Aggregation Behavior Of Particles Research Articles

Effect of aggregation behavior on microplastic removal by magnetic Fe3O4 nanoparticles

Magnetic nanotechnologies have been shown to be an efficient approach to the reduction of microplastic (MP) pollution in aquatic environments. However, uncertainties remain regarding the relationship between particle stability and MP removal under varying water conditions, hindering the practical application of magnetic nanotechnologies for MP removal. Herein, the influence of particle aggregation behavior on nano-scale MP removal by Fe3O4 nanoparticles (FNPs) was investigated, by monitoring dynamic light scattering parameters and analyzing the microstructures of particle aggregates. Results showed that 83.1 %–92.9 % of MPs could be removed by FNPs within 1 h, and MP removal exhibited a high degree of Pearson correlation (R = 0.95; P = 0.04) with particle aggregation behavior mediated by the FNPs dosage. Furthermore, pH-dependent electrostatic interactions significantly influenced particle aggregation behavior and the removal of MPs. Under pH <6.7 conditions, electrostatic attraction between electropositive FNPs and electronegative MPs led to charge neutralization-induced aggregation and efficient removal MP performance. Under increasingly saline conditions, compression of the electrical double layer enhanced the self-aggregation behavior of MPs, weakening the electrostatic repulsion between FNPs and MPs under alkaline conditions. Therefore, salinity improved the MP removal efficiency, especially under alkaline conditions, with MP removal increasing from 4.47 % to 55.1 % when the mass fraction of NaCl was increased from 0 % to 1 %. These findings further our understanding of the effect of aggregation behavior on MP removal by FNPs and highlight the potential for magnetic nanotechnology application in the removal of nano-scale MPs from aquatic environments, while also providing valuable insights for the design of FNP-based materials.

Boosted photocatalytic activity of LaFeO3/Ag3PO4 heterojunction via carbon quantum dots: Higher conductivity, stability, and dispersivity

Several restrictions including low photon conversion efficiency, unabiding material stability, and aggregation behavior hinder large scale applicability of conventional semiconductor photocatalysts for pollutants removal. In this work, the inexpensive carbon quantum dots (CQDs) was synthesized by facile one-step hydrothermal process and introduced into LaFeO3/Ag3PO4 nanocomposites for photodegradation of organic dyes. The morphology, surface chemical states, optical and electrochemical properties of as-prepared samples were systematically investigated using HRTEM, FT-IR, XPS, UV–vis,UV–vis, and PL. LaFeO3/Ag3PO4 with 3 wt% of CQDs presented the higher photocatalytic activity with 97.3 % removal rate of methylene blue (MB) organic dyes under 60 min visible light irradiation, which were three times that of the binary LaFeO3/Ag3PO4 composites. The effect of initial pH and co-existing inorganic ions on MB removal efficiency, particle aggregation behavior during photocatalytic process, and dominant reaction active species were investigated. The results showed that CQDs significantly improved the photoelectrochemical (PEC) performance of LaFeO3/Ag3PO4 composites, as well as protected Ag3PO4 from photo corrosion due to variation of electronic transfer path in composite material. Benefitting from numerous oxygen and nitrogen-containing functional groups, CQDs as a dispersing agent, improved water dispersibility and wettability of photocatalyst particles, and inhibited agglomeration of nano-photocatalyst on photocatalytic reactivity. These findings highlight the potential utility of CQDs in assisting a rapidly photodegrading molecular dye in an aqueous solution.

Colloidal particle aggregation: mechanism of assembly studied via constructal theory modeling

The assembly of colloidal particles into ordered structures is of great importance to a variety of nanoscale applications where the precise control and placement of particles is essential. A fundamental understanding of this assembly mechanism is necessary to not only predict, but also to tune the desired properties of a given system. Here, we use constructal theory to develop a theoretical model to explain this mechanism with respect to van der Waals and double layer interactions. Preliminary results show that the particle aggregation behavior depends on the initial lattice configuration and solvent properties. Ultimately, our model provides the first constructal framework for predicting the self-assembly of particles and could be expanded upon to fit a range of colloidal systems.

