Dispersion Behavior Of Particles Research Articles

Aggregation and Dispersion Behavior in the 0- to 2- µm Fraction of Luvisols

The migration of particles smaller than 2 µm in soil pores is responsible for the preferential transfer of various contaminants and for soil textural differentiation in Luvisols. Aggregation vs. dispersion mechanisms of clay particles are suspected to play a major role in this migration process. However, these mechanisms have mostly been studied with respect to pure and well-crystallized clay minerals rather than pedogenetic particles and have often been performed under physicochemical conditions, which are poorly representative of soil conditions. We studied the respective impacts of pH and Ca concentration on aggregation and dispersion behavior of clay particles in a Luvisol under conditions encountered in the soil solution. Both static and dynamic approaches were followed in studying particle interactions and dynamics under transient phenomena. Based on these experiments, we have drawn a phase diagram for soil clays as a function of pH and Ca concentrations and have identified mechanisms associated with the formation of these different phases. We find that soil particle behavior in suspensions is similar to that recorded for model clays in that they are driven by both pH and Ca concentrations. These two parameters are interrelated and tend to favor aggregation at higher Ca concentrations and/or lower pH. These effects are reversible over the gravitational water time scale, with the exception of dilution-induced dispersion. In situating these physicochemical mechanisms within a literature review of rainwater and soil solution chemistries, we determine the expected role of these mechanisms on the transport of particles in gravitational soil water.

Analysis of dispersion and aggregation behavior of carbon black particles in aqueous suspension by colloid probe AFM method

To clarify the role of polymer dispersants at the carbon black (CB) nanoparticle/liquid interface, the adsorbed structure of the dispersants and the interactions between particle surfaces was evaluated using colloid probe AFM. As it is difficult to prepare stable spherical granules consisting of CB nanoparticles with diameters on the scale of several microns, for a colloidal probe by spray drying and sintering, CB nanoparticles were uniformly coated on the surface of spherical resin particles using a physical composing process. In order to establish the mechanism of action of the CB polymer dispersant by using the prepared colloid probe, polyethyleneimine (PEI) and PEI functionalized with a hydrophobic toluoyl group (T-PEI) were compared. It was found that on the adsorption of T-PEI, the viscosity of the aqueous CB suspension and the size of the aggregates were remarkably decreased in acidic conditions. Although the amounts of PEI and T-PEI adsorbed onto the CB were almost the same, a larger repulsive interaction was observed in the case of the T-PEI. CB nanoparticle dispersion was promoted by the increase in steric repulsion due to the structure of the adsorbed T-PEI.

Dispersion of micro diamond particles in electroless nickel solution

The dispersion behavior of micro-diamond particles ranging from 0 to 0.5 micron was compared between in DI water and in electroless nickel solution. The effects of the concentration of electroless solution, temperature, ultrasonic treatment, stirring speed, and baffles on the size distribution of micro diamond particles in electroless nickel solution were studied. Results show that the dispersion of micro diamond particles in DI water is obviously superior to that in electroless nickel solution. Micro diamond particles agglomerate evidently when the concentration of electroless solution V elect:V DI in dispersion media exceeds 5‰. Diamond particles agglomerate more and more seriously with the increase of the ion concentration. Applying ultrasonic, increasing stirring speed and adding baffles are helpful to improving the dispersion of diamond particles in the electroless nickel solution and its uniform distribution in the Ni-P coating.

Particle Dispersion Behaviors of Dense Gas-Particle Flows in Bubble Fluidized Bed

An Euler-Euler two-fluid model incorporating a developed momentum transfer empirical coefficient is developed to study the particle dispersion behaviors of dense gas-particle flows in gas-fluidization reactor. In this model, the four-way couplings among gas-particles, particle-gas, and particle-particle collisions are fully considered based on kinetic theory of granular flows and an improved smooth continuous drag coefficient is utilized. Gas turbulent flow is solved by large eddy simulation. The particle fraction, the time-averaged axial particle velocity, the histogram of particle fluctuation velocity, and the wavelet analysis of pressure signals are obtained. The results are in good agreement with experimental measurements. The mean value and the variance of axial particle velocity are greater than those of radial particle velocities. Particle collision frequencies at bubble vibrant movement regions along axial direction are much higher than those of radial direction and attenuated along height increase. Low-frequency component of pressure signal indicating the bubble movement behaviors in the center of reactor is stronger than wall regions. Furthermore, the negative values represent the passed bubble and positive peak values disclose the continuous motion of single bubble.

