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Electrohydrodynamic (EHD) inkjet printing is a type of potential non-contact micro/nanoscale manufacturing technology. The printed droplet dimension plays an important role in EHD inkjet printing due to its significant influence on printing quality and the resolution of patterns. The complexity of the mechanism and the limited process optimization techniques present a challenge in obtaining the desired printing resolution, eventually becoming an expensive and time consuming endeavor. Recent developments in computational fluid dynamics (CFD) bring an effective alternative to alleviate the aforementioned challenges. In this study, a CFD model is proposed to investigate the mechanism of the cone-jet printing process in EHD inkjet printing. The complete cone-jet printing process is successfully simulated with four phases: Taylor cone formation, cone-jet generation, jet break and droplet expansion. A further analysis predicts the jetting diameter and printed droplet diameter with different operating parameters and substrates. The simulation has a satisfactory agreement with experiments in predicting the printing behavior and printing quality (jetting diameter, printed droplet diameter). Such advancement in modeling can be utilized to guide the quick determination of operation parameters for the desired printing resolution when given a new ink.

Electrohydrodynamic (EHD) printing is a promising inkjet technique to generate smaller droplet sizes due to the formation of a Taylor cone. However, the process is intricate and involves the fabrication of a printhead having a smaller nozzle diameter. Notable examples are present in the literature regarding printing through EHD but the underlying phenomenon which is responsible for generating the smaller droplet is obscure. In this work, we present a methodology which highlights the importance of nozzle shape which can govern smaller droplets even with a large head diameter. The work achieves a resolution of less than 2 μ m by fabricating the inkjet head using simple techniques and off-the-shelf inexpensive needles of nozzle diameter ranging from 500 μ m to 250 μ m. The study of various nozzle profiles resulted in a printed resolution which is 50 times smaller than the nozzle diameter. Moreover, the study also highlights the importance of the wetting area profile of the nozzle and explains the role of printhead design which facilitates fine resolution printing of conductive tracks which until now seemed to be obscure.

Paper Spray (PS) is an ambient ionisation technique that is conceptually simple, economical, direct and versatile. In its simplest form, the procedure for operation relies on the application of an electric potential to a triangular-shaped paper substrate with the addition of an extraction/spray solvent to generate charge droplets, without requiring any pneumatic assistance. Despite its promise and rapidly growing popularity, there are some practical challenges associated with PS implementation with scope to enhance its performance further. One such challenge relates to only a small fraction of the Taylor cone expansion being sampled at the MS inlet. In this work we propose a new arrangement for PS, which retains the inherent advantages of this popular technique without introducing additional variables, by using an ambient ion focusing lens that is held at the same potential as the paper substrate. A thorough investigation, consisting of visual spray inspection, electric field simulations and analytical evaluation, including analysis of paracetamol from saliva, shows that ambient ion focusing can provide up to a 50% improvement in spray stability, 60% increase in signal intensity and a 30% improvement in detection limits for routine paper spray mass spectrometry analysis.

We investigated the electrospray ionization inside the narrow channel of the ion inlet tube. An insulating emitter capillary made of fused silica with a 0.2 mm outer diameter was inserted into the ion inlet tubes with a 0.5 and 0.6 mm inner diameter to aspirate all the charged droplets. A custom-made ion inlet tube with two side holes near its entrance is used to observe the spraying condition. The spray current is measured and monitored during the MS acquisition using isolation amplifiers. Because the emitter is cylindrically surrounded in close proximity by the metallic inner wall, it is difficult to obtain a stable and symmetric Taylor cone with its apex at the center of the emitter. Instead, a stable operation under a flow rate of 1-4 μL/min is found to be in the form of a multicone-jet mode with two or more Taylor cones anchoring around the rim of the emitter. The emitted charged droplet jets are dragged from hitting the wall by the fast-flowing air inside the inlet tube. Comparison with the typical cone-jet and multijet mode operated several millimeters outside the inlet capillary shows signal enhancements for protein standards.

