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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.

The combustion characteristics of nanofluid fuels have been widely investigated, but rare studies on the atomization were reported. Atomization is an imperative and crucial step to improve the combustion performance of nanofluid fuels, and the secondary breakup of droplets is an important segment for atomization to produce uniform fine droplets and distribute nanoparticles in each droplet. This paper firstly presents the secondary breakup characteristics of single electrified Al/n-decane nanofluid fuel droplets and revealed the mechanism of the secondary breakup. The results demonstrated that fine droplets could be produced in the electrostatic field and Al nanoparticles were distributed in each droplet. Before the breakup, the single electrified droplets experienced surface charge transportation, deformation, and Taylor cone formation. A gradient of the electric field deformed the droplet to produce the Taylor cone. As the Taylor cones were stabilized, the fluid was extruded from the tips of stable Taylor cones to produce jet filament parallel to the electric field direction and correspondingly broke up into fine sub droplets. At the nanoparticle concentration range of 1.0~10 mg/mL, the minimum average diameter of breakup sub droplets could achieve ~55.4 &mu, m at 6.0 mg/mL. The Al nanoparticle concentration had a significant effect on the breakup performance by influencing the physical properties and charging. The order of the Charge-to-Mass ratio magnitude was 10&minus, 7~10&minus, 5 C/kg. Furthermore, the secondary breakup mechanism of single electrified nanofluid fuel droplets in the uniform electrostatic field was revealed by analyzing the droplet surface charge, deformation, Taylor cone formation, and nanoparticle concentration effect.

Particulate matter (PM) pollution has become a serious public health issue, especially with outbreaks of emerging infectious diseases. However, most present filters are bulky, opaque, and show low‐efficiency PM0.3/pathogen interception and inevitable trade‐off between PM removal and air permeability. Here, a unique electrospraying–netting technique is used to create spider‐web‐inspired network generator (SWING) air filters. Manipulation of the dynamic of the Taylor cone and phase separation of its ejected droplets enable the generation of 2D self‐charging nanostructured networks on a large scale. The resultant SWING filters show exceptional long‐range electrostatic property driven by aeolian vibration, enabling self‐sustained PM adhesion. Combined with their Steiner‐tree‐structured pores (size 200–300 nm) consisting of nanowires (diameter 12 nm), the SWING filters exhibit high efficiency (>99.995% PM0.3 removal), low air resistance (82%), and remarkable bioprotective activity for biohazard pathogens. This work may shed light on designing new fibrous materials for environmental and energy applications., A spider‐web‐inspired network generator (SWING)‐based air filter constructed from 2D electrostatic nanostructured networks is created by a unique electrospraying–netting technique. Due to the self‐sustained electrostatic adhesion driven by aeolian vibration and Steiner‐tree‐structured pores (size 200–300 nm) consisting of nanowires (diameter 12 nm), the SWING filters achieve >99.995% PM0.3 removal, 82% transmittance, and remarkable bioprotective activity.

Taylor cone can be easily observed in the electrospinning process, and its height can be used to control the fiber diameter. This paper gives a theoretical analysis of the relationship between the cone height and fiber diameter.

Water electrospray in the cone jet mode was performed by a polymer micro-atomizer. A high aspect ratio dielectric polymer micro-nozzle and an in-plane extractor were proposed to concentrate the electric field at the tip of the micro-nozzle, which prevent electrical discharge caused by the high surface tension of water. The effect of the in-plane extractor was confirmed by electric field simulation and electrospray experiment. A micro-pillar array was also proposed to prevent surface wetting of the polymer micro-atomizer during the electrospray. Water electrospray of the polymer micro-atomizer was operated in a flow rate of 0.15–0.30 ml/h with a voltage of 1.5–3.0 kV, −2.0 kV, and −4.0 kV at water, a guide ring, and a collector, respectively. The key features of the cone jet mode such as Taylor cone, jet, and water micro-droplets were visualized by using nanosecond pulsed laser illumination.

Electrospinning has been known for its’ ability in producing nanoporous fibres which uses electrical force to form a spinning jet out of a polymer solution. The electrospinning condition and polymer solution properties can influence the electrospinning jet formation as well as jet path. Polylactic acid (PLA) was dissolved in dimethylformamide (DMF) to produce a polymer solution. Bead is considered as a defect towards an electrospun fibres, yet previous study found that PLA/DMF produced beaded fibres for all concentrations. However, there is a limited study that explain the effect of concentration on the diameter of beads. Therefore, in this study we investigated the formation of electrospinning jet as well as the effect of PLA concentration of formation of beads, particularly the diameter of the beads. Polymer solution with different concentration was prepared. The concentration investigated in this study were 7.5, 10, 12.5, 15, 17.5, and 20 % w/v. Polymer solution was then subjected to the electrospinning process to evaluate the morphology of the electrospun produced via optical microscope. Simultaneously, the formation of electrospinning jet is observed with portable digital microscope. The morphology of the electrospun fibres, especially the fibre and bead diameter are analyzed using image analysis software, ImageJ. From this research, it is found that at voltage of 10 and 12.8 kV, a stable electrospinning jet can be formed which consists of ‘Taylor cone’, straight jet, and plume. Concentration from 7.5–20 % w/v were able to form electrospun fibres, yet only 12.5 and 15 % w/v PLA concentrations can produce an effective electrospun fibres with beads diameter of 3393 nm and 3642 nm, respectively. Also, the number of beads for both concentrations are 34 and 19, respectively. Since the main criteria in producing electrospun fibres is no beads or small and minimal beads at best, therefore 12.5 and 15 % w/v PLA concentration are considered as efficient electrospun fibres.

