Sign Of Charge Research Articles

Нелинейное поглощение растворов метиленового голубого в присутствии плазмонных наночастиц с различным поверхностным зарядом

By continuous-pump Z-scanning, the nonlinear light absorption of aqueous and alcohol solutions of methylene blue was studied. It was shown that the mechanisms of optical nonlinearity of these solutions vary depending on the dye concentration and type of solvent. The dependence of the amplitude of nonlinear absorption of dye molecules on the concentration and sign of the surface charge of gold and silver nanoparticles in solution is revealed. Mathematical models of optical nonlinearity for concentrated and diluted solutions of dye molecules are considered; in the latter case, the influence of plasmon nanoparticles on the nonlinear optical characteristics of methylene blue solutions is taken into account

Existence of in-Plane Magnetic Skyrmion and its Motion under Current Flow

A magnetic skyrmion isusually refers to a twisted spin texture surrounded by uniformly aligned out-of-plane spinsin the background of a uniformly magnetized state. The invariance of the magnetic skyrmion conserves its topological charge under any continuous transformations of the spin textures, leads to which represents the robustness of a magnetic skyrmion their texture against external perturbations, making it ideal to use skyrmions as . Such a behaviour is required for an ideal information carriers. To date, most magnetic skyrmion studies have been performedfocused on in perpendicularly magnetized systems, where the skyrmion topological number is determined by the relative orientation between the core and /outer perpendicular magnetization directions of the skyrmion is either up/down or down/up. Here we show that there also exists a new type of magnetic skyrmion with surrounding spins to be uniformly aligned to the in-plane direction. By continuous transformation and relaxation of the spin textures of out-of-plane skyrmions, we showed that an in-plane skyrmion, where the background magnetization is in the in-plane direction, is also possible. Different from the conventional perpendicular magnetic skyrmionsContrary to the skyrmions in a perpendicularly magnetized state, the in-plane magnetic skyrmions with opposite signs of topological charges can inherentlycharges can inherently coexist in the in-plane magnetization system coexist. Moreover, the iIn-plane skyrmions of opposite charge can move together by an electric current and exhibit with an opposite spin Hall effect. These findings showdemonstrate the inherent possibility of a double-bit transfer in a single magnetic wire that is not possible in a perpendicularly magnetized system.

Controls of transmitted electromagnetic waves for diverse functionalities using polarization-selective dual-band 2 bit coding metasurface

We present a polarization-selective transmission-type 2 bit coding metasurface (MS) to achieve dual-band performance, in which the operating frequency band is adjustable between the lower (Ku-band) and higher (K-band) bands by changing the polarization of the linearly polarized incident wave. Three coding MS devices are designed by using specific coding sequences of the proposed coding meta-atoms. Firstly, two coding MSs are presented for vortex beam generation that carries orbital angular momentum with different topological charges in the two operating bands. Secondly, a coding MS is proposed to anomalously refract the cross-polarized field with different deflection angles in the two frequency bands. Finally, the proposed scheme is extended to design a coding MS that focuses the transmitted fields at two frequencies by changing the polarization of the incident wave. Furthermore, the proposed designs are valid to perform the same functions for waves propagating along both the ‘+z’ and ‘−z’ directions in the same frequency bands but with orthogonal polarizations of incident waves. The sign of the topological charge can be altered by changing the direction of propagation from ‘+z’ to ‘−z’. To demonstrate the easiness of implementations, experiments of the fabricated samples are performed for the vortex beam generation and focusing. We believe that the proposed method may find potential applications in the future optical devices for multi-spectrum and multi-function operations.

Simultaneous identification of the azimuthal and radial mode indices of Laguerre-Gaussian beams using a spiral phase grating

Transfer of information using optical vortex beams as signal carriers can extremely extend the capacity and spectral efficiency in optical communication systems. One of the key problems is to accurately measure the mode indices including radial mode p and topological charge l at the receiver side of an optical vortices transmission system. In this paper, we present a new scheme to determine the mode indices of optical vortices by using spiral phase gratings. Based on the Fresnel diffraction integral theory, the far-field diffraction intensity distributions of vortex beams through the gratings are numerically calculated. Simulation results show that the annular-shaped intensity profiles of incident vortex beams evolve to bright spot array diffraction patterns, which render the information of the mode indices. Specifically, the magnitude of topological charge l and radial index p can be easily determined by counting the number of the corresponding bright stripes. And the orientation of the diffraction optical fields reveals the sign of the topological charge. Experiments are implemented to demonstrate the feasibility and validity of the proposed detecting method by uploading such phase gratings on a reflective phase-only liquid crystal spatial light modulator. The experimental observations are in good agreement with the theoretical predictions.