Study on the Capillary Interaction Between Particles on the Surface of High‐Temperature Melts

The aggregation behavior of particles affects the melting process and performance of metallic materials. The capillary interaction between particles on the surface of melts is studied based on Kralchevsky–Paunov model and simulation of contact line profile around particle. The calculated capillary force based on Kralchevsky–Paunov model indicates that the tendency for affecting the aggregation behavior is particle–melt contact angle &gt; particle radius &gt; distance between particle pairs &gt; particle density &gt; surface energy of melts. The chemical compositions of liquid steel superposition effect on the capillary force is great, and it is found that the capillary force between Al2O3 particle pair decreases with increasing O content, but increases with increasing S content. The capillary force between MgAl2O4 particle pair increases with increasing O and S contents. The calculated results are compared with the experimental results. It is found that the change trends of calculated capillary force and attraction force are same, but a majority of calculated capillary force is smaller than the observed one. The discrepancy between them is analyzed systematically in terms of selective attraction based on a simulation of the contact line profile for unwettable particles.

Adsorption and foaming properties of edible egg yolk peptide nanoparticles: Effect of particle aggregation

The adsorption and foaming properties of an edible colloidal nanoparticle (EYPNs), self-assembled from the food-derived, amphiphilic egg yolk peptides, were investigated, with the aim of evaluating their potential as efficient particulate stabilizers for development of aqueous food foams. The influence of particle aggregation induced by the changes of environmental conditions (mainly the pH) on these properties of EYPN systems was determined. Our results showed that the EYPNs are a highly pH-responsive system, showing the pH-dependent particle aggregation behavior, which is found to strongly affect the interfacial adsorption and macroscopic foaming behaviors of systems. Compared to high pH (6.0–9.0), the EYPNs at low pH (2.0–5.0) showed higher surface activity with a lower equilibrated surface tension as well as a higher packing density of particles and particle aggregates at the interface, probably due to the reduced electrostatic adsorption barrier. Accordingly, the EYPNs at these low pH values exhibited significantly higher foamability and foam stability. The presence of large particle clusters and/or aggregates formed at low pH in the continuous phase may contribute to the foam stability of EYPNs. These results indicate that our edible peptide-based nanoparticle EYPNs can be used as a new class of Pickering-type foam stabilizer for the design of food foams with controlled material properties, which may have sustainable applications in foods, cosmetics, and personal care products.

Developing a Coupled Statistical and Monte Carlo Approach for Geometric Modeling and Optimizing of Infiltrated Solid Oxide Fuel Cell Electrode

AbstractThis study proposes a novel geometric simulation methodology to estimate the performance of solid oxide fuel cells (SFOCs) electrodes using Monte‐Carlo approach coupled with a statistical algorithm to add infiltrated particles in the form of discrete voxels. Electrochemical performance of these infiltrated electrodes is then characterized by direct evaluation of triple phase boundary (TPB) density and active surface density of the particles. Study results, in agreement with experiment and analytical models, illustrate that there is an optimum point for particle loading, which is strongly depended on the backbone properties and particle aggregation behavior. Study also indicates that the reduction rate of the gas transport factor after adding particles strongly depends on the backbone porosity and the distribution of the particles. Further, it is shown that the average shape of aggregated particles alters the TPB density and gas transport behavior, but particle agglomeration always increases the surface density of particles. Finally, the geometric results are compared with electrochemical tests qualitatively and proposed theories in literature quantitatively. A case study is also performed to compare geometric properties of a realized model with a real reconstructed infiltrated electrode.

Surfactant mediated particle aggregation in nonpolar solvents.

The aggregation behavior of particles in nonpolar media is studied with time-resolved light scattering. At low surfactant concentrations particles are weakly charged and suspensions are not stable. The suspensions become progressively more stable with increasing surfactant concentration as particles become more highly charged. At high concentrations the particles become neutralized and aggregation is again fast. The theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO) is able to predict the stability ratios quantitatively by using the experimentally measured surface charges, screening lengths and van der Waals forces.

Electrohydrodynamic aggregation with vertically inverted systems.

