Effects Of Charged Particles Research Articles

Dependence of Nonlinear Electrophoresis on Particle Size and Electrical Charge

This study focuses on the dependence of nonlinear electrophoretic migration of particles on the particle size and particle electrical charge. This is the first report of the experimental assessment of the mobilities of the nonlinear electrophoretic velocity of colloidal polystyrene microparticles under two distinct electric field dependences. A total of nine distinct types of polystyrene microparticles of varying size and varying electrical charge were divided into two groups to study separately the effects of particle size and the effects of particle charge. The mobilities of the nonlinear electrophoretic velocity of each particle type were determined in both the cubic and 3/2 regimes (μEP,NL(3) and μEP,NL(3/2)). The results unveiled that both mobilities had similar relationships with particle size and charge. The magnitude of both μEP,NL(3) and μEP,NL(3/2) increased with increasing particle size and decreased with increasing magnitude of particle charge. However, the observed trends were not perfect as discussed in the Results and Discussion section but still provide valuable information. These findings will aid in the design of future size-based and charge-based separations of particles and microorganisms.

Influence of weak electrostatic charges and secondary flows on pneumatic powder transport

AbstractThe dynamics of the transported powder determines the functionality and safety of pneumatic conveying systems. The relation between the carrier gas flow, induced by the flown‐through geometry, and the powder flow pattern is not clear yet for electrostatically charged particles. This paper highlights the influence of relatively minor cross‐sectional secondary flows and electrostatic forces on the concentration and dynamics of the particles. To this end, direct numerical simulations (DNS) capture the interaction of the continuous and dispersed phases using a four‐way coupled Eulerian–Lagrangian strategy. The transport of weakly charged particles in channel flows, where turbopheresis defines the particle concentration, is compared to duct flows, where additional cross‐sectional vortices form. For both geometries, the Stokes number () and the electrical Stokes number () are varied, and the turbulent carrier flow was fixed to . The presented simulations demonstrate that secondary flows, for the same , , and , dampen the effect of particle charge. In a duct flow, vortical secondary flows enhance the cross‐sectional particle mobility against the direction of electrostatic forces. Compared to a duct flow, in a channel, the wall‐normal aerodynamic forces are weaker. Thus, electrical forces dominate their transport; the local particle concentration at the walls increases. Further, electrostatic charges cause a stronger correlation between the gas and particle velocities. In conclusion, despite being weak compared to the primary flow forces, secondary flow and electrostatic forces drive particle dynamics during pneumatic transport.

Defined Coadsorption of Prostate Cancer Targeting Ligands and PEG on Gold Nanoparticles for Significantly Reduced Protein Adsorption in Cell Media

A study on the surface chemistry of gold nanoparticles (AuNPs) utilizing gel electrophoresis is presented. The molecular design of targeting and stabilizing PEG ligands allows one to combine them in mixed ligand layers with control of relative composition. For all tested targeting and control ligands, coadsorption of PEG significantly reduces protein adsorption and matrix effects of cell media as compared to conjugates without PEG. Introducing carboxylic acid groups into the PEG ligand layer does not lead to increased protein adsorption as shown with carboxylic acid terminated PEG ligands. The controlled adsorption of PEG ligands with different molecular weights is used to disentangle the effects of particle charge and hydrodynamic diameter. Taken together, this study provides directions for the functionalization of nanoparticles to obtain conjugates which are well-defined in terms of composition and colloidally stable in complex media. This is in particular relevant for targeting applications and cell experiments.

Impact of Particle Shape and Surface Group on Membrane Fouling.

Membrane fouling remains one of the most critical drawbacks in membrane filtration processes. Although the effect of various operating parameters—such as flow velocity, concentration, and foulant size—are well-studied, the impact of particle shape is not well understood. To bridge this gap, this study investigated the effect of polystyrene particle sphericity (sphere, peanut and pear) on external membrane fouling, along with the effect of particle charge (unmodified, carboxylated, and aminated). The results indicate that the non-spherical particles produce higher critical fluxes than the spherical particles (i.e., respectively 24% and 13% higher for peanut and pear), which is caused by the looser packing in the cake due to the varied particle orientations. Although higher crossflow velocities diminished the differences in the critical flux values among the particles of different surface charges, the differences among the particle shapes remained distinct. In dead-end filtration, non-spherical particles also produced lower flux declines. The shear-induced diffusion model predicts all five particle types well. The Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DLVO (XDLVO) models were used to quantify the interaction energies, and the latter agreed with the relative critical flux trends of all of the PS particles. As for the flux decline trends, both the DLVO and XDLVO results are in good agreement.

