Emilio J. Vega

• Dr.
• Professor (Associate) at University of Extremadura

We propose using a dielectric beveled nozzle for electrospray and electrohydrodynamic jet printing. This nozzle stabilizes the liquid ejection of low-conductivity liquids, considerably reducing the minimum flow rate below which the flow becomes unstable. This translates into a significant reduction of the minimum jet diameter. Due to its dielectric...

We propose using a dielectric beveled nozzle for electrospray and electrohydrodynamic jet printing. This nozzle stabilizes the liquid ejection of low-conductivity liquids, considerably reducing the minimum flow rate below which the flow becomes unstable. This translates into a significant reduction of the minimum jet diameter. Due to its dielectric...

Electrohydrodynamic (EHD) jet printing is a well-known advanced manufacturing technique that uses electric fields to generate and control fine jets of fluid for high-precision deposition of materials. This method enables the printing of extremely fine features, making it ideal for applications such as printed electronics. However, little is known a...

We study the influence of bulk viscoelasticity on bubble bursting experimentally. We consider polymers with disparate molecular weights to analyze the effects of the polymer's extensional relaxation time and viscosity separately. Viscoelasticity suppresses the droplet emission roughly if the characteristic strain rate of the Worthington jet exceeds...

This paper analyzes experimentally and numerically the steady bubble rising in water with a surfactant dissolved at very low concentrations. We explain how traces of surfactant can significantly change the bubble dynamics. The tiny surface tension variation produced by the surfactant monolayer has a negligible effect on the capillary pressure. Howe...

Electrohydrodynamic (EHD) jet printing is a well-known advanced manufacturing technique that uses electric fields to generate and control fine jets of fluid for high-precision deposition of materials. This method enables the printing of extremely fine features, making it ideal for applications such as printed electronics. However, little is known a...

This paper analyzes experimentally and numerically the steady bubble rising in water with a surfactant dissolved at very low concentrations. We explain how traces of surfactant can significantly change the bubble dynamics. The tiny surface tension variation produced by the surfactant monolayer has a negligible effect on the capillary pressure. Howe...

We study the bursting of a bubble covered with an insoluble surfactant experimentally. We conclude that the bubble bursting takes longer than that of a surfactant-free bubble with the same equilibrium surface tension due to the interfacial elasticity. A tiny bubble is formed at the cavity bottom right before the free surface reversal due to the Mar...

There has been enormous interest in the production of fluids with rheological properties similar to those of real blood over the last few years. Application fields range from biomicrofluidics (microscale) to forensic science (macroscale). The inclusion of flexible microparticles in blood analogue fluids has been demonstrated to be essential in orde...

We study the production of fibers with Solution Blow Spinning (SBS) for low values of both the polymer molecular weight and the air-coflow pressure. Specifically, we analyze the influence of the air-coflow temperature and the spinneret position on the diameter and size polydispersity of poly(ethylene oxide) (PEO) fibers. Our results show that the f...

We find and study the viscoelastic transition in transonic flow focusing when polymers of low molecular weights are dissolved in water at the appropriate concentration. This phenomenon is explained in terms of the coil-stretch transition of the polymers crossing the tapering meniscus, where the airstream produces very large strain rates. The result...

Fire-shaped nozzles can be used to study the deformability of microcapsules, particles, or cells traveling in a flow. Though their geometry depends on the dimensions of the original glass capillary and the heating conditions, they all produce a strain rate peak approximately at the section where the diameter is 1.5 times the minimum. The intensity...

We study experimentally the stability of micrometer weakly-viscoelastic jets produced with transonic flow focusing. Highly stable jets are formed when a low molecular weight polymer is added to water at a given low concentration and the injected flow rate is reduced to its minimum value. In this case, the capillary instability is delayed, and the j...

We study experimentally the stability of micrometer weakly-viscoelastic jets produced with tran-sonic flow focusing. Highly stable jets are formed when a low molecular weight polymer is added to water at a given low concentration and the injected flow rate is reduced to its minimum value. In this case, the capillary instability is delayed, and the...