Static Electrification of Plastics under Friction: The Position of Engineering‐Grade Polyethylene Terephthalate in the Triboelectric Series

There is an emerging trend to replace moving metallic parts, such as bearings or bushes, with plastic components. The electrostatic hazard associated with plastic components subject to mechanical friction is well documented, but the magnitude as well as physical–chemical origin of this phenomenon remains debated. Using atomic force microscopy and Faraday pail measurements, the triboelectrification of Ertalyte®, a commonly used bearing‐grade formulation of polyethylene terephthalate, when rubbed against other polymers and metals, is studied. The sign and magnitude of the net charge that Ertalyte® gains in relation to the chemical nature—electron affinity and ionization energy—of the contacting material are analyzed, concluding that this material should be located toward the negative end of the triboelectric series. It is also shown that large charge densities and fast charge decays result from contact of Ertalyte® with polymers of a small Derjaguin–Muller–Toporov (DMT) modulus and unstable ions, suggesting that ion transfer leads to the electrification of a dynamic insulator/insulator contact. These findings have immediate implications in the choice of the material used to manufacture plastic parts subject to friction and wear and to help address ongoing fundamental questions over the nature of the charge carriers that leads to static electricity.

ANALYSIS OF ELECTROSTATIC PROPERTIES OF POLYSTYRENE FOAM FILTRATION MEDIA

The relevance of research. The analysis of the aqueous suspension filtration initial stage through clean polystyrene foam filtration media carried out. Such feature of its work as hydro-sorting is considered. The degree of imbalance and interaction with other electrostatic systems in aqueous suspension determines the layer of potential-forming ions, which is formed around the core of the system. It determines system’s sign and most of the electrical double layer charge. It is usually determined using a physical quantity such as electrostatic or ζ-potential. The aim of this work is to determine the electrostatic properties of polystyrene foam granules and the degree of influence on the process of retaining various nature colloidal particles on their surface when filtering an aqueous suspension through them.
 Research results. The relationship between the sizes of polystyrene foam granules and the concentrations of electrostatic charge on their surface analyzed. Using the Poison-Boltzmann theory, a relationship between an electrostatic charge and an electric double layer of polystyrene foam granules in aqueous suspension showed. The importance of the ζ-potential researching for controlling of colloidal suspensions filtering process substantiated. The electrostatic properties of different morphology colloids studied. Analysis of research data confirms the hypothesis of a very close connection between the various morphologies colloids ζ-potential magnitude and their electric double layer interaction force with electric double layer of polystyrene foam granules in an aqueous suspension. This means that the polystyrene foam filter “charging” time is closely connected to the values of colloids ζ-potential in the filtered aqueous suspension.
 Conclusions. The initial filtration stage through clean polystyrene foam media is significantly different from the main stage of filtration due to the electrostatic interaction forces predominance. The time difference of the colloidal crusts complete formation completion on polystyrene foam granules of different diameters is so insignificant that it can be neglected and this time is considered the same for polystyrene foam granules of different diameters. Regardless of the origin nature, the retention intensity of the colloids by polystyrene foam filtration media granules and, consequently, the polystyrene filter “charging” time is directly depends on their z-potential value.

AC EOF in a rectangular microannulus

Electrokinetic flow under an alternating current electric field is numerically studied in a rectangular microannulus whose inner and outer surfaces may have different zeta potentials. The main parameters that affect the shape of the flow field are electrokinetic diameter, dimensionless frequency, surface charge ratio, aspect ratio, and hydraulic diameter. An increase in the electrokinetic diameter leads to a decrease in the effective electric double layer thickness, while the reverse is true for the Poiseuille number, maximum velocity near the wall, and the flow rate. Very low-frequency flow exhibits lid-like velocity profiles; on the contrary, very high-frequency flow represents thin oscillating layers close to the walls and a nearly stationary bulk fluid. Within the limit of higher-than-one excitation frequencies, the response of the liquid inside the electric double layer to the time-periodic electric field is almost immediate, while the rest needs a finite time to follow the instantaneous changes in the applied electric field. Instantaneous one- or two-direction flow can be produced, depending on the relative sign of the surface charges. For a fixed value of the electrokinetic diameter, the Poiseuille number increases and the flow rate decreases as a result of an increase in the hydraulic diameter.

