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In this study, we investigate and propose an improved theoretical method to more accurately predict the performance of a field-emission electric propulsion (FEEP) thruster with its complex configuration. We identify critical flaws in the previous theoretical methods and derive corrected equations. Additionally, we define and implement the overall half angle of the Taylor cone to account for variations in the Taylor cone's half angle depending on the applied voltage. Next, we also establish an improved method of the electric filed simulation in a three-dimensional domain to accurately predict a trajectory of extracted ions and a resulting spatial beam distribution of the FEEP thruster by incorporating a configuration of the Taylor cone with the estimated overall half angle from the results of the present theoretical method. Through comparison with the experimental measurements, we found that the present improved methods for theoretical and electric field simulations can yield more accurate predictions than those of the previous methods, especially for higher V and Iem regimes, which correspond to the actual operating conditions of the FEEP thruster. Consequently, we anticipate that the proposed methods can enhance the reliability and efficiency of the design process by accurately predicting performance when developing the new FEEP thruster with its non-symmetric complex configuration to match specific thrust or spatial beam requirements. [ABSTRACT FROM AUTHOR]

Polycaprolactone (PCL) fibers have been widely used in the preparation of biological scaffolds. However, near-field electrospinning and melt electrospinning limitations in terms of molding height and residual charge, make it difficult to fabricate high-resolution complex PCL microstructures. This study proposes an electric field-driven melting deposition technique for direct writing of high-resolution PCL microstructures, which can be used to fabricate PCL micro-scaffolds. The basic process principle of continuous cone jet mode was analyzed, an electric field-driven melting deposition-based direct writing system was developed, and single-layer and multi-layer deposition experiments were systematically conducted. Further, the effect of collecting plate velocity on deposition morphology was investigated. The single-layer raster and grid structures were prepared. A model was established to predict the forming height of a single deposition line based on the deposition line width and solidification angle. The multi-layer deposition and direct writing of the “wall” structure was observed, and the multi-layer “wall” structure and the ring structure with a high aspect ratio were prepared. [ABSTRACT FROM AUTHOR]

This article presents a sharp immersed method for simulating electrohydrodynamic (EHD) flows that involve charge evaporation. This well‐known multi‐scale, multi‐physics problem is widely used in various fields, including industry and medicine. The method adopts a fully sharp model, where surface tension and Maxwell stress are treated as surface forces and free charges are concentrated on the zero thickness liquid‐vacuum interface. Incorporating charge evaporation imposes strict restrictions on the time‐step, as the rate of evaporation sharply increases with surface evolution. To overcome this challenge, an iterative algorithm that couples the electric field and surface charge density is proposed to obtain accurate results, even with significantly large time‐steps. To mitigate the numerical residuals near the interface, which may introduce parasitic flows and cause numerical instability, an immersed interface method‐based iterative projection method for the Navier–Stokes equations is proposed, in which a traction boundary condition involving multiple surface forces is imposed on the sharp interface. Numerical experiments were carried out, and the results show that the method is splitting‐error‐free and stable. The sharp immersed method is applied to simulate the electric‐induced deformation of an ionic liquid drop with charge evaporation. The results indicate that charge evaporation can suppress the sharp development of Taylor cones at the ends of the drops. These findings have significant implications for the design and optimization of EHD systems in various applications. [ABSTRACT FROM AUTHOR]

In this study, we investigate and propose an improved theoretical method to more accurately predict the performance of a field-emission electric propulsion (FEEP) thruster with its complex configuration. We identify critical flaws in the previous theoretical methods and derive corrected equations. Additionally, we define and implement the overall half angle of the Taylor cone to account for variations in the Taylor cone’s half angle depending on the applied voltage. Next, we also establish an improved method of the electric filed simulation in a three-dimensional domain to accurately predict a trajectory of extracted ions and a resulting spatial beam distribution of the FEEP thruster by incorporating a configuration of the Taylor cone with the estimated overall half angle from the results of the present theoretical method. Through comparison with the experimental measurements, we found that the present improved methods for theoretical and electric field simulations can yield more accurate predictions than those of the previous methods, especially for higher V and Iem regimes, which correspond to the actual operating conditions of the FEEP thruster. Consequently, we anticipate that the proposed methods can enhance the reliability and efficiency of the design process by accurately predicting performance when developing the new FEEP thruster with its non-symmetric complex configuration to match specific thrust or spatial beam requirements.

The properties of droplets produced by existing on-demand injection systems are typically determined by the nozzle diameter, i.e., only droplets with size larger than this diameter can be obtained. To solve this problem, a system for electric field-driven droplet injection and deposition was developed, and the related performances were compared with those of a standard pneumatic system. The results show that the diameter of droplets generated accordingly can be significantly smaller than the nozzle diameter. In particular, the effects of frequency and duty ratio on the number of droplets were studied by assuming microcrystalline wax as work material. A deposition matrix was obtained by using a nozzle with a diameter of 200 μm. The average diameter of the matrix was 80.17 μm with a standard deviation of 2.65 μm and the average spacing was 301.25 μm with a standard deviation of 6.80 μm. Four deposition states after droplet injection were considered and verified under different velocities of F60, F10, F3, and F0. We also provide an explanation for the existence of a series of inclined columns showing up during the deposition processs. [ABSTRACT FROM AUTHOR]

Silver nanoparticle (AgNP) based inks are widely used in printed electronics to form conductive patterns. However, high resolution and high electrical conductivity are still hard to achieve at the same time for the patterning of AgNP‐based electrodes. Herein, Ag patterns with a high resolution of sub‐10 µm and a high conductivity are realized by the electrohydrodynamic (EHD) printing. The parameters including the composition of Ag ink, printing speed, voltage, and working height are carefully controlled to increase the resolution, and the process window of the cone jet mode is established. With the help of the finite element simulation, the generation mechanism of the Taylor cone is clarified. Ag electrodes with various patterns and shapes are easily produced, which exhibited excellent patterning qualities, such as superior uniformity and flatness, narrow spacing, and clear edge definition. Finally, flexible light‐emitting diode (LED) circuits, transparent heaters, and supercapacitors are fabricated by EHD printed Ag grid electrodes. These results indicate that this work provides a simple and scalable strategy for fabricating ordered metal conductive patterns in the emerging printed electronics. [ABSTRACT FROM AUTHOR]

In the electrospinning process, the Taylor cone, as the jet source, directly affects the jet movement and the quality of the fiber membrane. Therefore, to understand the formation mechanism of the Taylor cone intuitively, a multiphysics coupling model that comprehensively considers the gravitational field, electrostatic field, and fluid field is established, and numerical simulations are conducted in this study. First, we construct a level-set function and analyze the force of the droplet. The gravity, surface tension, and electric field force are coupled to the incompressible Navier–Stokes equation as volume forces, and the nonconservation of the droplet area is solved by approximating the Dirac function with a smooth function. Subsequently, the deformation of the electrospun polyacrylonitrile (PAN) Taylor cone under different process parameters is simulated. Finally, data obtained from the numerical simulation and the average diameter of the electrospun PAN fiber membrane are analyzed via gray relational analysis. The results show that the volume force is the key factor affecting the average diameter of the fiber membrane (the correlation is 0.934). This article provides an effective reference and basis for the analysis and control of the electrospinning process.

