Charged Microparticles Research Articles

Butterflies and bifurcations in surface radio-frequency traps: The diversity of routes to chaos.

In the present article, we investigate the charged micro-particle dynamics in the surface radio-frequency trap (SRFT). We have developed a new configuration of the SRFT that consists of three curved electrodes on a glass substrate for massive micro-particles trapping. We provide the results of numerical simulations for the dynamical regimes of charged silica micro-particles in the SRFT. Here, we introduce a term of a "main route" to chaos, i.e., the sequence of dynamical regimes for the given particles with the increase of the strength of an electric field. Using the Lyapunov exponent formalism, typical Reynolds number map, Poincaré sections, bifurcation diagrams, and attractor basin boundaries, we have classified three typical main routes to chaos depending on the particle size. Interestingly, in the system described here, all main scenarios of a transition to chaos are implemented, including the Feigenbaum scenario, the Landau-Ruelle-Takens-Newhouse scenario as well as intermittency.

Positively Charged Microparticle in Plasma with High-Energy Electron Beam

The processes of recharging, heating and evaporation of a positively charged microparticle (MP) introduced into the plasma with an injected high-energy electron beam are considered. It is assumed that the MP is charged outside the plasma and then introduced into the plasma by an accelerating field, where plasma and beam electrons hitting the MP heat and evaporate it. In addition to introducing the MP into the plasma, the positive MP charge provides an additional source of energy needed to heat and evaporate it. Using the OML theory, the system of current and energy balance equations was numerically solved and the conditions, under which the MP is heated to the boiling point of its substance, resulting in its intense evaporation, were determined. The influence of the energy of the electron beam on the process of MP recharging, as well as on the rate of its heating and evaporation, has been studied. An estimate of the particle entry velocity into the plasma has been made; the distances at which its recharging, heating to the boiling point and complete evaporation occur are determined. The work is carried out in order to creating plasma of a given elemental composition.

All-Optical Domain Inversion in LiNbO3 Crystals by Visible Continuous-Wave Laser Irradiation.

LiNbO3 is a distinguished multifunctional material where ferroelectric domain engineering is of paramount importance. This degree of freedom of the spontaneous polarization remarkably enhances the applicability of LiNbO3, for instance, in photonics. In this work, we report the first method for all-optical domain inversion of LiNbO3 crystals using continuous-wave visible light. While we focus mainly on iron-doped LiNbO3, the applicability of the method is also showcased in undoped congruent LiNbO3. The technique is simple, cheap, and readily accessible. It relies on ubiquitous elements: a light source with low/moderate intensity, basic optics, and a conductive surrounding medium, e.g., water. Light-induced domain inversion is unequivocally demonstrated and characterized by combination of several experimental techniques: selective chemical etching, surface topography profilometry, pyroelectric trapping of charged microparticles, scanning electron microscopy, and 3D Čerenkov microscopy. The influence of light intensity, exposure time, laser spot size, and surrounding medium is thoroughly studied. To explain all-optical domain inversion, we propose a novel physical mechanism based on an anomalous interplay between the bulk photovoltaic effect and external electrostatic screening. Overall, our all-optical method offers straightforward implementation of LiNbO3 ferroelectric domain engineering, potentially sparking new research endeavors aimed at novel optoelectronic applications of photovoltaic LiNbO3 platforms.

Characterization of size-resolved charge distributions for triboelectrically charged microparticles via electrical mobility analysis coupled to optical particle spectrometry

In printing applications, microparticles are commonly triboelectrically charged with larger carrier particles. Here, we develop an impaction-differential mobility analyzer-optical particle spectrometer (DMA-OPS) system to examine the size-dependent charge distributions of toner particles in the 0.3 – 10 μm range resulting from triboelectric charging via acrylic-coated ferrite carrier. The toner-carrier blend is aerosolized, and toner particles are released from the carrier via inertial impaction of toner-carrier complexes. The toner particles are then classified by electrical mobility and their optical diameters are determined. We can produce toner particle size-dependent charge distributions, which can be converted to surface potentials, and charge-to-mass ratios.

