Effect of parameters on deposition pattern of ceramic nanoparticles in non-uniform AC electric field

In electrophoretic deposition (EPD), it is assumed that net movement of particles is zero under the influence of alternating current (AC) electric field. For this reason, AC electric field is not used for deposition of ceramic particles while in other areas scientists take the advantage of AC electric field for their purpose. By imposing some modifications on electric field, it is possible to use AC electric fields in processes such as fabrication of miniature ceramic parts. In this paper, non-uniform AC electric field was used to deposit TiO₂ nanoparticles on gold electrodes. Acetone was used as dispersing medium to avoid bubble formation at low frequencies. Effect of different parameters such as applied voltage and frequency, time and concentration on deposition pattern was studied and proper factors for optimization of the process were determined.     

Role of substrate potential on filling the gap between two planar parallel electrodes in electrophoretic deposition

Here we investigated low frequency AC electrophoretic deposition of TiO₂ nano-particles suspended in acetone by experiment and simulation. Deposition is done under influence of a non-uniform 1 Hz AC electric field. The non-uniform electric field is generated by two parallel planar gold electrodes coated on a glass substrate. Experiment shows that during deposition, TiO₂ nano-particles fill the gap between electrodes. Numerical simulation of electric field reveals the role of glass substrate on gap filling. Our model shows that existence of surface charge on the substrate between two electrodes is the reason why the TiO₂ nano-particles move to the gap between two electrodes and deposit there.     

Non-vanishing ponderomotive AC electrophoretic effect for particle trapping

We present here a study on overlooked aspects of alternating current (AC) electrokinetics-AC electrophoretic (ACEP) phenomena. The dynamics of a particle with both polarizability and net charges in a non-uniform AC electric trapping field is investigated. It is found that either electrophoretic (EP) or dielectrophoretic (DEP) effects can dominate the trapping dynamics, depending on experimental conditions. A dimensionless parameter γ is developed to predict the relative strength of EP and DEP effects in a quadrupole AC field. An ACEP trap is feasible for charged particles in 'salt-free' or low salt concentration solutions. In contrast to DEP traps, an ACEP trap favors the downscaling of the particle size.     

Electro-orientation in particle light valves

Electro-orientation of rod-like particles in liquids, under the application of an external AC field, is analysed. A rod shape is suitable for particle light valve (PLV) applications. When they are aligned with their long axes parallel to the electric field (and the direction of light is assumed to be parallel to the applied electric field), then it can lead to good transmission of light. Various criteria to arrive at appropriate parameters for PLV applications are proposed. It is found that good electric conductors are excellent rod materials for PLV applications. They lead to an appropriate orientation of the rods and at the same time result in maximum orientational torque. Water-like liquids with higher values of permittivity are appropriate choices as suspending liquids since the Brownian dispersion in the presence of the electric field is minimized. The time it takes the rods to fully diffuse in the orientational space, once the electric field is turned off, decreases with decreasing liquid viscosity.     

Aligned Immobilization of Proteins Using AC Electric Fields

Protein molecules are aligned and immobilized from solution by AC electric fields. In a single‐step experiment, the enhanced green fluorescent proteins are immobilized on the surface as well as at the edges of planar nanoelectrodes. Alignment is found to follow the molecules' geometrical shape with their longitudinal axes parallel to the electric field. Simultaneous dielectrophoretic attraction and AC electroosmotic flow are identified as the dominant forces causing protein movement and alignment. Molecular orientation is determined by fluorescence microscopy based on polarized excitation of the proteins' chromophores. The chromophores' orientation with respect to the whole molecule supports X‐ray crystal data.     

The Dynamics of Oblate Drop Between Heterogeneous Plates Under Alternating Electric Field

The dynamics of the incompressible fluid drop under the non-uniform electric field are considered. The drop is bounded axially by two parallel solid planes and the case of heterogeneous plates is investigated. The external electric field acts as an external force that causes motion of the contact line. We assume that the electric current is alternative current and the AC filed amplitude is a spatially non-uniform function. In equilibrium, the drop has the form of a circular cylinder. The equilibrium contact angle is 0.5π. In order to describe this contact line motion the modified Hocking boundary condition is applied: the velocity of the contact line is proportional to the deviation of the contact angle and the speed of the fast relaxation processes, which frequency is proportional to twice the frequency of the electric field. The Hocking parameter depends on the polar angle, i.e. the coefficient of the interaction between the plate and the fluid (the contact line) is a function of the plane coordinates. This function is expanded in a series of the Laplace operator eigenfunctions.     

