Presence Of Nonuniform Electric Field Research Articles

Formation of Ordered Patterns in Electroresponsive Polymer Ionic Liquid Blends

AbstractDirecting reaction‐diffusion (RD) phenomena, through the use of external stimuli has been one of the widely used approaches for designing multifunctional soft materials. Using modeling and simulation, it is demonstrated that the nonuniform electric field can be harnessed to create intricate ordered patterns in polymer ionic liquid (PIL) blends. The investigation begins with the establishment of the equilibrium phase diagrams of electroresponsive PIL blends and subsequently, use the Poisson–Nernst–Planck equations to model the kinetics of pattern formation. The simulations reveal that in the presence of nonuniform electric field the ionic liquid (IL) rich domains self‐aggregate in high electric field regions. Thus, the ordering of the electric field regions effectively dictates the ordering of the IL‐rich phase in the PIL blends. It is also demonstrated that the mechanism of spatiotemporal pattern formation is quite robust and can be dynamically controlled by varying the distribution of electric field. It is believed that the methodology provides a simplistic mechanism for creating ordered patterns in soft materials through RD phenomena that can be exploited for designing other similar stimuli‐responsive systems.

The secondary drop formation of nanoparticle/surfactant-stabilized water droplets under non-uniform electric fields

Electrocoalescence is an energy-efficient and environmentally-friendly process for breaking water-in-oil emulsions. It has been used extensively in the oil and petroleum industries. In this study, the electrocoalescence process of nanoparticle/surfactant-stabilized water droplets with a planar interface in the presence of non-uniform electric fields was experimentally investigated. The effects of electric field patterns (i.e. uniform and non-uniform fields) and nanoparticles (i.e. concentrations) on the drop-interface electrocoalescence process were systematically examined, analyzed, and discussed. The results showed that the presence of Sodium Dodecyl Sulfate (SDS) significantly increased the volume of secondary droplets and led to the apex disintegration of the main secondary droplet because of the low surface tension. At high SiO2 concentrations, the liquid bridge between the droplet and interface was difficult to form, and the whipping filament regime, sheet breakup regime, and varicose jet breakup regime, were observed, which were determined by the accumulating surface charge. In addition, three types of non-uniform fields induced by different geometrical electrode configurations, i.e. grid electrodes, mesh electrodes, and coupled electrodes, were proposed and the electric field distributions were calculated in COMSOL Multiphysics. With increasing SiO2 concentrations, coupled electrodes produced much smaller detached droplet volumes than those of pairwise mesh and grid electrodes, which was helpful to complete the coalescence of the drop and interface. Furthermore, flat electrodes, which induced a uniform electric field, produced much larger secondary droplet volumes than those of the electrodes generating non-uniform electric fields. In summary, the utilization of coupled electrodes had a positive effect on drop-interface coalescence and increased the overall separation efficiency. The outcome of this work is potentially useful in the design of compact and efficient oil-water electro-dehydration devices.

Numerical Analysis of Electron Runaway in the Presence of Enhanced Field in the Vicinity of a Microtip

Transition of field-emission electrons to the runaway regime in the region of enhanced electric field determined by the configuration of a microtip on a cathode is studied at several pressures of gas medium. The problem is solved using simulation of electron motion in the presence of nonuniform electric field with the aid of the Monte Carlo procedure in the 2D configuration. Nitrogen is used as a working gas. Passage through a relatively small region of the enhanced field in the vicinity of the microtip may substantially facilitate electron escape to the runaway regime, especially, at pressures of greater than 10 atm. In our opinion, the resulting runaway electrons may provide preionization of gas medium and formation of the initial stage of a 3D discharge.

Response of High-Pressure Micro Water Jets to Static and Dynamic Nonuniform Electric Fields

The manipulation of the trajectory of high-pressure micro water jets has the potential to greatly improve the accuracy of water jet related manufacturing processes. An experimental study was conducted to understand the basic static and dynamic responses of high-pressure micro water jet systems in the presence of nonuniform electric fields. A single electrode was employed to create a nonuniform electric field to deflect a high-pressure micro water jet toward the electrode by the dielectrophoretic force generated. The water jet's motions were precisely recorded by a high-speed camera with a 20× magnification and the videos postprocessed by a LabVIEW image processing program to acquire the deflections. The experiments revealed the fundamental relationships between three experimental parameters, i.e., voltage, pressure, and the distance between the water jet and the electrode and the deflection of the water jet in both nonuniform static and dynamic electric fields. In the latter case, electric signals at different frequencies were employed to experimentally investigate the jet's dynamic response, such as response time, frequency, and the stability of the water jet's motion. A first-order system model was proposed to approximate the jet's response to dynamic input signals. The work can serve as the basis for the development of closed-loop control systems for manipulating the trajectory of high-pressure micro water jets.