The influence of an externally applied electric field on residual microparticle charge in a spatio-temporal afterglow plasma

The residual charge of dust particles in spatial and temporal afterglow plasmas is relevant in many fundamental research fields and technological applications. It has been shown in both spatial and temporal afterglow plasmas that the presence of an externally applied electric field can greatly influence the residual dust particle charge. However, this has not yet been explored in a combined spatiotemporal afterglow plasma. In this work, the influence of an externally applied electric field on the residual microparticle charge is, therefore, investigated in a spatiotemporal afterglow plasma. It is found that the measured charge is predominantly affected by changes to the spatial component of the spatiotemporal afterglow when an electric field is applied, while the influence on the temporal component seems to be significantly less relevant. Our results contribute to an improved understanding of particle (de-)charging in afterglow plasmas and are highly relevant to the design of applications in which afterglow plasmas are present and where the charge of dust particles needs to be controlled for the sake of (nano)contamination control.

Concentration-polarization electroosmosis for particle fractionation.

Concentration-polarization electroosmosis (CPEO) refers to steady-state electroosmotic flows around charged dielectric micro-particles induced by low-frequency AC electric fields. Recently, these flows were shown to cause repulsion of colloidal particles from the wall of a microfluidic channel when an electric field is applied along the length of the channel. In this work, we exploit this mechanism to demonstrate fractionation of micron-sized polystyrene particles and bacteria in a flow-focusing device. The results are in agreement with predictions of the CPEO theory. The ease of implementation of CPEO-based fractionation in microfluidics makes it an ideal candidate for combining with current techniques commonly used to generate particle lift, such as inertial or viscoelastic focusing, requiring no extra fabrication steps other than inserting two electrodes.

Observation of the hexatic phase in a two-dimensional complex plasma using machine learning.

Complex plasmas consist of ionized gas and charged solid microparticles, representing the plasma state of soft matter. We apply machine learning methods to investigate a melting transition in a two-dimensional complex plasma. A convolutional neural network is constructed and trained with the numerical simulation. The hexatic phase is successfully identified and the evolution of topological defects is studied during melting transition in both simulations and experiments.

O rassloenii monosloya zaryazhennykh mikrochastits v parabolicheskom uderzhivayushchem potentsiale

The evolution of an initially planar monolayer of charged microparticles in a complex plasma (plasma crystal) in horizontal (in the plane of the monolayer) and vertical parabolic confinements has been considered. The separation (buckling instability) of a Yukawa system into several layers at the weakening of the vertical confinement, as well as structural changes in such a plasma crystal, has been studied using the molecular dynamics method. In particular, it has been shown that the radial inhomogeneity of the plasma crystal qualitatively changes the character of the separation compared to homogeneous systems. Indeed, the separation begins in the center of the crystal, where the average distance between particles is minimal, and propagates in the form of a wave towards the periphery of the system at the weakening of the vertical confinement. This explains features of the behavior of plasma crystals in recent experiments with the complex plasma.

On the Separation of a Monolayer of Charged Microparticles in a Parabolic Confinement

On the Separation of a Monolayer of Charged Microparticles in a Parabolic Confinement

Investigation of the Operation of the Flight Detector of High-Speed Charged Microparticles for a Time-of-Flight Mass Spectrometer

Investigation of the Operation of the Flight Detector of High-Speed Charged Microparticles for a Time-of-Flight Mass Spectrometer

Separation of Polydisperse Charged Microparticles in Air by an Electrodynamic Linear Trap

Separation of Polydisperse Charged Microparticles in Air by an Electrodynamic Linear Trap

Observing Real-Time Adhesion of Microparticles on Glass Surfaces.

