Search

The present research investigated the voltage polarity asymmetry phenomenon based on dielectric wetting. In an ITO–hydrophobic layer–droplet setup, three reagents with different pH values (3.96, 7.0, and 10.18), two types of hydrophobic materials (AF1601 and 6%T6), and two different thicknesses (340 nm and 2.5 μm) of each material were systematically investigated. The results show that the thickness of the hydrophobic dielectric layer and the pH of the droplets had a significant impact on the droplet contact angle variation with the voltage. The contact angle on the thick hydrophobic dielectric layer followed the Lippmann–Young equation as the voltage changed. The angle of the thin hydrophobic dielectric layer was affected by its own properties and the type of droplet, which led to the occurrence of voltage polarity asymmetry of the electrowetting phenomenon. After further investigation of this phenomenon, it was found that it mainly accounted for the decrease in electric field strength at both ends of the droplet, which was caused by electrochemical reactions and changes in circuit resistance. The leakage current is an important indicator, and this phenomenon can be prevented by increasing the thickness of the hydrophobic dielectric layer. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of various factors (charging voltage, spray distance and spray pattern) on the deposition coverage of tomato leaves, the Box–Behnken surface response methodology was used to design an outdoor air-assisted electrostatic spraying experiment with three factors and three levels. The deposition coverage of tomato leaves in the upper, middle and lower layers was collected under different polarity charging voltages (0, +10 kV, −10 kV), spray distances (1, 3, 5 m) and spray patterns (ascending spray, descending spray, fixed height spray). Regression analysis and variance analysis were performed on the experimental data to determine the optimal working parameters. The results showed that (1) spray distance is the most important factor affecting the droplet coverage rate in the process of air-assisted electrostatic spraying; (2) the droplet coverage rate of air-assisted electrostatic spraying is optimal when the charging voltage polarity is negative voltage, the spray distance is 2.75 m, and the spray pattern is descending spray. The following conclusions were obtained. (1) In air-assisted electrostatic spraying, the distribution of air flow had the greatest effect on droplet deposition on tomato leaf surface. (2) Compared with air-assisted non-electrostatic spray, air-assisted electrostatic spray had a better deposition effect. [ABSTRACT FROM AUTHOR]

This study investigates the counterintuitive behaviors of a microwave‐induced atmospheric pressure plasma jet (APPJ) under the influence of an external electrostatic field applied by one or a pair of parallel electrode plates subjected to DC voltages. The findings demonstrate that the plasma jet consistently deflects toward the electrode plate with an electrostatic potential, irrespective of the direction of the applied field. The deflection becomes more pronounced with increasing voltage on the electrode plate until the ionic wind generated by the high voltage significantly affects the jet's behavior. Remarkably, a negative voltage induces a greater deflection compared to a positive voltage. To further investigate this discovery, the dielectric properties and the non‐neutral characteristics of the APPJ are analyzed, and the simulations of the electric field distribution reveal a non‐uniform distribution, which plays a crucial role in understanding the mechanism behind the observed behaviors of the plasma jet. This study provides a comprehensive understanding of the underlying mechanism driving the observed phenomena and sheds light on the collective behavior of plasma jets under non‐uniform electric fields. The findings of this study offer valuable guidelines for investigating and controlling the behavior of APPJs. [ABSTRACT FROM AUTHOR]

Plasma contacting with liquid (PCL) provides many charged particles and reactive species into the liquid. The difficulty in controlling or selecting each specific species has significantly limited its applications in industry. Here, we present a study on using voltage polarity to regulate the type of charged particles absorbing from the plasma into the liquid. A detailed understanding of the processes at the plasmaâ€"liquid interface and electrolysis due to switching in voltage polarity was determined via a visual pH observation, measuring the concentration of H2O2 and solvated electrons. The results indicated that changes in voltage polarity strongly affect the plasma properties, chemical properties and electrolysis process in liquid, and also in the types of reducing species for gold nanoparticle (GNP) synthesis. The results also showed that using a suitable frequency could improve the efficiency of absorption of H2O2 from plasma into the bulk liquid as well as the yield in the production of GNPs. The results provide a way to select desired species from the plasma to be transferred into the liquid for a distinct purpose and to accompany other properties in the system of PCL. [ABSTRACT FROM AUTHOR]

Multi-terminal HVDC grid has extremely high demand for protection speed of DC lines, consequently, the sampling time window of the main protection is very short, which affects its selectivity and reliability. To make up for the insufficiency of the non-unit main protection, this paper proposes a pilot protection scheme based on the voltage polarities of current-limiting reactors at the ends of DC lines. Analysis shows that the voltage polarities of terminal reactors at the two ends of the DC lines are both positive when internal fault occurs, while they are opposite for external faults. Based on the aforementioned characteristic difference, a pilot protection criterion is built to discriminate between internal and external faults. To avoid mal-operation of the protection on healthy pole generated by the coupling effect, the polarity mutation of reactor voltage on healthy pole due to coupling effect is analyzed when single-pole-to-ground fault occurs. Based on the analysis, the fault voltage of current-limiting reactor is integrated, and its polarity can be identified based on the integration value. At last, a four-terminal modular multilevel converter (MMC)-based HVDC grid model is built in PSCAD/EMTDC, and the effectiveness of the protection scheme is verified by extensive simulations. [ABSTRACT FROM AUTHOR]