In this work, the effect of changing the spatial electric potential to the spray current and the threshold voltage in the single Taylor cone–jet mode of the electrospray deposition (ESD) process has been investigated. The spatial electric potential between a nozzle electrode and a counter electrode was deformed by using an additional ring-shaped ternary electrode. The voltage ranges of the stable single Taylor cone–jet were determined from the current–voltage (I–V) characteristics of the system. Depending on the changes occurring in the spatial electric potential around the nozzle electrode, a shift of the threshold voltage to form a stable single Taylor cone–jet was clearly observed. For further investigation, the spatial electric potential and electric-field lines were analyzed by numerical simulations based on the computational finite element method. The deformation of the electric-field lines between the nozzle and counter electrodes implies a lack of droplet adhesion onto the ternary ring electrode and a focus of electrospray. Finally, we demonstrated the ESD of polymer materials with an area of 371 ± 160 mm2 at a deposition rate of 314 ± 73 nm/min. The ESD technique is an important additive surface-modification method that is applicable to a variety of materials and suitable for highly viscous solutions and fragile biological samples.

The instability of an electrolyte surface to a high-frequency, 10 to 200kHz, electric field, normal to the interface is investigated theoretically. From a practical viewpoint, such a high frequency leads to the absence of undesired electrochemical reactions and provides an additional control parameter. The theory of unsteady electric double layer by Barrero and Ramos is exploited. At such a high frequency, which is much larger than the eigenfrequency of the mechanical system, the nonlinear mechanical term does not "feel" the fast part of the Coulomb force, but it feels its slower component. In fact, the system behaves as if the electric field were a DC field. The observed instability is qualitatively close to the Tonks-Frenkel instability. The problem of the linear stability of the 1D quiescent stationary solution is solved analytically. For the important limiting cases, simple analytical formulas are derived. The linear stability analysis is complemented by the DNS of the full nonlinear system of equations with broadband low-amplitude white-noise initial conditions. After a transition period, the linear instability mechanism filters out the broad spectrum except for a narrow band near the maximum growth rate in rather good agreement with the linear stability analysis. If the external field is large enough, the nonlinear evolution results in coherent structures with sharp tips resembling to a Taylor cone. An evaluation of the cone angle for different conditions gives its value of about 30° to 60° , which is smaller than the angle of 98.6° for DC field and qualitatively corresponds to the experiments (L.Y. Yeo et al., Phys. Rev. Lett. 92, 133902 (2004)) for the high-frequency AC field and to the theoretical evaluation of the AC Taylor cones in E.A. Demekhin et al., Phys. Rev. E 84, 035301(R) (2011).

In this paper, we report an interesting bubble melt electrospinning (e-spinning) to produce polymer microfibers. Usually, melt e-spinning for fabricating ultrafine fibers needs &ldquo, Taylor cone&rdquo, which is formed on the tip of the spinneret. The spinneret is also the bottleneck for mass production in melt e-spinning. In this work, a metal needle-free method was tried in the melt e-spinning process. The &ldquo, was formed on the surface of the broken polymer melt bubble, which was produced by an airflow. With the applied voltage ranging from 18 to 25 kV, the heating temperature was about 210&ndash, 250 &deg, C, and polyurethane (TPU) and polylactic acid (PLA) microfibers were successfully fabricated by this new melt e-spinning technique. During the melt e-spinning process, polymer melt jets ejected from the burst bubbles could be observed with a high-speed camera. Then, polymer microfibers could be obtained on the grounded collector. The fiber diameter ranged from 45 down to 5 &mu, m. The results indicate that bubble melt e-spinning may be a promising method for needleless production in melt e-spinning.

E-jet printing is a new type of micro-nano printing technology that has developed rapidly in recent years. It has advantages of high precision, wide printing materials, and simple structure. Nozzle based on structure can be divided into conductive nozzles and insulated nozzles. When conductive nozzle is applied with a high potential, it will generate electric corrosion around nozzle, destroying its nozzle structure. And corrosion will not happen to insulated nozzle, but insulating nozzle have a complex structure, which is cumbersome to manufacture with high experimental costs. In this paper, the numerical simulation of the E-jet forming state of insulating nozzle structure is carried out, and the jet-forming law of the E-jet printing under insulating nozzle structure is investigated. A two-dimensional axisymmetric Maxwell stress tensor is used to represent the electric field force and added to the N-S equation as a volume force. The phase field method is used to track the liquid-gas interface and calculate the surface tension. The finite element method is used to solve the problem. The results show that the jet forming law of insulating nozzles has the same trend of voltage and inlet pressure as that of conductive nozzle, but the jet forming time are smaller than that of conductive nozzle. Therefore, the use of insulating nozzle can improve the speed and stability of jet forming.