Possibility for separation of polarizable molecules using electric fields

The motion of polarizable molecules in the presence of nonuniform electric fields is analyzed. The separation of molecular flows in the presence of such fields is theoretically demonstrated. Angular dispersions are estimated for endofullerene (Sc@C82, Y@C82, La@C82, and Gd@C82) and fullerene (C60, C70, C82, and C84) molecules in the presence of the field that is generated by a system of parallel charged wires using the known dipole moments and polarizabilities. The numerical simulation shows that a separator of polarizable molecules can be constructed using such fields.

Comparative study of corona discharge simulation techniques for electrode configurations inducing non-uniform electric fields

Abstract Numerical modeling of corona discharges has followed the same set of procedures for many years. Corona discharges on large scales are modeled only for ion drift, neglecting ionization. Studies of the ionization zone are often conducted in uniform axisymmetric configurations. However, in configurations that induce non-uniform electric fields, a combination of the two procedures is necessary to accurately capture the discharge physics and ion distribution. The present study conducts numerical simulations of a wire-cylinder corona using both the models and demonstrates the necessity of including the ionization physics to obtain improved accuracy, particularly in the presence of non-uniform electric fields.

Vapor-liquid coexistence of the Stockmayer fluid in nonuniform external fields

We investigate the structure and phase behavior of the Stockmayer fluid in the presence of nonuniform electric fields using molecular simulation. We find that an initially homogeneous vapor phase undergoes a local phase separation in a nonuniform field due to the combined effect of the field gradient and the fluid vapor-liquid equilibrium. This results in a high-density fluid condensing in the strong field region. The system polarization exhibits a strong field dependence due to the fluid condensation.

Motion, deformation and aggregation of two cells in a microchannel by dielectrophoresis

The dynamic behavior of two cells in a microchannel subject to a nonuniform electric field is simulated numerically by a two-fluid model in the present work. Owing to the presence of nonuniform electric field, usually the cells are polarized and then the dielectrophoresis occurs. The dielectrophoretic force induces the movement and deformation of cells in the microchannel. Meanwhile, the cell membrane develops a mechanical force to resist the cell deformation. In addition, the intercellular interaction becomes dominant when the cell-cell distance is short enough such that an intercellular force is generated. The three forces are taken into account in the two-fluid model to characterize the dynamic behavior of cells. In order to validate the present model, the cell deformation is calculated and compared with the experimental results published previously, where a quantitative agreement is achieved. It is demonstrated by simulations that the cell conductivity mainly determines the motion and deformation of cells at low frequency. Instead of the cell conductivity however, the cell permittivity plays a critical and leading role at high frequency. These phenomena are consistent with the experimental observations. Furthermore, the intercellular interaction may cause the change in the dynamic behavior of cells.

Separation of mixtures of particles in a multipart microdevice employing insulator‐based dielectrophoresis

Dielectrophoresis is the electrokinetic movement of particles due to polarization effects in the presence of non-uniform electric fields. In insulator-based dielectrophoresis (iDEP) regions of low and high electric field intensity, i.e. non-uniformity of electric field, are produced when the cross-sectional area of a microchannel is decreased by the presence of electrical insulating structures between two electrodes. This technique is increasingly being studied for the manipulation of a wide variety of particles, and novel designs are continuously developed. Despite significant advances in the area, complex mixture separation and sample fractionation continue to be the most important challenges. In this work, a microchannel design is presented for carrying out direct current (DC)-iDEP for the separation of a mixture of particles. The device comprises a main channel, two side channels and two sections of cylindrical posts with different diameters, which will generate different non-uniformities in the electric field on the main channel, designed for the discrimination and separation of particles of two different sizes. By applying an electric potential of 1000 V, a mixture of 1 and 4 μm polystyrene microspheres were dielectrophoretically separated and concentrated at the same time and then redirected to different outlets. The results obtained here demonstrate that, by carefully designing the device geometry and selecting operating conditions, effective sorting of particle mixtures can be achieved in this type of multi-section DC-iDEP devices.

