Current Electric Field Research Articles

Dynamics of alternating current electric field-assisted non-Newtonian droplet formation with geometry confinement.

Recently, microfluidic techniques have been widely applied for biomaterial droplet manipulations due to their precision and efficiency. Many biosamples such as deoxyribonucleic acid and blood samples are non-Newtonian fluids with complex rheology, which brings challenges in control over them. The electric field is characterized by fast response and excellent adaptation to control microscale fluid flow. Here, we systematically investigate the alternating current electric field-assisted formation of non-Newtonian droplet in a flow-focusing microchannel with different sizes of channel orifice. The dependencies of flow conditions, microchannel geometries and electric parameters on the dynamics of non-Newtonian droplet formation are thus elucidated. An effective capacitance electric model is developed to reveal and predict the interaction between the fluid flow and the electric field. Furthermore, the flow field of non-Newtonian droplet formation is captured via the high-speed microparticle image velocimetry system. The characteristics of the regimes of droplet formation and the influences of the channel orifice are revealed quantitatively. Our work offers elaborate references to the control of non-Newtonian droplet formation, which benefits a wide range of applications in biology and chemistry.

Assembly of alumina particles in aqueous suspensions induced by high‐frequency AC electric field

AbstractThe role of high‐frequency alternating current (AC) electric field in the assembly of alumina particles in aqueous media was investigated. Field–particle interactions were in situ investigated for coarse and fine powder particles in very dilute suspensions. For both coarse and fine particles, AC field‐induced assembly led to the formation of chains of particles within a minute, which were aligned in the field direction. However, a much finer network of particle chains evolved in fine particle suspensions. Threshold field strength for chain formation was also lower for fine particles (28 V/mm) than for coarse particles (50 V/mm), suggesting stronger interactions for finer particles. Chain length increased with both field strength and field duration. Chain formation was attributed to mutual dielectrophoretic (DEP) interaction forces. Increase in DEP forces with field strength resulted in enhanced interactions. For finer particles, decreasing interparticle distance might have favored stronger interactions. Suspension microstructure was disrupted as soon as the field was removed. However, higher field duration was associated with an improved pattern stability and retention following the field removal. Finally, particle motion was studied in deliberately applied spatially nonuniform AC field, which revealed different mechanisms of chain formation for coarse (negative‐DEP) and fine (positive‐DEP) particles.

Reaction-Free Concentration Gradient Generation in Spatially Nonuniform AC Electric Fields.

The ability to generate stable, spatiotemporally controllable concentration gradients is critical for both electrokinetic and biological applications such as directional wetting and chemotaxis. Electrochemical techniques for generating solution and surface gradients display benefits such as simplicity, controllability, and compatibility with automation. Here, we present an exploratory study for generating microscale spatiotemporally controllable gradients using a reaction-free electrokinetic technique in a microfluidic environment. Methanol solutions with ionic fluorescein isothiocyanate (FITC) molecules were used as an illustrative electrolyte. Spatially nonuniform alternating current (AC) electric fields were applied using hafnium dioxide (HfO2)-coated Ti/Au electrode pairs. Results from spatial and temporal analyses along with control experiments suggest that the FITC ion concentration gradient in bulk fluid (over 50 μm from the electrode) was established due to spatial variation of electric field density, and was independent of electrochemical reactions at the electrode surface. The established ion concentration gradients depended on both amplitudes and frequencies of the oscillating AC electric field. Overall, this work reports a novel approach for generating stable and spatiotemporally tunable gradients in a microfluidic chamber using a reaction-free electrochemical methodology.

Tuning the resonance frequency of piezoelectric energy harvesters by applying direct current electric field on piezoelectric elements

Different from previous strategies utilized to improve the energy conservation efficiency of piezoelectric energy harvesters (PEHs) from the environment, by broadening the frequency-bandwidth of energy harvesters using a specifically designed structure or tuning their resonance frequency (RF) through changing the geometrical/dynamical constraints, we report a method—by applying a direct current (DC) electric field on piezoelectric elements—to tune the RF of PEH based on the phenomenon that the elastic parameters of piezoelectric material are related to its electric field boundary condition. The results of a confirmatory experiment revealed that with a pre-loading DC electric field of −0.5 to 0.75 kV/mm, the RF of a piezoelectric cantilever energy harvester can be tuned from 144 to 156 Hz. The effectiveness of this strategy was further verified by comparing the energy conservation output of the PEH at a frequency that deviates from its RF, and at the same frequency, with pre-loading DC electric field adjustment.

