Aggregation Kinetics Of Particles Research Articles

Structure evolution of porous alumina during aging process and its support effect on PtSn/Al2O3 catalyzed propane dehydrogenation

Precise control of porous alumina microstructures is always challenging due to the diversity and complexity of the growth process-related alumina crystalline phase and surface properties. In this work, we established a bottom-up synthesis route with a combination of rapid precipitation at high supersaturation and high-temperature aging in terms of enhancing particle aggregation kinetics. Surprisingly, we discovered that there were two distinct growth stages of alumina precursor (ammonium aluminum carbonate hydroxide) during the aging procedure, that is, oriented attachment at the early stage of crystallization and subsequent Oswald ripening. High-temperature aging can effectively strengthen the aggregation kinetics between the particles and produce large mesoporous (∼16 nm) and a remarkable number of defect sites with the exposure of up to 14 % unsaturated pentacoordinate aluminum ions. Owing to the presence of strong metal-support interactions, the alumina-supported PtSn catalyst exhibited excellent catalytic activity in the propane dehydrogenation reaction with propylene formation with 99 % selectivity and superior stability with a low deactivation rate of 0.007 h−1 over 24 h. These results suggested that it was feasible and instructive to achieve precise control of the structure and surface properties of alumina by manipulating the aggregation process of the initial particles during the aging stage.

Artificial intelligence-based framework for precise prediction of asphaltene particle aggregation kinetics in petroleum recovery

The precipitation and deposition of asphaltene on solid surfaces present a significant challenge throughout all stages of petroleum recovery, from hydrocarbon reservoirs in porous media to wellbore and transfer pipelines. A comprehensive understanding of asphaltene aggregation phenomena is crucial for controlling deposition issues. In addition to experimental studies, accurate prediction of asphaltene aggregation kinetics, which has received less attention in previous research, is essential. This study proposes an artificial intelligence-based framework for precisely predicting asphaltene particle aggregation kinetics. Different techniques were utilized to predict the asphaltene aggregate diameter as a function of pressure, temperature, oil specific gravity, and oil asphaltene content. These methods included the adaptive neuro-fuzzy interference system (ANFIS), radial basis function (RBF) neural network optimized with the Grey Wolf Optimizer (GWO) algorithm, extreme learning machine (ELM), and multi-layer perceptron (MLP) coupled with Bayesian Regularization (BR), Levenberg–Marquardt (LM), and Scaled Conjugate Gradient (SCG) algorithms. The models were constructed using a series of published data. The results indicate the excellent correlation between predicted and experimental values using various models. However, the GWO-RBF modeling strategy demonstrated the highest accuracy among the developed models, with a determination coefficient, average absolute relative deviation percent, and root mean square error (RMSE) of 0.9993, 1.1326%, and 0.0537, respectively, for the total data.

Soil particle aggregation and aggregate stability associated with ion specificity and organic matter content

Soil aggregate formation and stability are profoundly influenced by soil organic matter (SOM) content and electrolyte conditions by altering particle interactions during soil particle aggregation and aggregate breakdown. However, the effect of the ion-interface reaction, especially the newly discovered asymmetric hybridization of counterions, and its coupling with SOM on particle interactions and accordingly the particle aggregation and aggregate breakdown remain unclear. In this study, four black soils with different SOM contents were adopted to examine the particle aggregation kinetics using dynamic laser scattering method and aggregate stability using aggregate breakdown intensity in Li+, Na+, and K+ solutions with different concentrations. Combining experimental results with theoretical calculation of particle interactions, it found that different patterns of asymmetric hybridization between the three counterions produce ion specificity and lead to an ion sequence of Li+ < Na+ < K+ in promoting soil particle aggregation and reducing soil aggregate breakdown by decreasing the electrostatic repulsive force between soil particles. An increase in SOM, particularly its dissolvable fraction, increases the electrostatic repulsive force and steric repulsion and then inhibits soil particle aggregation, which is contrary to the effect of the ion sequence. The effects of ion specificity and SOM on particle aggregation could cancel each other in some specific cases of ion species and SOM contents. Moreover, similar to the above ion sequence, the increase in SOM also reduces soil aggregate breakdown and improves soil aggregate stability, because SOM greatly increases the van der Waals attractive force and short-range bonding interactions but rarely changes the electrostatic repulsive force between particles in soil aggregates.