In melt electrospinning, accurate control of jet evolution and Taylor cone process parameters helps to control the final fiber properties. High-speed photography was employed to observe the jet’s formation process and the Taylor cone’s morphology. A multi-physics model of nonisothermal heat transfer was used to predict the fluid flow direction and velocity change. In addition, we investigated the relationships between the process parameters of the Taylor cone and the diameter of melt electrospun fiber. The results show an excellent linear relationship between the process parameters (cone angle, curvature, and Taylor cone height) and fiber diameter. According to the simulation results, the axial fluid flow keeps the maximum and accelerates continuously until the collector captures it. In addition, with the increase of voltage, the fiber strength is lower, and the crystallinity is improved. This work analyzes diameter and process parameters and offers a fresh perspective on electrostatic-fluid interaction and a method to forecast fiber diameter. [ABSTRACT FROM AUTHOR]

A novel method for identifying the cone-to-jet transition region is proposed to characterize the electrospray dynamics, and thus the Taylor cone, a fundamental principle of ion extraction from the tip of the Taylor cone in an electric field to produce μN thrust for nanosatellites' application. A numerical model is developed and validated against the droplet's diameter with a proper characterization of the cone-to-jet transition region based on the hydrodynamic pressure gradient at the cone-jet axis. The results show that the cone-to-jet transition region is reduced when the electric potential increases and the flow rate decreases. Moreover, the current density is found to be higher for the lower flow rate and large electric potential. Interestingly, the current density at the jet axis increases significantly at the flow rate of 1 cc/hr. This implies that below a certain droplet diameter, the current density carried by the jet interface is completely migrated into the jet, and the substantial change in the current density occurs within the cone-to-jet transition region. When comparing the current density along the jet axis, the small flow rate and large electric potential carry the maximum current density at the jet interface. The identification of cone-to-jet transition region is central in modeling the ion beam trajectory via initial current density profile required for particle-in-cell calculation for assuring the performance of a field emission electric propulsion thruster. • Identification of cone-to-jet transition region based on the hydrodynamic pressure. • Characterization of cone-to-jet transition on the electric potentials and flow rate. • Estimation of current density profile from the identified cone-to-jet transition. [ABSTRACT FROM AUTHOR]

Electrohydrodynamic (EHD) printing is a very promising approach for micro/nanoscopic additive manufacturing but suffers from printing stability problems due to the insufficient knowledge of its controlling techniques. Here, we conduct a numerical study on EHD printing under six unconventional pulsed voltage waveforms and investigate the influences of upward/downward voltage time and waveform shape on liquid behaviors and printing outcomes. With the assistance of the clear snapshots, voltage distribution, and interface charge density obtained from the numerical results, it is discovered that the three upward voltage waveforms only alter the duration of Taylor cone formation with very minor impact on the printing process and deposited droplet volume. On the other hand, all three downward voltage waveforms exert a significant influence on liquid behaviors. The printing processes under the trapezoidal down waveform are the most stable ones owing to the continuous and smooth voltage reduction. The processes under the two steps down waveform are similar to the trapezoidal down waveform but become unstable when the downward time is too long. Due to the two drastic voltage drops, the processes under the one step down waveform are the least stable and produce more satellite droplets than the other two waveforms. The volume of deposited droplet generally decreases with increasing downward time for all three waveforms, and the droplets produced under the one step down waveform are smaller than the other two waveforms, resulting from the rapidly reduced electric force after the voltage switches. To our best knowledge, this is the first numerical work on EHD printing under various unconventional waveforms. The results obtained in this paper provide useful addition to the understanding of its complicated mechanisms. [ABSTRACT FROM AUTHOR]

The growing issue of particulate matter (PM) air pollution has given rise to extensive research into the development of high-performance air filters recently. As the core of air filters, various types of electrospun nanofiber membranes have been fabricated and developed. With the novel poly(acrylonitrile) (PAN)-CuCl2 composite nanofiber membranes as the filter membranes, we demonstrate the high PM removal efficiency exceeding 99% and can last a long service time. The nanoscale morphological characteristics of nanofiber membranes were investigated by scanning electron microscopy, transmission electron microscopy, and mercury intrusion porosimeter. It is found that they appear to have a special net structure at specific CuCl2 concentrations, which substantially improves PM removal efficiency. We anticipate the PAN-CuCl2 composite nanofiber membranes will be expected to effectively solve some pressing problems in air filtration. [ABSTRACT FROM AUTHOR]

[Display omitted] • The difference between electrospray in insulating liquid and air was experimentally investigated. • Electrospraying in insulating liquid has been found to be more stable than that in air. • This stability was due to the suppression of corona discharge in the insulating liquid. Electrospraying can be performed in both liquid and air media. We have found that electrospraying in insulating liquids is more stable under a wide range of applied voltages compared to that in air. The stability of the spray in insulating materials indicates a significant relationship between electrical interaction and spray stability within liquid media. The electrospray in air diminished with an increase in the applied voltage from 3 to +4 kV, while that in n -hexane generated a fine spray even at applied voltages exceeding +9 kV. The absence of corona discharge in a spray nozzle immersed in liquid n -hexane contributed to achieving a stable electrospray process with a narrow size distribution. However, in air, voltage-induced corona discharge caused by the ionization of atmospheric molecules (such as N 2 and O 2) led to a decrease in the stability of the electrospray. To elucidate the differences between the dynamic processes of electrospraying in air and n -hexane, we conducted measurements using high-speed camera imaging, analyzed the size distribution of charged droplets, and assessed circuit current. [ABSTRACT FROM AUTHOR]