We find and study the viscoelastic transition in transonic flow focusing when polymers of low molecular weights are dissolved in water at the appropriate concentration. This phenomenon is explained in terms of the coil-stretch transition of the polymers crossing the tapering meniscus, where the airstream produces very large strain rates. The result...

Microfluidics has proven to be an extraordinary working platform to mimic and study blood flow phenomena and the dynamics of components of the human microcirculatory system. However, the use of real blood increases the complexity to perform these kinds of in vitro blood experiments due to diverse problems such as coagulation, sample storage, and ha...

Long polymeric chains highly stretched and aligned with the flow confer a strong mechanical anisotropy on a viscoelastic solution. The electrically-driven transport of free ions under such conditions is far from being understood. In this paper, we determine experimentally whether the above-mentioned deviation from isotropy affects the electric char...

Long polymeric chains highly stretched and aligned with the flow confer a strong mechanical anisotropy on a viscoelastic solution. In this paper, we determine experimentally whether this deviation from isotropy affects the electric charge transport across the liquid. To this end, we measure the electrical conductivity in the flow (stretching) direc...

During the last two decades, several kinds of particulate blood analogue fluids have been proposed, but none of those were able to mimic the multiphase effects of real blood. Hence, it is clear that it is crucial to develop a simple multiphase blood analogue to be used for in vitro experiments at both macro- and microscale level. To the best of our...

We study both numerically and experimentally the breakup of a viscoelastic liquid bridge formed between two parallel electrodes. The polymer solutions and applied voltages are those commonly used in electrospinning and near-field electrospinning. We solve the leaky-dielectric finitely extensible nonlinear elastic-Peterlin (FENE-P) model to describe...

We study both numerically and experimentally the breakup of a viscoelastic liquid bridge between two parallel electrodes. We solve the leaky-dielectric FENE-P model to describe the dynamical response of the liquid bridge under isothermal conditions. The results show that the surface charge screens the inner electric field perpendicular to the free...

This study concerns the development and test of analogue fluids which can be used in tests focused on cell deformability studies. The analogue fluids were characterized in terms of their main physico-chemical properties, the size distribution of the particles (mimicking the cells) and on their deformability. From the various approaches tested here,...

A simple mass production emulsification technique was used to fabricate powder of flexible microparticles of PDMS. The insertion of a membrane/filter between the syringes in the two-syringe method allows to increase the monodispersity of the droplets collection, with sizes of a few microns. PDMS-water emulsions were made using this manual technique...

We study with ultra-high-speed imaging the thinning of the filament formed during the breakup of a pendant droplet of very weakly viscoelastic polymer solutions of polyvinylpyrrolidone (PVP) and polyethylene oxide (PEO). In the latter case, we consider two molecular weights: 105 g/mol (PEO100K) and 2×106 g/mol (PEO2M). The results allow us to measu...

Polydimethylsiloxane (PDMS) is one of the most widely used polymers in microfluidics. Furthermore, magnetic nanoparticles (MNPs), due their superior thermal properties, are also gaining a great interest among the industry and microfluidic scientific community. In this work, a technique based on a flow focusing principle was used to produce magnetic...

Polydimethylsiloxane (PDMS) has a wide variety of commercial and industrial applications due to its mechanical and rheological properties in a range similar to the living tissues. In this study, we demonstrate that PDMS can be used to produce deformable microparticles to be integrated in the development of particulate blood analogue fluids. The dif...

Most blood cells exhibit a natural deformation capability. Specifically, red blood cells (RBCs) are characterized by their great ability to deform and squeeze through microcapillary vessels, even with strict restrictions, recovering their shape after crossing them. That capability can be affected by various blood diseases (malaria, diabetes, etc),...

We apply the gaseous flow focusing principle to produce fibers of polyvinylpyrrolidone down to the nanometer scale. The polymer solution is injected in front of a glass converging micronozzle through which a high-speed air stream flows. The air stream sucks and drags the liquid forming a meniscus whose tip emits a thin jet. The jet flies while whip...

