Alternating Current Electric Field Research Articles

The influence of frequency and gravity on the orientation of active metallo-dielectric Janus particles translating under a uniform applied alternating-current electric field.

Theoretical and numerical models of active Janus particles commonly assume that the metallo-dielectric interface is parallel to the driving applied electric field. However, our experimental observations indicate that the equilibrium angle of orientation of electrokinetically driven Janus particles varies as a function of the frequency and voltage of the applied electric field. Here, we quantify the variation of the orientation with respect to the electric field and demonstrate that the equilibrium position represents the interplay between gravitational, electrostatic and electrohydrodynamic torques. The latter two categories are functions of the applied field (frequency, voltage) as well as the height of the particle above the substrate. Maximum departure from the alignment with the electric field occurs at low frequencies characteristic of induced-charge electrophoresis and at low voltages where gravity dominates the electrostatic and electrohydrodynamic torques. The departure of the interface from alignment with the electric field is shown to decrease particle mobility through comparison of freely suspended Janus particles subject only to electrical forcing and magnetized Janus particles in which magnetic torque is used to align the interface with the electric field. Consideration of the role of gravitational torque and particle-wall interactions could account for some discrepancies between theory, numerics and experiment in active matter systems.

Applying an alternating current to strontium titanate minimizes the change in oxidation state caused by flash sintering

This study estimated the amount of oxygen deficiency in SrTiO3 polycrystals that were flash sintered under direct current (DC) and alternating current (AC) electric fields, mainly by using the fine structural change of the Ti L23-edges collected by electron energy-loss spectroscopy. The DC electric field corresponded to formation of the maximum amount of oxygen deficiency at approximately δ = 0.07 as SrTiO3−δ, which corresponds to a lattice expansion of roughly 0.1% as a lattice constant of SrTiO3. Furthermore, the oxygen deficiency was distributed unevenly. The formation of dislocation networks in DC-flash-sintered SrTiO3 polycrystals might be related to the lattice strain field caused by this nonuniform oxygen deficiency. In contrast, an AC electric field did not correspond to the oxygen deficiency of SrTiO3, which is similar to the results in thermally sintered SrTiO3 polycrystals.

Outcomes of structure, function and flavor of pea protein isolate treated by AC, DC and pulsed electric fields

Based on the standpoint of low carbon footprint processing and less denaturation of plant protein ingredient, the effects of pulsed electric field (PEF), direct current electric field (DCEF), and alternating current electric field (ACEF) treatments on the structure, functional properties and volatile compounds of pea protein isolate were investigated. The results showed that the electric fields (EFs) caused both blueshifts (max. ∼8 cm−1) and redshifts (max. ∼7 cm−1) in the IR spectra and blueshifts (max. ∼5 nm) in the UV spectra. PEF caused an increase of emulsifying activity index and a decrease of emulsion stability index to DCEF and ACEF. A total of 27 volatile compounds were identified and the EFs could cause emerging of new volatiles and disappearing of inherent volatiles potentially to modify the flavor of products. Alterations were significantly observed among the types of EF, but seldomly among the operating parameter levels in the same EF.

Electrohydrodynamic drying of citrus (Citrus sinensis L.) peel: Comparative evaluation on the physiochemical quality and volatile profiles.

Based on the concept of circular economy, citrus peel was considered a valuable source of bioactive compounds for high-value foods. Electrohydrodynamic (EHD) drying is a novel technology appropriated for the dehydration of heat-sensitive products such as citrus peel. In current work, EHD drying of citrus peel was performed based on alternating current (AC) or direct current (DC) sources at various voltage levels (9, 18, 27, 36, and 45kV). The effect of EHD on drying characteristics, water retention capacity, enzyme inactivation, phytochemical contents (phenolic compounds and carotenoids), and volatile compounds of citrus peel were evaluated and compared. Results showed that the drying time in the AC electric field was shorter compared to DC electric field at the same applied voltages due to the polarization layer formed by unipolar charges. The applied voltage determined electric field strength as well as the degree of tissue collapse and cell membrane rupture. EHD elucidated the transformation and degradation of phytochemicals including phenolic compounds, carotenoids, and volatile composition in proportion to the applied voltage. The findings indicate that EHD drying with AC improves drying behaviors, inactivates enzymes, and retains the phytochemical properties of citrus peel.