We present basic experimental data and the theoretical background of a novel technique for fiber spinning from polymer solutions. The principal feature of the advanced process is realization of phase separation with detachment of a solvent, accompanied by the orientation of macromolecules, under the action of high extension rates. This is similar in some respects to dry spinning, though the driving force is not diffusion with subsequent evaporation of a solvent but redistribution of polymer-solvent interactions in favor of polymer-polymer and solvent-solvent ones governed by mechanical stresses. A promise of this approach has been demonstrated by experiments performed with polyacrylonitrile solutions in different solvents and solutions of the rigid-chain aromatic polyamide. We examined mechanotropic fiber spinning in model experiments with stretching jets from a drop of polymer solution in different conditions, and then demonstrated the possibility of realizing this process in the stable long-term continuous mode. During extension, phase separation happens throughout the whole section of a jet, as was confirmed by visual observation. Then a solvent diffuses on a jet surface, forming a liquid shell on the oriented fiber. Instability of this cover due to surface tension leads either to formation of separate solvent drops &ldquo, seating&rdquo, on the fiber or to the flow of a solvent down to the Taylor cone. The separate liquid droplets can be easily taken off a fiber. The physics underlying this process is related to the analysis of the influence of macromolecule coil-to-stretched chain transition on the intermolecular interaction.

The behavior of a conducting droplet and a dielectric droplet placed under an electric potential is analyzed. Expressions for drop height based on electrode separation and the applied voltage are found, and problem parameters associated with breakup and droplet ejection are classified. Similar to previous theoretical work, the droplet interface is restricted to an ellipse shape. However, contrary to previous work, the added complexity of the boundary condition at the electrode is taken into account. To gain insight into this problem, a two-dimensional droplet is addressed. This allows for conformal maps to be used to solve for the potential surrounding the drop, which gives the total upward electrical force on the drop that is then balanced by surface tension and gravitational forces. For the conducting case, the maximum droplet height is attained when the distance between the electrode and the drop becomes sufficiently large, in which case, the droplet can stably grow to about 2.31 times its initial height before instabilities occur. In the dielectric case, hysteresis can occur for certain values of electrode separation and relative permittivity.

We developed a low acceleration voltage X-ray microscope with a Li/W emitter. The Li/W emitter with Taylor cone has high angler current density and high total emission. An electron beam from emitter was focused by an electrostatic lens of two electrodes and an objective magnetic lens. At an acceleration voltage of 12 kV, X-ray intensity and spatial resolution of X-ray images were 10 μ Gy/min and better than 10 μ m, respectively. The spatial resolution is limited by the electron probe size on a target for X-ray excitation.

As a contribution to the feasibility of high-throughput electrospinning, here we report on the investigation into the production of polymer nanofiber mats through needleless electrospinning. For this study, we used poly(caprolactone) (PCL), poly(lactic acid) (PLA) and poly(vinyl alcohol) (PVA), widely used polymers in the field of electrospinning. Optimization studies were carried out to devise the characteristics of the rotating-disk electrospinning system in order to assess the processing window for each polymer. Other factors were also considered, where the production rate, fiber size distribution, and morphology of the specimens acquired by rotating-disk electrospinning and conventional electrospinning techniques were compared. Our studies also illustrate the similarities of this novel “bottom-up” process compared to the conventional one, where a high resolution image confirmed the formation of a cone-jet structure and a Taylor Cone.

High-efficiency production of nanofibers is the key to the application of electrospinning technology. This work focuses on multi-jet electrospinning, in which a threaded rod electrode is utilized as the needless spinneret to achieve high-efficiency production of nanofibers. A slipper block, which fits into and moves through the threaded rod, is designed to transfer polymer solution evenly to the surface of the rod spinneret. The relative motion between the slipper block and the threaded rod electrode promotes the instable fluctuation of the solution surface, thus the rotation of threaded rod electrode decreases the critical voltage for the initial multi-jet ejection and the diameter of nanofibers. The residual solution on the surface of threaded rod is cleaned up by the moving slipper block, showing a great self-cleaning ability, which ensures the stable multi-jet ejection and increases the productivity of nanofibers. Each thread of the threaded rod electrode serves as an independent spinneret, which enhances the electric field strength and constrains the position of the Taylor cone, resulting in high productivity of uniform nanofibers. The diameter of nanofibers decreases with the increase of threaded rod rotation speed, and the productivity increases with the solution flow rate. The rotation of electrode provides an excess force for the ejection of charged jets, which also contributes to the high-efficiency production of nanofibers. The maximum productivity of nanofibers from the threaded rod spinneret is 5–6 g/h, about 250–300 times as high as that from the single-needle spinneret. The self-cleaning threaded rod spinneret is an effective way to realize continuous multi-jet electrospinning, which promotes industrial applications of uniform nanofibrous membrane.