0101 円筒内を回転する楕円体によって印加されるせん断場における微粒子の凝集・分散非定常挙動(OS1-1 非ニュートン流体の流動現象,OS1 非ニュートン流体の流動現象)

A numerical analysis of unsteady behavior of particle aggregation/dispersion was performed in a non-uniform shear flow in a cylinder with a rotating elliptical rotor. In this model, it was considered that an aggregation/dispersion rate depends on Brownian coagulation, shear coagulation and shear breakup. Immersed boundary method was used to calculate a flow with rotating rotor. The diameter of the cylinder was 38 mm. The major and minor axes of the elliptical rotor were 32 and 26.6 mm. The rotor was rotated at 20 RPM. The diameter of particles and the viscosity of disperse media were 2.5 ?m and 195 Pa s. As a result, the cluster was broken by applying shear and the size of cluster decreased with time. The particle dispersion behavior varies with local position. The mean cluster size took a minimum value right after the major axis of the rotor passed. Then the mean cluster size increased again.

Investigating the particle dispersion in a spout-fluid bed using particle trajectory

Abstract Particle dispersion in a spout-fluid bed was investigated using time series of particle trajectory by evaluation of dispersion coefficient based on Einstein’s expression. A series of experiments were performed in a lab-scale spout-fluid bed using microwave heating and infrared thermal imaging (MH-ITI) technique for recording the position of a tracer. The influence of gas velocity on the particle dispersion in different flow regimes has been taken into account. The results show that the particle dispersion behavior depends on the flow regime. In the flow regime of internal jet, the increase of gas velocity improves the axial dispersion. In the case of jet in fluidized bed with bubbling, increasing fluidizing gas velocity promotes the radial dispersion at the lower part of bed and the axial dispersion at the upper part of bed. In the flow regime of jet in fluidized bed with slugging, the effect of fluidizing gas is related to the slug pattern. The result also indicates that the transition of flow regime can be evaluated from the particle trajectory.

PH-responsive flocculation and dispersion behavior of Janus particles in water

Gold was vacuum-deposited on one side of 6-μm-diameter SiO2 particles to prepare Janus particles (JPs). A thiol-terminated pH-responsive polymer (pAaH-SH), prepared via reversible addition–fragmentation chain transfer (RAFT) -controlled radical polymerization, was immobilized on the gold surface of the JPs as confirmed by attenuated total reflection-Fourier transform infrared and X-ray photoelectron spectroscopy measurement techniques. A fluorescein-labeled polymer (p(AaH/Flu)-SH) was also prepared via RAFT, and immobilization of p(AaH/Flu)-SH only on the gold surface of the JPs was confirmed by fluorescence microscopy observations. The flocculation and dispersion behavior of pAaH-SH-grafted JPs was observed with an optical microscope and was found to be varied with the solution pH.

Titanium dioxide sols synthesized by hydrothermal methods using tetrabutyl titanate as starting material and the application in dye sensitized solar cells

TiO 2 sols were synthesized via hydrothermal reaction using a less hydrolysable alkoxide or tetrabutyl titanate as the starting material. Using characterizations of X-ray diffraction, dynamic laser scattering and transmission electron microscopy, particle coarsening dynamics along with the particle dispersion behavior in the sols were studied via changing hydrothermal temperature from 160 °C to 250 °C. It was observed that, pure anatase phase was obtained in the whole examined temperature range. With temperature increasing, the particle size distribution in the sols first narrowed, and then broadened. Mono-dispersed nanocrystallites were obtained at the temperature of 220 °C. Aggregations were formed between the nanocrystallites at other temperatures. The causes of the aggregating behavior were analyzed and found to be different when the temperature was less than or beyond 220 °C. The as-synthesized TiO 2 sols were used in fabrication of dye sensitized nanocrystallite solar cell. The cells assembled from temperature of 220 °C came out with the best photo-to-electric energy conversion efficiency, which is ascribed to the improved dispersion of particles in TiO 2 sols.