Polycaprolactone (PCL) scaffolds have been widely used in biological manufacturing engineering. With the expansion of the PCL application field, the manufacture of high-resolution complex microstructure PCL scaffolds is becoming a technical challenge. In this paper, a novel PCL high-resolution fused deposition 3D printing based on electric field-driven (EFD) jet deposition is proposed to manufacture PCL porous scaffold structures. The process principle of continuous cone-jet printing mode was analyzed, and an experimental system was constructed based on an electric field driven jet to carry out PCL printing experiments. The experimental studies of PCL-fused deposition under different gas pressures, electric field voltages, motion velocities and deposition heights were carried out. Analysis of the experimental results shows that there is an effective range of deposition height (H) to realize stable jet printing when the applied voltage is constant. Under the stretching of electric field force and viscous drag force (FD) with increasing movement velocities (Vs) at the same voltage and deposition height, the width of deposition lines was also gradually decreased. The width of the deposition line and the velocity of the deposition platform is approximately a quadratic curve. The bending phenomenon of deposition lines also gradually decreases with the increase of the movement velocities. According to the experiment results, a single layer linear grid structure was printed under the appropriate process parameters, with compact structure, uniform size and good straightness. The experimental results verify that the PCL porous scaffold structure can be accurately printed and manufactured.

The growing issue of particulate matter (PM) air pollution has given rise to extensive research into the development of high-performance air filters recently. As the core of air filters, various types of electrospun nanofiber membranes have been fabricated and developed. With the novel poly(acrylonitrile) (PAN)-CuCl2 composite nanofiber membranes as the filter membranes, we demonstrate the high PM removal efficiency exceeding 99% and can last a long service time. The nanoscale morphological characteristics of nanofiber membranes were investigated by scanning electron microscopy, transmission electron microscopy, and mercury intrusion porosimeter. It is found that they appear to have a special net structure at specific CuCl2 concentrations, which substantially improves PM removal efficiency. We anticipate the PAN-CuCl2 composite nanofiber membranes will be expected to effectively solve some pressing problems in air filtration.

The present day environmental issues demand a lot from scientists and engineers to keep the planet earth safe for its habitats. There were lot of attempts for developing efficient air and liquid filters as the demand increases with an utmost concern of present environmental situations. Thanks to its large surface area to volume ratio, polymer nanofibers and composites are found to be good substitute for conventional filters. As per the research and analysis data, filtration efficiency increases proportional to the reduction of the average diameter of the fibers. In this study, the most efficient electrospinning technology was adopted to prepare polycarbonate (PC) nanofiber mat which yields a very fine surface morphology. There are earlier researches and associated data available about the preparation of PC nanofibers but with average fiber diameter above 1000 nm. In this study, a systematic methodology was instigated to generate PC nanofibers with least average diameter of 90 nm without using any surfactants or salts. The most suitable solvents, solvent proportion, polymer concentration and electrospinning conditions for the formation of the fiber mat are discussed elaborately. PC fiber mat of least average diameter was proved to be highly efficient for particulate matter adsorption using a dust sampling analyzer. [ABSTRACT FROM AUTHOR]

3D printing, also called additive manufacturing, is being used increasingly in tissue engineering. However, the printing accuracy remains limited, making it difficult to prepare a tissue engineering scaffold with high precision and high porosity. Melt electrowriting (MEW) technology is based on extrusion printing, in which an extruded material is pulled by the action of an electric field, thereby reducing the fiber diameter and improving the printing accuracy. However, MEW technology imposes high requirements on the material properties, and therefore, few printing materials are currently available for use in this process. The present study investigates the characteristics and molding conditions of polycaprolactone, a commonly used printing material, as well as other materials such as poly(lactic-co-glycolic acid), poly(ethylene glycol) diacrylate/polyethylene oxide, gelatin methacrylate, and hyaluronic acid methacrylate for MEW applications, and develops new and suitable inks for MEW that will provide more and better choices for constructing a bioactive scaffold in future tissue engineering research. Experiments suggest that a printing ink should have low electrical conductivity, suitable viscosity, and high curing speed for realizing successful printing. [ABSTRACT FROM AUTHOR]

The electrostatic spray method is a promising nonvacuum technique for efficient deposition of thin films from solutions or dispersions. The multitude of electrostatic spray process parameters, including surface tension, viscosity, and conductivity of the liquid, applied voltage, nozzle size, and flow rate, make electrostatic spray deposition very versatile for the morphological engineering of nanostructured films. The current state‐of‐the‐art in electrostatic spraying can produce exceptional morphologies. Such tailoring of morphologies is notably useful in electrochemical applications where high electrolyte‐accessible surface area often improves performance. Interesting morphologies of metal oxides and their composites are highlighted, including nanopillars, nanoferns, and porous microspheres produced by electrostatic spraying to enhance energy conversion and storage performance. The physics associated with the electrostatic spray process and morphology control using it are also presented. The manuscript highlights the potential of electrospray processing for producing thin films of controlled microstructure, from ultrasmooth layers in organic photovoltaics and perovskite photovoltaics to hierarchical nanostructured films for anodes and photoanodes. It aims to help researchers appreciate essential aspects of electrostatic spray deposition efficiency, process control, and morphology engineering for energy conversion (e.g., solar cell, fuel cell, and photoelectrochemical cell) and energy storage (e.g., lithium‐ion battery and supercapacitor) electrodes. [ABSTRACT FROM AUTHOR]

We have studied the spatial distribution of charges trapped at the surface of superfluid helium in the inhomogeneous electric field of a metallic tip close to the liquid surface. The electrostatic pressure of the charges generates a deformation of the liquid surface, leading to a "hillock" (called "Taylor cone") or "dimple", depending on whether the tip is placed above or below the surface. We use finite element simulations for calculating the surface profile and the corresponding charge density in the vicinity of the tip. Typical electric fields E are in the range of a few kV/cm, the maximum equilibrium surface deformations have a height on the order of (but somewhat smaller than) the capillary length of liquid 4He (0.5 mm), and the maximum number density of elementary charges in a hillock or dimple, limited by an electrohydrodynamic instability, is some 1013 m−2. These results can be used to determine the charge density at a liquid helium surface from the measured surface profile. They also imply that inhomogeneous electric fields at a bulk helium surface do not allow one to increase the electron density substantially beyond the limit for a homogeneous field, and are therefore not feasible for reaching a density regime where surface state electrons are expected to show deviations from the classical behavior. Some alternative solutions are discussed. [ABSTRACT FROM AUTHOR]