Hexagonal upconverting nanoparticles (UCNPs) of NaYF4:Er3+,Yb3+ (ca. 300 nm) have been widely used to measure the temperature at the nanoscale using luminescence ratio thermometry. However, several factors limit their applications. For example, changes in the peak shape, mainly is the S-band emission, hinders their ability to be used as a universal temperature sensor. Herein, we introduce a universal calibration protocol for NaYF4:Er3+,Yb3+ upconverting nanoparticles that is robust to environmental changes and gives a precise temperature measurement. We used this new procedure to calculate the temperature profile inside a Taylor cone generated with an electrospray jet. Inside the Taylor cone the fluid velocity increases toward the tip of the cone. A constant acquisition length leads to a decrease in excitation and acquisition time. This decrease in excitation time causes a peak shape change that corrupts the temperature measurement if the entire peak shape is integrated in the calibration. Our universal calibration circumvents this problem and can be used for time-resolved applications. The temperature at the end of the Taylor cone increases due to the creation of a whispering gallery mode cavity with 980 nm excitation. We use time-resolved energy balance equations to support our optical temperature measurements inside the Taylor cone. We believe that the findings of this paper provide a foundation for time-resolved temperature measurements using NaYF4:Er3+,Yb3+ upconverting nanoparticles and can be used to understand temperature-dependent reactions such as protein unfolding inside microjet/microdroplets and microfluidic systems.

Melt electrospinning is widely used to manufacture fibers with diameters in the low micrometer range. Such fibers are suitable for many biomedical applications, including sutures, stents and tissue engineering. We investigated the preparation of polybutylene succinate microfibers using a single-nozzle laboratory-scale device, while varying the electric field strength, process throughput, nozzle-to-collector distance and the temperature of the polymer melt. The formation of a Taylor cone followed by continuous fiber deposition was observed for all process parameters, but whipping behavior was enhanced when the electric field strength was increased from 50 to 60 kV. The narrowest fibers (30.05 µm) were produced using the following parameters: electric field strength 60 kV, melt temperature 235 °C, throughput 0.1 mL/min and nozzle-to-collector distance 10 cm. Statistical analysis confirmed that the electric field strength was the most important parameter controlling the average fiber diameter. We therefore report the first production of melt-electrospun polybutylene succinate fibers in the low micrometer range using a laboratory-scale device. This offers an economical and environmentally sustainable alternative to conventional solution electrospinning for the preparation of safe fibers in the micrometer range suitable for biomedical applications.

Melt electrowriting (MEW) is a high-resolution additive manufacturing technology that balances multiple parametric variables to arrive at a stable fabrication process. The better understanding of this balance is underscored here using high-resolution camera vision of jet stability profiles in different electrical fields. Complementing this visual information are fiber-diameter measurements obtained at precise points, allowing the correlation to electrified jet properties. Two process signatures-the jet angle and for the first time, the Taylor cone area-are monitored and analyzed with a machine vision system, while SEM imaging for diameter measurement correlates real-time information. This information, in turn, allows the detection and correction of fiber pulsing for accurate jet placement on the collector, and the in-process assessment of the fiber diameter. Improved process control is used to successfully fabricate collapsible MEW tubes; structures that require exceptional accuracy and printing stability. Using a precise winding angle of 60° and 300 layers, the resulting 12 mm-thick tubular structures have elastic snap-through instabilities associated with mechanical metamaterials. This study provides a detailed analysis of the fiber pulsing occurrence in MEW and highlights the importance of real-time monitoring of the Taylor cone volume to better understand, control, and predict printing instabilities.