A New Approach to Assess Gold Nanoparticle Uptake by Mammalian Cells: Combining Optical Dark‐Field and Transmission Electron Microscopy

Toxicological effects of nanoparticles are associated with their internalization into cells. Hence, there is a strong need for techniques revealing the interaction between particles and cells as well as quantifying the uptake at the same time. For that reason, herein optical dark‐field microscopy is used in conjunction with transmission electron microscopy to investigate the uptake of gold nanoparticles into epithelial cells with respect to shape, stabilizing agent, and surface charge. The number of internalized particles is strongly dependent on the stabilizing agent, but not on the particle shape. A test of metabolic activity shows no direct correlation with the number of internalized particles. Therefore, particle properties besides coating and shape are suspected to contribute to the observed toxicity.     

3D simulation of AC loss in a twisted multi-filamentary superconducting wire

In the AC loss simulation, it is a huge challenge to model the twisted wire at the filament level, due to the complex structure as well as long-time computation consumption. In this paper, we use 3D finite-element method based on H-formulation to study the AC loss in a twisted superconducting wire. The wire is treated as a homogenous material with the anisotropic conductivity in the filament region. We quantitatively simulate the AC loss induced by the AC transport current and magnetic field profile, and the effect of the twist pitch on the AC loss. In the case of AC transport current, larger pitch length leads to higher loss, and the pitch length effect is contrary to the case of applied magnetic field. The influences of the magnetic field direction and non-uniform current distribution subjected to the strand bending are also investigated. It is observed that, the transverse magnetic field has a more significant influence on the AC loss than the longitudinal magnetic field. The non-uniform current distribution can result in a higher AC loss, compared to a corresponding uniform current distribution.     

Measurement of electrostatic dipoles and net charge on particles suspended in air

Explanations of electrostatic behaviour of individual particulates have always invoked net electrostatic charge and neglected any fixed dipoles arising from nonuniform distribution of charge on their surface. Here for the first time, techniques are described to measure both net charge of each particle and its dipole moment by sampling, photography, and movement analysis of particles suspended in air. In this study, spherical dielectric particles were subjected to a non-uniform electric field (around a probe) and their trajectory was followed with a multi-flash high-speed video camera. These first results support the existence of fixed or “permanent” dipoles, on tribocharged particles.     

Effect of polyethylenimine on electrophoretic deposition of TiO2 nanoparticles in alternating current electric field

In this work, AC electric field was applied to deposit TiO₂ nanoparticles dispersed in Acetone on coplanar electrodes. The experiments were performed in presence and absence of an additive, polyethylenimine (PEI), at frequencies of 1 Hz and 10 kHz. It was revealed that deposition pattern changed dramatically by addition of PEI which makes particles to fill the inter electrode gap at both frequencies. When PEI is added, particles show different behavior. While they tend to fill the gap randomly at 1 Hz, they form chainlike pattern at 10 kHz. Chain formation of particles in the gap indicates presence of dielectrophoretic (DEP) forces. The ability of particles to polarize in both suspensions at 10 kHz are calculated by a multi-shell model in order to find DEP force. According to this model, the polarizability for particles in the suspension with PEI is more than the other, so DEP forces applied more strongly on them and promotes chain formation.     

Some New Views on the Principles of Magnetron Sputtering

In this paper, some common phenomena in magnetron sputtering are freshly analyzed and discussed on the basis of the motion of electrons in non-uniform orthogonal electric and magnetic fields. There exist magnetic confinements in three spatial dimensions on moving charged particles (including electrons) in this kind of non-uniform field. They are the longitudinal cycloidal motion, the horizontal simple harmonic-like motion (with varying amplitudes), and the vertical repelling action. The horizontal magnetic confinement in a mirror-like magnetic field keeps glow discharge lane completely parallel to the corridor of magnetic force lines, therefore only an effectively closed magnet array structure can form a relatively uniform and closed discharge lane. The main reasons for electrons' releasing from magnetic confinement are the vertical magnetic repelling force as well as a more and more weak confinement action in outer range etc. The dominant reasons for a comparatively low increase of substrate's temperature are that the density of bombarding electrons near the substrate is relatively low and their spatial distribution is relatively uniform (compared with that near the target surface). The erosion lane with an inverted Gauss's distribution shape on a magnetron sputtered target is due to that,with sputtering, the distribution width of the critical density of electrons shrinks continuously but the sputtering effect in the centerline of the corridor is always the most powerful.     