Galvanotactic Migration of Glioblastoma and Brain Metastases Cells.

Galvanotaxis, the migration along direct current electrical fields, may contribute to the invasion of brain cancer cells in the tumor-surrounding tissue. We hypothesized that pharmacological perturbation of the epidermal growth factor (EGF) receptor and downstream phosphatidylinositol 3-kinase (PI3K)/AKT pathway prevent galvanotactic migration. In our study, patient-derived glioblastoma and brain metastases cells were exposed to direct current electrical field conditions. Velocity and direction of migration were estimated. To determine the effects of EGF receptor antagonist afatinib and AKT inhibitor capivasertib, assays of cell proliferation, apoptosis and immunoblot analyses were performed. Both inhibitors attenuated cell proliferation in a dose-dependent manner and induced apoptosis. We found that most of the glioblastoma cells migrated preferentially in an anodal direction, while brain metastases cells were unaffected by direct current stimulations. Afatinib presented only a mild attenuation of galvanotaxis. In contrast, capivasertib abolished the migration of glioblastoma cells without genetic alterations in the PI3K/AKT pathway, but not in cells harboring PTEN mutation. In these cells, an increase in the activation of ERK1/2 may in part substitute the inhibition of the AKT pathway. Overall, our data demonstrate that glioblastoma cells migrate in the electrical field and the PI3K/AKT pathway was found to be highly involved in galvanotaxis.

Conductive Supramolecular Polymer Nanocomposites with Tunable Properties to Manipulate Cell Growth and Functions.

Synthetic bioactive nanocomposites show great promise in biomedicine for use in tissue growth, wound healing and the potential for bioengineered skin substitutes. Hydrogen-bonded supramolecular polymers (3A-PCL) can be combined with graphite crystals to form graphite/3A-PCL composites with tunable physical properties. When used as a bioactive substrate for cell culture, graphite/3A-PCL composites have an extremely low cytotoxic activity on normal cells and a high structural stability in a medium with red blood cells. A series of in vitro studies demonstrated that the resulting composite substrates can efficiently interact with cell surfaces to promote the adhesion, migration, and proliferation of adherent cells, as well as rapid wound healing ability at the damaged cellular surface. Importantly, placing these substrates under an indirect current electric field at only 0.1 V leads to a marked acceleration in cell growth, a significant increase in total cell numbers, and a remarkable alteration in cell morphology. These results reveal a newly created system with great potential to provide an efficient route for the development of multifunctional bioactive substrates with unique electro-responsiveness to manipulate cell growth and functions.

Conductivity effects during the transition from collisionless to collisional regimes in cylindrical inductively coupled plasmas

A numerical model is developed to study the conductivity effects during the transition from collisionless to collisional regimes in cylindrical inductively coupled argon plasmas at pressures of 0.1–20 Pa. The model consists of electron kinetics module, electromagnetics module, and global model module. It allows for self-consistent description of non-local electron kinetics and collisionless electron heating in terms of the conductivity of homogeneous hot plasma. Simulation results for non-local conductivity case are compared with predictions for the assumption of local conductivity case. Electron densities and effective electron temperatures under non-local and local conductivities show obvious differences at relatively low pressures. As increasing pressure, the results under the two cases of conductivities tend to converge, which indicates the transition from collisionless to collisional regimes. At relatively low pressures the local negative power absorption is predicted by non-local conductivity case but not captured by local conductivity case. The two-dimensional (2D) profiles of electron current density and electric field are coincident for local conductivity case in the pressure range of interest, but it roughly holds true for non-local conductivity case at very high pressure. In addition, an effective conductivity with consideration of non-collisional stochastic heating effect is introduced. The effective conductivity almost reproduces the electron density and effective electron temperature for the non-local conductivity case, but does not capture the non-local relation between electron current and electric field as well as the local negative power absorption that is observed for non-local conductivity case at low pressures.