Numerical investigation on gas–particle flows in horizontal channel under the reduced gravity environments

A unified second-order-moment gas–particle two-phase turbulent model incorporated with kinetic theory of granular flows (USM-θ) is developed to study the particle dispersion behavior of dense gas–particle flows in horizontal channel with 6.96 μm wall roughness and with earth, lunar and microgravity environments, respectively. Anisotropy of gas and particle two-phase stresses and the interaction between two-phase stresses are fully considered by constructing two-phase Reynolds stress model and the transport equation of two-phase stress correlation. The flow behavior of particles in a horizontal channel of Kussin and Sommerfeld [12] experiments is numerically simulated. Results show that the reduced gravity conditions affect the particle concentration distribution, particle velocity and fluctuation velocity, particle temperature, axial–axial fluctuation velocity correlation of gas and particle and particle collision frequency. Under microgravity conditions, particle temperature and collision frequency are much less than those of earth and lunar gravity. Compared with earth gravity, anisotropic of two-phase flow and sedimentation are weaker.

Hydrodynamic Modeling of Dense Gas-Particle Turbulence Flows Under Microgravity Space Environments

An Euler–Euler two-fluid model based on the second-order-moment closure approach and the granular kinetic theory of dense gas-particle flows was presented. Anisotropy of gas-solid two-phase stress and the interaction between two-phase stresses are fully considered by two-phase Reynolds stress model and the transport equation of two-phase stress correlation. Under the microgravity space environments, hydrodynamic characters and particle dispersion behaviors of dense gas-particle turbulence flows are numerically simulated. Simulation results of particle concentration and particle velocity are in good agreement with measurement data under earth gravity environment. Decreased gravity can decrease the particle dispersion and can weaken the particle–particle collision as well as it is in favor of producing isotropic flow structures. Moreover, axial–axial fluctuation velocity correlation of gas and particle in earth gravity is approximately 3.0 times greater than those of microgravity and it is smaller than axial particle velocity fluctuation due to larger particle inertia and the larger particle turbulence diffusions.

Rheology and Dispersion Behavior of Highly Filled Propylene-Ethylene Copolymer/Calcium Carbonate Composites

The rheology and dispersion behavior of commercial propylene-ethylene copolymer, highly filled propylene-ethylene copolymer/CaCO3 composites and highly filled propylene-ethylene copolymer/HDPE/CaCO3 composites prepared by melt-compounding were investigated. The pure propylene-ethylene copolymer exhibits pseudoplastic flow behavior obviously. The CaCO3 particles in the composites have achieved a homogeneous dispersion and the increasing shear rate has almost no influence on the dispersion behavior of CaCO3 particles. The high loading of CaCO3 particles influences the rheology behavior of propylene-ethylene copolymer slightly. For the highly filled propylene-ethylene copolymer/CaCO3 composites, the extensional viscosity only decreases slightly throughout the entire range of extension rates.

Numerical prediction of particle dispersions in downer under different gravity environments

Abstract Particle dispersion behavior of dense gas–particle flows in a downer affected by gravity environment is numerically simulated using an Euler–Euler two-fluid approach incorporating unified-second-order-moment two-phase turbulent models and kinetic theory of granular flows (USM-θ). Anisotropy of gas–solid two-phase stress and the interaction between two-phase stresses are fully considered by two-phase Reynolds stress model and the transport equation of two-phase stress correlation. The flow behavior of particles in a downer of Wang et al. (1992) [27] experiments is predicted under earth gravity, lunar gravity and microgravity environment. Simulation results of particle concentration and particle velocity are in good agreement with measurement data under earth gravity environment. Comparison earth gravity to lunar and microgravity condition, peak value of particle concentration is shifted to near center region and axial particle fluctuation velocity is larger than that of approximately 3.0 times. Particle temperature, particle heterogeneities dispersion and particle–particle collision are weakened due to decrease gravity. Furthermore, roles of particle and gas kinetic energy in particle–fluid system are alternated. Both particle kinetic energy and gas kinetic energy are greater than ones under earth gravity conditions.

