Capillary Nozzle Research Articles

Onset condition of pulsating cone-jet mode of electrohydrodynamic jetting for plane, hole, and pin type electrodes

In this work, electrohydrodynamic (EHD) jetting phenomena were observed for three different types of bottom electrode (plane, hole, pin) at constant back pressure condition of the reservoir. Especially, we have focused on the measurement and numerical prediction of the onset voltage for pulsating Taylor cone jetting, changing glass capillary nozzle diameter (outer diameter: 16–47 μm), hydrostatic back pressure head in the reservoir, and the distance between the nozzle and the bottom electrode to provide design information on the EHD multinozzle head.

Electrospraying tuned photoanode structures for dye-sensitized solar cells with enhanced energy conversion efficiency

Nanocrystalline TiO 2 electrodes have been fabricated using commercially available powers (P25) by electrospray coating (ESC) method. The structures and morphologies of the film, which ultimately influence the cell performance, can be controlled by changing the distance between the capillary nozzle and the FTO substrate (spraying distance). A possible mechanism of the evolution of the structures and morphologies has been discussed in detail. The optimized spraying distance for the maximum short-circuit photocurrent density of the cells is 6 cm, while accompanying with the lowest fill factor. The improvement of short-circuit photocurrent density can be mainly ascribed to the better ion-diffusion path, which is caused by presence of the electrolyte “relay stations” in the film. The low fill factor may be attributed to the increase of the resistance at FTO/TiO 2 interface, which may be caused by the secondary spheres in the film. In addition, enhanced energy conversion efficiencies have been observed by using a double-layer structure, which consists of a doctor-bladed 7-μm bottom layer and an electrospray coated 10-μm top layer.

Design and evaluation of single nozzle with a non-conductive tip for reducing applied voltage and pattern width in electrohydrodynamic jet printing (EHDP)

We investigated the effect of a non-conductive tip inserted into a capillary nozzle (inner diameter of 860 µm) on jet formation and pattern width in electrohydrodynamic jet printing. Simulated and experimental results showed that the non-conductive tip stabilized the jet, and reduced the effective nozzle diameter and the onset voltage needed for the cone-jet mode, by eliminating the backflow near the apex of the liquid cone while a tiny backflow away from the apex of the liquid cone still remained. Silver nanocolloid patterns with an average width of 18.5 µm (standard deviation: 1.5 µm) were obtained with an applied voltage of 2.7 kV, a flow rate of 3 µl min−1 and a stage velocity of 200 mm s−1.

Theoretical analysis of electrostatic field in electrospinning systems

In order to analyze the electrostatic field distribution from the capillary nozzle to the grounded plane in the electrospinning process, the typical electrospinning system is simplified to an electrical model. By the model the electrostatic field is formulated in different regions. According to the formulas, the magnitude of the electrostatic field and the potential at a point in the electrospinning space are, respectively, in scale with r − 2 and with r − 1(r is the distance from the point to the solution droplet), and the electrostatic field can be calculated from the voltage applied on the capillary.

Formation of viscoplastic drops by capillary breakup

The process of growth and detachment of drops from a capillary nozzle is studied experimentally by high-speed imaging. Newtonian drops are compared to shear-thinning and viscoplastic drops. Both Newtonian and shear-thinning fluid drops grow on the end of the capillary until a maximum supportable tensile stress is reached in the drop neck, after which they become unstable and detach. The critical stress is not influenced by variations in viscosity or in the degree of shear thinning. Viscoplastic fluids show a different behavior: at low values of the yield stress, the critical stability behavior is similar to that of Newtonian and shear-thinning drops. Above a threshold value, characterized in terms of the drop size, surface tension and tensile yield-stress magnitude, yield-stress forces are larger than surface forces, and the maximum tensile stress achievable in the drop neck at the point of critical stability is governed by the von Mises criterion.

Controlled free-form fabrication of nanowires by dielectrophoretic dispension of colloids

The vertical growth of conductive gold nanowires in ambient atmosphere through on-demand dielectrophoretically guided deposition of nanoparticle-laden colloids is demonstrated. Accelerated by dielectrophoresis, rapidly evaporating colloidal droplets leave a capillary nozzle (diameter of 500 nm) and are guided through an inhomogeneous electrostatic field. The nanoparticles in the colloidal droplets combine under the action of van der Waals attraction forces on the substrate to form highly flexible vertical nanowires with easily controllable lengths and diameters, here in the range of 150–800 nm. After bending to bridge an electrode pair and after annealing at 300 °C, the sample gold nanowires demonstrate excellent electrical conductivity considering their size.