Dielectrophoretic monitoring of microorganisms in environmental applications

Dielectrophoresis (DEP) is the motion of polarizable particles in the presence of nonuniform electric fields. This novel electrokinetic technique has successfully been employed in many miniaturized systems for the manipulation and detection of microbes. This review article depicts the application of dielectrophoresis for the monitoring of microorganisms in microfluidic devices for environmental applications. The research studies described here are mainly conceived for water- and air-monitoring assessments, and are classified considering the target aimed to detect, concentrate, and/or separate, including chemical and toxicant agents, and microorganisms ranging from virus to protozoa. Dielectrophoresis has also played an important role in biofilm formation studies. This review article comprises mainly studies published from 2000 to present. Even in this relatively short time frame, there have been many significant contributions of this powerful and nascent technique related to environmental monitoring; thus, unveiling its great potential for future research directions.

Topological design of electrode shapes for dielectrophoresis based devices

This research develops a topology optimization procedure to find out the optimal shapes of electrodes for cell sorter devices based on dielectrophoresis phenomenon which moves dielectrically polarizable particles in the presence of nonuniform electric field. After understanding the working principle of dielectrophoresis based devices mathematically, the spatial distributions of the square electric field is defined as the objective function and it is possible to define an optimization formulation in the framework of the standard topology optimization procedure. To show the potential of the developed procedure, optimized electrodes as well as some illustrative numerical examples are presented.

Oscillating fields about growing cells

Cells in the reproductive state seem to act like small signal generators and emit radiation which is detectable by small polarizable particles nearby in a medium of suitable osmolarity, but very low conductivity. Evidence for this was seen upon using mouse sarcoma (ascites) cells, and by comparing rapidly dividing mouse L fibroblasts with confluent ones. Reproducing cells attracted many more highly polarizable BaTiO3 particles than they did of the much less polarizable BaSO4 (dielectric constants 4000 and 11, respectively). This preferential attraction of certain cells for highly polarizable small particles is interpreted as due, in large measure, to the action of dielectrophoresis on a very small scale—evoked by the presence of nonuniform electric fields of cellular origin acting upon the nearby neutral, polarizable particles—a process called microdielectrophoresis. Consideration of the conductive nature of the surrounding medium forces the conclusion that the cell-generated fields must be oscillatory in nature and have a frequency in the order of a megahertz. These observations recall predictions made earlier by Szent-Gyorgyi on cellular electronic processes, and by Frohlich on the possibility of Bose-Einstein condensations to a single quantum state of oscillatory ferroelectric character, due to cooperative long-range interactions among dipolar features of cells. The persistence of oscillatory energy in the lower modes is reminiscent of the Fermi-Pasta-Ulam problem.

A dielectrophoresis-based microchannel system

In this paper, we will propose a dielectrophoresis-based microchannel system. Based on numerical calculations and theoretical analysis, we investigate the dynamic behaviors of a microparticle in this system, in the presence of nonuniform electric fields generated by point microelectrodes. Good agreement is shown between them. It is found that the microelectrodes enable the system equilibrium to shift between monostable and bistable states. Further, we reveal that the microparticle can oscillate along the microchannel with a fixed period for the ideal case without a drag force, and that it can be located in either monostable or bistable states for the cases with drag forces. In view of these findings, we carefully address the possibility to design several microfluidic devices, namely, a microparticulate clock for timing, a binary random number generator for conducting stochastic calculations, and a flip-flop device for system memory.

Forces at the nuclei of a molecule in the presence of non-uniform electric field

The interaction Hamiltonian within the Bloch gauge for the potentials of the electric field has been used to define electric multipole moment operators. Perturbation theory has been applied to evaluate the induced electronic moments and electric field at the nuclei in the presence of spatially non-uniform electric fields of high intensity. Multipole nuclear electric shielding tensors have been defined to describe the contributions arising from a non-homogeneous electric field. These quantities are useful to rationalize linear and non-linear responses of a molecule in the presence of intense external electric perturbations.