Mean-field models of structure and dispersion of polymer-nanoparticle mixtures

We review some recent research developments in coarse-grained modeling based on mean-field approaches of the equilibrium dispersion and structure of polymer nanoparticle composites. We focus on three issues: (i) dispersion and phase behavior of particles in homopolymer matrices; (ii) dispersion in mixtures of homopolymers with grafted nanoparticles; (iii) self-assembly and organization of nanoparticles in block copolymer matrices. In each of these topics, we highlight that the dispersability and the resulting structure of the nanoparticle suspension may exhibit far more complexities than one may deduce using simple miscibility criterion involving the energetic interactions between the polymer matrix and the particle. In each case, we review our own research contributions accompanied by a brief discussion of related theoretical studies and some possible future directions.

Vertical dispersion of light inertial particles in stably stratified turbulence: The influence of the Basset force

The dispersion of light inertial particles [ρp/ρf=O(1)] in statistically stationary stably stratified turbulence is studied by means of direct numerical simulations. The light particle dispersion behavior is found to be comparable to that of heavy particles when displayed as a function of the Stokes number. Deviations from fluid particle dispersion are found already for small Stokes numbers; the length of the typical plateau for vertical dispersion is shorter for the light inertial particles. All the forces in the Maxey–Riley equation are taken into account and they are found to be of similar magnitude as the Stokes drag for particles with ρp/ρf=O(1). However, not all forces directly influence the particle dispersion. It is shown that especially the often neglected Basset force plays a considerable role in the vertical dispersion of light particles in stratified turbulence. Neglecting this force results in an overprediction of the vertical dispersion by about 15%–20%.

Investigations on particle surface characteristics vs. dispersion behaviour of l-leucine coated carrier-free inhalable powders

Aerosol microparticles of salbutamol sulphate are gas-phase coated with an amino acid l-leucine. Depending of the saturated state of l-leucine, the coating is formed by the surface diffusion of l-leucine molecules within a droplet or by the physical vapour deposition (PVD) of l-leucine or by the combination thereof. The PVD coated particles showed excellent aerosolization characteristics in a carrier-free powder delivery from an inhaler. The aerosolization of the fine powders is compared with surface energy parameters analysed by inverse gas chromatography (IGC). The dispersion testing is conducted by a Inhalation Simulator using a fast inhalation profile with inhalation flow rate of 67 l min −1. It is found that the powder emission is affected by the morphology, surface roughness (asperity size and density) of the particles and acidity of particle surface. The latter affects the dispersion and dose repeatability of fine powder in a case if l-leucine content is high enough. However, there is no direct correlation between dispersive surface energies and aerosolization performances of the powders. Crucial factors for the improved aerosolization rely weakly on surface acid–base properties but strongly on particle morphology and fine-scale surface roughness.

Characterization of particles emitted by incense burning in an experimental house

The potential health effects of fine and ultrafine particles are of increasing concern. A better understanding of particle characteristics and dispersion behavior is needed. This study aims at characterizing spatial and temporal variations in fine and ultrafine particle dispersion after emission from a model source in an experimental house. Particles emitted by an incense stick burning for 15 min were characterized. Number concentration, specific surface area and mass were measured. Partial chemical analysis of particles was also realized. Near the burning incense stick, the maximum concentration was 25,500 particles/cm(3); the indoor PM(2.5) concentration reached 197 microg/m(3), and the specific surface area concentration was 180 microm(2)/cm(3). The estimated incense smoke density was 1.1 g/cm(3). Time of Flight Aerosol Mass Spectrometer measurements indicated that the organic fraction was predominant in the aerosol mass detected, and other minor components identified were K(+), NO(3)(-), and Cl(-). The combustion of an incense stick in the living room was associated with significant modifications of the concentrations of particles measured in the different rooms of the house. This demonstration of pollution by particle dispersion by a model source of moderate intensity may have significant implications in terms of assessment of indoor exposure to such particles. Practical Implications The particles emitted in a domestic environment by a source of moderate intensity such as burning incense disperse throughout the house, even in rooms with closed doors and in rooms as far away as the next floor. This dispersion has significant implications in terms of evaluating human indoor exposure to fine and ultrafine particles.