Alternating electric field-based ionic control and layer-by-layer assembly of anion exchange membranes for enhancing target anion selectivity

Separation and recovery of target anions from wastewater is a sustainable method for chemical production industry. In this study, the novel anion exchange membranes with high antifouling and target ion selectivity performance were designed by the layer-by-layer (LbL) assembly of dopamine, positive and negative polyelectrolytes under the alternating current electric field and ionic control (AC[ion]) process. The resulting membranes were fabricated with different LbL assembled multilayers to evaluate the target ion selectivity. Besides, the different LbL assembled methods, including the electrostatic deposition self-assembly (EDS), AC[Cl−] assembly and AC[NO3−] assembly methods were carried out to evaluate the ion effect in membrane assembly process on final target ion permeation rate, respectively. With the initial concentration of 50 mM of NaCl, NaNO3 and Na2SO4 in mixed solution and the constant current density of 5.00 mA cm−2 of electrodialysis, the permselectivity of resulting membrane could be enhanced by the increased multilayers. Besides, the ion control in the alternating current electric field assembly process could enhance the relevant target ion permeation rate. The increased values of membrane surface electrical resistance fouled by organic pollutants were used to evaluate the antifouling property of membranes in electrodialysis, and the resulting membranes showed a high antifouling performance. This work provided a promising membrane separation technology in target anion recovery from wastewater for sustainable development.

Non-volatile multi-state magnetic domain transformation in a Hall balance

High performance of the generation, stabilization and manipulation of magnetic skyrmions prompts the application of topological multilayers in spintronic devices. Skyrmions in synthetic antiferromagnets (SAF) have been considered as a promising alternative to overcome the limitations of ferromagnetic skyrmions, such as the skyrmion Hall effect and stray magnetic field. Here, by using the Lorentz transmission electron microscopy, the interconversion between the single domain, labyrinth domain and skyrmion state can be observed by the combined manipulation of electric current and magnetic field in a Hall balance (a SAF with the core structure of [Co/Pt]4/NiO/[Co/Pt]4 showing perpendicular magnetic anisotropy). Furthermore, high-density room temperature skyrmions can be stabilized at zero field while the external stimulus is removed and the skyrmion density is tunable. The generation and manipulation method of skyrmions in Hall balance in this study opens up a promising way to engineer SAF-skyrmion-based memory devices.

An Electro-Optic Sensor for Measurement of Intensive DC Electric Field

A lithium niobate (LN) integrated electro-optic (EO) sensor incorporated with a rotating shielding electrode has been designed, fabricated and experimentally demonstrated for measurement of intensive direct current (DC) electric field. As only the shielding electrode is rotated, there is no optical fiber rotation connection problem. Experimental results reveal that the sensor can be used to detect the DC electric field from 4 kV/m to 220 kV/m in the time domain, and the linear correlation coefficient of the input/output is 0.9997. The sensor has potential capability to be used for measurement of the intensive DC electric field.

Direct Current Electric Field Coordinates the Migration of BV2 Microglia via ERK/GSK3β/Cofilin Signaling Pathway.

Direct current electric field (DCEF) steers the migration of various neural cells. Microglia, as macrophage of the central nervous system (CNS), however, have not been reported to engage in electrotaxis. Here, we applied electric fields to an in vitro environment and found directional migration of BV2 microglia toward the cathode, in a DCEF strength-dependent manner. Transcriptome analysis then revealed significant changes in the mitogen-activated protein kinase cascades. In terms of mechanism, DCEF coordinated microglia movement by regulating the ERK/GSK3β/cofilin signaling pathway, and PMA (protein kinase C activator) reversed cell migration through intervention of the ERK/GSK3β/cofilin axis. Meanwhile, LiCl (GSK3β inhibitor) showed similar functions to PMA in the electrotaxis of microglia. Furthermore, pharmacological and genetic suppression of GSK3β or cofilin also modulated microglia directional migration under DCEF. Collectively, we discovered the electrotaxis of BV2 microglia and the essential role of the ERK/GSK3β/cofilin axis in regulating cell migration via modulation of F-actin redistribution. This research highlights new insight toward mediating BV2 directional migration and provides potential direction for novel therapeutic strategies of CNS diseases.

Physical methods of treatment in ophthalmology

The review discusses the treatment methods based on physical phenomena in clinical ophthalmology. The physical nature and treatment techniques using electric current and electromagnetic field, light and laser radiation, mechanical energy and sound waves, high and low temperature in various ocular pathologies are considered. It is noted that reliable evaluation of the effectiveness of physical treatment methods for the different diseases and pathological conditions requires the implementation of protocols that include objective testing methods of the structure and functioning of the visual system. Once the clinical effectiveness of the particular physical treatment methods and techniques is confirmed, further development and improvement of the most efficient ones becomes possible.