Effect of particle charge on aerosol dynamics in Teflon environmental chambers

The contribution of particle charge to the rate of particle wall deposition has been a persistent source of uncertainty for experiments performed in environmental chambers. By tracking the preferen...

Field-Assisted Contact Line Motion in Thin Films.

The balance of intermolecular and surface forces plays a critical role in the transport phenomena near the contact line region of an extended meniscus in several technologically important processes. Externally applied fields can alter the equilibrium and stability of the meniscus with concomitant effects on its shape and spreading characteristics and may even lead to an oscillation. This feature article provides a detailed account of the present and past efforts in exploring the behavior of curved thin liquid films subjected to mild thermal perturbations, heat input, and electrical and magnetic fields for pure as well as colloidal suspensions, including the effects of particle charge and polarity. The shape-dependent intermolecular force field has been evaluated in situ by a nonobtrusive optical technique utilizing the interference phenomena and subsequent image processing. The critical role of disjoining pressure is identified along with the determination of the Hamaker constant. The spatial and temporal variations of the capillary forces are evaluated for the advancing and receding menisci. The Maxwell-stress-induced enhanced spreading during electrowetting, at relatively low voltages, and that due to the application of a magnetic field are discussed with respect to their distinctly different characteristics and application potentials. The use of the augmented Young-Laplace equation elicited additional insights into the fundamental physics for flow in ultrathin liquid films.

Correcting for particle size effects on plasma actuator particle image velocimetry measurements

Particle image velocimetry (PIV) is often used to characterize plasma actuator flow, but particle charging effects are rarely taken into account. A parametric study was conducted to determine the effects of particle size on the velocity results of plasma actuator PIV experiments. Results showed that smaller particles more closely match air flow velocities than larger particles. The measurement uncertainty was quantified by deconvolving the particle image diameter from the correlation diameter. The true air velocity was calculated by linearly extrapolating to the zero-size particle diameter.

Modeling for collective growth of fume primary particles with charge effect in arc welding

A model is developed to calculate the collective growth of fume primary particles with charging due to collisions with ions and electrons from the plasma. The model also expresses a particle size distribution with any shape and calculates its transient behavior due to a collective growth of particles through homogeneous nucleation, heterogeneous condensation, and coagulation on the basis of aerosol dynamics. Using the model, numerical calculation is performed to reveal the mechanism of the particle formation and the charge effect on the growth process during MIG welding. In consequence, it is found that almost all particles generated in a typical condition of MIG welding are negatively charged. The effect of particle charge plays an important role on the collective growth process of primary particles of welding fume because the particle charge causes a repulsive Coulomb force which prevents the particles from growing by coagulation. It is recommended that charge effect should be taken into account for studying fume particle formation in MIG welding.

Design and Application of Magnetic Photocatalysts for Water Treatment. The Effect of Particle Charge on Surface Functionality

Core-interlayer-shell Fe3O4/SiO2/TiO2, CoFe2O4/SiO2/TiO2 and BaFe12O19/SiO2/TiO2 magnetic photocatalysts were obtained. A water-in-oil microemulsion system with suitable surfactants was used for functionalization of the magnetic core with silica interlayer and TiO2-based photocatalyst. Uncoated and coated particles were characterized by electrophoretic measurements, X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area (BET) measurements, diffuse reflectance spectroscopy (DRS) and vibrating sample magnetometer (VSM) analysis. The pH of the solution and corresponding zeta potential was found to be essential for appropriate formation of ferrite core/silica interlayer/TiO2 shell nanocomposite, since the electrical charge controls interactions during functionalization of the magnetic core particles. Thus, the development of multilayer structure in the isoelectric point (IEP) region enhanced adhesion of ferrite, silica and titania particles. The obtained Fe3O4/SiO2/TiO2, CoFe2O4/SiO2/TiO2 and BaFe12O19/SiO2/TiO2 nanocomposites revealed superparamagnetic behavior. The decomposition rate of phenol and carbamazepine allowed to estimate their photocatalytic activity. Progress of photocatalytic mineralization of organic compounds was evaluated by total organic carbon (TOC) measurements. Photocatalytic activity measured in four subsequent cycles showed good reusability as no loss of efficiency of phenol degradation was observed.