Flow patterns surrounding particles suspended near electrodes within an electrolyte solution can be induced with an electric field due to an electrohydrodynamic (EHD) force. Depending on electrolyte, particle, and field properties, a variety of particle packing and stability states have been observed in EHD flow. In this work, we report evidence of EHD flow-induced aggregation of 2-μm sulfonated latex beads in NaCl and NaOH electrolyte solutions, in inverted particle-electrode orientations. Experimental conditions were chosen to match previous work where aggregation was observed at a bottom electrode. Particles remain stable at the top electrode for times greater than 1 h, and aggregation behavior is quantified in terms of growth rate and particle packing density and order. Similar aggregation behavior is seen at both top and bottom electrodes, with aggregate growth occurring more quickly within NaCl solutions than NaOH solutions at both the bottom and top electrode. In addition, an observed secondary location of stability for the vertical position of particles in NaOH electrolyte at the bottom electrode is not seen at the top electrode. Comparing these metrics to predictions made by a scaling model for EHD flow, particle aggregation behavior is successfully predicted at both top and bottom electrodes, but some of the observed differences in aggregate packing are not. Thus we suggest that modifications to existing models or their interpretation may be needed to improve predictions of the behavior of such systems.

Visualization of collision and aggregation behavior of particles simulating movement of inclusions in molten steel

Inclusions with sizes less than 1 μm in molten steel are difficult to float up to the molten steel and slag interface owing to their slow terminal velocity. Thus, increasing the size of inclusion is essential for accelerating the removal of inclusions. Polystyrene particles simulating inclusions in molten steel were quantified by direct observation of the particle collision behavior in a turbulent flow in a water model. The box-counting fractal dimension of particles was calculated by processing the binary images of aggregated particles. The fractal dimension of the outer contours of the single plastic particles was smaller than that of the aggregated particles. The fractal dimension was varied from 1.14 to 1.35. When two or more monomer particles collide, the aggregates are separated more easily, as the temperature increases from 40 to 80 °C. The aggregated particles were loose and easy to separate in the high-temperature aqueous solution. The effect of temperature on the surface tension of liquid and the interfacial tension of solid and liquid is obvious. The particles are wetting in the water solution at a temperature more than 60 °C. The relationship between the velocity of the particles and the fractal dimension of the solid particles with the equivalent diameter was discussed.

Particle aggregation behavior during photocatalytic ethanol reforming reaction and its correlation with the activity of H2 production

When dispersed in water, nanoscale photocatalysts tend to aggregate due to their high surface energy. Complex interaction of the incident light with the aggregated particles is expected due to their comparable length scales. In this study, the aggregation behavior of TiO2 nanoparticles during photocatalytic ethanol reforming was investigated by the dynamic light scattering (DLS). DLS results demonstrated that UV light can significantly inhibit the aggregation of TiO2 compared to that under visible light or in the dark. Considering that the ethanol photo-reforming over TiO2 can only occur under UV light, we correlated the significant light-induced particle aggregation with the photocatalytic reactions. Three different aggregation degrees for TiO2 were employed to study the effect of aggregation on its activity for photocatalytic H2 production. The H2 production is found to decrease with the increase of aggregates in the suspension. Our results should be of great value for the understanding of the dynamics in photocatalyst particle suspension during the photocatalytic reaction. More importantly, it is supposed that one can improve the activity of the photocatalytic reaction by controlling the particle aggregation through carefully adjusting the external physical fields such as the intensity of the incident light at certain wavelength interval.

Investigation of the geometric property hull for infiltrated solid oxide fuel cell electrodes