Numerical Study of the Time-Periodic Electroosmotic Flow of Viscoelastic Fluid through a Short Constriction Microchannel.

Electroosmotic flow (EOF) is of utmost significance due to its numerous practical uses in controlling flow at micro/nanoscales. In the present study, the time-periodic EOF of a viscoelastic fluid is statistically analyzed using a short 10:1 constriction microfluidic channel joining two reservoirs on either side. The flow is modeled using the Oldroyd-B (OB) model and the Poisson-Boltzmann model. The EOF of a highly concentrated polyacrylamide (PAA) aqueous solution is investigated under the combined effects of an alternating current (AC) electric field and a direct current (DC) electric field. Power-law degradation is visible in the energy spectra of the velocity fluctuations over a wide frequency range, pointing to the presence of elastic instabilities in the EOF. The energy-spectra curves of the velocity fluctuations under a DC electric field exhibit peaks primarily beneath 20 Hz, with the greatest peak being observed close to 6 Hz. When under both DC and AC electric fields, the energy spectra of the velocity fluctuations exhibit a peak at the same frequency as the AC electric field, and the highest peak is obtained when the frequency of the AC electric field is near 6 Hz. Additionally, the frequency of the AC electric field affects how quickly the viscoelastic EOF flows. Higher flow rates are obtained at relatively low frequencies compared to under the DC electric field, and the greatest flow rate is found close to 6 Hz. But as the frequency rises further, the flow rate falls. The flow rate falls to a level below the DC electric field when the frequency is sufficiently high.

Effects of willow and Sedum alfredii Hance planting patterns on phytoremediation efficiency under AC electric field.

Heavy metal contamination to soil is tricky due to its difficult removal, long retention time, and biomagnified toxicity. The green and low-cost phytoremediation with electric field treatment and planting pattern selection is an emerging and more effective approach to remove heavy metals from soils. In this study, alternating current (AC) electric field-assisted phytoremediation was examined with different planting patterns, i.e., monoculture willow (Salix sp.), monoculture Sedum alfredii Hance, and interplanting of willow and S. alfredii. AC electric field greatly increased phytoremediation efficiency to soil cadmium (Cd) regardless of planting patterns, either single plant species of willow or S. alfredii. The Cd removal capacity of willow and S. alfredii raises apparently under 0.5Vcm-1 AC electric field. Under different planting patterns of AC electric field treatment, Cd accumulation in the whole plant by interplanting was 5.63 times higher than monoculture willow, but only 0.75 times as high as monoculture S. alfredii. The results showed that AC electric field-assisted interplanting of willow and S. alfredii is a promising remediation technique for efficiently clean-up Cd-contaminated soil.

Mixing performance of an expansive mixer on viscoelastic solutions under alternating current electric field

Development of effective technologies for mixing viscoelastic solutions with reagents is still a challenge, which plays an important role in the fields of disease diagnosis, water desalination, and immunoassay. The purpose of this paper is to numerically study the mixing performance of an expansive mixer on the viscoelastic solution under the impact of an alternating current (AC) electric field through the analyzation of mixing efficiency, the concentration distribution, and average outlet velocity. A poly acrylic acid (PAA) water solution with different concentrations characterized by the Oldroyd-B constitutive model is used as a mixed medium, and an open-source toolbox called rheoTool based on finite volume algorithm is applied to solve the governing equations. We quantitatively determine the mixing efficiency for different PAA concentrations, AC electric field strengths, and frequencies and compare the mixing efficiency created by AC and direct current (DC) electric fields. Our investigation indicates that the mixing efficiency of the mixer diminishes with the PAA concentrations but enhances with the AC electric field strengths for a relatively high polymer concentration, and AC electric fields with different frequencies lead to a larger mixing efficiency than DC electric fields for a low polymer concentration. Additionally, the influence of the model parameters on the average outlet velocity and concentration distribution is discussed at length. Our numerical simulation results show that the mixer has an excellent mixing performance for both Newtonian and viscoelastic solutions, with a mixing efficiency of more than 99% at a low polymer concentration and a stable outflow velocity.