Impact of the maturation process on soot particle aggregation kinetics and morphology

Mature soot aggregates exhibit a morphology which is currently mimicked by diffusion-limited aggregation (DLCA) codes, i.e. with a sticking probability = 1 when two aggregates collide. Nevertheless, nascent soot particles may grow in the reaction-limited aggregation regime (RLCA), i.e. with a sticking probability ≪ 1. Yet, it remains to be seen how fast the transition from RLCA to DLCA occurs for soot particles and what is the impact on aggregation kinetics, particle size distribution and morphology. This work intends to fill this gap by exploring the aggregation of soot particles formed in a laminar premixed flame through numerical simulations. Results show that the transition from RLCA to DLCA is very fast and produces a moderate impact on soot formation dynamics and morphology. However, soot particles mass bulk density is found to play an important role and should be considered in future simulations of soot formation in flames.

Microstructural changes during alkali- and heat induced gelation of konjac glucomannan

We investigate structural changes of konjac glucomannan (KGM) during heat induced gelation of pre-deacetylated samples. We combine rheology at higher concentrations, with light scattering and AFM studies on low concentration samples. Macroscale rheology demonstrates that gelation requires both heat and alkali-induced deacetylation. With Dynamic Light Scattering (DLS) we investigated the time evolution of KGM particle hydrodynamic radius (Rh) during the deacetylation reaction. Before deacetylation we observe that heating leads to swelling of the KGM particles in solution. From the kinetics of particle aggregation, we deduce that deacetylation itself is the rate-determining step and that aggregation occurs immediately after deacetylation. In Atomic Force Microscopy (AFM), native KGM particles appear as compact globular objects. Consistent with the light scattering results, we observe that heating leads to opening and swelling of these particles, and that deacetylation leads to their interaction to each other into a network. Our DLS and AFM results help understand the microscopic origins of heat- and alkali-induced gelation of KGM.

Modeling bacteriophage-induced inactivation of Escherichia coli utilizing particle aggregation kinetics

Targeted inactivation of bacteria using bacteriophages has been proposed in applications ranging from bioengineering and biofuel production to medical treatments. The ability to differentiate between desirable and undesirable organisms, such as in targeting filamentous bacteria in activated sludge, is a potential advantage over conventional disinfectants. Like conventional disinfectants, bacteriophages exhibit non-linear concentration-time (Ct) dynamics in achieving bacterial inactivation. However, there is currently no workable model for predicting these observed non-linear inactivation rates. This work considers an approach to predicting bacteriophage-induced inactivation rates by utilizing classical particle aggregation theory. Bacteriophage-bacteria interactions are represented as a two-step process of transport by Brownian motion, differential settling, and shear, followed by attachment. Modifying classical expressions for particle-particle aggregation to include bacterial growth, death, and bacteriophage reproduction, the model was calibrated and validated using literature data. The calibrated model captures much of the observed non-linearity in inactivation rates and reasonably predicts the final host concentration. This model was shown to be most useful in systems more likely to reflect an industrial setting, where the initial multiplicity of infection, or MOI (the ratio of bacteriophage to host organisms), was 1 or greater. For systems of an initial MOI of less than 1 the model showed increased sensitivity to changes in input parameters and a less pronounced ability to reasonably predict inactivation rates.