High-voltage electric field-driven jet deposition technology is a novel high resolution micro scale 3D printing method. In this paper, a novel micro 3D printing method is proposed to fabricate wax micro-structures. The mechanism of the Taylor cone generation and droplet eject deposition was analyzed, and a high-voltage electric field-driven jet printing experimental system was developed based on the principle of forming. The effects of process parameters, such as pulse voltages, gas pressures, pulse width, pulse frequency, and movement velocity, on wax printing were investigated. The experimental results show that the increasing of pulse width and duration of pulse high voltage increased at the same pulse frequency, resulting in the micro-droplet diameter being increased. The deposited droplet underwent a process of spreading, shrinking, and solidifying. The local remelting and bonding were acquired between the contact surfaces of the adjacent deposited droplets. According to the experiment results, a horizontal line and a vertical micro-column were fabricated by adjusting the process parameters; their size deviation was controlled within 2%. This research shows that it is feasible to fabricate the micro-scale wax structure using high-voltage electric field-driven jet deposition technology.

The electrospray thruster relies on a large number of emission sites that simultaneously emit ions or charged droplets to generate thrust. The operation uniformity of the emission sites is of great significance to ensure the stable work of the thruster and improve its thrust level. However, there was little in-depth study of it before, especially of its influence on the thruster's characteristics. To this end, four porous electrospray thrusters with different degrees of non-uniform operation of emission sites were adopted, and their emission site distribution characteristics, volt-ampere characteristics, and current fluctuation characteristics were investigated. Emission site distribution of all thrusters showed a certain degree of unevenness. On their emission surfaces, there were some dark zones where few emission sites located on, highlight zones where emission sites were too concentrated, and intermediate zones where emission sites repeatedly appeared and disappeared. The appearance of a dark zone could cause a decrease in the growth rate of emitted current with voltage, and electric sparks that happened in the highlight zones could directly interrupt the operation of thrusters and suppress the increase of thrusters' thrust level. A periodic fluctuation, which should be caused by the flow rate difference between emission sites, emerged on the plume current of almost all thrusters. Various experimental results indicated that part of the liquid in high-flow-rate areas spread to low-flow-rate areas while the current fluctuated periodically. It could effectively reduce negative effects caused by the non-uniform operation of emission sites. The flow resistance of one of the four thrusters was greatly reduced. As a result, the operation uniformity of emission sites was greatly improved, but the overflow problem in high-flow-rate areas was exacerbated. • The evolution of the emission site array with voltage was obtained by collecting the emitted faint light. • A low-frequency periodic fluctuation of the plume current was discovered. • Properly reducing the flow resistance of the thruster can improve the operation uniformity of emission sites. • A mathematical model for volt-ampere characteristics of porous ES thrusters was derived. [ABSTRACT FROM AUTHOR]

In this study, the visualization of the flow inside a Taylor cone formed during an electrohydrodynamic (EHD) spraying is conducted to analyze its stability among five liquid candidates. A micro-PIV with a micro-nozzle is used for the visualization, and the physical properties as well as measured values are utilized in the analysis. First, in forming the Taylor cone, the electrohydrodynamic force is required to be sufficiently large in order to overcome the surface tension of the liquid. Thus, among the five liquids tested here, three, in this case IPA, EtOH, and MeOH, form a Taylor cone due to the relatively low surface tension levels as compared to the others. Once electrohydrodynamic jetting occurs, the average and maximum velocities become monotonically proportional to the average current. As the velocities are the smallest in using IPA, the circulation flow becomes superior to the extrusive flow, which yields the stable formation of a Taylor cone. Also, low fluctuation of the instantaneous currents supports the stable formation of IPA. Consequently, IPA shows the most stable formation of the Taylor cone in our condition due to the lowest average current and low-level surface tension. Eventually, micro-PIV would be a good tool in choosing an optimal fluid for stable EHD spraying. [ABSTRACT FROM AUTHOR]

A common method in the synthesis of functionalized carbon particles such as laser ablation of graphite required time and complicated method. Therefore, electrospraying method was used to synthesize functionalized candle soot particles. Electrospraying method uses electric force to produce monodispersed micro and nanoparticles. Thus, the flow rates and voltages were manipulated to investigate the size of functionalized soot particles and Taylor cone‐jet formation. In this study, soot was collected through direct burning of candles and functionalized with 1 M of nitric acid in 9 hr. The electrospray was set up at 27°C by applied high voltage 6.6 to 8.7 kV to the needle (23 G) with an internal diameter of 0.34 mm, aluminum foil as a collector, and tip to collector distance of 10 cm. The process parameters were manipulated by varying the flow rate from 0.3, 0.5, and 0.8 to 1.0 ml/hr. The functionalized soot particles size and morphology were examined using a digital microscope and processed using ImageJ software. The particles diameter increased from 1.23 up to 2.46 μm when the flow rate increased from 0.3 to 1.0 ml/hr. This is due to increase volume of solution ejected from the needle, which inhibits the solvent from evaporating. [ABSTRACT FROM AUTHOR]

This work aims at bridging experimental and numerical approaches to determine the optimal operating parameters for the fabrication of well-shaped polyvinylpyrrolidone (PVP) particles via electrohydrodynamic atomization. Particular emphasis is given to the role of the PVP solution viscosity. Solutions of PVP at various concentrations dissolved in Dimethylformamide (DMF) were prepared and analyzed. Numerical simulation using a coupled electro-CFD model was used to determine the ranges of experimental flow rate and the voltage, ensuring that well-shaped spherical particles are produced. It was deduced that the optimal combination of the parameters (flow rate, voltage, and polymer concentration) can be well approximated by a scaling law. The established relationship allowed determination of a stability island that guarantees that the given polymer solution will form spherical particles. Analyzing morphology and sizes of the particles manufactured in the optimal parameters range, we show, among others, that the size of the PVP particles can be predicted as a function of the flow rate by a power scaling relationship.