Design of optimal microstructures for infiltrated solid oxide fuel cell (SOFC) electrodes is a complicated task because of the multitude of electro-chemo-physical phenomena taking place simultaneously that directly affect working conditions (cell temperature, current density, and flow rates) of the SOFC electrode and therefore its performance. In this study, an innovative design paradigm is presented to obtain a part of geometry-related electrochemical and physical properties of an infiltrated SOFC electrode. A range of digitally realized microstructures with different backbone porosity and electrocatalyst particle loading under various deposition conditions are generated. Triple phase boundary (TPB), active surface density of particles, and gas transport factor are evaluated in realized models on the basis of selected infiltration strategy. On the basis of this database, a neural network is trained to relate desired range of input geometric parameters to a property hull. The effect of backbone porosity, loading, distribution, and aggregation behavior of particles is systematically investigated on the performance indicators. It is shown that from the microstructures with very high amount of TPB and particle contact surface density, a relatively low gas diffusion factor should be expected; meanwhile, increasing those parameters does not have sensible contradiction with each other. Excessive agglomerating of particles has a negative effect on TPB density, but the distribution of seeds always has a positive effect. Direct search and genetic algorithm optimization techniques are used finally to achieve optimal microstructures on the basis of assumed target functions for effective geometric properties.

A geometric modeling approach to find the best Microstructure for infiltrated SOFC electrodes

In this study, a novel design paradigm is presented to obtain some geometry-related electrochemical and physical properties of an infiltrated SOFC electrode. A range of digitally realized microstructures with different backbone geometric properties and virtual electro-catalyst particle loadings under various deposition conditions are generated. Triple Phase Boundary (TPB), the active surface density of particles and gas transport factor are evaluated in those realized models based on selected infiltration strategy. Based on this database, a neural network is trained to relate the desired range of input geometric parameters to a property hull. The effect of porosity and geometric anisotropy in backbones in addition to the loading, distribution and aggregation behavior of particles is systematically investigated on those performance indicators. The results indicated that microstructures with very high amount of TPB and contact surface density of particle have a relatively low gas diffusion factor, meanwhile increasing these parameters does not involve a sensible contradiction. Also, by adding particles, the TPB density variation is changed as a function of backbone porosity and the average shape of aggregated particles. A direct search into the microstructure and property hull is applied to find the best parameters in modeling approach aiming the maximum effective geometric properties. Finally, a genetic algorithm is employed to detect appropriate geometric factors getting the maximum acquirable performance in infiltrated SOFC electrodes.

Targeting Behavior of Magnetic Particles Under Gradient Magnetic Fields Produced by Two Types of Permanent Magnets

Fully understanding the dynamics of particles induced by magnetic fields with considering particle-particle interaction is an interesting and important issue for delivering magnetic particles to a target site with a high efficiency. For this purpose, permanent magnets with horizontal and vertical magnetization directions respectively have been taken for generating two types of gradient magnetic fields, which are applied to produce similar gradient magnetic forces while with different magnetic interaction forces between particles. On this basis, the distributions of particles under the two gradient magnetic fields are investigated and compared using Monte Carlo simulations. The results show that the concentrated particles have chainlike structures and their distributions are configuration dependent with the magnetization direction of permanent magnets: parallel and perpendicular to the bottom line for horizontal and vertical magnetization directions, respectively. Above all, a detailed microscopy study reveals that the movement trajectories of magnetic particles are affected by both transport and aggregation behavior of particles and the microscopic visualizations of particle distributions in the target region are in agreement with simulation predictions.

Experimental research on particle aggregation behavior in nanorefrigerant–oil mixture

The objective of this study is to experimentally investigate the effects of primary particle size, primary particle concentration and temperature on particle aggregation behavior in nanorefrigerant–oil mixture. The nanoparticles, refrigerant and lubricating oil for experiments were TiO2, R141b and ATMOS NM56, respectively. Experimental conditions included primary particle size from 25 to 100 nm, primary particle concentration from 50 to 500 mg L−1, temperature from 6 to 27 °C, and oil concentrations of 1, 3 and 5 wt%. Time evolutions of the hydrodynamic diameter of aggregates were measured by dynamic light scattering (DLS) method. It is shown that the presence of lubricating oil inhibits the particle aggregation, and the inhibition is strengthened with the increase of oil concentration; the hydrodynamic diameter of aggregates is enlarged with the increase of primary particle size, primary particle concentration or temperature, and the enlargement increases with the increase of oil concentration.

Salting-out and salting-in: competitive effects of salt on the aggregation behavior of soy protein particles and their emulsifying properties.