On the kinetics of chitosan/tripolyphosphate micro- and nanogel aggregation and their effects on particle polydispersity

Submicron chitosan/tripolyphosphate (TPP) particles are widely investigated as nanocarriers for drugs, genes and vaccines. One of the key particle properties that requires control is their size distribution, which depends on the extent of chitosan/TPP primary nanoparticle aggregation into higher-order submicron colloids. To provide a better understanding of this higher-order aggregation process, this study analyzes the factors that control chitosan/TPP particle aggregation kinetics in the presence of free TPP (such as present during particle formation). The aggregation rates exhibit a sharp power-law decrease with the monovalent salt concentration and a power-law increase with the free TPP concentration. Moreover, the aggregation rates increase with the pH and with the chitosan degree of deacetylation (DD). These variations in aggregation rates reflect the effects of monovalent salt, TPP concentration, pH and chitosan DD on particle bridging by the surface-bound TPP. Furthermore, these aggregation rates are much faster than those predicted based on Derjaguin and Landau, Verwey and Overbeek (DLVO) interaction potentials, which might reflect nonuniformities in particle shape and charge, and/or complications caused by particle softness. Finally, implications of the above aggregation kinetics on the uniformity of chitosan/TPP micro- and nanogel size are analyzed, where we: (1) show how particle polydispersity can be diminished by lowering the chitosan DD; and (2) explain the opposing results on how chitosan/TPP particle polydispersity is affected by monovalent salt.

Synthesis and Application of Modified Zero-Valent Iron Nanoparticles for Removal of Hexavalent Chromium from Wastewater

Zero-valent iron nanoparticles (nZVI) modified with sodium dodecyl sulfate (SDS) as an anionic surfactant were successfully synthesized and applied to Cr (VI) removal. The prepared nanoparticles were characterized by field emission scanning electron microscope (FSEM), energy-dispersive spectrometry (EDS), and Fourier transform infrared spectrophotometer (FT-IR). Meanwhile, the surface charges of the stabilized nanoparticles were also determined. In this study, the kinetics of particle aggregation and sedimentation were investigated. It was found that the modified nanoparticles had great stabilization. Effects of pH, contact time, dosage of nanoparticles, and initial Cr(VI) concentrations on removal efficiency of the heavy metal ions were investigated and optimized. The maximum removal efficiency of Cr(VI) was obtained at pH 3.0 and 25 °C, at the value of 98.919 %. Cr(VI) removal occurred fast, and achieved equilibrium after 120 min. The maximum removal capacity reached up to 253.68 mg g−1 dry nanoparticles at a 300-mg L−1 Cr(VI)-containing sample. Kinetics study showed a rapid removal dynamics fitting pseudo-second-order kinetic model. The equilibrium data was nicely fit to the Freundlich model and indicates the adsorption of Cr(VI) was highly favorable. The obtained results indicated that nZVI modified by SDS could be used as an efficient alternative for removal of heavy metals with enhanced removal capacity and application stability.

Agglomeration front dynamics: Drying in sessile nano-particle laden droplets

The drying of sessile, nano-silica laden water droplet is studied under ambient conditions, in the absence of any convection. The drying process can be divided into two distinct regimes. During regime 1, the outer edge of the droplet remains pinned and particles agglomerate at the droplet periphery similar to the traditional coffee ring. However in regime 2, with further evaporation, both the liquid contact line and the agglomeration front starts moving radially inwards from the initial contact edge. The contact between the liquid and the agglomerate is maintained throughout regime 2 and the vaporisation driven liquid edge recession essentially drives the inward growth of the particle deposition. Fast kinetics of particle aggregation results in rapid growth of this agglomeration front as seen from the experiments. A theoretical formulation involving a simplistic model of the agglomeration front growth based on particle mass balance has been proposed.