We determine experimentally, with an unprecedented spatiotemporal resolution, the evolution of the liquid free surface during the pinching of a pendant droplet. We observe the transition from the inertio-capillary regime to the inertio-viscous-capillary final stage for a low viscosity liquid. Experiments with 5-cSt silicone oil show the formation o...

Polydimethylsiloxane (PDMS), due to its remarkable properties, is a suitable polymer for the production of microparticles with industrial and medical applications. The micro-sized PDMS liquid droplets suffer a pronounced shrinkage while curing to turn into solid particles. In this article, we report the calibration of the shrinkage phenomenon in th...

DOI:https://doi.org/10.1103/PhysRevLett.120.099901

Previous theoretical studies have indicated that liquid bridges close to the Plateau-Rayleigh instability limit can be stabilized when the upper supporting disk vibrates at a very high frequency and with a very small amplitude. The major effect of the vibration-induced pressure field is to straighten the liquid bridge free surface to compensate for...

The flow focusing principle has recently been shown to successfully generate micrometer viscoelastic jets. In this technique, the liquid jet is gently extruded by the smooth suction caused by the acceleration in the discharge orifice of a coflowing gas stream. Nozzle clogging is a rare phenomenon in flow focusing because the emitted jet is much thi...

Splash suppression during drop impact continues to be a grand challenge. To date, only a few techniques for the complete suppression of splash exist. Reducing the ambient pressure and using complex surfaces (microstructured and/or soft) are two of the recently discovered ones which may not be very practical in many technological processes. The idea...

We examine both theoretically and experimentally the breakup of a pendant drop loaded with an insoluble surfactant. The experiments show that a significant amount of surfactant is trapped in the resulting satellite droplet. This result contradicts previous theoretical predictions, where the effects of surface tension variation were limited to solut...

The characterization of the extensional rheology of polymeric solutions is important in several applications and industrial processes. Filament stretching and capillary breakup rheometers have been developed to characterize the extensional properties of polymeric solutions, mostly for high-viscosity fluids. However, for low concentration polymer so...

We examine experimentally the effects of surface-active impurities on the small-amplitude free oscillations of axisymmetric liquid bridges. The surface tension, oscillation frequency, and damping rate are measured at different instants from the free surface formation. The experiments with n-hexadecane and n-dodecane show that none of these interfac...

Polydimethylsiloxane (PDMS), due to its remarkable properties, is one of the most widely used polymers in many industrial and medical applications. In this work, a technique based on a flow focusing technique is used to produce PDMS spherical particles with sizes of a few microns. PDMS precursor is injected through a hypodermic needle to form a fil...

The production of viscoelastic capillary jets with gaseous flow focusing is studied experimentally. In this technique, the liquid is injected at a constant flow rate through a feeding capillary located in front of the discharge orifice. A gas stream coflows with the jet across the orifice driven by a constant pressure drop. The gas stream sucks and...

A liquid bridge is a liquid column held captive between two coaxial and parallel solid disks. It is an excellent test bench where measuring the surface tension. In this paper, we used this fluid configuration to examine experimentally the effects of ambient impurities on the surface tension over time. For this purpose, the liquid bridge equilibrium...

The study of the blood flow behaviour through microchannels is crucial to improve our understanding about blood flow phenomena happening in the human microcirculatory system. However, the difficulties associated with the use of in vitro blood, such as coagulation and sample storage, have promoted the increasing interest to develop fluids with rheol...

We analyze both theoretically and experimentally the dynamical behavior of an isothermal axisymmetric liquid bridge close to the minimum-volume stability limit. First, the nature of this stability limit is investigated experimentally by determining the liquid bridge response to a mass force pulse for volumes just above that limit. In our experiment...

We analyze both experimentally and numerically the formation of microbubbles in the jetting regime reached when a moderately viscous liquid stream focuses a gaseous meniscus inside a converging micronozzle. If the total (stagnation) pressure of the injected gas current is fixed upstream, then there are certain conditions on which a quasisteady gas...

We propose and validate an experimental method to analyze the propagation of micrometer surface waves over a liquid column held between two rods, 100 μm in radius. One of the rods vibrates at frequencies of the order of several kHz, while the other remains still. Surface waves, very few microns in amplitude, travel from the oscillating rod to the o...