Since the introduction of electrostatic spray technology for several decades, it has been configured most frequently with a vertical discharge nozzle. With a recent expansion in application areas, electrostatic spray with a horizontal nozzle has been studied in a narrow range of low volumetric flowrates. In this study, a horizontal discharge nozzle with an upright collector plate is experimented in consideration of its application to electrostatic precipitators. Using a large volumetric flowrate at the scale of milliliters per minute, the operation modes with horizontal nozzle are observed with high-speed digital cameras under different test conditions of nozzle sizes, nozzle-to-plate distances, and volumetric flowrates. The operation modes were classified and compared with the conventional electrostatic spraying modes. From the experiment, it is found that the nozzle diameter and the volumetric flowrate influence the spraying pattern while the applied voltage and nozzle-to-plate distance have a more defined impact on the determination of the modes. A novel spray map diagram was provided according to Reynolds number and electric field intensity. This diagram will serve to predict which modes will occur at certain geometric and flowrate conditions. [ABSTRACT FROM AUTHOR]

Powderization of oils has been used as a method to enhance the stability of polyunsaturated fatty acids. Previously, we successfully powderized soybean oil via nozzleless electrostatic atomization. The process of nozzleless electrostatic atomization process was applied to the one‐step process of encapsulating oil in wall materials. The encapsulation of oils in powder is dependent on the wall materials. The present study aimed to resolve the behavior of oil encapsulated in particles using a novel method of electrostatic atomization, and to investigate the effect of wall materials on the oil content in the encapsulated formulations. The size of particles surrounding oil was dependent on the type of wall materials used for encapsulation, and the oil content within the encapsulation decreased with increase in particle size. Furthermore, wall materials with higher hydrophobicity increased the oil content within the encapsulation, as more hydrophobic particles could absorb the oil more effectively. Practical Application: Nozzleless electrostatic atomization is a new method for preparing encapsulation of oil using various wall materials. [ABSTRACT FROM AUTHOR]

A magnetic-field-assisted setup design is presented as effective and economical way to generate nanofibers with controlled fiber diameter and deposition region by changing the magnetic/electric field. The established analysis model of this multidisciplinary design offers in-depth insight into physical understanding of many complex phenomena combining experiment results and theoretical models. • A magnetic-field-assisted setup was developed to control electrospinning process. • An analytical model based on Maxwell's theory was developed on the basis of magnetic field intensity. • The instability and fiber generation can be controlled applying helix tube. Electrospinning technology is taken as the most versatile process to generate continuous nanofibers. However, effects should be taken to achieve better understanding and precisely control the actual mechanics in the formation of nanofibers through better system design. In this article, the diameter and the deposition area of the as-prepared nanofibers can be controlled by added helix tube which can provide external electric-magnetic field. The spinning process can be controlled employing a magnetic flux (B) analytical model which is based on the magnetic field calculation model of the solution and the electrostatic charge repulsion in the jet. This method includes the thermo-mechanical properties based on as-prepared electrospun nanofiber films and the capability of tribology-mechanical and mathematical physics. A novel investigation of the whole output increase at per unit spinning area is presented in this article to describe the whipping instability which is an important feature of the Taylor Cone phenomenon. The present design and process for electrospinning are based on a solution differential calculus, which a single stainless steel spinning nozzle can generate multi-squirt flow. With the purpose of providing useful jet initial behaviour design for the further technology applications, we attempt to set up a differential calculus method with evenly distributed circumferential electric field, yet giving more design guidance to produce controllable nanofibers through magnetic-field-assisted electrospinning technology. [ABSTRACT FROM AUTHOR]

The Taylor cone formed at the tip of the syringe used for delivering the solution plays an important role in jet formation. This study presents a novel multiphysics model to simulate the dynamic processes occurring within the cone jet from a flat spinneret and a single needle spinneret. The electric field, volume fraction and velocity magnitude of the polymer jet ejecting from two different kinds of spinnerets are calculated by the multiphysics simulation model. A high-speed camera is employed to capture the jet formed by the Taylor cone. The simulation results are validated by comparison with experimental results. It is found that the spinneret configuration could be the key factor in determining cone morphology in the electrospinning process. [ABSTRACT FROM AUTHOR]

Abstract Many oil-encapsulation techniques, in which particles are used to improve the stability of polyunsaturated fatty acids (PUFAs) against oxidation and the handling of oils, have been reported. We developed techniques for encapsulating oil within powders with a liquid–liquid interfacial crystallization by using nozzleless electrostatic atomization. This process was used to prepare fine spherical encapsulated soybean oil particles with a microscale single process. An inexpensive soybean oil containing PUFAs was chosen as the oil phase. W/O emulsion systems were synthesized via the electrostatic atomization process. After the W/O emulsions were prepared, glycine and taurine well provided in supplements were used as the wall material for encapsulation. The soybean oil content of the encapsulated particles and their stability at high temperatures were evaluated. The oxidative stability of the soybean oil during high-temperature storage was improved for the encapsulation. Highlights • Glycine and taurine can encapsulate oils via nozzleless electrostatic atomization. • The size of the encapsulated particles is dependent on the wall material. • The oxidation stability of the soybean oil is improved by encapsulation. [ABSTRACT FROM AUTHOR]

Electrosprayed polycaprolactone (PCL) microparticles are widely used in medical tissue engineering, drug control release delivery, and food packaging due to their prominent structures and properties. In electrospraying, the selection of a suitable solvent system as the carrier of PCL is fundamental and a prerequisite for the stabilization of electrospraying, and the control of morphology and structure of electrosprayed particles. The latter is not only critical for diversifying the characteristics of electrosprayed particles and achieving improvement in their properties, but also promotes the efficiency of the process and deepens the applications of electrosprayed particles in various fields. In order to make it systematic and more accessible, this review mainly concludes the effects of different solution properties on the operating parameters in electrospraying on the formation of Taylor cone and the final structure as well as the morphology. Meanwhile, correlations between operating parameters and electrospraying stages are summarized as well. Finally, this review provides detailed guidance on the selection of a suitable solvent system regarding the desired morphology, structure, and applications of PCL particles. [ABSTRACT FROM AUTHOR]

Electrospinning is a modern and versatile method of producing nanofibers from polymer solutions or melts by the action of strong electric fields. The complex, multiscale nature of the process hinders its theoretical understanding, especially at the molecular level. The present article aims to contribute to the fundamental picture of the process by the molecular modeling of its nanoscale analogue and complements the picture by laboratory experiments at macroscale. Special attention is given to how the process is influenced by ions. Molecular dynamics (MD) is employed to model the time evolution of a nanodroplet of aqueous poly(ethylene glycol) (PEG) solution on a solid surface in a strong electric field. Two molecular weights of PEG are used, each in 12 aqueous solutions differing by the weight fraction of the polymer and the concentration of added NaCl. Various structural and dynamic quantities are monitored in production trajectories to characterize important features of the process and the effect of ions on it. Complementary experiments are carried out with macroscopic droplets of compositions similar to those used in MD. The behavior of droplets in a strong electric field is monitored using an oscilloscopic method and high-speed camera recording. Oscilloscopic records of voltage and current are used to determine the characteristic onset times of the instability of the meniscus as the times of the first discharge. The results of simulations indicate that, at the molecular level, the process is primarily driven by polarization forces and the role of ionic charge is only minor. Ions enhance the evaporation of solvent and the transport of polymer into the jet. Experimentally measured instability onset times weakly decrease with increasing ionic concentration in solutions with low polymer content. High-speed photography coupled with oscilloscopic measurement shows that the measured instability onset corresponds to the formation of a sharp tip of the Taylor cone. Molecular-scale and macroscopic views of the process are confronted, and challenges for their reconciliation are presented as a route to a true understanding of electrospinning.