Comparison of solid dispersions produced by supercritical antisolvent and spray-freezing technologies

Oxeglitazar is a new orally administered poorly water soluble active substance used in the treatment of type II diabetes. The objective of this work was to improve its dissolution kinetics using supercritical antisolvent (SAS) and spray-freezing (SF) techniques. Oxeglitazar was formulated with various excipients, including: Poloxamer 188 and 407, polyethylene glycol (PEG) 8000 and polyvinilpyrrolidone (PVP) K17 in a 1:1 weight ratio. In the SAS technology, pharmaceutical ingredients were dissolved in an appropriate solvent, and the feed solution was dispersed through a capillary nozzle in supercritical CO 2 (SC CO 2). Dichloromethane (DCM), chloroform (CHCl 3), and a binary co-solvent system of chloroform–ethanol (EtOH/CHCl 3 50:50, v/v%) were tested. In the SF process, tert-butanol ( tBuOH) was used as solvent. The feed solution was injected into liquid nitrogen through a capillary nozzle located above the surface of the boiling nitrogen. Frozen particles were collected and freeze-dried for 30 h. Formulations were compared in terms of particle morphology, particle size, flow properties, crystallinity, polymorphic purity, residual solvent content, precipitation yield, drug content, specific surface area and dissolution kinetics. SAS and SF processed formulations exhibited enhanced dissolution rates. Within 5 min, the amount of dissolved drug varied from 31.6 to 64.3% for SAS and from 77.9 to 96.9% for freeze-dried formulations while only 30.5% was dissolved from raw drug. Apart from oxeglitazar/PVP K17, SAS prepared solid dispersions were characterized by high crystallinity and acicular shape. Freeze-dried formulations consisted of porous spherical particles with high amorphous content (94.2–100%).

Laser Desorption/Ablation Plumes from Capillary-Like Restricted Volumes

Laser desorption/ionization from structured surfaces has been the object of recently renewed interest. Conditions in the plume of material ablated from such surfaces may differ from those of a sample which is ablated in bulk. Since recombination and secondary ion-molecule reactions in the plume play a major role in determining the types and quantities of ions observed at the detector, these differences are analytically relevant. Desorption/ionization substrates with channels of high aspect ratio are modeled as capillary nozzles, from which free jets are emitted. A previously developed matrix-assisted laser desorption/ionization ablation/ionization model is adapted for these jets. More primary ions reach the detector when ablated from a capillary orifice, but fewer analye ions are created in secondary reactions. These differences in ion yield can persist for arrays of capillaries on the surface, depending on the ratio of their diameter to spacing.

Electrostatic deposition of nanothin films on metal substrate

Electrostatic deposition of nanothin films on metal substrateThin solid film has been deposited by electrohydrodynamic spraying (electrospraying) onto a metal substrate. Electrospraying is a low-energy physical process in which tangential stress exerted by electric field on the surface of a liquid flowing form a capillary nozzle causes jet elongation, and the Coulomb repulsive forces disintegrate of this jet into fine droplets. By this method TiO2, ZnO, MgO, or Al2O3particles of size from 20 to 100 nm electrosprayed from a colloidal suspension were deposited onto a stainless steel substrate. The advantage that electrospray has over other methods for thin solid film production is that the growth rate of the layer is relatively high, the process can be carried out in an ambient atmosphere, in air or other gas, and at low temperature, without the need for a complex reactor and vacuum systems.

Formation of deagglomerated PLGA particles and PLGA-coated ultra fine powders by rapid expansion of supercritical solution with ethanol cosolvent

Rapid expansion of supercritical solution (RESS) was used for preparing polymer particles and polymer coating of ultra fine powders. The polymer of pharmaceutical interest was Poly(lactic-co-glycolic acid) (PLGA with PLA : PGA ratio of 85 : 15 and MW of 50,000-75,000) and the simulated core particles were 1.4-µm SiO2 and 70- nm TiO2 particles. The supercritical solution was prepared by dissolving PLGA in supercritical carbon dioxide with ethanol as a cosolvent. Supercritical solution of CO2-PLGA was sprayed through capillary nozzles to ambient con- ditions, resulting in formation of submicron PLGA particles. Similarly, rapid expansion of supercritical solution of CO2- PLGA suspended with the core particles could provide solvent evaporation and deposition of submicron PLGA par- ticles on the surface of the core particles, resulting in the formation of coating films on dispersed particles of SiO2 and agglomerates of TiO2. The influences of the core particle size, spray nozzle diameter as well as powder-to-polymer weight ratio were also investigated and discussed with respect to the coating performance.