Particle-size sorting system of lunar regolith using electrostatic traveling wave

A particle-size sorting system of lunar regolith using an electrostatic traveling wave is developed for In-Situ Resource Utilization on the Moon to extract indispensable resources from the regolith and realize long-term exploration. The regolith is sorted by utilizing a balance between the electrostatic and gravitational forces, which are determined depending on particle size, in vacuum conditions where the particles are not subjected to air drag. In this study, the effect of particle charge on the particle motion is confirmed by conducting model experiments and numerical calculations based on the distinct element method. In addition, it was experimentally demonstrated that particles less than approximately 20 μm in diameter were efficiently separated from the bulk of a lunar regolith simulant FJS-1 in a vacuum condition (∼1.5 × 10−2 Pa), and the performance of the size sorting system on the Moon was predicted by the numerical calculations. The system utilizes only the electrostatic force, and it does not require any gas, liquid, or mechanical moving parts.

Design and Application of Magnetic Photocatalysts for Water Treatment. The Effect of Particle Charge on Surface

Core-interlayer-shell Fe3O4/SiO2/TiO2, CoFe2O4/SiO2/TiO2 and BaFe12O19/SiO2/TiO2 magnetic photocatalysts were obtained. A water-in-oil microemulsion system with suitable surfactants was used for functionalization of the magnetic core with silica interlayer and TiO2-based photocatalyst. Uncoated and coated particles were characterized by electrophoretic meaurements, X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmision electron microscopy (TEM), specific surface area (BET) measurements, diffuse reflectance spectroscopy (DRS) and vibrating sample magnetometer (VSM) analysis. The pH of the solution and corresponding zeta potential was found to be essential for appropriate formation of ferrite core/silica layer/TiO2 shell nanocomposite, since the electrical charge controls interactions during functionalization of the magnetic core particles.

Photo-Crosslinkable Colloids: From Fluid Structure and Dynamics of Spheres to Suspensions of Ellipsoids.

Recently-developed photo-crosslinkable PMMA (polymethylmethacrylate) colloidal spheres are a highly promising system for fundamental studies in colloidal physics and may have a wide range of future technological applications. We synthesize these colloids and characterize their size distribution. Their swelling in a density- and index- matching organic solvent system is demonstrated and we employ dynamic light scattering (DLS), as also the recently-developed confocal differential dynamic microscopy (ConDDM), to characterize the structure and the dynamics of a fluid bulk suspension of such colloids at different particle densities, detecting significant particle charging effects. We stretch these photo-crosslinkable spheres into ellipsoids. The fact that the ellipsoids are cross-linked allows them to be fluorescently stained, permitting a dense suspension of ellipsoids, a simple model of fluid matter, to be imaged by direct confocal microscopy.

Constraints on the microphysics of Pluto's photochemical haze from New Horizons observations