Nanoparticle charging with mixed reverse micelles in apolar media

The charging of colloidal particles using mixed surfactants in apolar media is investigated. Previous work has shown that one can predict the sign and magnitude of particle charge by comparing the acid-base properties of an oil-soluble surfactant to the acid-base properties of a specific particle. The present work sought to tune the acid-base properties by using mixed surfactants. Unexpected mineral oxide particle charging results were obtained however, from mixing the acidic surfactant sorbitan monooleate (SPAN 80), with the basic surfactant polyisobutylene succinimide (OLOA 11000), requiring further investigation into the mixed reverse co-micelle particle charging mechanism. Conductometric titrations and small-angle neutron and x-ray scattering measurements showed that the surfactant mixtures formed spherical reverse co-micelles. Quartz crystal microbalance adsorption measurements demonstrated that both surfactants can adsorb to the particle surface. Lastly, electrophoretic mobility measurements showed that the surfactant mixture produced negative particle charging for nearly all surfactant ratios, and a greater magnitude of negative charging than that produced by the OLOA 11000 surfactant alone. It was discovered that in the mixed surfactant system studied, the basic surfactant would charge the hydroxyl groups on both the oxide surface, and the adsorbed acidic surfactant head groups. The results showed that particle charging behavior in apolar media using mixed micelles requires knowledge beyond that for the individual surfactants and their proportions in the mixture.

Variable surface charge of humic acid-ferrihydrite composite: Influence of electrolytes on ciprofloxacin adsorption

Antimicrobial compounds are found in a range of environments as pollutants. Here, we evaluated the influence of two common anions, NO3− and PO43-, on ciprofloxacin adsorption on humic acid/ferrihydrite composite (HA-DIG/Fh), synthetic ferrihydrite (Fh), and humic acid (HA-DIG) under controlled pH (7.0), ionic strength (0.1 M) and temperature (25 °C). All materials were characterized by isoelectric point (IEP), while the composite and the iron oxide were characterized by Mössbauer spectroscopy. Kinetic and isotherm adsorption studies were carried out using cyclic voltammetry (in KH2PO4) and square wave voltammetry (in KNO3). The application of kinetic models for both anions revealed Fh to fit to a pseudo second order model (R2 = 0.941); while HA-DIG (R2 = 0.950) and HA-DIG/Fh (R2 = 0.993) were fitted to pseudo first order models. The adsorption results showed a high dependency electrolyte, especially in Fh, where different shape curves (H-type in KNO3 and C-type in KH2PO4) and maximum experimental adsorbed amount Cm were observed. This finding is supported by the distinct IEP values and change in sign of surface charge between the two ions. Finally, results suggest that HA-DIG could be potentially used in environmental remediation to remove antibiotics from natural matrices, though the risk of antibiotic transportation increased with depth in the soil profile.

Polarization-dependent orbital angular momentum flipping in fibers with acousto-optic interaction

In this paper we consider the evolution of linearly polarized optical vortices in circular optical fibers with a propagating fundamental flexural acoustic wave. A new polarization-dependent mode conversion is found out, in which the sign of the topological charge (and orbital angular momentum) of the outgoing vortex beam is governed by the direction of the incident linear polarization. This effect can be used for implementing polarization-controlled orbital angular momentum flipping. This paves the way to implementation of the all-fibre stable controlled-NOT gate, in which the linear polarization carries the control qubit and the topological charge carries the target. Such a gate is able to produce optical beams with entanglement between polarization and orbital degrees of freedom in regime of linear optics. Yet, such orbital angular momentum controlling should be useful in micromechanics, classical and quantum information encoding, and classical simulation of quantum algorithms.

Influence of the sign and magnitude of a surface charge on the breakdown voltage of a barrier corona discharge in Ar

The topic of this article is related to the breakdown phenomena in the surface dielectric barrier discharge (SDBD). The surface charge, locally deposited on the dielectric barrier, changes markedly the configuration and intensity of the electric field both on the barrier and in the gas gap. In turn, a change in the local electric field affects the rate of ionization multiplication of electrons in this area and, accordingly, influences the breakdown conditions of both volume and surface barrier discharges. In the case of sinusoidal SDBD, the first breakdown in each next half-cycle will be controlled by the charge deposited on the barrier during the previous half-cycle. Contrariwise, if there are several successive breakdowns in the half-cycle, each next breakdown after the first one will be controlled predominantly by the charge and plasma created by the previous breakdown in this half-cycle but not only by the charge deposited in the previous half-cycle. These features of the SDBD breakdown were investigated by the example of the barrier corona in argon at atmospheric pressure in the pinto-plane configuration. This discharge allows us the controlling of the location of the deposited charge. Surface charge was deposited in advance and by the SDBD itself.