Convective specific-heat transfer in liquids in the presence of non-uniform electric field

The electroconvective specific-heat transfer coefficient has been measured in various liquids (methanol, kerosene, silicon oil and ethanol) from a single platinum wire (diameter=0.025 mm) mounted along the axis of a copper cylinder (diameter=53 mm). The heat transfer coefficient has been evaluated under the influence of a.c. and d.c. fields. An a.c. field always causes an enhancement in the heat transfer coefficient. A d.c. field causes an inhibition in heat transfer in methanol. A similar trend is noticed in kerosene, but the heat transfer coefficient increases again as the field is increased. An enhancement in the heat transfer coefficient is observed in silicon oil, and a similar trend is noticed in ethanol, but the heat transfer coefficient decreases again as the field is increased. The effect of cylinder orientation on convection is studied. The efficiency of convection has been calculated for various liquids using an empirical relation. The efficiency obtained in a d.c. field is found to be higher than in the a.c. field. A similar trend is also noticed for the electric Nusselt number.

Do cells in a reproductive state exhibit a fermi-pasta-ulam-fröhlich resonance and emit electromagnetic radiation?

Cells in the reproductive state seem to act like small signal generators and emit radiation which is detectable by small polarizable particles nearby in a medium of suitable osmolarity, but very low conductivity. Evidence for this was seen upon using mouse sarcoma (ascites) cells, and by comparing rapidly dividing mouse "L" fibroblasts with confluent ones. Reproducing cells attracted many more highly polarizable BaTiO3 particles than they did of the much less polarizable BaSO4 (dielectric constants 4000 and 11, respectively). This preferential attraction of certain cells for highly polarizable small particles is interpreted as due in large measure to the action of dielectrophoresis on a very small scale.…evoked by the presence of nonuniform electric fields of cellular origin acting upon the nearby neutral, polarizable particles.…a process called microdielectrophoresis. Consideration of the conductive nature of the surrounding medium forces the conclusion that the cell-generated fields must be oscillatory in nature and have a frequency in the order of a megaherz. These observations recall predictions made earlier by Szent-Gyorgyi on cellular electronic processes, and by Frohlich on the possibility of Bose-Einstein condensations to a single quantum state of oscillatory ferroelectric character, due to cooperative long-range interactions among dipolar features of cells. The persistence of oscillatory energy in the lower modes is reminiscent of the Fermi-Pasta-Ulam problem.

Particle Aspect Analysis of E×B Drift Instability in the Presence of Non-Uniform Electric Field

A physical mechanism and the dynamical details of the drift wave instability have been studied by investigating the trajectories of the charge particles in the presence of ambient magnetic field and non-uniform electric field. The effect of finite gyro-radius corrections have also been accounted. The general dispersion relation for the electrostatic drift wave has been obtained. The expression for the growth rate have been derived from an energy balance approach. Our expression reduces to well known results under limiting conditions. The finite gyroradius correction due to inhomogeneous electric field is found to have a destabilising effect. The important geophysical situations for the existence of inhomogeneous electric field have been outlined and potential application of this result have been indicated.

Flute modes in a plasma in the presence of nonuniform electric fields

The effects of the presence of a nonuniform electric field on the stability of flute modes in a plasma is studied in the approximation of small Larmor radius. Most of the work is concerned with discussing and applying to the corresponding eigenvalue problem a step approximation for the profiles of the electric and diamagnetic drifts. Furthermore, a new sufficient stability criterion for flute modes is formulated. The influence of the drifts on the stability properties of the flute modes is discussed, and, in particular, the stabilizing effect of a density gradient is displayed.

Effects of nonuniform radial electric fields on plasma low-frequency stability

The stability of a low-β magnetized plasma column, in the presence of radial nonuniform electric fields, has been numerically investigated in a weakly collisional regime. The analysis has been done for electrostatic low-frequency perturbations of the drift type. Numerical results for the frequency and the growth of the waves are presented as a function of the electric-field amplitude and the dimensionless parameter $$\varepsilon ^* = \omega ^* v_{ei} /k_\parallel ^2 v_e^2 (\omega ^* $$ being the drift frequency,v ei the electron-ion collision frequency,v e the electron thermal speed andk ll the wave number component parallel to magnetic lines). It is shown that in the presence of a nonuniform electric field more than one mode can be unstable.

Flute instability in the presence of non-uniform electric fields

A general equation describing the flute instability in a low-β plasma, in the presence of a non-uniform electric field perpendicular to the magnetic field, is derived from guiding centre equations. The equations obtained by Rosenbluth and Simon and by Damm et al. correspond to two different limiting cases of this more general equation. The physical significance of various stabilizing terms is discussed. In the high density, zero gyro-radius limit, the shear flow resulting from the non-uniform electric field has a de-stabilizing effect. At low densities the imbalance between the equilibrium ion and electron densities has a significant stabilizing effect.