Fouling on glass surfaces reduces the solar panel efficiency and increases water consumption for cleaning. Superhydrophobic coatings on glass enable self-cleaning by allowing water droplets to carry away dirt particles. Observing the interaction between charged particles and surfaces provides insights into effective cleaning. Using a high-speed camera and a long-distance objective, we analyzed the in situ deposition of variously functionalized and charged silica dust microparticles on chemically treated glass. The ambient charges for the control, hydrophobic, and positively charged particles were approximately -0.5, -0.13, and +0.5 nC, respectively. We found that a positively charged particle of 2.3 ± 1.2 μm diameter adhered to hydroxylated glass in ∼0.054 s, compared to 0.40 and 0.45 s for quaternary ammonium- and fluorosilane-functionalized hydrophobic glass. Experiments suggest that quaternary ammonium-functionalized glass surfaces are about 77.8% more resistant to soiling than bare surfaces.

Sedimentation of a Charged Spherical Particle in a Viscoelastic Electrolyte Solution.

When a charged particle translates through an electrolyte solution, the electric double layer around it deforms in response to the fluid motion and creates an electric force opposite the direction of motion, decreasing the settling velocity. This is a multidisciplinary phenomenon that combines fluid mechanics and electrodynamics, differentiating it from the classical problem of an uncharged sedimenting particle. It has many applications varying from mechanical to biomedical, such as in drug delivery in blood through charged microparticles. Related studies so far have focused on Newtonian fluids, but recent studies have proven that many biofluids, such as human blood plasma, have elastic properties. To this end, we perform a computational study of the steady sedimentation of a spherical, charged particle in human blood plasma due to the centrifugal force. We used the Giesekus model to describe the rheological behavior of human blood plasma. Assuming axial symmetry, the governing equations include the momentum and mass balances, Poisson's equation for the electric field, and the species conservation. The finite size of the ions is considered through the local-density approximation approach of Carnahan-Starling. We perform a detailed parametric analysis, varying parameters such as the ζ potential, the size of the ions, and the centrifugal force exerted upon the particle. We observe that as the ζ potential increases, the settling velocity decreases due to a stronger electric force that slows the particle. We also conduct a parametric analysis of the relaxation time of the material to investigate what happens generally in viscoelastic electrolyte solutions and not only in human blood plasma. We conclude that elasticity plays a crucial role and should not be excluded from the study. Finally, we examine under which conditions the assumption of point-like ions gives different predictions from the Carnahan-Starling approach.

On the Effect of Particles on the Electrical Conductivity of Liquid Dielectrics

In this paper, an attempt to evaluate the effect of particles on the electrical conductivity of liquid dielectrics is made. For this purpose, a conductivity model is formulated taking into account the presence of relatively large charged microparticles in the dielectric. Based on calculations using the model, a comparative assessment of electrical conductivity was carried out. It is shown that in sufficient quantities, particles can significantly increase the electrical conductivity when forming double electric layers near their surface.

Surface Tension of a Cloud of Charged Microparticles in a Gas-Discharge Plasma

Surface Tension of a Cloud of Charged Microparticles in a Gas-Discharge Plasma

Period-doubling bifurcation in surface radio-frequency trap: Transition to chaos through Feigenbaum scenario.

We have numerically investigated the dynamics of charged microparticles in a "five-wire" surface radio-frequency trap. The period-doubling bifurcation conditions have been shown to depend on the particle, the trap, and the alternating voltage parameters. For a comprehensive study of the dynamics chaotization through a cascade of period doubling, we have used Fourier analysis of a particle trajectory as well as the calculations of a non-trivial Lyapunov exponent map. We have demonstrated that the period-doubling bifurcation is consistent with a Feigenbaum scenario. A new approach to particle property determination can, thus, be based on observing a period-doubling bifurcation.