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. Electrohydrodynamic atomisation (EHDA) is an emerging technique for the production of micron and nano-scaled particles. The process often involves Taylor cone enablement, which results in a fine spray yielding formulated droplets, which then undergo drying during deposition. In this work novel multi-tip emiiter (MTE) devices were designed, engineered and utilised for potential up-scaled EHDA, by comparison with a conventional single needle system. To demonstrate this, the active ketoprofen (KETO) was formulated using polyvinylpyrrolidone (PVP) polymer as the matrix material. Here, PVP polymer (5% w/v) solution was prepared using ethanol and distilled water (80:20) as the vehicle. KETO was incorporated as 5% w/w of PVP. Physical properties of resulting solutions (viscosity, electrical conductivity, density and surface tension) were obtained. Formulations were electrosprayed through both single and novel MTEs under EHDA conditions at various flow rates (5-300 μl/min) and applied voltages (0-30 kV). The atomization process using MTEs and single nozzle was monitored at using various process parameters via a digital optical camera. Resulting particles were collected 200mm below processing heads and were analyzed using differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Digital recordings confirmed stable MTE jetting at higher flow rates. Electron micrographs confirmed particle size variation arising due to nozzle head design and evidenced stable jetting derived greater near uniform particles. DSC, XRD and TGA confirm KETO molecules were encapsulated and dispersed into PVP polymer particles. In conclusion, novel MTE devices enabled stable atomisation even at higher flow rates when compared to the conventional single needle device. This indicates an exciting approach for scaling-up (EHDA) in contrast to current efforts focusing on multiple nozzle and pore based processing outlets.

In a typical electro-spinning process, the steady stretching process of the jet beyond the Taylor cone has a significant effect on the dimensions of resulting nanofibers. Also, it sets up the conditions for the onset of the bending instability. The focus of this work is the modeling and simulation of the initial stable jet phase seen during the electro-spinning process. The perturbation method was applied to solve hydrodynamic equations, and the electrostatic equation was solved by a boundary integral method. These equations were coupled with the stress boundary conditions derived appropriate at the fluid-fluid interface. Perturbation equations were discretized by the second-order finite difference method, and the Newton method was implemented to solve the discretized nonlinear system. Also, the boundary element method was utilized to solve the electrostatic equation. In the theoretical study, the fluid is described as a leaky dielectric with charges only on the jet surface in dielectric air. In this study, electric charges were modeled as static. Comparison of numerical and experimental results shows that at low flow rates and high electric field, good agreement was achieved because of the superior importance of the charge transport by conduction rather than convection and charge concentration. In addition, the effect of unevenness of the electric field around the nozzle tip was experimentally studied through plate-plate geometry as well as point-plate geometry.

Molecular dynamics (MD) electrospray simulations of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-${\mathrm{BF}}_{4}$) ion liquid were performed with the goal of evaluating the influence of long-range Coulomb models on ion emission characteristics. The direct Coulomb (DC), shifted force Coulomb sum (SFCS), and particle-particle particle-mesh (PPPM) long-range Coulomb models were considered in this work. The DC method with a sufficiently large cutoff radius was found to be the most accurate approach for modeling electrosprays, but, it is computationally expensive. The Coulomb potential energy modeled by the DC method in combination with the radial electric fields were found to be necessary to generate the Taylor cone. The differences observed between the SFCS and the DC in terms of predicting the total ion emission suggest that the former should not be used in MD electrospray simulations. Furthermore, the common assumption of domain periodicity was observed to be detrimental to the accuracy of the capillary-based electrospray simulations.

© Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ Mass production of ordered nanostructures with enhanced optical properties such as colloidal crystals for applications such as solar cells or organic light emitted diodes demands low-cost and large-scale manufacturing techniques. In order to enlarge the deposition area of colloidal crystals, this paper presents the results of two different approaches that use the electrospray technique. Areas as large as 25¿cm2 have been achieved by using an array of needles, whereas up to 7.5¿cm2 areas were achieved by using an additional focusing electrode placed on the same plane as the needle nozzle. COMSOL simulations have been used as a guide for the set up design. The ordered deposition of the nanoparticles has been assessed by reflectance measurements and SEM/FIB observations.

In this work, the use of molecular dynamics as a predictive tool for modeling the atomistic behavior of electrospray propulsion is discussed. 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF 4 ) and ethylammonium nitrate (EAN) were considered as two limits of ionic liquid (IL) propellants that tend to operate in an ion versus a droplet mode. The emission modes were found to depend on the electro-chemical properties of the IL propellant. The aprotic EMIM-BF 4 -based electrospray emitted primarily monomers and trimers as the dominant species and only small quantities of droplets. In contrast, trimers were the dominant emitted species in the protic EAN emissions with a significantly large contribution from droplets towards the total emission current, suggesting that EMIM-BF 4 -based colloid thrusters operate in ion mode and EAN-based devices operate in the droplet mode. Furthermore, the formation of the Taylor cone was found to depend on the mass flow rate and the external electric field strength. This paper provides a framework that can be extended for use to simulate any other ILs or their combinations.