Study on the influencing factors of space charge dynamic behavior in XLPE insulation under alternating current electric field

The dynamic behavior of space charges is one of the potential factors that cause electrical aging. In this paper, a bipolar space charge transport model was established under an AC electric field in cross-linked polyethylene. The effects of physical parameters on the dynamic behavior of space charges in an AC electric field were explored by changing the injection barrier heights, mobilities, trapping coefficients, and detrapping barrier heights of positive and negative charges. The effects of voltage conditions on space charge behavior were explored by changing the amplitude and frequency. The effects of temperature were studied by setting a temperature gradient similar to that of real cable operation. The asymmetry of the physical parameters could seriously aggravate the accumulation of space charges in the AC field. A set of physical parameters based on these results was identified. Both the increase in voltage amplitude and decrease in frequency enhanced the amount of and penetration into the insulation of the accumulated space charge. The dynamic behaviors of the space charges were more active with increased voltage amplitude and frequency. The temperature gradient in the cable insulation implies that the degree of accumulation, penetration into material, and activity of dynamic behaviors of the space charges at the warmest electrode are greater than those at the coldest. Compared with the DC field, the dynamic behavior of space charges in the AC electric field is more active and releases more energy. This research provides a theoretical basis for inhibiting the accumulation of space charges in an AC electric field.

Investigation on the influence of AC electric filed and KCl on the structure and gel properties of Konjac glucomannan

The influence of alternating current (AC) electric field and KCl on the structure and gel properties of Konjac Glucomannan (KGM) were studied in this work by high-performance gel permeation chromatography (HPGPC), acid-base titration, solid-state nuclear magnetic resonance (NMR), X-ray diffraction (XRD), simultaneous differential scanning calorimetry/thermo gravimetric analyzer (DSC/TGA) and a rheometer. HPGPC showed KGM was degraded by AC electric field and Acid-base titration showed that under the action of AC electric field and KCl KGM removed part of acetyl groups, which were consistent with the analysis of NMR. XRD and temperature sweep measurements respectively showed that the electrotreatment time and KCl concentration had important effects on the gel formation and its three-dimensional network. Simultaneous DSC/TGA and temperature sweep measurements both demonstrated the gel had good thermal stability.

Simulation of the electrical stimulation of the rat brain using sleep frequencies: A finite element modeling approach

A realistic rat brain model was used to simulate current density and electric field distributions under frequencies characteristic of sleeping states (0.8, 5, and 12 Hz). Two anode-electrode setups were simulated: plate vs. screws-anode, both with a cephalic cathode. Our simulations showed that these frequencies have limited impact on electric field and current density; however, the highest frequency evidenced higher values for both variables. The type of electrode setup had a greater effect on current distribution and induced fields. In that sense, the screws setup resulted in higher values of the modeled variables. The numeric results obtained are within the range of available data for rodent models using the finite elements method. These modeled effects should be analyzed regarding anatomical consequences (depth of penetration of the currents) and purpose of the experiment (i.e., entrainment of brain oscillations) in the context of sleep research.

A novel and controllable SERS system for crystal violet and Rhodamine B detection based on copper nanonoodle substrates

Copper nanostructures have attracted more and more attention due to low preparation cost, similar thermal conductivity and optical characteristics to silver nanostructures. A novel macroscopic dendritic copper nanonoodles with the length of 3–50 mm prepared by solid-state ionics method at 10 μA direct current electric field (DCEF) using fast ionic conductor RbCu4Cl3I2 films was reported. The surface-enhanced Raman scattering (SERS) performance of prepared copper nanonoodles was detected by crystal violet (CV) and rhodamine B (RB) aqueous solution as analyte molecules. The results present that the copper nanonoodles assembled by short-range order copper nanowires and the diameters of nanowires changed from 20 nm to 80 nm, many regularly arranged nanoparticles with the diameter from 5 to 10 nm existed on the prepared copper nanonoodles, which lead to the nanonoodles have high surface roughness. The copper nanonoodles contain only Cu element, no O element and the fractal dimension of copper nanonoodles is 1.355 because of macroscopic dendritic structures. The prepared copper nanonoodles composed of pure Cu have high surface roughness and the free electrons on the rough copper nanonoodles resonate with the atomic nuclei inside the copper nanonoodles to form a locally enhanced electromagnetic field under the excitation of incident light, so the limiting concentrations for CV and RB detected by the prepared copper nanonoodles are as low as 1 × 10−11 mol/L and 1 × 10−12 mol/L, respectively. The centimeter-scale copper nanonoodles with low limiting concentration of analyte molecules can be used to detect harmful food additives.