Spin Catalysis in Photochemical Reactions and Its Applications to Quantum Information Nanotechnology

Chemistry as a science about spin and electric charge of micro particles which provide driving forces of atomic interactions and molecular structure transformations fits pretty well to the modern Quantum Information Science (QIS) requirements. Today’s computers operate only electric current signals in the semiconductor networks but the electron-spin properties are not exploited in a large extend. Spintronics provides spin-polarized currents and manipulates magnetic spin interactions; it uses mostly solid state chemistry of heavy elements. But a rich organic chemistry of solvents and fin films offers a great potential for molecular electronics and quantum computing. Photo-excited organic complexes of the “chromophore–radical” type provide good promise for many technological applications in molecular spintronics and electronics, including QIS technology. The doublet state photo excitation of stable organic radical being delocalized onto the linked anthracene molecule within picoseconds and subsequently evolved into a quartet state for big radicals (a pure high spin state) of the mixed radical-triplet character presents a sensible spin-optical interface for qubit in quantum computing. This high-spin state is coherently addressable with EPR microwaves even at room temperature, with the optical read-out induced by intersystem crossing (ISC) to emissive triplet state. Such integration of radical luminescence and high-spin states EPR provides the organic materials involvement into emerging QIS technologies

Cation-exchange performance of a citric-acid esterified cellulose nanofibrous membrane for highly-selective proteins' permeability and adsorption capacity

The usage of low-cost, readily available, or even disposable, single-use membranes in macromolecules’ purification and separation is still in the development phase. In this research, highly porous (>95 %), water- and compression stable cation-exchange membranes were prepared by freeze-casting using cellulose nanofibrils (CNF) and citric acid (CA) acting as a crosslinker and source of weak anionic (carboxylic) surface groups arising from the mono-esterified CA. The membranes were characterized by different analytical techniques, and evaluated for the ionic adsorption efficacy of different proteins in dead-end filtration mode using a Tri-buffer of pH 8. The membrane's internal microstructure (porosity and density) with the available (quantity and access) carboxylic groups was confirmed, to determine not only the proteins' specific (related to the net charged and molecular weight) adsorption dynamic (>52 % of positive Lysozyme/Cytochrome, <8 % of negative BSA/Myoglobin; ≤0.5 g/L) at extremely high flow rates (>3.000 hL/h*MPa*m2), but also their desorption (>97 %) and re-equilibration (using NaCl) with flux recovery (>80 %). Such efficiency was achieved with up to 5 consecutive filtering cycles. The high permeability (>87 %) of the spherical and negatively surface charged microparticles (used as models) also suggests the likelihood of removing larger microbial species, which, while retaining relatively smaller and positively charged proteins, further increases their potential in biopharma applications.

Generatsiya elektricheskogo polya v pylevoy plazme

A nonuniform dusty plasma, micrometer-size particles or microdroplets of which are located in a dense gas or in atmospheric air, is excited by an energy pulse leading to the weak ionization of the gas. As a result, the particles charge through the attachment of gaseous ions to them. The stability of dusty plasma is determined by the low mobility of charged microparticles. The conditions under which the separation of negative and positive charges occurs in a dusty plasma with the creation the electric field are considered. The criteria are presented for the generation of atmospheric electricity in a dense cloud as a result of the gravitational falling of charged water microdroplets in the atmosphere, the weak ionization of which occurs under the action of cosmic rays. It is shown that this is possible only under a nonuniform space distribution of water microdroplets in the cloud. The peculiarities of a dusty plasma are considered. This plasma exists in Saturn’s rings and in the flow of coal combustion products, as well as in the dusty atmosphere of a coal mine.

POSITIVELY CHARGED MICROPARTICLES IN PLASMA

The processes of recharging and changing the temperature of a positively charged microparticle (MP) introduced into plasma are considered. It is assumed that the MP is charged to a positive charge outside the plasma, and then enters the plasma due to the accelerating field. For various values of plasma density and temperature, a numerical solution of the energy and current balance equations of a MP is obtained. The equation that determines the evaporation of particles is solved numerically. The time dependence of the radius of a MP during evaporation has been obtained.