0.6 bar and 773/823 K, showing the characteristic of bubble inertia control growth.

Rheology and microstructure of discontinuous shear thickening suspensions

We report experimental studies on rheology and microstructure in discontinuous shear thickening of fumed silica suspensions. Formation of particle clusters was observed after the critical shear rate, and their size increases during shear thickening. At higher shear rates, these clusters were found to break down due to strong shear forces, and a continuous decrease in viscosity was observed. The suspension viscosity and the first normal stress difference variation with the shear rate showed similar dependence. The sign of first normal stress difference was negative during shear thickening, which is consistent with the hydrodynamic model of cluster formation. A linear variation of the first normal stress difference with shear rate during shear thickening further indicates its predominant hydrodynamic origin and supports the recent Stokesian dynamics simulation studies on discontinuous shear thickening based on the hydrodynamic model of nonsmooth colloids by Wang et al. [J. Rheol. 64, 379–394 (2020)]. On the other hand, a nonlinear decrease in the first normal stress difference with shear rate in the second shear-thinning region is primarily due to breaking of large clusters into smaller ones and with a possibility of frictional contacts within these hydroclusters. The oscillatory shear measurements were also performed and the samples displayed strain thickening similar to shear thickening. The similarity between the steady and dynamic shear rheology at high strain amplitudes was observed using the modified Cox–Merz rule.

Organic Brake Friction Composite Materials: Impact of Mixing Duration on Microstructure, Properties, Tribological Behavior and Wear Resistance.

The lack of knowledge on the link between the manufacturing process and performance constitutes a major issue in brake lining development. The manufacturing process of organic brake friction composite materials includes several steps (mixing, preforming, hot molding and post-curing), which define their final microstructure, properties and performances. This study focuses on the effect of mixing duration on the microstructure, properties and tribological behavior of organic friction composite materials. The adopted methodology is based on simplified formulations effective in limiting synergistic effects by reducing the number and size distribution of constituents. Two simplified materials are here developed according to the mixing duration of the constituent introduction sequence. The microstructural characteristics are studied using 2D and 3D analyses, and then correlated with the thermophysical and mechanical properties. Wear mechanisms and tribological behavior are studied in relation to the microstructure and properties of the materials. The results show the effect of mixing duration as regards particle distribution and fiber arrangement. The distribution and size of fiber entanglements contribute to the formation of carbonaceous particle clusters, which create bulk bridges improving thermal conductivity. Moreover, the arrangement of rock fibers affects density, porosity and thermo-physical properties. In addition, the mixing disrupts the cohesion of fiber bundles with the matrix, affecting compressive modulus and wear behavior. This microstructural defect also fosters abundant third-body source flow, which disturbs the tribological circuit and behavior. Porosities induced by fiber entanglements, having a large and irregular size and distribution on the frictional surface, result in low wear resistance and alter the frictional stability.