Emulsions stabilized by protein particles have gained increasing research attention due to their combined advantages of biocompatibility and superior stability. In this study, colloidal particles consisting of soy protein isolates (SPIs) prepared through a heat-treatment procedure are used to make oil-in-water emulsions at a protein concentration of 10 g L(-1) and a pH of 5.91. We investigate parallelly the effects of NaCl on the stability and rheological properties of the particle suspensions and their stabilized emulsions at salt concentrations of 0, 100 and 400 mM. The aggregation behavior of the particles is strongly dependent on the NaCl concentration, showing signs of sedimentation at low NaCl concentration (100 mM) but redispersion again at high NaCl concentration (400 mM). The extensive particle aggregation is beneficial to the formation of a continuous interfacial film for the emulsions, and hence results in a remarkable increase of creaming stability and interfacial viscoelastic moduli. The results can be explained in terms of two competitive effects of NaCl: salting-out and salting-in, which are attributed to complex electrostatic interactions between the particles as a function of NaCl concentration. The delicate balance between salting-out and salting-in provides an interesting insight into the nature of underlying protein particle interactions in aqueous suspensions and a possible mechanism for tailoring their emulsifying properties via salt effects.

Probing Active Particle Assembly in Lithium-Ion Battery Electrode Processing

Lithium-ion batteries (LIB) are currently considered as the primary choice for electric drive vehicles. The electrode microstructure and composition play an important role in determining the performance of the LIB. To this end, the processing of the multi-phase slurry consisting of active nanoparticles, conductive additives, binder and solvent determines the electrochemical properties and performance of the electrode. Morphology and the size of the active nanoparticles affect the LIB performance due to large active surface area, short diffusion length and fast kinetics. On the contrary, the aggregation of the active nanoparticles might have a detrimental effect. Therefore, fundamental understanding of the aggregation behavior of the active particles in the slurry is of paramount importance.In this regard, the evaporation dynamics of the slurry is a key factor which determines the microstructural heterogeneity of the electrode. The morphology of the aggregated particles is governed by a variety of physicochemical factors such as interaction between nanoparticles, diffusion rate of the nanoparticles and evaporation rate of the solvent. In this work, we present a mesoscale modeling approach in order to investigate the influence of evaporation on active particle assembly in LIB electrode processing. Our mesoscale model is based on a coarse-grain formalism combining lattice gas and kinetic Monte Carlo methodologies. We will present a comprehensive study of the active particle aggregation behavior and resultant influence due to the (1) evaporation rate of the solvent, (2) active particle and binder interaction, and (3) active particle morphology. Figure 1 shows representative aggregation characteristics of different active particle morphology. Reference J. Li, B. L. Armstrong, J. Kiggans, C. Daniel and D. L. Wood, Langmuir, 28, 3783-3790 (2012).J. Li, C. Daniel and D. L. Wood, Journal of Power Sources, 196, 2452-2460 (2011).H. Zheng, R. Yang, G. Liu, X. Song and V. S. Battaglia, Journal of Physical Chemestry C, 116, 4875-4882 (2012).E. Rabani, D. R. Reichman, P. L. Geissler and L.ha E. Brus, Nature, 426, 271-274 (2003).