Preparation of silver coated nickel particles by thermal plasma with pre-treatment using ball milling

Recently, reducing noble metals in electric devices has been identified as a key factor to lower product cost. Among these, noble metal coated particles are considered an alternative with the potential to dramatically reduce the usage of noble metals. A dense coating of noble metals over all surfaces is desirable for maintaining the properties of noble metal. However, our previous research showed that coated surfaces onto which the nanoparticles were attached were non-uniform because of evaporation of the raw materials. Therefore, in this study, we improved the coverage ratio of silver coated nickel particles using thermal plasma processing followed by ball mill pre-treatment. Silver and nickel particles were mixed using a ball mill, then injected into the thermal plasma jet. The silver particles were subsequently attached onto the surface of the nickel particles through ball mill processing, after which the silver attached nickel particles were melted through thermal plasma processing to produce silver coated nickel spherical particles. The cross section of the as-prepared particles showed a dense silver shell and nickel core, while the sintered body of the as-prepared particles showed the net-like silver covering over the nickel cores. These findings suggest that attachment of silver on nickel could lead to complete silver coatings by limiting the formation of nanoparticles.     

Single nanodimensional emitting protrusion on the surface of a tungsten carbide field emitter

Variations in the shape of a tungsten carbide emitter under the simultaneous action of strong electric fields and high temperatures have been studied by field emission microscopy techniques. Using controlled decrease in the applied electric field strength at a certain temperature of the emitter, it is possible to grow a single nanodimensional surface protrusion capable of emitting charged particles with stability comparable to that of carbon-based materials. The values of emission currents, current densities, emission angles, and reduced brightnesses are comparable to those known for emitters based on carbon nanotubes. Advantages of single nanoprotrusions as emitters are their complete reproducibility and the ability to emit both electrons and ions     

Controlled formation of dielectric chain aggregates on material surfaces

This paper investigated the formation of chain aggregates from fine particles suspended in gas stream onto material surfaces under the action of electric field. The results showed that the shape of aggregate formed on material surface was greatly influenced by the field intensity and the surface condition of materials. In a weak electric field without corona discharge, particles tended to form clustered aggregates on a metal plate with smooth surface, but on a metal mesh and a porous alumina substrate, to form chain aggregate. On the other hand, in a corona discharge field, these surfaces were coated uniformly. Consequently, for forming chain aggregates on material surface, an electric field without corona discharge and a rough surface are necessary conditions. On rough surface, chain aggregates of dielectric particles or conductive particles grew from the protrusions of the surface and could form a rough and porous layer. When the external electric field was removed, the chain aggregates remained long time due to the Van der Waals forces. After sintered at proper temperature, the chain aggregates became fiber-like. The results indicate that the formation of chain aggregate can be controlled by electrostatic force, and sintering can be used as a method for increasing their mechanical strength.     

Nanoparticles in ambient air. measurement methods

Methods for the measurement of the parameters of aerosol particles with the use of an analyzer based on the differential mobility of nanoparticles and with a diffusion aerosol spectrometer are described and tested. A comparison of the results of measurements of the diameters of nanoparticles by the two methods is performed. Results of inter-laboratory comparisons of the analyzers based on the differential mobility of nanoparticles and studies of the electric motors of household appliances which are generators of the aerosols of nanoparticles with dimensions in the range 6–50 nm are presented.     