Ultrathin fibers have been widely used in thermal insulation, catalysts, drug delivery, tissue scaffolds, wound dressing, energy storage, energy harvesting, environment engineering, and textile industries. Electrospinning is a facile, universal, and cost-efficient technology for fabricating ultrathin nanofiber materials. On the other hand, porous structure and functional modification can be generated through interfacial assembly method. Accordingly, interfacial electrospinning assembly is emerged as an excellent strategy to prepare multifunctional ultrafine nanofibers. However, the traditional electrospinning using a single Taylor cone is facing a major challenge–low production efficiency, which can no longer meet the actual demand. Therefore, diverse multi-Taylor cone sited electrospinning have been developed, such as multi-needle, various needleless electrospinning and so on. In this review, different electrospinning methods of preparing ultrathin fibers are summarized, especially from the point of view of single Taylor cone site to multi-Taylor cone sites. The precursor materials species, electrospinning apparatus, nanofiber structure and scale-up equipment are critically discussed. It is foreseeable that multi-Taylor cone sited electrospinning can overcome the drawbacks of one Taylor cone sited electrospinning and make the large-scale industrial production possible.

An electric-field-driven (EFD), &mu, 3D printed, fused polymer technique has been developed for the fabrication of large-area microscale prototype molds using typical polymer materials, including microcrystalline wax (MC-wax), polycaprolactone (PCL), and polymathic methacrylate (PMMA). This work proposes an alternative for large area microscale modes and overcomes the limitation of high cost in the traditional mold manufacturing industry. The EFD principle enables printing of fused polymers materials more than one order of magnitude lower than the nozzle diameter, contributing to the necking effect of the Taylor cone jet, which is the key factor to achieve the microscale manufacturing. Numerical simulation of electric field distribution between the meniscus and substrate was carried out to elucidate the dependence of electric field distribution on the meniscus condition of three types of polymers under printable voltage, and the electrical field parameters for the EFD &mu, 3D printing were determined. A number of experiments were printed successfully using a large range of viscosity materials, ranging from tens of mPa&middot, s to hundreds of thousands of mPa&middot, s of PCL and PMMA. The differences in parameters of different materials, such as viscosity, tensile properties, and surface energy, were studied to assess their use in different fields. Using proper process parameters and a nozzle with an inner diameter of 200 &mu, m, three different application cases were completed, including a Wax microarray and microchannel with a minimum dot diameter of 20 &mu, m, a PCL mesh structure with a minimum line width of 5 &mu, m, and a PMMA large-area mold with a maximum aspect ratio of 0.8. Results show that the EFD &mu, 3D printing has the outstanding advantages of high printing resolution and polymer material universality.

This work investigates the effect of gravity during melt electrospinning writing (MEW) and explores the feasibility of developing MEW devices with lateral and upside down print head configurations. Average fibre diameters of printed constructs using different printing directions and their variability reveal particular differences. These give an insight into the effect of gravity, which was observed to affect the Taylor cone, yet interestingly not the fibre jet. Additionally, stable processing conditions were studied and showed that it is possible to reproducibly print from all directions using MEW.

The characteristics of the propellant film on the tip surface of the field-emission electric propulsion thruster have a close relationship with the work state of the thruster. In this paper, the distributions of both the liquid film thickness and the fluid velocity along the needle tip have been calculated by building the liquid mechanics equations and a cone coordinate system suitable for the tip. The results show that the film thickness is tens to hundreds of nanometers and the fluid velocity along the needle tip is from tens of µm/s to a few mm/s.

The specifics of behavior of viscous electrolytes (exemplified by glycerol) subjected to spark discharges with direct connection of electrodes and in the induced charge mode have been studied. The transformation of a Taylor cone into a frustum, the stable existence of which depends on the polarization time, has been observed for the first time with cyclic discharges in the interelectrode space localized between an anodepolarizable viscous dielectric liquid (glycerol) and an overhanging cathode-polarizable metal electrode. The frustum development criteria (high dynamic viscosity and electric strength of the solution and low conductivity) have been determined.