A simplified Eulerian model for the description of steady state electric charge dispersion in vacuum, including space-charge effects, is introduced. The model is based on a potential velocity field for the charged particles, which is valid if all the particles are emitted with the same kinetic plus potential energy. Despite the high simplicity of the present model, the mathematical system still encompasses several types of singularities, which are analyzed here in full detail, thus enabling the numerical solution of the system. The model is applied to the description of electrospray emission in vacuum, in the limit of high electric conductivity liquids, assuming that all particles are emitted with zero initial velocity. Our main result in this regard is a relation existing between the cone semiangle α and the electrospray beam angular width. In particular, we show that the cone semiangle can only take values between a minimum angle ca. 21.89 deg, and a maximum value given by Taylor's angle (ca. 49.29 deg), with lower values of α corresponding to wider beams, while higher values of α correspond to narrower beams. [ABSTRACT FROM AUTHOR]

This paper summarizes the design and construction of an adaptable electrospinner capable of spinning fluids over a large range of viscosities. The design accommodates needless electrospinning technologies and enables researchers to explore a large range of testing parameters. Modular parts can be exchanged for alternative versions that adapt to the research question at hand. A rotating drum electrode immersed halfway into a solution bath provides the liquid film surface from which electrospinning occurs. We tested and assessed several electrode designs and their electrospinning performance at higher (< 500 poise) viscosities. Relative humidity was found to affect the onset of electrospinning of highly viscous solutions. We demonstrate robust device performance at applied voltage up to 90 kV between the electrospinning electrode and the collector. Design and fabrication aspects are discussed in practical terms, with the intent of making this device reproducible in an academic student machine shop.

The concrete relationship between the process parameters and nanoproduct properties is an important challenge for applying nanotechnology to produce functional nanomaterials. In this study, the relationships between series of process parameters and the medicated nanofibers’ diameter were investigated. With an electrospinnable solution of hydroxypropyl methylcellulose (HPMC) and ketoprofen as the core fluid, four kinds of nanofibers were prepared with ethanol as a sheath fluid and under the variable applied voltages. Based on these nanofibers, a series of relationships between the process parameters and the nanofibers’ diameters (D) were disclosed, such as with the height of the Taylor cone (H, D = 125 + 363H), with the angle of the Taylor cone (α, D = 1576 − 19α), with the length of the straight fluid jet (L, D = 285 + 209L), and with the spreading angle of the instable region (θ, D = 2342 − 43θ). In vitro dissolution tests verified that the smaller the diameters, the faster ketoprofen (KET) was released from the HPMC nanofibers. These concrete process-property relationships should provide a way to achieve new knowledge about the electrostatic energy-fluid interactions, and to meanwhile improve researchers’ capability to optimize the coaxial process conditions to achieve the desired nanoproducts.

Electrosprayed polycaprolactone (PCL) microparticles are widely used in medical tissue engineering, drug control release delivery, and food packaging due to their prominent structures and properties. In electrospraying, the selection of a suitable solvent system as the carrier of PCL is fundamental and a prerequisite for the stabilization of electrospraying, and the control of morphology and structure of electrosprayed particles. The latter is not only critical for diversifying the characteristics of electrosprayed particles and achieving improvement in their properties, but also promotes the efficiency of the process and deepens the applications of electrosprayed particles in various fields. In order to make it systematic and more accessible, this review mainly concludes the effects of different solution properties on the operating parameters in electrospraying on the formation of Taylor cone and the final structure as well as the morphology. Meanwhile, correlations between operating parameters and electrospraying stages are summarized as well. Finally, this review provides detailed guidance on the selection of a suitable solvent system regarding the desired morphology, structure, and applications of PCL particles.

The influence of the conductivity of a water droplet formed at a capillary electrode on the negative corona discharge and production of nano-sized droplets was investigated. Conductivity of a water droplet was adjusted from 1 μS/cm of deionized water to 48 mS/cm of nitric acid water solution. The size distribution of nanometer sized water particles yielded at a disruption of a Taylor cone was measured. The higher conductivity of a droplet, the larger corona pulses appeared and the more number of charged droplets was generated. [ABSTRACT FROM AUTHOR]

In this study, a new electrostatic field–induced electrolyte jet electrical discharge machining method has been proposed, which can automatically generate the tool electrode. Then, a series of experiments have been carried out to reveal the machining mechanism and test the machining ability of this method. The continuous observation experiments and the online current detection experiments have demonstrated that the electrolyte jet discharge machining is a pulsing, dynamic and cyclic process. Moreover, the 20-min time long reverse polarity experiments on the silicon surface have revealed that the machining is an electrical discharge machining process during the negative polarity machining; however, in the positive polarity machining, it is a hybrid electrical discharge machining and electrochemical machining process. Furthermore, the craters as small as 2 µm in diameter on stainless steel and silicon are produced by this electrolyte jet electrical discharge machining, which has proved the micro-machining ability of this method. [ABSTRACT FROM AUTHOR]