Coulomb fission of charged droplets (The terms drop and droplet are often used synonymous. Throughout this manuscript, to avoid confusion, the terms drop and droplet will be used for liquid spheres with radii in the millimeter range and the micrometer range, respectively. In our experiments, the first correspond to the parent drop while the latter describes the ejected progeny droplets.) is a well-studied natural phenomenon. Controlled droplet fission is already successfully employed in several technological applications. Still, since the occurring surface rupture relies on the exact understanding and description of the liquid gas boundary, some details are still under debate. Most empirical systematic studies observe falling micrometer droplets passing through the electric field inside a plate capacitor. This approach, although easily applicable and reliable, limits the experimental degrees of freedom regarding the observable time and the maximum size of the drops and can only be performed in consecutive individual observations of different subsequent drops. Here we present a novel setup to study the field induced breakup of acoustically levitated drops. The design does not bear any restrictions towards the temporal window of observation, and allows handling of drops of a tunable radius ranging from 10 μm to several millimeters and a real-time monitoring of one single drop. Our comprehensive study includes a time resolved visual inspection, laser shadowgraphy, laser induced fluorescence imaging, and ambient mass spectrometric interrogation of the nascent Taylor cone. The results shown for a millimeter sized drop, previously inaccessible for Coulomb fission experiments, are mostly comparable with previous results for smaller drops. The major difference is the time scale and the threshold potential of the drop rupture. Both values, however, resemble theoretically extrapolations to the larger radius. The technique allows for a systematic study of breakup behavior of drops of different charge, material, and size.

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.

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.

Initial jet usually has a large primary droplet hanging at flying end before the onset of effective electrospinning. The primary droplet is undesired as its diameter is several orders of magnitude higher than that of electrospun nanofibres. A new method is used to derive micro-scaled initial jet and fine primary droplet under applied small-aperture needle by utilizing low solution flow rate and pre-applied electric potential before the extrusion of polymeric solution out of the needle. Small-aperture needle reduces the base of conical pendant, while low solution flow rate prevents a fluidic inrush into conical pendant. The pre-applied electric potential preforms a miniature liquid cone, as an origin of initial jet, within the needle. The conic preformation reduces the formation time of Taylor cone in order to escape from a swollen Taylor cone under a continuous inflow of polymeric solution. The miniature conical pendant grows so acute that it emits fine primary droplet rapidly from its tip with accumulated ions. Carrying primary droplet, thin initial jet experiences axial elongation and circumferential rotation in the space.

Numerical models that are capable to quantitatively elaborate the formation of novel two-dimensional (2D) nanonets during electrospinning/netting would have broad technological implications for areas ranging from sensing devices and individual protection to industrial filtration and separation; however, creating such models has proved extremely challenging. Here we report novel numerical models for clarifying the origin, evolution, and regulation of the nanonets via combining the ejection modes of Taylor cone apex and the phase separation of charged droplets. Our models propose two critical condition formulas for the generation of jets and droplets, and a LCST phase diagram combined with concentration sweep paths for the nanonets or non-porous films. The resulting model predications exhibit excellent agreement with the experimental results obtained via varying the solution properties and process parameters. The successful model derivation for the nanonets formation may provide new insights into the design and development of 2D multifunctional nanomaterials for various applications.

There dispersion of drops hanging on an upper electrode or lying on a bottom one, due to the instability of their equilibrium in an electric field, is experimentally investigated. The existence of two modes (drops and cones) of hanging-drop instability is established. In case of the drop mode, a smaller drop detaches itself from the parent drop at the onset of instability. In case of the cone mode on the drop end, a Taylor cone attended with the detachment of fine droplets, or continuous trickles, or a spark breakdown is formed. In case of lying drops the cone mode always occurs. Our semiempirical estimations are in good agreement with the experimental results.

The use of borosilicate theta glass capillaries as nanoelectrospray ionization emitters has recently been demonstrated as a method for mixing two solutions as they are sprayed into the mass spectrometer for analysis. All previous experiments resulted in a solution mixing timescale limited to the time the analytes spend in the Taylor cone and subsequent droplets (i.e. sub-millisecond timescale). In an effort to extend the solution mixing timescale to the milliseconds regime, we demonstrate that solution can be moved from one channel of the theta tip to the opposite channel via electroosmosis by applying a potential difference between the two wire electrodes inserted into each channel of the theta tip. First, we establish that electroosmosis is responsible for solution movement using fluorescence microscopy to track fluorescent tracer dyes. We then demonstrate the utility of this technique in varying the extent of denaturation of holomyoglobin to apomyoglobin on the millisecond timescale just prior to analysis by mass spectrometry. Finally, we induce additional turbulence for better mixing by applying a square wave potential to one of the wire electrodes while holding the opposite wire at a constant voltage between the low and high potentials of the square wave. This experiment was found to provide nearly complete mixing after a single cycle of the square wave. The use of electroosmosis significantly expands the flexibility of theta tips for altering solutions prior to nESI without the need for off-line sample manipulation. Copyright © 2015 John Wiley & Sons, Ltd.

Picoliter or femtoliter droplets generated with high frequency is very useful for many applications in different valuable fields, such as microarray generation, drug delivery or biochips. Pulsed electrohydrodynamic inkjet printing (Pulsed EHDP) is an advanced technology which is used for generating fine droplets in recent years. Apparently, the deposition frequency of droplets is a key parameter, and it is influenced by various factors. In this paper, the effect of duty cycle and voltage frequency on deposition frequency is investigated in the pulsation mode. A simple scaling law is proposed to demonstrate relationships between these two parameters and deposition frequency. Results show that volume of the liquid accumulated at the apex of the nozzle changes during the non-electric field period, which affects taylor cone deformation time and deposition frequency. High deposition frequency can be achieved by increasing the duty cycle up to 0.7, and choosing voltage frequency between 10Hz to 40Hz. These analysis is valuable for understanding Pulsed EHDP deeply and fabricating the micro/nanoapplications.