Characterization and surface reactivity of natural and synthetic magnetites

Magnetite is an Fe (II/III) oxide mineral that occurs naturally and potentially as small particles with significant surface reactivity, and although much work is reported on synthetic material, little work exists for natural samples. The goal of the present work was to carefully characterize four natural magnetite samples from an iron ore deposit and two synthetic commercial reference samples, and to compare their surface characteristics and reactivity with the aim of evaluating their geochemical behavior towards adsorption of environmentally relevant ions, as well as their potential for use as environmental remediation sorbents. The techniques used were wet chemistry, X-ray diffraction, Raman spectroscopy, magnetic measurements (hysteresis curves), dynamic light scattering, scanning electron microscopy, low and high resolution transmission electron microscopy, BET Nitrogen adsorption, and electrophoresis. In addition, their As(V) adsorption behavior was measured at pH6, and was analyzed as related to the surface characteristics and particle aggregation behavior determined. The analyses revealed high magnetite purity in the natural samples, and specific surface areas (SSA) ranging from 1 to 8m2/g. Small alumino-silicate impurities were found in natural magnetites, apparently occurring at the particle surfaces and thus significantly lowering their isoelectric points as compared to the pure synthetic materials. All samples are composed of aggregates of 39–52nm magnetite particle units, but highly aggregated with very large size dispersions. The synthetic sample with the smallest particle size (30nm in average — 39m2/g) showed its entire surface area available for adsorption, despite its highly aggregated state observed, suggesting an open and highly dynamic aggregate framework. The other larger samples showed more complex aggregation behavior, which produced: (1) a widely variable As(V) adsorption behavior with no clear predictable pattern among samples; and (2) a large decrease of the As(V) adsorption maxima with increasing solids concentration imposed in the experimental set-up for any one particular sample. Therefore, we recommend high caution in using the BET-SSA and solids concentration parameters when performing experimental adsorption work with microsized magnetite, especially when extrapolating laboratory results to field geochemical or engineered conditions for evaluating contaminant adsorption.

Directed Motion of Colloidal Particles in a Galvanic Microreactor

The mechanisms leading to the deposition of colloidal particles in a copper-gold galvanic microreactor are investigated. Using in situ current density measurements and particle velocimetry, we establish correlations between the spatial arrangement and the geometry of the electrodes, current density distribution, and particle aggregation behavior. Ionic transport phenomena are responsible for the occurrence of strongly localized high current density at the edges and corners of the copper electrodes at large electrode separation, leading to a preferential aggregation of colloidal particles at the electrode edges. Preferential aggregation appears to be the result of a combination of electrophoretic effects and changes in bulk electrolyte flow patterns. We demonstrate that electrolyte flow is most likely driven by electrochemical potential gradients of reaction products formed during the inhomogeneous copper dissolution.

Investigation the complex dynamic evolvement mechanism of particle cluster and surface integrity in the chemical mechanical planarization

The surface planarization in the chemical mechanical planarization is mainly realized by the mechanical effect which depends on the micro-tribology behavior of nanoparticles. The material removal rate is decreased and micro-scratch is generated in the wafer surface due to the agglomeration of particles. The slurry particles hold definite energy level and microstructure which makes the classical materials processing theory unable to give reasonable explanation about this process. Large-scale classical molecular dynamic simulation of interaction among nanoparticles and solid surface has been carried out to investigate the evolvement mechanism of particle cluster and surface planarization. It is showed that the particle aggregation behavior is a size-dependent process because of the high ratio of surface atoms to bulk atoms which leads to the active reactivity and catalytic activity of nanoparticles. The substrate materials (nanoparticle) become transforming from low-energy stable system to high-energy unstable system after the two-body collision which is favorable for aggregation process. There exists obvious geometry boundary between the particle elements in the large aggregates and only the dendritic aggregates formed. The larger particles have definite microstructure and additional internal degree of freedom which can be used to take up, store, and transfer energy, thus lower the activity of chemical reaction which weaken the particle aggregation process.

Effects of Ultrasound on Behavior of Fine Solid Particles in Solid-Liquid Mixture (Classification of Particle Aggregation and Sound Pressure Profiles under Horizontal Irradiation)

Particles in a liquid under standing ultrasonic waves have been known to aggregate. However, particle aggregation behavior remains unclear. Thus, ultrasonic waves horizontally irradiated particles in tap water or degassed water with a relatively large disk-type acoustic transducer. We observed the particle behavior and measured the sound pressure profiles. The following results were obtained. The behavior of particles in water under ultrasonic waves was classified as “band”, “point”, “particle clump”, and “non-aggregation”. Experimental conditions producing “band”, “point”, “particle clump”, and “non-aggregation” in tap water were found to be different from those in degassed water. Moreover, the point aggregations at a frequency f of 96.3 kHz were observed at many more locations (higher spatial density) than those at a frequency f of 23 kHz. The sound pressure profile for f = 96.3 kHz had many more peaks than that for f = 23 kHz in the vertical direction, which corresponds to the spatial densities of the point aggregation.