PH Gradients in Spatially Non-Uniform AC Electric Fields around the Charging Frequency; A Study of Two Different Geometries and Electrode Passivation.

Dielectrophoresis (DEP), a precision nonlinear electrokinetic tool utilized within microfluidic devices, can induce bioparticle polarization that manifests as motion in the electric field; this phenomenon has been leveraged for phenotypic cellular and biomolecular detection, making DEP invaluable for diagnostic applications. As device operation times lengthen, reproducibility and precision decrease, which has been postulated to be caused by ion gradients within the supporting electrolyte medium. This research focuses on characterizing pH gradients above, at, and below the electrode charging frequency (0.2-1.4 times charging frequency) in an aqueous electrolyte solution in order to extend the parameter space for which microdevice-imposed artifacts on cells in clinical diagnostic devices have been characterized. The nonlinear alternating current (AC) electric fields (0.07 Vpp/μm) required for DEP were generated via planar T-shaped and star-shaped microelectrodes overlaid by a 70 μm high microfluidic chamber. The experiments were designed to quantify pH changes temporally and spatially in the two microelectrode geometries. In parallel, a 50 nm hafnium oxide (HfO2) thin film on the microelectrodes was tested to provide insights into the role of Faradaic surface reactions on the pH. Electric field simulations were conducted to provide insights into the gradient shape within the microelectrode geometries. Frequency dependence was also examined to ascertain ion electromigration effects above, at, and below the electrode charging frequency. The results revealed Faradaic reactions above, at, and below the electrode charging frequency. Comparison experiments further demonstrated that pH changes caused by Faradaic reactions increased inversely with frequency and were more pronounced in the star-shaped geometry. Finally, HfO2 films demonstrated frequency-dependent properties, impeding Faradaic reactions.

Exploring the potential of alternative current electric field treatment for preservation and the tissue softening mechanism in Pleurotus ostreatus

Pleurotus ostreatus (P. ostreatus) is one of the common edible fungi; however, enzyme reactions during the storage period destroys its texture, resulting in a short shelf life (<10 days) and eventually resulting in wastes. Previous studies have demonstrated that the application of high electrostatic field treatment effectively suppresses the browning of P. ostreatus during storage by inhibiting oxidase activity. In the present study, P. ostreatus was employed as a model to explore cell wall decomposition alleviation by treatment with direct current electric field (DCEF) and alternative current electric field (ACEF). The results indicated that ACEF (400 kV m−1, 90–120 min) led to lower weight loss, lower firmness loss (400 kV m−1, 120 min), and reduced moisture migration during storage. Further research confirmed that ACEF (600 kV m−1, 120 min) treatment inhibited chitinase and β-1,3-glucanase activities by 72% ± 6% and 53% ± 3%, respectively, thereby delaying the disintegration of P. ostreatus during storage. In addition, as a noncompetitive inhibitor, ACEF reduced the Km and Vmax of chitinase and β-1,3-glucanase in P. ostreatus. In conclusion, ACEF treatment significantly alleviated texture loss in P. ostreatus, with a preservation rate of 9.3% ± 0.3%. These findings highlight the potential of ACEF treatment as a promising strategy for enhancing the preservation and commercialization of edible fungi.

Preparation and Orthogonal Analysis for Dual-Responsive Electrochromic Polymer Dispersed Liquid Crystal Devices.

