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Interfacially driven flows are ubiquitous in biological processes and engineering applications. In these systems, the interface separating adjacent fluid phases is subject to mechanical stresses that drive the fluid into motion and cause deformations. The origin of interfacial stresses may vary from one physical system to another. In some cases, such as in electrohydrodynamic flows, an external electric field induces interfacial stresses that drag the fluid into motion. Alternatively, in active matter systems, an internal mechanism converts chemical energy into mechanical work and drives the system out of equilibrium. The main challenge in studying these systems lies in unraveling the complex interplay between the bulk flow, nonlinear transport on the interface, and interface mechanics, which collectively give rise to intricate dynamical behaviors.We develop robust theoretical and computational frameworks to address these challenges. In the first part of this thesis, we employ analytical and numerical analyses to study different canonical electrohydrodynamic problems. The interfacial charge dynamics is modeled by considering different transport mechanisms including Ohmic conduction, advection by the flow, and finite charge relaxation. Using this model, we identify different modes of instability and explore how the non-equilibrium evolution of flow and interfacial charge dynamics lead to nonlinear phenomena observed in experiments, such as tip streaming in liquid films, Quincke rotation in drops, tip formation, and the growth of charge density shocks in stratified systems.Furthermore, our investigation extends to biological surfaces that exhibit in-plane order, such as nematic or polar, and are driven internally by microscopic chemical reactions. We study morphological dynamics in a freely-suspended viscous drop with surface nematic activity, which serves as a simplified model for understanding self-organized behaviors in active living systems such as cells. We demon

We study experimentally and numerically the onset of tip streaming in an electrified droplet. The experiments show that, for a sufficiently small dimensionless conductivity, the droplet apex oscillates before ejecting a liquid jet. This effect is caused by the limited charge transfer from the bulk to the interface. This reduces the electrostatic pressure at the droplet's stretching tip, preventing liquid ejection. This reduction of the electrostatic pressure is compensated for by the electric shear stress arising during apex oscillations, which eventually leads to the jet formation. The stability limit calculated from the global stability analysis perfectly agrees with experimental results. However, this analysis predicts non-oscillatory, non-localized instability in all the cases, suggesting that both the oscillatory behavior and the small local scale characterizing tip streaming arise during the nonlinear droplet deformation.

In this work, a numerical model for the simulation of two-phase electrohydrodynamic (EHD) problems is proposed. It is characterized by a physically consistent treatment of surface tension as well as a jump in the electric material properties. The formulation is based on a finite element method enriched with special shape functions, capable of accurate capturing discontinuities both in the fluid pressure and the gradient of the electric potential. Phase interface is, thus, represented as a zero-thickness boundary. The proposed methodology allows modeling the electric force as an interfacial one, strictly abiding with the physics. The approach is tested using the droplet deformation benchmarks. Moreover, application of the method to study a three-dimensional (3D) case, not characterized by symmetry of revolution, is shown. The proposed methodology defines a basis for an enriched finite element method for a wide range of EHD problems., The authors acknowledge the financial support of the Ministerio de Ciencia, Innovaci on e Universidades of Spain via the “Severo Ochoa Programme” for Centres of Excellence in R&D (Referece No. CEX2018-000797-S) given to the International Centre for Numerical Methods in Engineering (CIMNE). The work of C. Narvaez-Mu~noz was supported by the “Severo Ochoa Ph.D. Scholarship” Reference No. PRE2020-096632. Parts of this work were done in the framework of DIDRO project (Toward establishing a Digital twin for manufacturing via drop-on-demand inkjet printing. Proyectos Estrat egicos Orientados a la Transici on Ecol ogica y a la Transici on Digital. Reference No. TED2921-130471B-I00) supported by the Ministerio de Ciencia, Innovaci on e Universidades of Spain. M. Hashemi acknowledges the funding received from European Union’s Horizon 2020 Research and Innovation Programme (European High-Performance Computing Joint Undertaking Grant Agreement No. 955558) as part of EFLOWS4HPC project. P. Ryzhakov and J. Pons-Prats are Serra Hunter fellows., Peer Reviewed, Postprint (published version)

The electrohydrodynamics' (EHD) perfect dielectric model was added into computational fluid dynamics (CFD) software OpenFOAM® in order to improve its usability for the EHD field and specifically for the mentioned model. Based on the investigated literature, it can be said that this is the most complete implementation of the said model. Two sets of numerical simulations with two different fluids are presented and analyzed. One set is one-dimensional. The other set is with a drop of one fluid surrounded by other fluid. Oscillations can be observed with certain expressions or calculation strategies for the electrostrictive force, and used for disregarding them. Results that are closer to analytical predictions can be obtained by using appropriate expression for the dielectric force. The electrostrictive force was implemented not only for nonpolar, but also for polar fluids, and it is shown that it might significantly influence the drop deformation. Calculated and analytically predicted drop deformations were close or comparable even up to around 0.25, what is significantly higher and different from a previous study made by other authors. Different expressions for the electric permittivity and usage of limiters for volume fractions were investigated. Conclusions from this paper can be transferred to more complicated models.

The electrohydrodynamics' (EHD) perfect dielectric model was added into computational fluid dynamics (CFD) software OpenFOAM® in order to improve its usability for the EHD field and specifically for the mentioned model. Based on the investigated literature, it can be said that this is the most complete implementation of the said model. Two sets of numerical simulations with two different fluids are presented and analyzed. One set is one-dimensional. The other set is with a drop of one fluid surrounded by other fluid. Oscillations can be observed with certain expressions or calculation strategies for the electrostrictive force, and used for disregarding them. Results that are closer to analytical predictions can be obtained by using appropriate expression for the dielectric force. The electrostrictive force was implemented not only for nonpolar, but also for polar fluids, and it is shown that it might significantly influence the drop deformation. Calculated and analytically predicted drop deformations were close or comparable even up to around 0.25, what is significantly higher and different from a previous study made by other authors. Different expressions for the electric permittivity and usage of limiters for volume fractions were investigated. Conclusions from this paper can be transferred to more complicated models.