Influence of Radioactivity on Surface Charging and Aggregation Kinetics of Particles in the Atmosphere

Radioactivity can influence surface interactions, but its effects on particle aggregation kinetics have not been included in transport modeling of radioactive particles. In this research, experimental and theoretical studies have been performed to investigate the influence of radioactivity on surface charging and aggregation kinetics of radioactive particles in the atmosphere. Radioactivity-induced charging mechanisms have been investigated at the microscopic level, and heterogeneous surface potential caused by radioactivity is reported. The radioactivity-induced surface charging is highly influenced by several parameters, such as rate and type of radioactive decay. A population balance model, including interparticle forces, has been employed to study the effects of radioactivity on particle aggregation kinetics in air. It has been found that radioactivity can hinder aggregation of particles because of similar surface charging caused by the decay process. Experimental and theoretical studies provide useful insights into the understanding of transport characteristics of radioactive particles emitted from severe nuclear events, such as the recent accident of Fukushima or deliberate explosions of radiological devices.

Kinetic study of aggregation of milk protein and/or surfactant-stabilized oil-in-water emulsions by Sedimentation Field-Flow Fractionation

Milk proteins are able to facilitate the formation and stabilization of oil droplets in food emulsions. This study employed Sedimentation Field-Flow Fractionation (SdFFF) to monitor changes in particle size distribution of freshly prepared emulsions with varying weight contributions of sodium caseinate (SC) and whey protein concentrate (WPC). The effect of the addition of Tween 80 (T) on the initial droplet size was also investigated. The results indicated that emulsifying ability follows the order Tween 80>WPC>SC, with corresponding weight average droplet diameter of 0.319, 0.487 and 0.531μm respectively, when each of the above emulsifiers was used solely. The stability of sodium caseinate emulsions was studied at 30.5 and 80.0°C by measuring the particle size distribution for a period of 70h. Emulsions withstood the temperatures and exhibited an initial increase in particle size distribution caused by heat-induced droplet aggregation, followed by a decrease to approximately the initial droplet size. The rate of droplet aggregation depends on the severity of thermal processing, as revealed by the kinetics of particle aggregation during aging at different temperatures. Comparison of the experimental rate constants found from SdFFF, with those determined theoretically gives invaluable information about the oil droplet stability and the aggregation mechanism. Based on the proposed mechanistic scheme various physicochemical quantities, which are very important in explaining the stability of oil-in-water emulsions, were determined. Finally, the advantages of SdFFF in studying the aggregation of the oil-in-water droplets, in comparison with other methods used for the same purpose, are discussed.

Study of colloidal particle Brownian aggregation by low-coherence fiber optic dynamic light scattering

The aggregation kinetics of particles in dense polystyrene latex suspensions is studied by low-coherence fiber optic dynamic light scattering. Low-coherence fiber optic dynamic light scattering is used to measure the hydrodynamic radius of the aggregates. The aggregation kinetics data obtained can be fitted into a single exponential function, which is the characteristic of slow aggregation. It is found that the aggregation rate of particles increased with higher electrolyte levels and with larger particle concentrations. The experimental results can be explained by use of the Derjaruin–Landau–Verwey–Overbeer (DLVO) theory.

The RNA core weakly influences the interactions of the bacteriophage MS2 at key environmental interfaces

The effect of the RNA core on interfacial interactions of the bacteriophage MS2 was investigated. After removal of the RNA core, empty intact capsids were characterized and compared to untreated MS2. Electron density of untreated MS2 and RNA-free MS2 were characterized by transmission electron microscopy (TEM) and synchrotron-based small angle spectroscopy (SAXS). Suspensions of both particles exhibited similar electrophoretic mobility across a range of pH values. Similar effects were observed at pH 5.9 across a range of NaCl or CaCl2 concentrations. We compared key interfacial interactions (particle–particle and particle/air–water interface) between suspensions of each type of particle using time resolved dynamic light scattering (TR-DLS) to observe and quantify aggregation kinetics and axisymmetric drop shape analysis to measure adsorption at the air–water interface. Both suspensions showed insignificant aggregation over 4 h in 600 mM NaCl solutions. In the presence of Ca2+ ions, aggregation of both types of particles was consistent with earlier aggregation studies and was characterized by both reaction-limited and diffusion-limited regimes occurring at similar [Ca2+]. However, the removal of the RNA from MS2 had no apparent effect on the aggregation kinetics of particles. Despite some differences in the kinetics of adsorption to the air–water interface, the changes in surface tension which result from particle adsorption showed no difference between the untreated MS2 and RNA-free MS2. The interactions and structure of particles at the air–water interface were further probed using interfacial dilational rheology. The surface elasticity (Es) and surface viscosity (ηs) at the interface were low for both the untreated virus and the RNA-free capsid. This observation suggests that the factors that impact the adsorption kinetics are not important for an equilibrated interface.