In this work, we provide a fabrication method for dual-responsive electrochromic (EC) polymer dispersed liquid crystal (PDLC) devices. The EC PDLC device was developed by combing the PDLC technique and a colored complex formed via a redox reaction without a specific EC molecule in a simple preparation method. The mesogen played dual roles in the device for scattering in the form of microdroplets and participating in the redox reactions. Orthogonal experiments were performed with the acrylate monomer concentration, the ionic salt concentration, and the cell thickness as factors to investigate the electro-optical performance for the achievement of optimized fabrication conditions. The optimized device presented four switchable states modulated by external electric fields. The light transmittance of the device was changed by an alternative current (AC) electric field while the color change was realized by a direct current (DC) electric field. Variations of mesogen and ionic salt species can modulate the color and hue of devices, which solves the disadvantage of a single color for traditional EC devices. This work lays the foundation for realizing patterned multi-colored patterned displays and anti-counterfeiting via screen printing and inkjet printing techniques.

Electrothermally excited plasma droplet evolution on the laser-patterned surface

Droplet behavior involving electrothermal coupling fields has gradually attracted the attention of researchers, one of which includes electrosurgical scalpels that often contact biofluids. However, the evolution of bio-droplets exposed to the surface of electrosurgical scalpels is not yet well understood. Here, we experimentally studied the effect of different heating temperatures on plasma droplets on the laser-patterned surface (LPS) and the original surface (OS) under defined direct-current (DC) or alternating-current (AC) electric fields. The results show that at a lower heating temperature, the evolution of plasma droplets was dominated by electrolysis. Oxygen bubbles generated on the papillae on the LPS in the DC field inhibited the targeted adsorption of plasma proteins on this surface. In contrast, in the AC field, only a small number of bubbles was generated, which is not sufficient to inhibit protein adsorption, leading to the formation of coagulation on the papillae after heating. At higher heating temperatures, the rapid formation of coagulation resulted in the suppression of electrolysis. The plasma proteins were then transported by the Marangoni flow causing coagulation to reach a thickness of stress mutation. Stress release over the entire coagulation caused its edges to bend and then detach from the papillae. Thus, the LPS exhibited excellent anti-adhesive properties to plasma droplets under electrothermal excitations compared to the OS. This study provides valuable information for understanding the mechanisms of contact behavior between biofluids and electrosurgical scalpels and demonstrates great promise for their anti-adhesive performance.

Salt rejection and scaling on non-conductive membranes in direct- and alternating-current electric fields

This study provides a comprehensive study about the salt rejection and fouling on non-conductive membranes in the electric fields of direct current (DC) and alternating current (AC). A simple membrane cell design that facilitates the application of electric field on traditional non-conductive membrane was built. Then different salts and foulants were applied as the feeds in the electric fields with varying voltage, frequency, waveform and bias. The impact of AC and DC within 1V on ion rejection and organic fouling is insignificant due to the low current flow and membrane conductivity. However, scaling can be effectively mitigated by both DC and AC at tuned conditions. Current direction, frequency, waveform and bias are found to substantially influence the scaling tendency. The anti-scaling performance in AC field is attributed to the continuous motion of ions that disturbs nucleation and crystal growth. Compared to DC, AC may operate at lower power consumption, thus offering an energy-effective strategy for scaling reduction.

Treatment of simulated saline brine water by membrane distillation process enhanced through alternating current electric field

Treatment of saline brine has been a tricky challenge in recent years, and membrane distillation (MD) is considered as a promising alternative technology. But it was found that the normalized flux significantly decreased to 0.6 within 15 h when treating simulated salinity brine, which was caused by the deposition of the humic acids (HA), CaSO4, and HA-Ca complex, suggesting the severe membrane fouling. In this study, a composite membrane was fabricated by coating carbon nanotubes (CNT) on the commercial PTFE membrane, and an alternating current (AC) electric field was subsequently applied that aimed to improve MD performance. Specially, the application of 50 Hz square wave dramatically retarded the inorganic fouling and the intensity of membrane organic matter was reduced by 60.6% due to its hydrophilic surface and instantaneous polarity conversion, thus its normalized flux even maintained around 0.9 after 15 h operation. Coupled with the modified XDLVO analysis, the coating CNT layer exhibited good resistance of HA due to their electrostatic repulsions, both of which carried a strong negative charge and high density hydrophilic functional groups. It was also found that except the movement distance of charged substances far greater than the thickness of the fixed electrostatic double layer, AC electric field with certain frequency significantly reduced the coexistence time for substances with opposite charge by keeping them in motion that could further alleviate the fouling. This study suggested that a hybrid system of AC electric field and MD would provide a potential alternative for treating the salinity brine water.