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 (&lt, 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 malodor attached to textiles not only causes indoor environmental pollution but also endangers people's health even at low concentrations. Existing technologies cannot effectively eliminate the odor. Herein, an effective and environmentally friendly technology was proposed to address this challenging issue. This technology utilizes electrospraying process to produce Engineered Water Nanostructures (EWNS) in a controllable manner. Upon application of a high voltage to the Taylor cone, EWNS can be generated from the condensed vapor water through a Peltier element. Smoking, cooking and perspiration, considered the typical indoor malodorous gases emitted from human activities, were studied in this paper. A headspace SPME method in conjunction with GC-MS was employed for the extraction, detection and quantification of any odor residues. Results indicated that EWNS played a significant role in the deodorization process with removal efficiencies for the three odors were 95.3 ± 0.1%, 100.0 ± 0.0% and 43.7 ± 2.3%, respectively. The Reactive Oxygen Species (ROS) contained in the EWNS, mainly hydroxyl (OH˙) and superoxide radicals are the possible mechanisms for the odor removal. These ROS are strong oxidative and highly reactive and have the ability to convert odorous compounds to non-odorous compounds through various chemical reaction mechanisms. This study showed clearly the potential of the proposed method in the field of odor removal and can be applied in the battle against indoor air pollution.

Droplet generation process can directly affect process regulation and output performance of electrohydrodynamic jet (E-jet) printing in fabricating micro-to-nano scale functional structures. This paper proposes a numerical simulation model for whole process of droplet generation of E-jet printing based on the Taylor-Melcher leaky-dielectric model. The whole process of droplet generation is successfully simulated in one whole cycle, including Taylor cone generation, jet onset, jet break, and jet retraction. The feasibility and accuracy of the numerical simulation model is validated by a 30G stainless nozzle with inner diameter ~160 &mu, m by E-jet printing experiments. Comparing numerical simulations and experimental results, period, velocity magnitude, four steps in an injection cycle, and shape of jet in each step are in good agreement. Further simulations are performed to reveal three design constraints against applied voltage, flow rate, and nozzle diameter, respectively. The established cone-jet numerical simulation model paves the way to investigate influences of process parameters and guide design of printheads for E-jet printing system with high performance in the future.

Electrospinning is commonly used to produce polymeric nanofibers. Potential applications for such fibers include novel drug delivery systems, tissue engineering scaffolds, and filters. Electrospinning, however, has shortcomings such as needle clogging and limited ability to control the fiber-properties in a non-chemical manner. This study reports on an orifice-less technique that employs high-intensity focused ultrasound, i.e. ultrasound-enhanced electrospinning. Ultrasound bursts were used to generate a liquid protrusion with a Taylor cone from the surface of a polymer solution of polyethylene oxide. When the polymer was charged with a high negative voltage, nanofibers jetted off from the tip of the protrusion landed on an electrically grounded target held at a constant distance from the tip. Controlling the ultrasound characteristics permitted physical modification of the nanofiber topography at will without using supplemental chemical intervention. Possible applications of tailor-made fibers generated by ultrasound-enhanced electrospinning include pharmaceutical controlled-release applications and biomedical scaffolds with spatial gradients in fiber thickness and mechanical properties.

A dielectric barrier discharge over distilled water was investigated by means of synchronized, fast electrical and optical diagnostics. For this purpose, a single, alumina-covered electrode was placed above a water surface and a grounded tungsten electrode underwater, while the gas gap was constantly flushed with synthetic air at atmospheric pressure. Discharge events occur at rising and falling slopes or at the plateaus of the applied high-voltage pulse. Due to the synchronized diagnostics, a direct comparison of electrical characteristics and optical features of individual discharge events was performed. In most cases, a single discharge channel develops between the tips of the dielectric and the Taylor cone. Surface discharge channels can also occur in the upper part of the electrodes, which can be explained by a water layer being formed on the dielectric and acting as a virtual electrode. The discharge morphology and dynamics were found to be independent of the voltage polarity, which contradicts to known experiments with bare metal pin electrodes instead of dielectric-covered ones.