Effect of shear on nanoparticle dispersion in polymer melts: A coarse-grained molecular dynamics study

Coarse-grained, molecular dynamics (MD) simulations have been conducted to study the effect of shear flow on polymer nanocomposite systems. In particular, the interactions between different components have been tuned such that the nanoparticle-nanoparticle attraction is stronger than nanoparticle-polymer interaction, and therefore, the final equilibrium state for such systems is one with clustered nanoparticles. In the current study, we focus on how shear flow affects the kinetics of particle aggregation at the very initial stages in systems with polymers of different chain lengths. The particle volume fraction and size are kept fixed at 0.1 and 1.7 MD units, respectively. Through this work, shear has been shown to significantly slow down nanoparticle aggregation, an effect that was found to be a strong function of both polymer chain length and shear rate. To understand our findings, a systematic study on effect of shear on particle diffusion and an analysis of relative time scales of different mechanisms causing particle aggregation have been conducted. The aggregation rate obtained from the time scale analysis is in good agreement with that determined from the aggregation time derived from the pair correlation function monitored during simulations.

Effect of Concentration on the Photoinduced Aggregation of Polymer Nanoparticles

We describe the effect of concentration on the photoinduced flocculation and aggregation of a nonaqueous dispersion of core−shell nanoparticles (diameter = 50 nm), which consist of a tightly cross-linked core composed of poly(butyl methacrylate-co-ethylene glycol dimethacrylate) and a lightly cross-linked shell of poly(butyl methacrylate-co-ethylene glycol dimethacrylate-co-methacrylic acid). The particles could be dispersed in cyclohexane after modification of the acid groups by ester formation with 2-bromo-1-phenyl-octadecan-1-one. Photocleavage of these substituents (λ = 310 nm) regenerated the −COOH groups and led to aggregation of the destabilized particles. Since the rate of aggregation is relatively slow in this system, we were able to study the process of particle aggregation kinetics by a combination of static and dynamic laser light scattering. Our results indicate, for particle dispersions from 0.23 mg/mL to 0.93 mg/mL, that there are three stages in the aggregation process. Initially, several ...

Photoinduced Aggregation of Polymer Nanoparticles in a Dilute Nonaqueous Dispersion

We describe the photoinduced flocculation of a nonaqueous dispersion of core−shell nanoparticles (diameter = 50 nm). The particles consist of a tightly cross-linked core composed of poly(butyl methacrylate-co-ethylene glycol dimethacrylate) and a lightly cross-linked shell of poly(butyl methacrylate-co-ethylene glycol dimethacrylate-co-methacrylic acid). After converting the acid groups in the shell to 1-phenylketo-2-octadecyl ester groups, the particles could be dispersed in cyclohexane, sterically stabilized by the alkyl substituents of these ester groups. Photocleavage of these substituents (λ = 310 nm) regenerated the −COOH groups and led to slow aggregation of the destabilized particles. This system allowed us to study the process of particle aggregation kinetics in the absence of long-range electrostatic interaction by using a combination of static and dynamic laser light scattering. Our results show that there exist two stages in the aggregation process. Initially, several particles come into contact to form small, elongated clusters. Subsequently, these clusters undergo further aggregation to form larger aggregates characterized by a fractal dimension of 2.3. Our results indicate that aggregation in the second stage follows a reaction-limited cluster−cluster aggregation mechanism. We also found that the average radius of gyration <Rg> during aggregation scaled with time with an exponent of 1.4 ± 0.1, much higher than predicted and found in previous experiments.