Programmable UV-Curable Resin by Dielectric Force.

In this study, UV-curable resin was formed into different patterns through the programmable control of dielectric force. The dielectric force is mainly generated by the dielectric chip formed by the interdigitated electrodes. This study observed that of the control factors affecting the size of the UV resin driving area, current played an important role. We maintained the same voltage-controlled condition, changing the current from 0.1 A to 0.5 A as 0.1 A intervals. The area of droplets was significantly different at each current condition. On the other hand, we maintained the same current condition, and changed the voltage from 100 V to 300 V at 50 V intervals. The area of droplets for each voltage condition was not obviously different. The applied frequency of the AC (Alternating Current) electric field increased from 10 kHz to 50 kHz. After driving the UV resin, the pattern line width of the UV resin could be finely controlled from 224 um to 137 um. In order to form a specific pattern, controlling the current and frequency could achieved a more accurate shape. In this article, UV resin with different patterns was formed through the action of this dielectric force, and after UV curing, tiny structural parts could be successfully demonstrated.

Conical breakup of droplets in dielectric liquid medium

The conical breakup behavior of droplets in immiscible dielectric liquids under non-uniform alternating current (AC) electric fields is experimentally investigated using high-speed photography. The optical-microscopic morphological characteristics of the dynamic behavioral process of charged droplets under different electric field conditions are precisely captured. Two distinct conical breakup configurations, called the trident vibration and lotus vibration modes, are proposed, and their detailed structural parameters are discussed. The extremely small stable conical meniscus (semi-angles range of 11°–18.6°) is found in the liquid–liquid system. The distribution of cone angles under various spatial conditions is determined. In addition, the multilevel asymptotic characteristics of conical fragmentation are found due to the variances in spatial and temporal scales. The diameters of the droplets produced under the cone-jet mode could be as small as a few micrometers. The differences between the droplet breakup mode of AC and DC electric fields are also discussed. Overall, several interesting features are reported for the axisymmetric multi-cone broken morphology when droplets undergo breakup.

Synergistic effect of alternating current-based electric and acoustic fields on flux recovery in crossflow microfiltration of synthetic wastewater

The main objective of this study was to investigate the feasibility of synergistic recovery of flux (i.e., 1 + 1 > 2) and fouling mitigation, in the presence of simultaneous application of alternating current (AC)-based electric and acoustic fields during crossflow microfiltration of synthetic wastewaters. We, first, designed a novel crossflow microfiltration apparatus to investigate synergistic effect of AC electric and acoustic fields; secondly, conducted fouling studies on (a) synthetic wastewater alone and (b) synthetic wastewater containing 1.2 × 108 particles/L of silica particles (300 nm SiO2), Micrococcus luteus (500–1000 nm), or a mixture of SiO2 and M. luteus at 50 % each by count, respectively; thirdly, studied the effect of several parameters, including AC electric field strength, acoustic field frequency, foulant type and composition, and pH of synthetic wastewater on fouling; and finally, assessed the significance of synergistic effect of fields on flux recovery using 22 two-level factorial analysis. Results revealed that the application of combined fields recovered 21 % of clean water flux which is significantly higher than those obtained by electric field (4 %) or acoustic field (6 %) alone. The non-linear relationship between flux recovery and each test parameter suggested that the effectiveness of field-assisted membrane processes is determined by multiple competing or mutually enhancing mechanisms − such as electro- and acousto-kinetics, and adsorption and agglomeration of particles − which were proposed to explain the synergistic effect of fields on flux recovery. This study demonstrated the combined AC electric and acoustic fields can synergistically amplify the flux recovery in crossflow microfiltration of synthetic wastewaters.