Existing 3D printing techniques are still facing the challenge of low resolution for fabricating polymer matrix composites, inhibiting the wide engineering applications for the biomedical engineering (biomimetic scaffolds), micro fuel cells, and micro-electronics. In order to achieve high resolution fabrication of polylactic acid (PLA)/multi-walled carbon nanotube (MWCNT) composites, this paper presents an electric-field-driven (EFD) fusion jetting 3D printing method by combining the mixing effect and material feeding of the micro-screw and the necking effect of Taylor cone by the EFD. The effects of main process parameters (the carbon loading, the voltage, the screw speed, and the printing speed) on the line width and the printing quality were studied and optimized. To demonstrate the printing capability of this proposed method, meshes with line width of 30 &micro, m to 100 &mu, m and 1 wt.% to 5 wt.% MWCNT for the application of conductive biomimetic scaffold and the anisotropic flexible meshes were prepared. The electrical properties were investigated to present the frequency dependence of the alternating current conductivity and the dielectric loss (tan&delta, ), and the microstructures of printed structures demonstrated the uniformly dispersed MWCNT in PLA matrix. Therefore, it provides a new solution to fabricate micro-scale structures of composite materials, especially the 3D conductive biomimetic scaffolds.

Dual-channel nano-electrospray has recently become an ionization technique of great promise especially in biological mass spectrometry. This unique approach takes advantage of the mixing processes that occurs during electrospray. Understanding in more detail the fundamental principles influencing spray formation further study of the origins of the mixing processes: (1) in a Taylor cone region, (2) in charged droplets or (3) in both environments. The dual-channel emitters were made from borosilicate theta-shape glass tubes (O.D. 1.2 mm) and had a tip diameters of less than 4 μm. Electrical contact was achived by deposition of a thin film of an appropriate metal onto the surface of the emitter. The experimental investigation of the Taylor cone formation in a dual-channel electrospray emitter has been carried out by injection of polystyrene beads (diameter 3 μm) at very low concentrations into one of the channels of the non-tapered theta-glass tubes. High-speed camera experiments were set up to visualize the mixing processes in Taylor cone regions for dual-channel emitters. Mass spectra from dual nano-electrospray are presented.

The current trend for increasing technical complexity in the field of CE-ESI-MS interfaces has incited for more accessible alternatives. In this work, a simple low sheath-flow ESI interface operating in the submicroliter nanospray regime without nebulizing gas assistance was evaluated. The use of sheath liquid enabled improving the ionization of the analytes, while the absence of nebulizing gas minimized sample dilution and loss of efficiency. After a rapid qualification, the effect of main operational parameters such as sheath liquid composition and flow rate, working distance and ESI potential was studied. Simulation of the mixing processes inside the Taylor cone proved its size to be of utmost importance in band broadening processes. As a proof of concept, the interface was eventually applied to a set of representative basic drugs analyzed by CE-TOF/MS. Limits of detection reached the 25-100 ppb range with suitable robustness and repeatability results. This design has demonstrated good performance while being simple and accessible to the user.

The paper presents the results of experimental research on the possibilities of micro-geometry modification of conductible and semiconductor surfaces, that gives them new functional properties. It emphasizes that surface micro-geometry modification occurs in practically all cases of the action by concentrated sources of energy, but a prescribed geometry can be reached only under strict conditions. The process of this geometry formation is a function of the physical and mechanical properties and the chemical composition of the processed material, the gradient of applied energy, the intensity of electric field applied in the interstice between the workpiece and the tool-electrode, the connection mode of the workpiece (as anode or as cathode) in the discharge circuit of the current impulse generator, etc. It highlights the fact that on the processed surface can be formed spherical shaped craters, round asperities or Taylor cone shaped asperities. Depending on the shape and the size of asperities, the active surface area, and, respectfully, the emission and absorption properties of elementary particles and light radiation are modified.

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.

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.

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.

© 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.

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.

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.

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.

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.

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.

Crater-like Taylor cone electrospinning is a novel, simple, and powerful approach to mass produce nanofibers. The Taylor cone, crater-like liquid bump on the free liquid surface, in this electrospinning process plays a key role to produce multiple fluid jets which finally solidifies nanofibers. A multi-physics coupled FEM method was employed to simulate the dynamic formation process of crater-like Taylor Cone in crater-like electrospinning. A blended k−ω /k−ε model for turbulence and dynamic overset grids to resolve large amplitude motions were used to simulate two-dimensional uncompressed flow, which was described in axisymmetrical coordinates. The numerical calculation results were obtained by a computational fluid dynamics (CFD) method. The effect of gas flow on the formation of crater-like Taylor cone and the production of nanofibers were also discussed. The experiments were carried out to validate the numerical results. The Polyvinyl Alcohol (PVA)/ distilled water solution with 18wt% and the air pressures ranged varied from 4 to 50kPa were used in our experiments. The results showed that the numerical results were in good agreement with the experimental results. This work provides a deep understanding of the mechanisms of micro fluid jets production in electrospinning processes and two-phase flow in specific type of industrial equipment.