In recent years, the application of natural/synthetic based nanofibers in different industries such as textile, environmental engineering, biomedical engineering, energy and electronics have been the subject of many researches. This is particularly due to their unique properties (particularly high surface-to-volume ratio that is approximately 1,000 times more than that of human hair). Electrospinning is a straightforward and promising technique used to fabricate ultrafine quality of continuous nanofibers within a diameter range of 20-1000 nm. As a customary setup for electrospinning, a high potential electrical field is applied to the emerging solution at the spinneret nozzle tip for transforming the jet into the nanofibers. Electrospinning can be employed in a laboratory as well as in industries when expanded. Obviously, the process/system parameters involved influence the structural and mechanical properties of electrospun nanofibers. The microstructure of nanofibers and subsequently the macro-properties of electrospun mats can be modified by varying the parameters involved in electrospinning process. The fabricated electrospun mats are interconnected, non-woven nanofibers deposited over the collector surface. High porosity, remarkable mechanical properties such as an elastic modulus within the MPa/GPa range and capacity to be formed into a variety of shapes are the other properties of electrospun nanofibers. Co-axial electrospinning is an advanced method of electrospinning where a dual nozzle spinneret is used for fabricating a core/shell structure of nanofibers. Any conductive polymer solution can be used as the shell for any other conductive polymer solution or nanoparticles depending on the application. This review of an electrospinning technique provides detailed information on the background of electrospinning, fundamental principles and theory, investigation on parameters involved in nanofibers' structural/biological/mechanical characteristics, advantages of superb properties and biomedical applications of electrospun nanofibers, particularly in tissue engineering heart valves. In addition, the reasons for common instabilities, which result in the failure of Taylor cone formation and subsequently the failure of fiber production, are also explained. [ABSTRACT FROM AUTHOR]

In the present experimental study, the effects of electrical conductivity on electrospraying modes and its produced droplets are investigated. A metallic nozzle with 0.6 mm ID as high voltage electrode were employed in a point to ring electrode configuration in this work. Experiments were carried out in still room temperature. Four different aqueous KCl solutions were sprayed in various high voltages and flow rates. Results confirmed that spraying modes are more dependent on electrical conductivity rather than flow kinetics. Applied electrical field required to form a cone shape on the nozzle tip decreases with increasing conductivity. Moreover, results revealed that electrical conductivity of dispersed solution plays a decisive role on elongation of the cones in ES procedure. Smaller size of produced droplets was obtained by increasing conductivity of dispersed liquid while velocity of filaments emanated from liquid jet decreases at the same time. In this study, we have presented insight to the role of physicochemical properties on the pulsating modes of spraying. [ABSTRACT FROM AUTHOR]

Low-frequency oscillations occurring in the electrospray of liquids with low electric conductivity were studied. Based on spectral measurements of oscillations in the range of voltages typically used in mass spectrometry, it was shown that the spectrum reveals the control frequency, which accounts for ≈80% of power oscillations, and a set of overtones. The magnitude of the main frequency varies in the range 200-800 Hz and increases with increasing voltage up to breakdown. Immediately after the collapse of oscillations, the most stable spraying mode is realized. A model describing the mechanism of oscillations due to the role of space charge accumulated on the counter electrode was proposed. [ABSTRACT FROM AUTHOR]

Electrospinning is always used to fabricate one-dimensional nanofibers. Cylindrical fibers are formed during the spinning process due to the minimal-surface principle. However, when the moving jet has high rigidity, which can counteract the surface tension for a minimal surface, beltlike fibers can be obtained. Using the Hall–Petch effect, the rigidity of the moving jet can be greatly enhanced by adding nanoparticles. Polyethylene glycol with a nanometric crystallite size of 4 nm and ZrO2 nanoparticles are used as additives in the experiment, a theoretical analysis is carried out, and the theoretical predictions are verified experimentally.

Formation of a stable Taylor cone is an important phenomenon during electrospinning of nanofibers for controlling nanofiber properties. Optimizing electrospinning process parameters such as solution feed rate, applied electric voltage and tip to mandrel distance, a stable Taylor cone can be achieved and by maneuvering the parameters within a certain range, the height of the cone can be controlled. Here, we study the influence of the process parameters on the height of the Taylor cone and the corresponding nanofibers produced for polyvinylidene fluoride (PVDF) using dimethylformamide (DMF) as solvent. Characterization of the produced fibers and image analysis confirmed the optimal values as 1 mL/h, 10.8 kV and 10 cm for feed rate, applied voltage and spinning distance, respectively. Observations from the study reveal that contrary to proportional variation of Taylor cone height with nanofiber diameter in case of changing feed rate and applied voltage, the relationship gets inversely proportional when tip to mandrel distance is varied. [Display omitted] • Investigates the effect of electrospinning process parameters on Taylor cone and nanofiber diameter to establish relationships between them. • At optimized values of voltage, feed rate and spinning distance are10.8 kV, 1 mL/h and 10 cm, respectively, nanofiber diameter and stable TC height are 257.4 ± 3.5 nm and 907.1 μm, respectively, for 18 wt% PVDF. • TC height varies proportionately with nanofiber diameter for changing feed rate and applied voltage but inversely with spinning distance. [ABSTRACT FROM AUTHOR]

Molecular modeling has revealed that the presence of charged macromolecules (macroions) in liquid droplets dramatically changes the pathways of droplet fission. These mechanisms are not captured by the traditional theories such as ion-evaporation and charge-residue models. We review the general mechanisms by which macroions emerge from droplets and the factors that determine the droplet fission. These mechanisms include counter-intuitive “star” droplet formations and extrusion of linear macroions from droplets. These findings may play a direct role in determining macromolecule charge states in electrospray mass spectrometry experiments. [ABSTRACT FROM AUTHOR]

This investigation addresses concerns in micro-electrical discharge machining (EDM) such as high tool electrode preparation cost, tool electrode wear, and tool electrode compensation by proposing a new electrostatic field-induced electrolyte jet tool electrode. This method utilizes the theory that in a strong direct current electric field, the electrolyte at the capillary tube outlet can form a Taylor cone based on the balance of electric field force and surface tension. Coupled with the increase of electric field intensity, a very fine jet can eject from the tip of the Taylor cone, and this induced charge on the tip leads to a discharge to the workpiece which can remove debris from the workpiece surface. After the discharge, the induced charge at the tip is neutralized, leading to the surface tension outweighing the electric field force and the withdrawal of the fine jet. As a result, the cyclic pulse discharge process is generated. During the process, the tip of the fine jet serves as the tool electrode. This paper identifies this cyclic pulse electrolyte jet tool electrode generation and discharge process in action and tests the machining ability of this tool electrode on a silicon wafer. This electrolyte jet tool is also shown to have no wear or compensation issues, and the cost compared to conventional EDM is shown to be small. [ABSTRACT FROM AUTHOR]

A brief literature review is given of studies concerning the method of standard electrospinning, which is used for producing long nanofibers. Experimental setups - the first version and the new, modified pulse electrospinning setup - are described. The results of works on producing short fibers using pulse electrospinning are reported in the present article. Data on short fibers produced experimentally from such polymers as polymethyl methacrylate and cellulose acetate are presented. [ABSTRACT FROM AUTHOR]