The New Horizons flyby of Pluto confirmed the existence of hazes in its atmosphere. Observations of a large high- to low- phase brightness ratio, combined with the blue color of the haze (indicative of Rayleigh scattering), suggest that the haze particles are fractal aggregates, perhaps analogous to the photochemical hazes on Titan. Therefore, studying the Pluto hazes can shed light on the similarities and differences between the Pluto and Titan atmospheres. We model the haze distribution using the Community Aerosol and Radiation Model for Atmospheres assuming that the distribution is shaped by downward transport and coagulation of particles originating from photochemistry. Hazes composed of both purely spherical and purely fractal aggregate particles are considered. General agreement between model results and solar occultation observations is obtained with aggregate particles when the downward mass flux of photochemical products is equal to the column-integrated methane destruction rate ∼1.2×10−14gcm−2s−1, while for spherical particles the mass flux must be 2–3 times greater. This flux is nearly identical to the haze production flux of Titan previously obtained by comparing microphysical model results to Cassini observations. The aggregate particle radius is sensitive to particle charging effects, and a particle charge to radius ratio of 30e−/µm is necessary to produce ∼0.1–0.2µm aggregates near Pluto's surface, in accordance with forward scattering measurements. Such a particle charge to radius ratio is 2–4 times higher than those previously obtained for Titan. Hazes composed of spheres with the same particle charge to radius ratio have particles that are 4 times smaller at Pluto's surface. These results further suggest that the haze particles are fractal aggregates. We also consider the effect of condensation of HCN, C2H2, C2H4, and C2H6 on the haze particles, which may play an important role in shaping their altitude and size distributions.

Modelling of particle resuspension by a turbulent airflow and the role of particle size, surface roughness and electric charge

A resuspension model based on the Lennard–Jones intermolecular potential is applied to a monolayer deposit of spherical particles. The model considers the interactions between a particle and a surface under the influence of an external turbulent airflow. The particle–surface interaction was modelled with and without particle deformation due to elastic flattening. The resuspension rate was calculated by a kinetic force-balance approach whereby particle detachment occurs when the instantaneous joint contribution of the lift and drag forces exceeds the total adhesive force of the particle–surface system. Enhanced aerodynamic particle removal driven by the moment of the lift and drag forces was determined. Model predictions suggest that inclusion of the moment of the aerodynamic forces provides a suitable model for particle detachment (initiated by rolling). The importance of elastic deformation was found to depend on adhesive forces, characteristics of the substrate surface (surface roughness) and particle size. The model was applied to a number of laboratory experiments. For one set of experiments, we identified two resuspension regimes depending on whether small non-deformable or large deformable (equivalently, strongly or weakly bound) particles resuspended at high or low friction velocities. A modified model incorporating the effect of particle charge is also presented. Results indicate that particle resuspension is possible even when electrostatic forces are present, but the resuspension rate decreases considerably, depending on particle size, particle charge and surface roughness.

Relationship between particle charge and electrostatic enhancement of filter performance

As an important particle collection method, filtration is significantly affected by particle precharging. The filtration of differently charged fly ash particles using membrane and fibrous filters was experimentally studied. Particle charge was directly measured and quantitatively related to the enhancement of filter performance. Particle penetration, which was observed in the fibrous filter during the early stages of filtration, exponentially decreased with increasing particle charge when the filter was clean and rapidly decreased with increasing particle load. A penetration reduction factor ψ was defined to represent the effect of particle charge on penetration, and its correlation with particle charge was defined on the basis of the fitting experimental results. The average porosity of the dust cakes that were formed on both filters increased with particle charge, which in turn exponentially decreased the pressure drop. The electrostatic effect on pressure drop was less prominent than that on penetration. A pressure drop reduction factor θ was defined to quantify the effect of particle charge on pressure drop. Correlations for predicting the evolution of average cake porosity and pressure drop in consideration of particle charge were proposed on the basis of the fitting experimental results.

Interactions and Aggregation of Charged Nanoparticles in Uncharged Polymer Solutions.

We employ an extension of the single chain in mean field simulation method to study mixtures of charged particles and uncharged polymers. We examine the effect of particle charge, polymer concentration, and particle volume fraction on the resulting particle aggregates. The structures of aggregates were characterized using particle-particle radial distribution functions and cluster size distributions. We observe that the level of aggregation between particles increases with increasing particle volume fraction and polymer concentration and decreasing particle charge. At intermediate regimes of particle volume fraction and polymer concentrations, we observe the formation of equilibrium clusters with a preferred size. We also examined the influence of manybody effects on the structure of a charged particle-polymer system. Our results indicate that the effective two-body approximation overpredicts the aggregation between particles even at dilute particle concentrations. Such effects are thought to be a consequence of the interplay between the respective manybody effects on the depletion and electrostatic interactions.