A three-dimensional optical tomography technique was developed to reconstruct three-dimensional objects using a set of two-dimensional shadowgraphic images and normal gray images. From three high-speed cameras, which were positioned at an offset angle of 45° between each other, number, size, and location of electrohydrodynamic jets with respect to the nozzle position were analyzed using shadowgraphic tomography employing multiplicative algebraic reconstruction technique (MART). Additionally, a flow field inside a cone-shaped liquid (Taylor cone) induced under an electric field was observed using a simultaneous multiplicative algebraic reconstruction technique (SMART), a tomographic method for reconstructing light intensities of particles, combined with three-dimensional cross-correlation. Various velocity fields of circulating flows inside the cone-shaped liquid caused by various physico-chemical properties of liquid were also investigated.

Polyethylene glycol (PEG) hydrogel microspheres of controlled sizes and narrow size distribution were fabricated via electrospraying. To facilitate the formation of microspheres through electrospraying, the gelation time of PEG hydrogels by Michael’s addition reaction between acrylate and thiol were optimized. The effect of electrospraying parameters such as applied voltage, flow rate, needle gauge, and tip to collector distance (TTCD) on Taylor cone formation and microsphere size and distribution was determined. Applied voltage and TTCD had the strongest influence on Taylor cone formation and microsphere size and distribution. By careful design of process parameters a wide range of PEG hydrogel microspheres were obtained, namely 70– 700mm in diameter. The biodegradable PEG hydrogel microspheres developed in this study through a combination of mild gelation chemistry and electrospraying will be valuable in a variety of biological applications including drug and protein delivery, cell encapsulation, and biosensors.

Electrospinning has recently been used for micropatterning. The electrospinning method as a patterning tool has the advantage of a rapid patterning speed because it is based on a continuous printing mode rather than a drop-ondemand mode. To obtain stable continuous printing, a high molecular weight polymer must be mixed with functional materials for patterning. In this paper, polyethylene oxide (PEO) was used. The effect of polymer on viscosity and formation of a Taylor cone jet from the electrospinning nozzle was investigated. Finally, the electrospinning patterning results of a silver paste ink on a glass substrate were investigated. † Corresponding Author, kskwon@sch.ac.kr C 2015 The Korean Society of Mechanical Engineers

The kinetics of a liquid cone at the surface of a liquid electrode before and after a spark discharge over the vertex of a Taylor cone is investigated using a high-speed video camera. The features of oscillatory processes on the liquid electrode with different dynamic characteristics (glycerol and a 1% solution of H2SO4) in electric fields with a strength of E ≤ 30 kV/cm (U ≤ 16 kV) are studied.

Crater-like electrospinning is a novel and cost-effective method for the mass scale production of nanofibers. The gas channel in the polymer solution plays a key role to produce a bubble Taylor cone or a crater-like Taylor cone, which is the key to eject the thin fluid jets (finally solidified into nanofibers) in electrospinning process. However, the formation mechanism of gas channel of crater-like Taylor cone is still unclear, which hinders further development of this process. In this work, a simple and effective scaling model was firstly established to predict the period of the gas-channel formation in the polymer solution during electrospinning process. Our theoretical analysis showed that the gas-channel formation period was mainly determined by the input air pressure during the process. The relationship between the formation period and the input air pressure followed a scaling law. In order to verify the model, crater-like electrospinning process was carried out and a high-speed digital camera was employed to observe the gas channel. The experimental results agree well with the scaling model, which indicates that the proposed system is feasible. The scaling model could be useful in helping us to understand the process.

A number of processing techniques such as drawing, template synthesis, phase separation, self-assembly, drawing, melt blowing and electrospinning, can be used to prepare nanofibres. Among them, electrospinning stands out as the most promising method for nanofibre production [1, 2]. Electrospinning is a process where fibres are created due to the electrostatic forces acting between two electrodes. This method has been known for more than 100 years, since the beginning of the 20th century, when John Francis Cooley filed the first patent for electrospinning in 1900. Further developments were made by William James Morton and John Zeleny. The latter published his work on the behaviour of fluid droplets at the end of metal capillaries. From 1931 to 1944, Anton Formhals took out at least 22 patents on the theory of electrospinning. From literature sources, it is known that Nikolai Albertowich Fuchs, Igor’ Vasil’evich Petryanov-Sokolov, Natalya D Rosenblum, also Sir Geoffrey Ingram Taylor, Darrell Reneker and others distinguished themselves in this area. During 1964–1969, Sir Geoffrey Ingram Taylor made a significant development in electrospinning and modelled the shape of the Taylor cone formed by a fluid droplet under the influence of an electric field [3-6]. Nevertheless, it was only at the end of 20th century that this method began to be used more widely after new technologies has been created and the ability to manufacture fibres on the nanoscale emerged. By electrospinning, it is possible to manufacture nanofibres from a polymer solution or melt on the scale of a few dozen to a few hundred nanometres [7]. The main advantage of a web from such nanofibres is the very high surface area of polymeric fibres, manufactured from a very small quantity of polymer having very high barrier properties – the pores of such a web can be smaller than those of red blood cells.