Electrohydrodynamic jet (e-jet) printing technology has the capability of sub-micrometer resolution with large-range viscous inks, but is incompatible with nonplanar and insulating substrates. Here, we develop a theoretical model for an electrostatic lens that is incorporated into an e-jet system to shape the electric field inside the printhead. The electrostatic lens can generate electrostatic focusing to drive a Taylor cone for the generation of jetting, without a voltage being applied between the printhead and the substrate, which avoids the influence of standoff height on the nonplanar substrate and the charge repulsion from polarization of the insulating substrate. The theoretical model, in combination with finite element simulation, is established to reasonably calculate each design parameter of the electrostatic lens-integrated printhead. Further, the e-jet printhead is successfully utilized to direct-write conductive lines with high-viscosity solutions and drop-on-demand print complex pattern with low-viscosity solutions on both insulating and curvilinear substrates. It leads to high-resolution e-jet printing on the arbitrary substrate in a direct, precise and low-voltage manner. The electrostatic lens-integrated printhead thoroughly breaks the restrictions of printing on insulating and nonplanar substrates and significantly broadens its applications.

Electrohydrodynamics (EHD) micro-jet printing technology has become a new method of micro/nano patterning and fabrication because of high resolution, good compatibility and simple structure. Firstly, stresses that Taylor cone meniscus subjected to under pulse voltage are discussed in EHD micro-jet printing system and tangential electric stress grows faster than normal electric stress, and tangential electric stress helps to “push” jet generation. Secondly, apply a pulse voltage superimposed over DC voltage, and investigate correlations between pulse frequency and drop spacing and then pulse frequency and drop diameter, and then compare and analyze the theoretic results with the experimental ones. Finally, as a result that it’s possible to obtain droplets with almost the same interval and desired size in the certain situation through controlling pulse frequency.

Electrified interfaces have been used to produce fine particles. Here, we investigate the behavior of planar electrified interface in the presence of vertical electric field. Corn oil and four KCl aqueous solutions with different concentrations are employed. During the experiments, for the first time, four distinct behaviors of electrified interfaces were disclosed and named as: Hump figure of interface, Taylor cone appearance and its rotary motion on the interface, intermittent jetting and thorough ascending of the interface. Taylor cones’ mean droplet diameter and their angles, discharging velocity at the tip of the cone, the frequency of Taylor cones appearance, and their merging to each other are studied in this paper. Additionally, the circumstances of interface levitation affected by electric field are some of the major results of this study to gain some insight into the electrified interfaces issue.

The paper investigated describes the patterning of a series of drops generated by pulsed cone-jet electrohydrodynamic atomization. The authors concluded that when the voltage frequency is higher than the drop generation frequency, the drops formed and the spacing between one another are no longer uniform. The authors did not calculate the frequency where this transition occurs. A formula has been proposed that can be used to calculate this fulcrum frequency. It is noted that this relation only applies when the capillary is itself conductive. The proposed relation relies primarily on a formula proposed by Suvorov and Zubarev to calculate the Taylor cone formation time.