In additive manufacturing (AM), three-dimen sional objects are built layer by layer by joining each layer to the previous one. Those layers can be formed from the direct deposition of metallic drops resulting from the breakage of a micrometer jet. The jet is produced by ejecting through a nozzle/orifice a metal melted in a crucible. In this paper,...

A new technique is proposed in this paper to produce jets, droplets, and emulsions with sizes ranging from tens of microns down to the submicrometer scale. Liquid is injected at a constant flow rate through a hypodermic needle to form a film over the needle's outer surface. This film flows toward the needle tip until a liquid ligament is steadily e...

We present a robust and computationally efficient numerical scheme for simulating steady electrohydrodynamic atomization processes (electrospray). The main simplification assumed in this scheme is that all the free electrical charges are distributed over the interface. A comparison of the results with those calculated with a volume-of-fluid method...

A new technique for producing steady metallic jets is proposed. It allows the production of supercritical jets with Weber numbers well below unity, which entails important technological advantages over existing techniques. The metallic liquid is injected through a micrometer converging nozzle located inside a gas stream. Both the liquid jet and the...

We present an experimental setup for studying the steady air flow in a diesel engine chamber. An engine block containing the inlet manifold was placed on a test bench. A steady air stream crossed the inlet manifold and entered a glass chamber driven by a fan. A PIV system was set up around the bench to measure the in-chamber flow. An air spray gun...

Backlight optical imaging is an experimental technique with an enormous potential in microfluidics to study very varied fluid configurations and phenomena. In this paper, we show the capability of this technique to precisely characterize the capillary waves growing in electrified microjets. For this purpose, images of electrified liquid jets formed by e...

We evaluate the precision of backlight optical imaging to locate the position of a free surface close to the diffraction limit. For this purpose, we acquired and processed images of liquid films at equilibrium deposited on a capillary 10 μm in diameter. The detected contours were compared with the solution of the exact Young–Laplace equation. Devia...

In this paper, we assess the validity of a universal solution based on the slenderness approximation to describe the velocity and shape of viscous capillary jets produced by two very different mechanisms: the action of the constant gravity force and the focusing effect of a coflowing gas stream. In the gravitational case, the jet's velocity distrib...

The dynamical response of an isothermal liquid bridge to a coaxial gas stream is examined from axisymmetric numerical simulations of the Navier–Stokes equations. The simulation method is previously validated by calculating the temporal evolution of the first oscillation mode in both cylindrical and axisymmetric liquid bridges. The comparison with o...

In the flow focusing technique, a liquid flow rate Q is injected through a microcapillary to form a meniscus attached to its edge. The meniscus is stretched until a thin jet tapers from its tip due to the action of a gas stream driven by a pressure drop Δp. Both the liquid jet and the gas stream cross the orifice of a plate located in front of the...

We discuss the use of flame-shaped glass micro-nozzles for ultra-fine liquid atomization by flow focusing (DePonte et al 2008 J. Phys. D: Appl. Phys. 41 195505), which may have great importance in very varied technological fields, such as biotechnology, biomedicine and analytical chemistry. Some advantages offered by these nozzles over the original...

We analyzed experimentally the damping of both axial and lateral free oscillations of small amplitude in axisymmetric liquid bridges. We excited the first oscillation mode in nearly inviscid and in moderately viscous liquid bridges, and measured the parameters which characterize that mode. The axial spatial dependence of those parameters was determ...

The precision of optical imaging to study free surface dynamics is analyzed. The damping of a liquid bridge free surface oscillation is used to validate this method. Images are acquired with a digital camera at relatively high frame rates and processed by several techniques. Oscillations with amplitudes of about 20 times smaller than the pixel size...

In this note, we explore the precision of the optical imaging method for measuring the free surface position of a micrometer fluid shape. For this purpose, images of a liquid film deposited on a rod were acquired and processed. The resulting contour was compared with the corresponding solution to the Young-Laplace equation. The average deviation wa...