The phenomenon of electrospraying of liquids is presented from the perspective of the electrochemistry involved. Basics of current and liquid flow in the capillary and spray tip are discussed, followed by specifics of charging and discharging of the sprayed liquid surface. Fundamental theories and numerical modeling relating electrospray current to solution and spray parameters are described and then compared with our own experimentally obtained data. The method of mapping potentials and currents inside the electrospray capillary by using an inserted electrically-isolated small wire probe electrode is discussed in detail with illustrations from new and published data. Based on these experimentally obtained results, a new mathematical model is derived. The introduced 'nonlinear resistor electrospray capillary model' divides the electrospray capillary into small sections, adds their contributions, and then, by transition to infinitely small section thickness, produces analytical formulas that relate current and potential maps to other properties of the electrospraying liquid: primarily conductivity and current density. The presentation of the model is undertaken from an elementary standpoint, and it offers the possibility to obtain quantitative information regarding operating parameters from typical analytical systems subjected to electrospray. The model stresses simplicity and ease of use; examples applying experimental data are shown and some predictions of the model are also presented. The developed nonlinear resistor electrospray capillary model is intended to provide a new quantitative basis for improving the understanding of electrochemical transformations occurring in the electrospray emitter. A supplemental material section gives full derivation of the model and discusses other consequences. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Direct ESI-MS of proteins in nonvolatile buffer requires the generation of very fine initial droplets to resolve the peak for meaningful analysis. This is usually achieved using nanoESI capillary with an inner diameter of ∼1 μm or smaller. Recently we reported the generation of "true nanoelectrospray" from a micropipette tip with a large inner diameter under the super-atmospheric pressure condition (J. Am. Soc. Mass Spectrom. 2022 , 33 , 491–498). The flow rate in the nL/min regime can be reproducibly adjusted using high voltage with the spray current as the indicator for flow rate. Here two further works are done on the same ion source. First, the validation of the spray current-flow rate relationship has been extended to 0.5 MPa, and the achievable minimum spray current is found to reduce with the ion source pressure. Second, the ion source is applied to study the flow rate effect on the charge state distribution in the nanoflow regime for proteins and peptides in volatile (formic acid and ammonium acetate) and the nonvolatile (phosphate buffer saline (PBS) and 1 M Tris-HCl) buffers. For the nonvolatile buffers, clean nanoESI mass spectra are only obtained at a low flow rate of ∼1 nL/min. The average charge state of the tested proteins is primarily determined by the type of buffer. For acidic solutions, the charge state shifts to a higher value at a lower flow rate. For non-denaturing solutions, the average charge number remained relatively constant but the variation with the flow rate appeared to be analyte and buffer dependent. [Display omitted] • Ultra-low-flow rate nanoESI operation using a disposable micropipette tip. • Q 1/2 scaling law validated down to nL/min flow regimes. • Direct detection of proteins from high-salt buffers. • Fine-tuning of flow rate to study CSD without changing capillary. [ABSTRACT FROM AUTHOR]

Many devices can be produced in micro, even nano scales with the aid of MEMS technology. These devices' requirements are associated with their respective dimensions. For example, required thrust for the orbital control of a nano satellite is in the order of millinewtons, or the required droplet size for operating a small combustion system is only in the order of a few microns. These requirements dictate old methods to be put aside. Nevertheless, electrospray technique is quite suitable for such applications. This is a unique technique in the sense that it provides equal droplet size distribution at very low flow rates. Thus, electrospray injection is a rather proper choice for liquid hydrocarbon atomization in miniature energy conversion devices. In this study, electrospray theory is briefly described, and then design and characterization of an electrospray system presented and the effect of extractor electrode on electrospray behavior is discussed. Methanol and ethanol are used as dielectric liquids in the experiments. Glass capillary tube and insulin needle were used as conduits for electrospray injection with their respective radiuses of 0.1 mm and 0.23 mm respectively. Ratio between the liquid extractor voltages can be adjusted by means of a rheostat. Various extractor radius values and different extractor to capillary distances are examined during parametric study. Starting and ending voltages are measured for 3 mm and 3.8 mm extractor radius values. At the ending voltage the conical form of electrospray injection is altered such that the electrospray is not able to flow regularly. Starting and ending voltages increase in direct proportion to the increase of extractor to liquid voltage ratio. These results are consistent with the theory. Besides, measured starting voltage is quite similar to the calculated value. Only starting voltage was measured for 5.2 mm extractor radius. These results can be utilized for the design of multiplexed array of fuel emitters. Especially, ending voltage values provide an idea to designer in terms of maximum hole diameter on the extractor ring, which could be used in multiplexed electrospray systems. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Textiles & Engineers / Tekstil ve Mühendis is the property of Union of Chambers of Turkish Engineers & Architects, Chamber of Textile Engineers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Highlights: [•] We studied the W/O interface different regimes in vertical electric field. [•] 4 distinct regimes are revealed during the study. [•] Discharge velocity and droplets’ size distribution emanated from cone are studied. [•] For the first time, the Taylor cone merging on the interface is reported. [•] The circumstances of emerging another Taylor cone on the interface are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Corona discharge from a fine water droplet always involves deformation of the droplet shape or Taylor-cone formation, emission of fine water jets or disruption of droplet. Therefore, corona discharge from a water droplet always manifests complicated aspects. In addition, disruption of Taylor cone simultaneously affects not only discharge current but also motion of water droplet. To confirm corona discharge phenomena from a water droplet protruded from a tip of a metal capillary tube with a diameter of 1 mm, negative corona discharge was investigated by using a water droplet located at a tip of grounded rod electrode facing a ring electrode with positive dc voltage superimposed by ac one. Since the droplet has inherent resonant vibrating frequency defined by the size or volume, the volume of water droplet was adjusted at 20 nL where the corresponding resonant frequency was 500 Hz. The period of the event of successive corona discharge is exactly consistent with resonant frequency defined by the size of the water droplet. As a result, corona pulse trains with a definite duration appeared intermittently corresponding to its resonant vibration. When dc voltage superimposed by ac voltage with resonant frequency of 500 Hz was applied to the water droplet, corona pulse trains appeared at the period corresponding to the frequency. The maximum value of corona current reasonably increased with the applied voltage. Even when the frequency of ac field superimposed on dc field was varied from the resonant frequency, corona pulse trains occur corresponding to not only the superimposed field frequency but also resonant frequency. [Copyright &y& Elsevier]