Optimized Alternating Current Electric Field and Light Irradiance for Caulerpa lentillifera Biomass Sustainability—An Innovative Approach for Potential Postharvest Applications

Recently published preliminary data proposed alternating current electric field (ACEF) as a promising technique for the postharvest storage of seagrape (Caulerpa lentillifera). The current study suggested a combination of storage light irradiance (SLI) and ACEF (intensity and time) to enhance seagrape physicochemical quality (PQ). It utilized Taguchi orthogonal array design (OAD) to optimize the processing conditions. Results showed all the processing parameters had significant (p &lt; 0.05) effects on seagrape PQ. This study found that 50 kV/m for 60 min (ACEF) and 9 mol photons m−2 s−1 performed the best inhibition on seagrape PQ deterioration. It revealed that adjusting the processing parameters in the range explored in this study (50, 125, 200 kV/m of ACEF intensity; 30, 60, 90 min of ACEF treatment time; 2, 9, 16 mol photons m−2 s−1 of SLI) can reduce up to 60% of total voltage usage compared to the previous study. With a sufficient SLI and an intermediate treatment time, the finest seagrape PQ can be sustained with a lower electric strength. Therefore, this method can benefit seagrape industries and contribute to realizing sustainable development goals by strengthening resource efficiency and lowering energy consumption.

Shell-like structure to limit further densification formed during flash sintering under alternative current electric field for 8 mol %Y&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-doped ZrO&lt;sub&gt;2&lt;/sub&gt;

A phenomenon often appears that the final achieved density is limited during conventional flash sintering even under alternative current electric field. By observing the cross-sectional microstructure of the flash sintered 8 mol %Y2O3-doped ZrO2 at this state, we found that a thin surface portion with near full density surrounds a porous inside with lower density. The densified thin surface portion is shell-like structure covering a whole of the sintered compact. The formation of this characteristic shell-like structure in the early stage of flash sintering greatly restricts subsequent densification of porous inside. In order to suppress the formation of the shell that inhibit densification, a technique of controlling a steep power spike at a flash event must be necessary to be appropriately transitioned.

Evolution of electro-induced blood plasma droplets on a superhydrophobic microstructured surface

Formation of severe adhesion on electrosurgical devices during their interaction with biofluids is an inherent problem that often causes reduced cutting efficiency and failed hemostasis. The introduction of (super-) hydrophobic surfaces is a favorable option for anti-adhesion, but the mechanisms related to their evolution with biofluids under electric fields are still not fully understood. Here, we investigated the evolution of blood plasma droplets on a superhydrophobic microstructured (SHM) surface under direct-current (DC) and alternating-current (AC) electric fields. The electrolysis of plasma droplets leads to the formation and diffusion of bubbles accompanied by a rise in temperature, while in turn, the electrolysis is suppressed as the bubbles fill the droplets, followed by a decrease in temperature. We show that under the DC electric field, the bubbles produced by papillae on the SHM surface can effectively prevent directional adsorption of plasma proteins compared to the flat surface, whereas the AC electric field induces oscillations in plasma proteins, resulting in even less adhesion. These findings provide valuable basic information for understanding the anti-adhesion mechanism of electrosurgical devices at a microscopic level.

Dynamically color-changing polymer-dispersed liquid crystals containing ionic liquid for smart window applications

ABSTRACT In this work, we report a bifunctional dynamically colour-changing polymer-dispersed liquid crystals (PDLCs) for smart windows by doping a supporting electrolyte ionic liquid into the conventional PDLC system. The transmittance spectra were used to measure the electrically colour-changing properties of the system, while the electro-optical curves were employed to examine the electrically switchable performances. The SEM was used to observe the surface morphology of the polymer microstructure. The result obtained from this work suggested that such device could obtain four independent states under different electric fields. The initial state was opaque and colourless due to the randomly dispersed liquid crystal droplets. The transparent and colourless state was obtained as a result of reorientation of liquid crystal under alternative current (AC) electric field. The opaque and green state was achieved under direct current (DC) electric field owing to the oxidation reaction in the system. Besides, the transparent and green state was realised via applying DC and AC electric field simultaneously or in steps. The convenience and simplification of switching between the four states enable the system to provide some interesting applications for smart windows.