This technical note documents the use of ballpoint pen tips as robust electrospray emitters. The embedded microsphere helps stabilize Taylor cones by effectively reducing the height of the liquid meniscus and significantly decreasing the viscous damping time of the Taylor cone. The microsphere also provides a mechanism for the Taylor cone to continuously adapt its base diameter to match the voltage applied. As a result, the ballpoint pen electrospray emitter noticeably expands the operation envelope in the flow rate-voltage space.

Although several interfaces for CE-MS hyphenation are commercially available, the development of new versatile, simple and yet efficient and sensitive alternatives remains an important field of research. In a previous work, a simple low sheath-flow interface was developed from inexpensive parts. This interface features a design easy to build, maintain, and adapt to particular needs. The present work introduces an improved design of the previous interface. By reducing the diameter of the separation capillary and the emitter, a smaller Taylor cone is spontaneously formed, minimizing the zone dispersion while the analytes go through the interface and leading to less peak broadening associated to the ESI process. Numerical modeling allowed studying the mixing and diffusion processes taking place in the Taylor cone. The analytical performance of this new interface was tested with pharmaceutically relevant molecules and endogenous metabolites. The interface was eventually applied to the analysis of neural cell culture samples, allowing the identification of a panel of neurotransmission-related molecules. An excellent migration time repeatability was obtained (intra-day RSD0.5% for most compounds, and3.0% for inter-day precision). Most metabolites showed S/N ratios10 with an injected volume of 6.7 nL of biological extract.

Emission characteristics of a colloid thruster or electrospray depends strongly on the electrochemical property of the ionic liquid as well as its response to the external electric field. Using molecular dynamics, the evolution of the Taylor cone formation for an electrospray device can be analyzed at an atomic level. From our previous work1, it was observed that the electric field strengths required to create and sustain a stable Taylor cone are correlated to the internal nanostructure of the propellant ionic liquid. The location of the applied extraction potential with respect to the capillary produces differences in the strength and the shape of the resulting external electric fields. The varying electric fields are strongest at the mouth of the capillary and affect the emission rate, Taylor cone stability, as well as the internal nanostructure of the ionic liquid. In this work, we will study the effects of variable electric field shape and strength on the Taylor cone structure.

Electrically charged metallic micro- and nanoparticles are trapped under a free surface of superfluid He in a vertical static electric field. We observe a static deformation of the charged liquid surface in the form of a Taylor cone and the emission of a charged liquid helium jet (electrospray). Our numeric calculations reproduce the static shape of the cone.

Electrospinning is an electrohydrodynamic-based technique capable of generating controlled fibers with diameters well below the micron. However, the low typical throughput of a single Taylor cone demands the use multicone sources for industrial applications. The two alternatives with their advantages and drawbacks are compared: multinozzle injectors and later needleless spinnerets. Industrial scale up efforts and electrospinning development of biomedical devices and products are described.

The Electrospray technique allows the formation of small droplets from aqueous solutions that may contain nanoparticles of different materials in suspension, leading to the deposition of layers of the nanoparticles. The geometry of the nozzle and the electric field lines from the tip to substrate are key parameters to concentrate the jet of nanodroplets to enhance the deposition control. This work examines the introduction and effect of a guard ring placed at a specific distance from the nozzle. We have been able to make observations with a CCD camera of the fast formation of the Taylor cone with a long elongated jet of deionized water when both the guard ring and substrate are connected to ground. Main results show that the guard ring allows to concentrate the spray jet, reduces the voltage required to shape the cone and reduce the dispersion of the deposit.

The electrospun microfibers of high-viscosity polyacrylonitrile (PAN) solution possess stronger tensile strength, but poor electrospinnability. Sonication treatment was introduced to improve the electrospinnability of high-viscosity PAN solution. The influences of sonication time on the solution properties, including dynamic rheological properties, electric conductivity and surface tension, as well as the deformation of Taylor cone and electrospinning jet whipping behavior were investigated. The surface morphology of the resultant fibers was observed using scanning electron microscope, and the mechanical properties of the fiber mats were measured through tensile test. The experimental results indicated that the electrospinnability of the PAN solution was significantly improved by the sonication treatment due to the improved rheological properties, increased electric conductivity and reduced surface tension. It was also found that sonication treatment could elongate the Taylor cone and drastically intensify the whipping instability of the electrospinning jet. When the solution was treated for 4 min (720 W), the average diameter of the obtained electrospun PAN fibers reduced from 3,180.46 to 2,657.23 nm as the unevenness rate reduced from 16.38 to 15.27 %. The tensile strength of microfiber mats increased from 2.50 to 6.61 MPa, showing an increment of 164 %, while the Young’s modulus is strengthened fivefold, increasing from 39.49 to 248.97 MPa.

This paper presents the results of experimental research on Taylor cone shaped menisci formation on the surfaces of pieces by applying electric discharges in pulse. It examines the influence of energy stored in the capacitor and of pulse duration on their formation. The modification of piece surface micro-geometry aims to increase the capacity of absorption of radiation and of particle emission. It shows that the size of formed menisci depends on the energy regime of machining, on the gap size, on the duration of electric discharges in pulse and on thermal physical properties of the material used to execute the piece.