Charge‐induced electromagnetic resonances in nanoparticles

Electromagnetic theories have reproduced the scattering properties of differently shaped particles and successfully been used to characterize numerous systems. However, certain anomalous features remain unexplained that include enhanced extinction when particles are much smaller than the wavelength. Here we explain these features exploiting recent research in electromagnetic scattering theories that suggests incorporating the effect of particle charge results in new physical outcomes that deviate appreciably from what is predicted by electromagnetic interaction from uncharged systems. For electrically charged particles, the resonant excitation of surface modes is governed by excess charges deposited on the particle surface. Charge effects become large when particles are small compared to the incident wavelength, and we show that the electrostatic approximation is not valid for modelling the electromagnetic interaction from such particles. Charge‐induced resonances appear in such systems that can reproduce previously unexplained phenomena, for instance, amplified microwave attenuation observed in sandstorms. image

Effect of Charging and Position of Metallic Particle Adhered to Spacer on PDIV and PRPD Characteristics in GIS

Gas Insulated Switchgears (GIS) are widely used due to their many benefits. The reliability of GIS is challenged due to the presence of spacer defects and/or metallic particles. Free metallic particles can tremendously reduce the insulation strength of GIS especially when they enter the triple junction region (consisting of the spacer, the electrode and the gaseous medium interface) around the spacer. Therefore, there a need to investigate the effect of charged metallic particle on the field intensification produced along the spacer surface and its consequences on the Partial Discharge Inception Voltage (PDIV). In this study, simulation and experimental results are reported for metallic particles adhering to a cylindrical spacer. The effect of particle charging on the resulting field intensification, particle initiated partial discharge inception voltage as well as Phase Resolved Partial Discharge (PRPD) characteristics are presented in this study. The particle adversely affects the electric field uniformity in the area between the two electrodes. A particle in contact with the electrode causes the most severe intensification in the electric field, while the effect caused by the particle at the gap centre is the least severe.

Single-step microfluidic synthesis of various nonspherical polymer nanoparticles via in situ assembling: dominating role of polyelectrolytes molecules.

In this paper, a microfluidic approach has been used for the synthesis of ellipsoidal, dumbbell, rodlike, and necklacelike polymer nanoparticles. High yields of special types of nonspherical nanoparticles have been achieved by the implementation of an emulsion polymerization into microfluidic arrangement with a micro hole-plate reactor for the formation of monomer droplets. Here, in particular, the formation of nonspherical polymer nanoparticles is dependent on the presence of polyelectrolyte surface active molecules such as poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSS-co-PM), poly(sodium-p-styrenesulfonate) (PSSS), and polyanetholesulfonic acid sodium salt (PAES). The shapes and sizes of the interparticle nanoassemblies are precisely controlled by adjusting the concentration of polyelectrolytes in the aqueous phase, and by choosing suitable flow rate ratios (aqueous to monomer phase), respectively. The formation of polymer nanoparticles with different morphologies can be explained by a spontaneous in situ assembling under partial electrostatic repulsive control in the single step synthesis. The effect of particle charge and the competition between thermal motion of particles and electrostatic repulsion on the spontaneous assembling under the condition of a limited polarizability are discussed here as an important factor for the formation process of nonspherical polymer nanoparticles.

Effect of electrostatic charge on oral-extrathoracic deposition for uniformly charged monodisperse aerosols

An in vitro study was conducted with the aim of investigating the effect of particle charge on deposition in the oral-extrathoracic airways of human adults. To generate monodisperse droplets with uniform charge, an atomizer was designed and built. The atomizer generates monodisperse droplets using controlled Rayleigh jet breakup and charges the droplets uniformly via electrostatic induction. Experiments were conducted at various aerodynamic particle diameters (3.3, 4.6 and 5.9μm) and volume flow rates (15 and 30L/min) for a wide range of charges per particle (0–25,000 elementary charges). The results show substantial increases in deposition due to induced charge electrostatics, especially for smaller particle sizes. A dimensionless empirical correlation was developed for predicting deposition in the mouth–throat region of human adults including induced charge electrostatic effects.