Dispersion Behavior of Low-density Particles and Water Flow in a Bath under Offset Agitation with an Immersion Cylinder

Particle image velocimetry measurements have been carried out to understand the characteristics of fluid flow containing low-density particles in a bath under mechanical offset agitation with an immersion cylinder. The particles disperse deeply and widely in the bath under this agitation method. The water flow pattern does not change drastically with the immersion cylinder. The tip of the vortex tube however shifts from the center of the rotation axis of the impeller to the tip of the impeller blade. The dispersion of low-density particles is highly enhanced by this vortex tip shift.

Nanosized Glass Frit as an Adhesion Promoter for Ink‐Jet Printed Conductive Patterns on Glass Substrates Annealed at High Temperatures

AbstractInk‐jet printed metal nanoparticle films have been shown to anneal at high temperatures (above 500 °C) to highly conductive metal films on glass or ceramic substrates, but they suffer from cracking and inadequate substrate adhesion. Here, we report printable conductive materials, with added nanosized glass frit that can be annealed at 500 °C to form a crack‐free dense microstructure that adheres well to glass substrates. This overcomes the previous challenges while still retaining the desired high film conductivity. Controlling the particle characteristics and dispersion behavior plays an important role in successfully incorporating the glass frit into the conductive inks.

Modelling of heavy and buoyant particle dispersion in a two-dimensional turbulent mixing layer

Heavy and buoyant particle dispersion in the turbulent mixing layer was investigated numerically using a two-phase flow discrete vortex modelling. It was revealed from the modelling that inclusion of two-way momentum coupling is essential for properly modelling heavy particle dispersive transport in turbulent free shear flows. For heavy particles with small Stokes numbers, the dispersion is predominated by the large-scale vortex structures and they exert small influence on the carrier fluid flow. Heavy particles with large St directionally align along the braid region between the neighbouring vortices. However, the lateral dispersion of particles of large St is smaller than that of particles of small St. For buoyant particles with the density being slightly greater than that of the carrier fluid, numerical simulation revealed that the buoyant particles scatter over the whole vortex core rather than collect along the fringes of the vortex. The Lagrangian statistics calculation of buoyant particle dispersion showed that both the inertial and crossing-trajectory effects affect the particle dispersion behaviour and particle eddy diffusivity. The dispersion behaviour of buoyant particles is highly associated with the particle Stokes number. Large St buoyant particles exhibit a larger dispersion. It was also indicated from the numerical simulation that buoyant particles might disperse larger than the fluid tracers. The correlation between the buoyant particle and fluid tracer velocities was affected by including the coupling effect.

The nucleation, crystallization and dispersion behavior of PET–monodisperse SiO 2 composites

To more accurately investigate the nucleation, crystallization and dispersion behaviors of silica particles in polymers, the composites of PET with monodisperse SiO 2–PS core–shell structured particles were prepared with SiO 2 size from 380 nm to 35 nm. For these SNPET samples, DSC results showed that the nucleation rate of silica particles increased as their size decreased, in which 35 nm SiO 2 particles produced the most obvious nucleation effect. At 2.0 wt.% load of 35 nm silica, Avrami equation proved that the isothermal crystallization rate G of SNPET was ca. 30% higher than that of pure PET and the crystallization activation energy for SNPET was −218.7 kJ mol −1 lower than −196.1 kJ mol −1 for PET. While, the non-isothermal crystallization Δ E for SNPET was −199.8 kJ mol −1 lower than −185.5 for PET. On non-isothermal crystallization, Jeziorny equation presented the primary and secondary crystallization stages in PET and SNPET, in which nano SiO 2 accelerated the crystallization rate. Their Ozawa number m was from 2.1 to 2.7, which was smaller than that of Avrami number n. The nucleation and dispersion behaviors of SiO 2 particles were directly observed. POM results demonstrated that SNPET samples crystallized more quickly from melt and their crystallization rate increased as silica load increases but accelerated at 2–3 wt.%. The spherulites grew well in PET but their size was smaller in SNPET due to the silica barrier on their growth. SEM and TEM observed the homogeneous silica dispersion morphology and the vivid ordered patterns formed in SNPET. The monodisperse particles are highly expected to give more accurate and valuable references than multi-scale ones in obtaining novel advanced PET composites.