Electric-field induced modulation of amorphous protein aggregates: polarization, deformation, and reorientation

Proteins in their native state are only marginally stable and tend to aggregate. However, protein misfolding and condensation are often associated with undesired processes, such as pathogenesis, or unwanted properties, such as reduced biological activity, immunogenicity, or uncontrolled materials properties. Therefore, controlling protein aggregation is very important, but still a major challenge in various fields, including medicine, pharmacology, food processing, and materials science. Here, flexible, amorphous, micron-sized protein aggregates composed of lysozyme molecules reduced by dithiothreitol are used as a model system. The preformed amorphous protein aggregates are exposed to a weak alternating current electric field. Their field response is followed in situ by time-resolved polarized optical microscopy, revealing field-induced deformation, reorientation and enhanced polarization as well as the disintegration of large clusters of aggregates. Small-angle dynamic light scattering was applied to probe the collective microscopic dynamics of amorphous aggregate suspensions. Field-enhanced local oscillations of the intensity auto-correlation function are observed and related to two distinguishable elastic moduli. Our results validate the prospects of electric fields for controlling protein aggregation processes.

Field emission microscope for a single fullerene molecule

Applying strong direct current (DC) electric fields on the apex of a sharp metallic tip, electrons can be radially emitted from the apex to vacuum. Subsequently, they magnify the nanoscopic information on the apex, which serves as a field emission microscope (FEM). When depositing molecules on such a tip, peculiar electron emission patterns such as clover leaves appear. These phenomena were first observed seventy years ago. However, the source of these emission patterns has not yet been identified owing to the limited experimental information about molecular configurations on a tip. Here, we used fullerene molecules and characterized the molecule-covered tip by an FEM. In addition to the experiments, simulations were performed to obtain optimized molecular configurations on a tip. Both results indicate that the molecules, the source of the peculiar emission patterns, appear on a molecule layer formed on the tip under strong DC electric fields. Furthermore, the simulations revealed that these molecules are mostly isolated single molecules forming single-molecule-terminated protrusions. Upon the excellent agreements in both results, we concluded that each emission pattern originates from a single molecule. Our work should pave the way to revive old-fashioned electron microscopy as a powerful tool for investigating a single molecule.

Effects of electro-thermal cycles on the densification and properties of W–Mo–Cu alloys prepared via large current electric field sintering

In this study, we fabricated a novel ternary alloy of W–Mo–Cu by constant and cyclic large current electric field sintering at a relatively low temperature (950 °C) and within a short time (5 min). We subsequently investigated the effects of the electro-thermal cycles on the densification, microstructure, and properties of the sintered alloy. The electro-thermal cycles process generated greater amounts of Joule heating and provided more energy under the additional effect of field emission by repeating the heating and cooling treatments. W–Mo–Cu alloy was experimentally proven to densify significantly under the effect of electro-thermal cycles. Indeed, as compared with the microstructures of W–Mo–Cu alloy prepared via constant temperature sintering, the microstructures derived by cyclical sintering were far denser. It was also found that the relative density and hardness of cyclically sintered W–Mo–Cu alloy were higher, and its electrical resistivity was lower than those of constantly sintered alloy. In general, cyclically sintered W–Mo–Cu alloy, with 10 wt% Cu added, exhibited optimal comprehensive properties. It can be concluded that cyclic large current electric field sintering is a promising method for preparing W–Mo–Cu alloy with enhanced densification and properties.

Preparation and electroactuation of water-based polyurethane-based polyaniline conductive composites

Abstract Ionic polymer-based conductive composite is a new type of ionic electroactive polymer smart material, which is composed of two electrodes, the ion-exchange polymer matrix film and the polymer surface and is a three-layer sandwich structure. The conductive composite material has the advantages of flexibility, portability, and biocompatibility, which has attracted a large number of researchers to study it in the fields of biomimetic flexible actuators and biomedical materials, but the conventional matrix film has the disadvantage of high preparation cost. In this study, using sulfonated waterborne polyurethane membrane as matrix membrane and aniline as monomer, polyaniline (PANI) was synthesized by in situ oxidation polymerization reaction, and the conductive composites with PANI as electrode were prepared. After applying alternating current electric field, a new brake with PANI as electrode is obtained. A low-frequency signal generator was used to study the electromechanical properties of the prepared materials. The results show that the waterborne polyurethane/PANI composite film produces a continuous and stable driving performance at 0.2 Hz and 20 V, and the maximum output displacement of the terminal is 40 mm. When the driving voltage and frequency are changed, the displacement output also changes, showing a good controllable performance. Its structure and morphology were characterized.