Flocs Restructuring during Aggregation: Experimental Evidence and Numerical Simulation

Aggregate structure, i.e., fractal dimension, has a coupled geometric and hydrodynamic impact on the aggregate collision frequencies. In this work, we evaluated different collision frequency kernel calculation schemes to simulate experimentally determined latex particle aggregation kinetics. Light scattering was used to simultaneously measure aggregate size and fractal dimension throughout the latex aggregation experiments. The intermediate collision scheme proposed by Veerepanneni and Wiesner (J. Colloid Interface Sci.177, 45–57 (1996)) is in agreement with experimental aggregation kinetics if considered along with experimentally determined fractal dimension evolution. Aggregate restructuring was found to be an important mechanism in explaining aggregation kinetics.

Kinetics of Adsorption of Diethylene-triaminomethylated Polyacrylamide on Dispersed Kaolin Accompanied by Flocculation

The kinetics of the adsorption of diethylene-triaminomethylated polyacrylamide on kaolin dispersed in water has been investigated. An influence of the flocculation of kaolin dispersion on polymer adsorption has been found. The kinetics of particle aggregation under the influence of dissolved polymer has been studied. Polymer adsorption and particle aggregation proceed simultaneously, accompanied by a steady decrease in the amount of adsorbed polymer per unit mass of kaolin. A mathematical model of the adsorption process, consistent with the experimental data, is described. The rate constants and their ratios have been determined.

Colloid aggregation: numerical solution and measurements

A model has been developed that describes the kinetics of particle aggregation by a numerical solution of the von Smoluchowski equation. While the complete model incorporates surface chemical phenomena, this paper discusses only the physical aggregation process, and focuses on long-term aggregation where aggregates composed of many primary particles (up to 2000) are formed. Model simulations were compared with laboratory experiments that were conducted with hematite spheres aggregating with no applied shear stress. Comparison was achieved by minimizing the sum of squared differences between the model and experimental data using two fitting parameters: the collision efficiency and the fractal dimension of the aggregates. The model was sensitive to the two parameters, which had a small degree of dependence on one another as evidenced by the orientation of the joint confidence regions. Estimates of the fractal dimension varied inversely with collision efficiency and were between 1.25 and 1.5; lower than many estimates by others for diffusion-controlled processes but consistent with cluster–cluster aggregation of aggregates comprised of very dense particles. The collision efficiency was estimated to be 1×10 −4 for slow aggregation conditions, and 2×10 −4 under rapid aggregation; these values reflect inclusion of hydrodynamic interactions and their significance in a system dominated by differential settling.

Kinetics of fine particle aggregation in turbulence

The kinetics of particle aggregation, including coagulation and hydrophobic flocculation, in turbulent flow has been studied. It is discovered by both theoretical analysis and experimental results that the macroscopic kinetic model of particle aggregation is closely correlated with the microscopic particle–particle interaction. The energy barrier U max between the approaching particles determines whether a particle collision can result in effective aggregation or not. While the adhesive strength J of aggregated particles determines whether the formed aggregates are disrupted by the surface erosion in the viscous subrange of turbulence or by the fragmentation in the inertial subrange of turbulence. The maximum aggregate size d max depends on the ratio of the aggregate strength and the disruption stress of turbulent flow. Due to the apparently distinguished natures of particle–particle interaction in coagulation and hydrophobic flocculation, the aggregation kinetics of the two are different. Experimental results has proven that the coagulation process is generally accompanied with the surface erosion of aggregates in the viscous subrange of turbulence, whilst the hydrophobic flocculation process is mainly affected by the fragmentation mechanism of aggregate disruption in the inertial subrange of turbulence due to the much stronger strength of the flocs. Based on the theoretic analysis and the experimental results a general kinetic model of particle aggregation has been proposed.