Unsteady natural convection flow of a suspension comprising Nano-Encapsulated Phase Change Materials (NEPCMs) in a porous medium

The free convection phase change heat transfer of a suspension comprising Nano-Encapsulated Phase Change Materials (NEPCMs) in a porous space is theoretically addressed. The core of the nanoparticles is made of a phase change material and encapsulated in a thin shell. Hence, the core of the nanoparticles of the suspension undergoes a phase change at its fusion temperature and release/store large amounts of latent heat. The phase change of nanoparticles is modeled using a sine shape temperature-dependent heat capacity function. Darcy-Brinkman model is used to model the flow in the porous medium. The governing equations including the conservation of mass, momentum, and heat are transformed into a non-dimensional form before being solved by the finite element method in a structured non-uniform mesh. The influence of the porosity, Darcy number, Rayleigh number, fusion temperature of nanoparticles, and the unsteady time-periodic boundary conditions on the thermal behavior of the porous medium in the presence of NEPCM particles is investigated. The results show that the presence of NEPCM particles improves the heat transfer. The increase of porosity improves the heat transfer when the volumetric concentrations of NEPCM particles are higher than 3%. There exists an optimal dimensionless fusion temperature of NEPCM nanoparticles for the interval [0.25; 0.75].     

DEM numerical studies on the design and efficiency of the continuous operating triboelectric separator

Triboelectric separation has gained importance as a dry separator for mineral and coal beneficiation. The different grade components of coal powder can be classified, beneficiated, and segregated with the help of the triboelectric separator. A batch-mode triboelectric separator is being used in CSIR-Institute of Minerals & Materials Technology for separating pure coal particles from gangue quartz and kaolinite particles. The sticking of particles on the electrode plates forces the separator to be paused for cleaning the electrode plates. A moving belt over an electrode plate can prevent its direct contact with particles and also carries the particle down towards collection bins. The feasibility study of installing moving belts along with the optimum conditions for design and operating parameters were studied with the help of DEM simulations. The bi-modal frequency distributions of coal and quartz in collection bins ware observed. The rationale for observation of bi-modal distribution is attributed to the varying initial angles and velocities of the particles entering the active electric field region. The non-uniform probabilistic opportunities of the particles to attach with the respective belts resulted in two groups of particles; (a) particles attached to belt followed by their collection in the expected bins (b) particles with initial inclination opposite to the direction of external force and their collection in the bins on the other side. The second group of particles followed trajectories governed by external forces and got collected into the bins on the other side. The phenomena resulted in the bi-modal distribution of mass distribution.     

Sub-micrometer particles produced by a low-powered AC electric arc in liquids

The article presents the report of the production of composites of sub-micrometer metal particles in matrix consisted of the metal compounds by means of an AC electric arc in water and paraffin solutions using electrodes carbon-metal and metal-metal (metal: Ni, Fe, Co, Cu). The advantage of this method is the low electric power (from 5 to 10 W) needed in comparison to standard DC arc-discharge methods (0.8 to 3 kW). This method enables the production of particles from conductive material also in wide range of temperature and in solvent which could be either transparent to light or opaque. Moreover the solvent can be electrolyte or insulating liquid. The microstructure of the composite layer was investigated by scanning electron microscopy (SEM), Electron Probe Microanalysis (EPMA) and X-ray. During particles production in water metal oxides were created. Additionally using cobalt-copper, nickel-copper as couple electrodes, insoluble in water copper (II) hydroxide crystal grains were created additionally which crystals shape was depended on transition metal. For iron-copper couple electrodes system the copper (II) hydroxide was not formed. Experiments with sequence production of Ni and Fe particles with C electrode assisting in molten paraffin let to obtain both Ni and Fe particles surrounded by paraffin. After solidification the material was insulator but if locally magnetic field influenced on the liquid solution in that place after solidification a new composite was created which was electric current conductor with resistivity around 0.1 omega x m, was attracted by magnetic field and presented magneto resistance around 0.4% in changing magnetic field in a range 150 mT. After mixing the concentrated paraffin with normal paraffin resistivity of the mixture increased and it became photosensitive and created small voltage under light influence.     

Levitation jet synthesis of nickel ferrite nanoparticles

Pseudospherical nickel ferrite particles 25 to 70 nm in average size were prepared by a crucibleless aerosol method through cocondensation of Fe and Ni vapors in an inert-gas flow containing a small amount of air. The particles were characterized by transmission electron microscopy, X-ray microanalysis, X-ray diffraction, BET measurements, and vibrating-sample and SQUID magnetometry. The results were used to optimize process parameters for the preparation of particles with a tailored size, specific surface area, and saturation magnetization. A dc electric field applied to the condensation zone can serve to improve the phase purity of nickel ferrite nanoparticles, reduce their size, and change their Curie temperature.