Electrohydrodynamic drop-on-demand patterning in pulsed cone-jet mode at various frequencies

The patterning of a series of drops was investigated by the electrohydrodynamic printing method in the drop-on-demand fashion. A positive pulse voltage was applied to the capillary nozzle periodically to eject a pulsed liquid jet. The ejected jet was directed to the moving substrate, to which DC bias voltage was applied. High-speed imaging revealed that a Taylor cone was established at the nozzle tip during the ejection of the liquid jet, and that the jet directly struck the substrate to form a drop without the jet break-up. The frequency of drop generation can be controlled precisely, because the frequency of the pulsed voltage was almost same as the pulsating frequency of the liquid in pulsed cone-jet mode. The deposited patterns showed a series of uniformly sized drops with a regular spacing. At the pulse voltage frequency of 25 Hz, the diameter of the drops was approximately 95 μm. Using this drop-on-demand method, it is feasible to produce a variety of patterns of dots and continuous/discontinuous lines.

Supercritical antisolvent production of biodegradable micro- and nanoparticles for controlled delivery of paclitaxel

Paclitaxel and poly ( l-Lactic acid) (PLA) were co-precipitated to form micro and submicron particles in a manner similar to that used in the supercritical antisolvent with enhanced mass transfer (SAS-EM) process. As compared with conventional processes, a major advantage of supercritical CO 2 as an antisolvent in the SAS-EM process is the effective removal of residual organic solvents. In this work, the organic phase was sprayed into supercritical CO 2 (for CO 2, Tc = 31.1 °C, Pc = 73.8 bar) from a 500 μm ID capillary nozzle. Ultrasonic vibration with an amplitude of 0 to 120 μm (from a 3/8″ tip diameter titanium probe) was employed in the high pressure vessel during the antisolvent process to provide enhanced mixing between the solvent and antisolvent phases. The role and effects of ultrasonication on the properties of the resulting particles were studied. When no ultrasonication was applied, micrometer-sized particles were obtained. When ultrasonication was applied, more uniform particles in the submicron size range were obtained. The size of the particles was found to vary with the ultrasonic vibration amplitude. Encapsulation efficiencies up to 83.5% and controlled release of paclitaxel for more than 30 days were achieved with the particles fabricated in this study.

Numerical simulation of microdroplet formation in coflowing immiscible liquids

AbstractMonodisperse microdroplets can be formed when a liquid is injected via a capillary needle nozzle into another immiscible coflowing liquid in a microchannel. Such system has been applied in microfluidic devices to produce monodisperse microdroplets with controllable size. In this article, the drop formation in a coflowing system is simulated numerically using a front tracking/finite volume method to investigate the droplet formation mechanism. This numerical method solves a single set of Navier–Stokes equations for both liquid phases on a fixed Eulerian two‐dimensional cylindrical coordinate mesh to account for the fluid flow dynamics. The front tracking method is applied to track the movement of the interface between the two immiscible liquids as well as the surface tension force. The simulation results demonstrate that the process of droplet formation in the coflowing immiscible liquids can be reasonably predicted. Two droplet generation modes (namely dripping and jetting), which have been observed in experiments, are successfully produced through the numerical simulations under certain flow conditions. Moreover, the effects of the continuous phase flow speed, viscosity, and the interface tension on the droplet size are investigated. The correlation of the nondimensional droplet size (r) with the continuous phase flow parameters such as the Reynolds number (Reo), Weber number (Weo), Capillary number (Cao), and viscosity ratios (μ*) can be obtained as r ∝ Cao−1/2 Reo−1/6 for the dripping mode and as r} ∝ Cao1/3 Weo−1/2 μ*−1/2 for the jetting mode from the current simulations. © 2007 American Institute of Chemical Engineers AIChE J, 2007