Electrospinning has introduced a powerful means of fabricating polymer nanofibres into the broader realm of nanotechnology and polymer science. It has attracted considerable attention due to its outstanding versatility and numerous applications, such as the incorporation of nanoparticles within the fibres. The Taylor cone formed at the tip of the syringe that delivers the solution (or melt) plays an important role in controlling the structure, and thus the mechanical and functional properties of the fibres produced. Characterising the dynamic processes that occur within the cone is a challenging experimental task. In this study, operando synchrotron X-ray techniques were used to observe the Taylor cone formed during electrospinning. The combination of imaging with spatially resolved mapping by small angle and wide angle X-ray scattering provides a wealth of information about the cone exterior shape, surface orientation and inner morphology. This express note illustrates the rich body of data that can be collected using multi-modal X-ray imaging and scattering setup. From the observed patterns it is possible to extract information concerning particle density and flow patterns that persist within the Taylor cone. Keywords: Electrospinning, Taylor cone, SAXS, WAXS, Radiography

A method for the in situ creation of field emission structures possessing highly desirable physical characteristics is described. Field emitters are produced by rapid solidification of electrostatically formed high-temperature Taylor cones formed on the ends of laser melted refractory-metal wires. The present state of the technology, progress to employ these field emitters in an ultrafast pulsed electron gun, and potential future advances are summarized.

In this Letter, a three-dimensional (3D) optical correction method, which was verified by simulation, was developed to reconstruct droplet-based flow fields. In the simulation, a synthetic phantom was reconstructed using a simultaneous multiplicative algebraic reconstruction technique with three detectors positioned at the synthetic object (represented by the phantom), with offset angles of 30° relative to each other. Additionally, a projection matrix was developed using the ray tracing method. If the phantom is in liquid, the image of the phantom can be distorted since the light passes through a convex liquid–vapor interface. Because of the optical distortion effect, the projection matrix used to reconstruct a 3D field should be supplemented by the revision ray, instead of the original projection ray. The revision ray can be obtained from the refraction ray occurring on the surface of the liquid. As a result, the error on the reconstruction field of the phantom could be reduced using the developed optical correction method. In addition, the developed optical method was applied to a Taylor cone which was caused by the high voltage between the droplet and the substrate.

Electrospinning is commonly used to produce very fine polymeric fibers. In this technique, a conducting liquid is pumped from an electrified needle into a surrounding dielectric media and the meniscus formed exhibits a conical shape, known as Taylor cone, due to the balance of electrical and surface tension forces. If the needle electrical potential is sufficiently high, the very strong electric field generated at the cone apex cannot be balanced by surface tension and a very thin jet is issued which eventually develops lateral instabilities that are responsible of additional stretching. In this work, we use a theoretical model that describes the kinematic of the midline of the jet, its radius and convective velocity from an Eulerian framework. Balances of mass, linear and angular momentum applied to a slice of the jet, as well as viscous law for stretching, bending and torsion describe the dynamics (nonlinear PDE in time and arclength of the midline). Capillary and electric forces are included in the momentum balance. If periodic orbits are explored, the time dependence of the PDE disappears when the motion is considered with respect to a frame rotating with the jet. One obtains a boundary value problem of ODEs with the frequency as a free parameter. This model is also suitable for describing other kinds of instabilities, such as the axisymmetric one which takes place in drop formation (dripping regime, electrospray).

To solve the problem of salivate,an unsteady phenomenon caused by the mismatch of feed velocity and high-voltage in the electrospinning to fabricate nanoscale fibers,this paper proposes an on-line monitor system based on the multi-featured pattern recognition for realizing both the stability of nanofiber manufacturing and the controllability of fiber diameter.Firstly,an industry CCD is used to collect the image of the Taylor cone continously,and then these images are preprocessed by sharpening,filtering and threshold segmentation.The perimeter,area and height of the Taylor cone are recognized by the multi-featured pattern recognition algorithm to judge the shape and size of the Taylor cone.Finally,the result of pattern recognition is viewed as the feedback signal to adjust the feed module and high-voltage module.Experimental results indicate that when the voltage is 8 kV,the system can be stabilized in 0.43 s,and it maintains a stable shape of Taylor cone without the salivate phenomenon.Moreover,obtained nanoscale fiber shows a uniform diameter.In conclusion,this method has reliably and effectively solved the instability and uncontrollability of nanoscale fiber manufarturing.