Bipolar Beams with Charge and Current Compensation

One-dimensional flows of charged particles with opposite sign of charge moving in one direction are considered for an electronic diode (or diode with negative ions) shot through by positive ions, and an ionic diode shot through by relativistic electrons. Options with varying extent of spatial charge compensation at the output of the diode are investigated, along with full compensation for charge, current, and magnetic field.

Sectorial perturbation of vortex beams: Shannon entropy, orbital angular momentum and topological charge

Transformations of the vortex beams structure subjected to sectorial perturbation were theoretically and experimentally studied. The analysis was based on computing (measuring) the vortex spectrum that enables us to find the orbital angular momentum (OAM) and Shannon entropy (informational entropy). We have revealed that, in the general case, the number of vortices caused by an external perturbation is not related to the topological charge. For arbitrary perturbation, the topological charge remains equal to the initial topological charge of the unperturbed vortex beam. Growth of the vortex number induced by perturbations is associated with the optical uncertainty principle between the sectorial angle and the OAM. The computer simulation has shown that OAM does not depend on the number of vortices induced by perturbations. Moreover, two maxima are formed both in the positive and negative regions of the vortex spectrum. As a result, the OAM does not practically change in a wide range of perturbation angles from 0 to 90 °. However, at large perturbation angles, when the energy is almost equally redistributed between the vortex modes with opposite signs of the topological charge, the OAM rapidly decreases. At the same time, the Shannon entropy monotonically increases with growing perturbation angle. This is due to the fact that the entropy depends only on the number of vortex states caused by external perturbations.

A Limiting Case of Constant Counterion Electrochemical Potentials in the Membrane for Examining Ion Transfer at Ion-Exchange Membranes and Patches.

Ion passage through ion-exchange membranes is vital in electrodialysis desalination, batteries and fuel cells, and water splitting. Simplified models of ion transport through such membranes frequently assume complete exclusion of co-ions (ions with the same sign of charge as the fixed charge in the membrane) from the membrane. However, a second assumption of constant counterion electrochemical potentials across the membrane leads to simple analytical expressions for ion fluxes and transmembrane potentials. Moreover, linear corrections to account for a small membrane electrical resistance yield analytical expressions with a wider applicability. For bi-ionic potential measurements and current-induced concentration polarization at low salt concentrations, these analytical solutions match the fluxes and potentials obtained numerically without the limiting assumptions. This gives confidence in both the limiting assumptions (under appropriate conditions) and the numerical solutions. At low ion concentrations, the analytical solutions may enable rapid characterization of membrane coatings or boundary layers in solution, and such boundary layers are important in many applications of ion-exchange membranes. In fact, the assumption of complete co-ion exclusion is sometimes more limiting than the constraint of constant electrochemical potentials of counterions across the membrane. Remarkably, this limiting case readily yields the ion accumulation and depletion regions above "ion-exchange patches" that reside beneath a solution with an applied electric field. Such regions are important for sample preconcentration in microfluidic devices.

Inverted field interferometer for measuring the topological charges of optical vortices carried by short pulses

In this work, we present an improved technique for measuring both the magnitude and sign of the topological charge of input optical vortex beams carried by short laser pulses. Numerical simulations and experimental evidences for the interference signal obtainable at the output of an inverted field interferometer (IFI) valid for both continuous wave and femtosecond optical vortex beams and pulses with an eventual pulse front tilt are in an excellent agreement. An IFI also appears to be a valuable tool for calibrating a built-in variable delay line and for estimating an eventual pulse front tilt of the input ultrashort laser pulses without any realignments. As a trivial side effect, by blocking alternatively one of the two arms of the interferometer, one can use OV beams/pulses of opposite TCs, which are well located in the plane of a desired target, eventually — at precisely known time delays.

Tuning the topological features of quantum-dot hydrogen and helium by a magnetic field

The topological charge of the spin texture in a quantum dot with spin-orbit couplings is shown analytically here to be stable against the ellipticity of the dot. It is directly tunable by a single magnetic field and is related to the \textit{sign} of the Land\'e $g$ factor. In a quantum-dot helium, the overall winding number could have different property from that of the single-electron case (quantum-dot hydrogen), since tuning the number of electron affects the winding number by the Coulomb interaction and the $z$ component angular momentum $\langle L^{}_z \rangle$. The density profile and the spin texture influence each other when the Coulomb interaction is present. When $\langle L^{}_z \rangle$ is biased away from an integer by the spin-orbit couplings, the rotational symmetry is broken which induces strong density deformation. The sign of the topological charge may also be reversed with increasing magnetic field. These findings are of major significance since the applied magnetic field alone now provides a direct route to control the topological properties of quantum dots.