This study deals with the influence of hydrostatic pressure on discharges propagating at solid/liquid insulating interface submitted to a divergent electric field under AC and DC voltages. The investigated insulator samples are of phenoplast resin (bakelite) and the considered liquid is mineral oil. The experimental results show that the hydrostatic pressure and the waveform, amplitude and polarity of voltage greatly influence the characteristic parameters of creepage discharges. The stopping (or final) length, Lf, which is the maximum extension of these discharges increases with voltage; it is reduced when applying a hydrostatic pressure. Lf increases quasi‐linearly with the voltage and decreases quasi‐linearly when the hydrostatic pressure is increased, whatever the voltage waveform. These results are of great interest especially for design and dimensioning of insulation systems in high voltage oil‐filled apparatus and especially non‐breathing components. [ABSTRACT FROM AUTHOR]

This paper concerns the studies on streamer propagation in mineral oil, synthetic ester and natural ester at standard lightning impulse inception voltage in small point‐plane gaps. The inception voltages of both polarities were measured using step method and then analysed statistically. Simultaneously, streamer characteristics such as shape, emitted light and propagation velocity were compared between the liquids tested. The obtained results showed that the inception voltages were close to each other for all the three liquids tested. Concerning streamer characteristics, it was seen that the spatial shapes of the streamers were similar taking into consideration the given voltage polarity. The same may be said about the propagation velocities, indicating that the velocities of the positive streamers were twice as high as the negative ones. In the case of registered time courses of emitted light, the frequencies of the light pulses corresponding to the propagation of the streamers in both esters were a little bit higher than the pulses emitted by the streamers, which developed in mineral oil. In general, in all three liquids the streamers at inception voltages developed as so‐called 'stopping length' streamers. [ABSTRACT FROM AUTHOR]

Effects of the radius of a coaxial pulse corona reactor and the polarity of an applied voltage on \NOx (nitrogen oxide) removal are investigated for industrial applications of the \NOx removal technology. Three radii of the pulse corona reactors (10, 30, and 50 mm) were chosen in the experiments of ozone generation and \NOx removal, and their energy efficiencies were measured. The 50-mm-radius reactor with the positive pulsed voltage was found to be suitable for the removal of large amount of \NOx and ozone generation. On the other hand, it was clarified that the 10-mm-radius reactor with the negative pulsed voltage is effective for the removal of small amount of \NOx and ozone generation. In the case of the 30-mm-radius reactor, energy efficiencies versus ozone concentration characteristics became a single curve at both the positive and negative polarities. For the purpose of the industrial application, a parallel reactor system and a reactor having a dielectric barrier were also tested experimentally. Through these experiments, the value of the energy efficiency of the parallel reactor system was confirmed to keep almost the same value as that of the single-reactor system. The reactor with the dielectric barrier on the outer electrode had higher energy efficiency than that without one. [ABSTRACT FROM AUTHOR]

Electrospinning is an old but yet immature process which is now used to form nanoscale polymer fibers. This paper describes the use of SEM and measurements of jet currents to investigate the effects of key parameters on fiber formation during electrospinning of a polyethylene oxide solution (PEO). The ambient humidity and voltage polarity are key factors influencing fiber formation, but this process has not been carefully analyzed. The influence of the ambient humidity can be overcome by choosing a solvent with a larger difference between the saturated vapor pressure and the actual vapor pressure in air or by lowering the ambient humidity when water is used as the solvent. The process works with both negative and positive voltages, but the polarity influences the stability and the fiber diameters. Variations of the current were found to correspond with variations of the fiber diameters. Short target distances were found to prevent fiber formation while long distances resulted in a larger distribution of fiber diameters. The experiments also showed that ultra fine fibers were found between the ends of broken fibers due to a strong electrical force on fibers with little solvent. [ABSTRACT FROM AUTHOR]

Electrospun polycaprolactone (PCL) fibers show extensive filopodia formation wrapping the fibers after 3 days of cell culture, which is observed on this SEM micrograph. PCL fibers are electrospun with negative voltage polarities to obtain higher surface potential and enhance the bone tissue regeneration. More details can be found in article number 1801211 by Sara Metwally, Urszula Stachewicz, and co‐workers. [ABSTRACT FROM AUTHOR]

A single‐step electrospinning approach enables controlling surface potential of fibers by changing voltage polarities during scaffolds production to enhance cells biointegration. This innovative and facile way of fibers production regulates the interfacial properties to enhance cells adhesion and filopodia formation on fibrous tissue scaffolds for possible bone regeneration. Tuning surface chemistry of polycaprolactone (PCL) by altering voltage polarity during electrospinning allows to double the surface potential on fibers up to 145 mV, which is directly measured using Kelvin probe force microscopy. The obtained surface potential on PCL fibers is directly correlated with surface chemistry analyzed at the grazing angle by X‐ray photoelectron spectroscopy, showing lower oxygen content at PCL fiber surfaces, produced with negative voltage polarity, PCL (−). These fibers create well‐engineered scaffolds that are able to increase significantly cell proliferation that is visualized with fluorescence microscopy, and filopodia formation on positively charged fibers, investigated with high‐resolution scanning electron microscopy. This work introduces electrospun PCL fibers without a need for chemical modification to tune electrostatic interactions between cells and fibrous scaffolds for biomaterials used in regenerative medicine. This study shows an innovative way of a single‐step electrospinning approach enabling to control surface potential of the fibers by alternating voltage polarities during scaffolds production. The produced polycaprolactone scaffolds with negative voltage polarities increase twice their surface potential measured directly with Kelvin probe force microscopy and enhance cells proliferation, adhesion, and filopodia formation on electrospun fiber surfaces for bone regeneration. [ABSTRACT FROM AUTHOR]