An Electrospray Method Using a Multi‐Capillary Nozzle Emitter

AbstractA multi‐capillary nozzle emitter consisting of one metal plate with capillary nozzles and a ring type counter electrode was used as a multi‐electrospray atomizer. The number of capillary nozzles, flow rate of the liquid and the interval between the capillary nozzles were changed, and the droplet diameter and the voltage required for a steady cone‐jet mode were measured. For the multi‐capillary nozzle emitter, the interaction between the capillary nozzles is the important factor for obtaining fine droplets of uniform size. These fine droplets are obtained when there is only a small interaction between the capillary nozzles, and the equations obtained from the single capillary nozzle case are also applicable for the multi‐capillary nozzle emitter. When the number of capillary nozzles decreases (a situation which is not good for obtaining a large amount of droplets) or the interval between the capillary nozzles increases, the interaction between the capillary nozzles can be reduced. As the number of capillary nozzles increase, a higher voltage is required to obtain a fine droplet of uniform size.

Micronization of salicylic acid and taxol (paclitaxel) by rapid expansion of supercritical fluids (RESS)

The particle sizes of the pharmaceutical substances are important for their bioavailability. The bioavailability can be improved by reducing the particle size of the drug. In this study, salicylic acid and taxol were micronized by the rapid expansion of supercritical fluids (RESS). Supercritical CO 2 and CO 2 + ethanol mixture were used as solvent. Experiments were carried out to investigate the effect of extraction temperature (318–333 K) and pressure (15–25 MPa), pre-expansion temperature (353–413 K), expansion chamber temperature (273–293 K), spray distance (6–13 cm), co-solvent concentration (ethanol, 1, 2, 3, v/v, %) and nozzle configuration (capillary and orifice nozzle) on the size and morphology of the precipitated salicylic acid particles. For taxol, the effects of extraction pressure (25, 30, 35 MPa) and co-solvent concentration (ethanol, 2, 5, 7, v/v, %) were investigated. The characterization of the particles was determined by scanning electron microscopy (SEM), optical microscopy, and LC–MS analysis. The particle size of the original salicylic acid particles was L/D: 171/29–34/14 μm/μm. Depending upon the different experimental conditions, smaller particles (L/D: 15.73/4.06 μm/μm) were obtained. The particle size of taxol like white crystal powders was reduced from 0.6–17 μm to 0.3–1.7 μm The results showed that the size of the precipitated salicylic acid and taxol particles were smaller than that of original particles and RESS parameters affect the particle size.

The effect of nozzle geometry on the flow characteristics of small water jets

A wide variety of processes make use of plain orifice nozzles. Fuel injectors for internal combustion engines incorporate these nozzles to generate finely atomized sprays. Processes such as jet cutting, jet cleaning, and hydroentanglement, on the other hand, use similar nozzles, but require coherent jets. The spray or jet characteristics depend on the stability of the flow emerging from the orifice. This problem has been extensively researched for nozzles with diameters above 300 μm. Much less is known about the characteristics of jets produced by nozzles with smaller diameters, where viscous effects and small geometric variations due to manufacturing tolerances are likely to play an increasing role. Results are presented of a wide-ranging investigation of geometry effects on the flow parameters and jet characteristics of nozzles with diameters between 120 and 170 μm. Nozzles with circular cross-section and conical, cone-capillary and capillary axial designs were investigated. For conical and cone-capillary nozzles, the effect of cone angle and effects due to interactions between adjacent nozzles in the multi-hole cone-capillary nozzles were studied. For capillary nozzles, the effects of diameter variations and inlet edge roundness for capillary nozzles were considered. Furthermore, the effect of varying the aspect ratio (ratio of major and minor axes) of elliptical nozzles was studied. Flowrate and jet impact force measurements were carried out to determine the discharge coefficient Cd, velocity coefficient Cv, and contraction coefficient Cc of the nozzles for supply pressures between 3 and 12 MPa. Visualizations of the jet flow were carried out in the vicinity of the nozzle exit in order to identify near-nozzle flow regimes and to study jet coherence. The relationship between nozzle geometry, discharge characteristics, and jet coherence is examined.