Electrospun fibrous mats have emerged as powerful tissue engineering scaffolds capable of providing highly effective and versatile physical guidance, mimicking the extracellular environment. However, electrospinning typically produces a sheet-like structure, which is a major limitation associated with current electrospinning technologies. To address this challenge, highly porous, volumetric hydrogel-hybrid fibrous scaffolds were fabricated by one Taylor cone-based side-by-side dual electrospinning of poly (ε-caprolactone) (PCL) and poly (vinyl pyrrolidone) (PVP), which possess distinct properties (i.e., hydrophobic and hydrogel properties, respectively). Immersion of the resulting scaffolds in water induced spatial tortuosity of the hydrogel PVP fibers while maintaining their aligned fibrous structures in parallel with the PCL fibers. The resulting conformational changes in the entire bicomponent fibers upon immersion in water led to volumetric expansion of the fibrous scaffolds. The spatial fiber tortuosity significantly increased the pore volumes of electrospun fibrous mats and dramatically promoted cellular infiltration into the scaffold interior both in vitro and in vivo. Harmonizing the flexible PCL fibers with the soft PVP-hydrogel layers produced highly ductile fibrous structures that could mechanically resist cellular contractile forces upon in vivo implantation. This facile dual electrospinning followed by the spatial fiber tortuosity for fabricating three-dimensional hydrogel-hybrid fibrous scaffolds will extend the use of electrospun fibers toward various tissue engineering applications.

Due to the relative ease for fabricating fibers with a core–shell structure, emulsion electrospinning has been investigated intensively for making nanofibrous delivery vehicles for local and sustained release of biomolecules such as growth factors. In this investigation, water-in-oil (w/o) emulsions consisting of deionized (DI) water or phosphate buffer saline (PBS), poly(lactic-co-glycolic acid) (PLGA) solution and a surfactant were electrospun into fibers for studying the evolution of core–shell structures in emulsion electrospun fibers. Optical microscopy, high speed imaging, fluorescence microscopy and transmission electron microscopy were employed to examine the morphology of the water phase in fibers at different locations of the jet (or fiber) trajectory during emulsion electrospinning. The results indicated that the water phase in emulsion jets underwent multi-level stretching and breakup. When the jet (or fiber) diameter was large (i.e., for the jet near the Taylor cone), the water phase within the jet (or fiber) exhibited a discrete morphology whereas in ultrafine fibers collected beyond certain distance from the Taylor cone, a mostly continuous water phase core was formed. The Rayleigh/capillary instability determined the breakup point of the deformed water phase. When the water phase in emulsions for electrospinning was changed from DI water to PBS, it changed from a continuous state to a discontinuous state in electrospun nanofibers.

The combination of electrospinning and forcespinning (otherwise called electrostatic-centrifugal spinning) was first proposed in our laboratory. A viscoelastic jet has a stretching force in the axial ( a x → ) and tangential ( a y → ) directions under electrostatic and centrifugal forces. The jet radius (R0) will be dramatically decreased, and the jet velocity (υ0) will be substantially increased due to a particular stretching force. The radius of curvature, the jet length, and the Taylor cone of a viscoelastic jet will be completely different when the jet velocity (υ0) increases. A strong stretching force and a fast extension speed will form after optimizing the radius of curvature (by Reynolds (Re) and Weber (We) numbers), jet length (by Peclet (Pe) and Epsilon (e) numbers), and Taylor cone (by dimensionless stress (Π1) and Ohnesorge (Oh) numbers). Through dimensionless number and group analysis, higher Re(PC = 9.38 × 10−2, PLA = 1.52 × 10−1 and PAN = 1.53 × 10−2) and We(PC = 13.8, PLA = 15 and PAN = 13.3) number of all three systems can collect the bead-free and uniform nanofibers. Similarly, higher П1(PC = 1.83 × 10−5, PLA = 2.86 × 10−5 and PAN = 5.13 × 10−9) and Oh(PC = 39.60, PLA = 29.22 and PAN = 238.94) numbers refer to viscosity and electrostatic force dominate the jet behavior and obtained the nanofiber with high modulus, hardness, crystallinity and good molecular orientation. Hence, the uniaxially aligned polycarbonate, polylactic acid and polyacrylonitrile nanofibers with superior physical properties (modulus ⩾ 2.77 GPa, 3.3 GPa and 1.46 GPa, hardness ⩾ 0.32, 0.26 and 0.22 and crystallinity ⩾ 3%, 37% and 21%) can be successfully manufactured in this process.

Monte Carlo and molecular dynamics simulations on pure water and aqueous electrolyte solutions exposed to a strong external electric field were used to model the electrospinning process from the free liquid surface, with the goal of assessing their potential to gain insight into the molecular-level mechanisms underlying the process. Three regimes involved in the electrospinning process—the free liquid surface, the apex of the Taylor cone, and the erupting jet—were selected for simulation using three different strategies. All simulations provide the same qualitative picture and exhibit scenarios consistent with experimental observations. It is found that ions play only a rather secondary role, in the sense that the process is driven by the water molecules. The strong electric field near the tip of the Taylor cone initially arranges the water molecules, creating an embryo of a jet into which the ions subsequently enter. At high concentrations, the ions can destabilize the jet, leading to electrospraying. At...