This article demonstrated a new approach for fabrication and sharpening of metal tips of scanning probe microscopes. Experimentally, a metal tip was heated and melted by a focused laser light. The tip was then sharpened by a strong electric field and consolidated as the laser was turned off. With a low-vacuum and a high-voltage source, a 25-µm indium-coated platinum wire was sharpened to a tip with diameters below 50 nm. The minimal tip radius by this method is estimated to be below 1 nm. With this technique, in situ tip sharpening for SPM would be possible.

Electrospinning is an effective and versatile technology to fabricate ultrafine nanofiber,however further development is urgently limited due to the low uniformity distribution and unpredictable feature of the fiber deposited. For that sake, experiment has been done and analyzed to address these problems. Relation between process physics-Taylor cone and fiber diameter characters has been discovered. Furthermore, the feature parameters of the Taylor cone are extracted effectively by CCD detection and image processing. The above experiments results and processing data is analysis and examed by the steady jet theory. This paper offers significant theoretical guidance and technical support to the online control of electrospinning fiber diameter.

Co-electrospinning has been one of the most important and viable methods to prepare microfibers with hollow structure. In the process of co-electrospinning, microfibers were formed from polymer solution or melt by the action of high voltage electric field. In this article, the compound Taylor cone, a major parameter determining success or failure to prepare the hollow microfibers, was studied and the patterns of compound cone were summarized. The microfibers with single, double and triplicate holes in the cross-section were fabricated successfully under the guide of these patterns. The morphology of hollow microfibers was observed by scanning electron microscope (SEM).

The charged liquid micro-jet issued from a Taylor cone may develop a special type of non-axisymmetric instability, usually referred to in the literature as a whipping mode. This instability usually manifests itself as a series of fast and violent lashes of the charged jet, which makes its characterization in the laboratory difficult. Recently, we have found that this instability may also develop when the host medium surrounding the Taylor cone and the jet is a dielectric liquid instead of air. When the oscillations of the jet occur inside a dielectric liquid, their frequency and amplitude are much lower than those of the oscillations taking place in air. Taking advantage of this fact, we have performed a detailed experimental characterization of the whipping instability of a charged micro-jet within a dielectric liquid by recording the jet motion with a high-speed camera. Appropriate image processing yields the frequency and wavelength, among the other important characteristics, of the jet whipping as a function of the governing parameters of the experimental set-up (flow rate and applied electric field) and liquid properties. Alternatively, the results can be also written as a function of three dimensionless numbers: the capillary and electrical Bond numbers and the ratio between an electrical relaxation and residence time.

In this paper, we propose an electrospraying microfluidic chip which utilizes the microfluidic cross-junction and strong electric field to generate uniform emulsions and fiber. Our strategy was based on flow-focusing for the formation of a series emulsions by changing concentration of span 80 and applying the electric field to control the size of emulsion. In the results, as the electric filed increased, the size of the emulsion decreased. In additional, the fiber is generated at high voltage of 5000 V. When applying the electric field, the Taylor cone is form and generates the smaller emulsions and fibers, the minimum PLGA emulsion size is about 4 μm and fiber is about 7 μm width.

Solutions of two biodegradable polymers, that is, poly(dl-lactic acid) (PDLLA) and poly(3-hydroxy butyrate) (PHB), were individually delivered to the inner and outer channel of a coaxial-tube spinneret for electrospinning to prepare core−shell fibers used for drug release applications. By interchanging the inner- and outer-channel solutions, either PDLLA/PHB or PHB/PDLLA core−shell fibers could be conveniently obtained. Their fiber diameters were readily controlled by the flow rate of the core fluid (Qc). The effects of Qc on the morphologies of the Taylor cone, the whipping jet, and the electrospun fibers were investigated. Several scaling laws describing the Qc dependence of the outer fiber diameter (Df) and the inner fiber diameter (df) were derived, that is, Df ∼ Qc0.02 and df ∼ Qc0.18 for the PDLLA/PHB fluids and Df ∼ Qc0.30 and df ∼ Qc0.59 for the PHB/PDLLA fluids. These scaling laws provided the processing guidelines for the manipulation of the final diameters of the core−shell fibers for a given p...