Design and Performance of a New Thin‐Layer Radial‐Flow Holder for a Quartz Crystal Resonator of an Electrochemical Quartz Crystal Microbalance

AbstractA new compact holder for either 5‐ or 10‐MHz AT‐cut quartz crystal resonator of an electrochemical quartz crystal microbalance was designed, fabricated and characterized. The holder is a hydrodynamically controlled thin‐layer radial‐flow microelectrochemical cell. Its unique feature consists of (i) a micrometer‐screw adjustable distance between the movable coaxial assembly of the Ag/Ag+ pseudoreference electrode and the inlet capillary nozzle with respect to the metal‐film working electrode of the quartz crystal resonator, and (ii) a U‐clamp mountable resonator, easily accessible for change without using any tools. The inlet solution stream is centered axially against the working electrode. The holder performance was tested under different flow conditions. These include hydrodynamic voltammetry measurements on the Fe(CN)$\rm{ {_{6}^{4-}}}$/Fe(CN)$\rm{ {_{6}^{3-}}}$ couple, i.e., a redox system with no mass transfer across the solution–electrode interface, as well as simultaneous chronoamperometry and chronoelectrogravimetry measurements under flow injection analysis (FIA) conditions on the Ag/Ag+ couple, i.e., a system with electrodeposition of a rigid metallic film. Moreover, simultaneous changes of resonant frequency and dynamic resistance were measured under FIA conditions for a glycerol solution, i.e., an electroinactive viscous medium. For the 30<Fm<180 μL min−1 volume flow rate of solution and 50<d<250 μm nozzle‐to‐resonator distance, the holder operates in a thin‐layer radial‐flow regime at a fully developed laminar flow. For Fm=30 μL min−1 and d=100 μm, both mass and charge conversion accompanying silver electrodeposition is appreciably high and close to 35%. Simultaneous measurements of the resonant frequency change and current‐potential or current‐time transients allowed investigations of electrochemical processes involving mass changes of rigid deposits while those of the frequency change and dynamic resistance change involve changes of viscoelastic properties of medium.

Gas Chromatography-Microchip Atmospheric Pressure Chemical Ionization-Mass Spectrometry

An atmospheric pressure chemical ionization (APCI) microchip is presented for combining a gas chromatograph (GC) to a mass spectrometer (MS). The chip includes capillary insertion channel, stopper, vaporizer channel, nozzle and nebulizer gas inlet fabricated on the silicon wafer, and a platinum heater sputtered on a glass wafer. These two wafers are joined by anodic bonding creating a two-dimensional version of an APCI microchip. The sample from GC is directed via heated transfer line capillary to the vaporizer channel of the APCI chip. The etched nozzle forms narrow sample plume, which is ionized by an external corona discharge needle, and the ions are analyzed by a mass spectrometer. The GC-microchip APCI-MS combination provides an efficient method for qualitative and quantitative analysis. The spectra produced by microchip APCI show intensive protonated molecule and some fragmentation products as in classical chemical ionization for structure elucidation. In quantitative analysis the GC-microchip APCI-MS showed good linearity (r(2) = 0.9989) and repeatability (relative standard deviation 4.4%). The limits of detection with signal-to-noise ratio of three were between 0.5 and 2 micromol/L with MS mode using selected ion monitoring and 0.05 micromol/L with MS/MS using multiple reaction monitoring.

Rheological Comparison of Chemical and Physical Blowing Agents in a Thermoplastic Polyolefin

The influences of popular blowing agents (BAs), both chemical and physical types, in solution with a thermoplastic polyolefin (TPO) were investigated with an in-line capillary rheometer nozzle attached to a conventional reciprocating 55-ton injection molding machine. In the experiments, two types of masterbatch chemical BAs (endothermic and exothermic type) were dry mixed with the TPO resin and compared against two types of physical BAs (carbon dioxide and nitrogen) directly injected into a specially designed injection nozzle containing static mixer elements (SMX type). The effects of the main processing conditions (injection speed, pressure, temperature, and BA type and concentration) on the TPO melt rheology were studied. The viscosity reduction behaviors of chemical BAs and physical BAs were compared. The type of BA had a strong influence on the viscosity reduction behavior of the TPO melt, with the maximum viscosity reduction of 47% with 3.2 wt % CO2 at 250 °C. Both physical and chemical BAs were found to successfully fit a previously developed viscosity model for single-phase gas−polymer solutions.

Microscopic fused silica capillary nozzles as supersonic molecular beam sources

Use of fused silica microcapillary tubing for supersonic molecular beam nozzles is reported. Speed ratio measurements were made with nozzles of various diameters and sidewall profiles, demonstrating that these nozzles perform as well as the best conventional nozzles. Commercial microcapillary nozzles therefore offer an effective and inexpensive alternative to conventional metal nozzles.