Adsorption of amino acids at clay surfaces and implication for biochemical reactions: Role and impact of surface charges

Almost all clay minerals carry an abundance of surface charges. The role and impacts of surface charges during adsorption of amino acids and biochemical reactions are of great importance while currently remain elusive, which are to be tackled in this study by first-principles density functional calculations. A wide range of surface charges (−0.42˜ + 0.42 C m−2) have been considered. Distribution of different amino acid isomers and their interaction with clay minerals rely strongly on the sign and amount of surface charges. Zwitterionic structures remain stable for all negative surface charges and become dominant when negative surface charges are abundant (σ ≤ −0.28 C m−2), whereas only very high positive surface charges (σ ≥ +0.35 C m−2) can stabilize zwitterionic glycine. Increase of surface charges pronouncedly enhances the interactions of amino acids with clay minerals, which favors their gathering at clay surfaces and condensation to protein fragments. The superior binding of amino acids by negatively rather than positively charged clay minerals is due to stronger H bonding and electrostatic interactions. The biochemical reactions are greatly accelerated at higher surface charges and zwitterion formation becomes almost barrierless; however, the reverse reactions of forming canonical isomers have so moderate activation barriers that can occur facilely and get ready for the condensation to protein fragments. Accordingly, clay minerals, even in the anhydrous state, should be the suitable birthplace for life, where surface charges play a central role.

CO2-responsive graphene oxide nanofiltration membranes for switchable rejection to cations and anions

Inspired by biological membranes with charge-gated channels that allow the transport of water and ions but restrict the undesired substances, various regulated nanofiltration (NF) membranes containing charge-gated channels have been developed for water purification. However, most of these membranes are mono-charged (positively or negatively) that show high rejection only to the corresponding co-ions but low rejection to the counter-ions, which limits their wider applications. Herein, we report NF membranes with gas-tunable charge-gated channels and high rejection to different salts on demand. The membranes are prepared by assembling a CO2-responsive polymer, poly(N,N-dimethylaminoethyl methacrylate), on the surface of graphene oxide (GO). As a result of CO2-induced reversal of the charge sign, the membranes exhibit “self-regulation” of their surface charges. Upon bubbling CO2 into water, the membranes are positively charged, which shows high rejection to MgCl2. After bubbling Ar to remove CO2, the membranes gradually transform to negatively charged, and high rejection to Na2SO4 is obtained. This study demonstrates the gas-tunable charge-gated ion transport behavior of the CO2-responsive NF membranes, and opens up new avenues for the design of on-demand NF membranes.

Average size and zeta potential of nanobubbles in different reagent solutions

In the present study, we analyzed the average size and zeta potential of nanobubbles (NBs) in chemical reagent solutions. Here, we proposed the possible mechanisms for the size growth and for negative and positive NB creation. NBs were produced by dispersing a supersaturated air-water mixture in a mixing chamber, and then causing the breakup of microbubbles in a Teflon hose. The size and zeta potential of the NBs were measured by dynamic light scattering. The NB size had no dependency on pH and grew over time. The proposed mechanism of the NBs’ size growth related to their coalescence in the solutions. The bubbles were charged negatively in the presence of glucose, ethylenediaminetetraacetic acid, and Na+, while they were charged positively in the addition of dimethyldioctadecylammonium bromide, Al3+, and Fe3+. The NB zeta potential decreased in all solutions, while their pH increased from 2 to 12. Zeta potential values remained stable for 150 min, proving the long-term permanence of bubbles in the bulk solutions. The charged NBs were created from the adsorbed species such as OH− and DODA+ and possible aqueous speciation (through the addition of metal ions) on its surface. Our results indicate that the type of chemical reagent solution can influence both the sign of the surface charge and the size of NBs, allowing them to be applicable in many treatment processes for water treatment.

Modified Mach-Zehnder interferometer for determining the high-order topological charge of Laguerre-Gaussian vortex beams.

This study demonstrates a self-referenced interferometric method to estimate the magnitude and sign of a high-order topological charge (TC) carried by incoming optical vortex beams. The proposed method uses a right-angle prism in a Mach-Zehnder interferometer setup with controlled lateral shift and tilt between the wavefronts of interfering beams. The in-line interference with its conjugate results in a petal-shaped fringe pattern, where the number of petals reveals the magnitude of the TC. When the direction of one of the interfering beams is laterally displaced and rotated to emerge at a small angle for off-axis interference such that the vortices overlap at the output plane, then a fork-like interference pattern with better visibility is obtained, which can be used for estimating the magnitude as well as the sign of the TC. Through numerical simulation and optical experiment, it is shown that the technique is capable of estimating the TC of Laguerre-Gaussian beams even with a nonzero radial index.