This thesis focuses on two topics involving electric field-fluid interactions. The first is the experimental realization of a coherent, macroscopic state of aligned dipolar filaments of water molecules under an applied electric field. The second is the conception and design of an electroosmotic micropump with gate voltage-induced giant Onsager coefficient. The first topic is relevant to a new kind of electrorheological (ER) fluids, purely composed of water molecules dispersed in silicone oil. This is inspired by the microscopic mechanism of giant ER (GER) effect as well as water’s evident polar characteristic when confined in nanoscale structures. We fabricated a setup including an active region with 60% porosity to permit only vaporized water molecules passing through. The vaporized water molecules from a thermostatic reservoir are shown to form filamentary or columnar structures, penetrating through the porous silicone oil, as a state with minimum energy in response to an external electric field. The formation of such structures is visualized directly by utilizing water-soluble fluorescent probe and captured by inverted confocal microscopy through a transparent electrode. The attendant GER effect, represented by a well-defined yield stress, is measured as a manifestation of such a coherent new molecular state. A phenomenological theory is presented to support the experimental data, with excellent quantitative agreement. The second topic of this thesis is the conception and design of a novel micropump actuated by the electroosmotic (EO) effect. The efficiency for the traditional EO micropumps is limited by the non-slip boundary condition at the liquid/solid interface, typically not surpassing 1%. This ceiling can be broken by our new design of gate voltage-induced EO micropump coupled with slipping effect from superhydrophobic surfaces. The basic idea is first separating the bulk ions by using a pulsed gate voltage, then driving the separated bulk ions with tangent

There has been an explosive interest in 2D- and 3D-printing production methods during the past decade due to the ability to rapidly create almost arbitrary structures. Challenges of printing control are encountered for instance when pushing the methods to produce smaller and smaller structures. Electrostatic printing methods ejects an ink from a nozzle onto the printing surface using a strong electric field. Distortions in the electric field causes the printing to behave in ways that may not be expected, and therefore decrease the control of printing of smaller structures. In the first part of the thesis we introduce a guiding electrode to actively correct the printing paths of the ejected material by changing the electric field. This technique was used to create 2D- and 3D-structures of plastic and increased the printing control when the guiding electrode was active. The second part of the thesis is focused on using electrowriting to spray a suspension of graphene oxide to create thin films on substrates. The suspension will partially evaporate in the spray. The solid content of the suspension, the graphene oxide, undergoes folding and crumpling as the spray droplet size decreases due to solvent evaporation. Too little evaporation at close spraying distances will result in coffee-stain type of effects. We have shown the possibility to control the microstructure of the graphene oxide thin films by optimization of the spraying distance. The increased control in the electrowriting methods will allow us to create structures of supercapacitors for energy storage. We will use these methods to evaluate the possible electrical energy storage possible through microstructure optimization.

A perfect dielectric model was incorporated into the OpenFOAM® software and used for investigation and, possibly, improvements of electrohydrodynamic calculations. Two different sets of numerical simulations were analyzed, in which two different fluids were present. The first set was one-dimensional, while in the second, a drop of one fluid was surrounded by the other fluid. It is shown that oscillations and possibly artificial generation of a curl of the electric field strength can be observed at applying certain expressions or calculation strategies, which can be thus abandoned. Usage of dynamic meshes, at least those present in the used software, and of limiters for the gradient of the electric field strength can lead to large numerical errors. It is also shown that usage of certain cell face values could improve the results. An electric Courant number was derived by dimensional analysis, and it could be suggested for future calculations. Conclusions made in this paper are expected to be transferable to other more complicated models., Model idealnog dielektrika je uključen u programski paket OpenFOAM® (OpenFOAM Foundation, UK) i korišćen za ispitivanje i moguće poboljšavanje elektrohidrodinamičkih proračuna. Analizirana su dva različita seta numeričkih simulacija, u kojima su bila modelovana dva različita fluida. Prvi set je bio jednodimenzionalan dok je u drugom setu kap jednog fluida bila okružena drugim fluidom. U radu je pokazano da se određeni izrazi ili strategije izračunavanja mogu odbaciti usled pojave oscilacija i mogućeg veštačkog stvaranja rotora jačine električnog polja. Korišćenje pokretnih mreža, barem onih prisutnih u programskom paketu OpenFOAM®, i limitera za gradijent jačine električnog polja mogu dovesti do velikih numeričkih grešaka. Takođe je pokazano da bi korišćenje određenih vrednosti sa površi ćelija moglo poboljšati rezultate. Izraz za električni Kuronov broj je izveden dimenzionom analizom i mogao bi se preporučiti za buduće proračune. Očekuje se da su zaključci iz ovog rada prenosivi na druge, komplikovanije modele.

There has been an explosive interest in 2D- and 3D-printing production methods during the past decade due to the ability to rapidly create almost arbitrary structures. Challenges of printing control are encountered for instance when pushing the methods to produce smaller and smaller structures. Electrostatic printing methods ejects an ink from a nozzle onto the printing surface using a strong electric field. Distortions in the electric field causes the printing to behave in ways that may not be expected, and therefore decrease the control of printing of smaller structures. In the first part of the thesis we introduce a guiding electrode to actively correct the printing paths of the ejected material by changing the electric field. This technique was used to create 2D- and 3D-structures of plastic and increased the printing control when the guiding electrode was active. The second part of the thesis is focused on using electrowriting to spray a suspension of graphene oxide to create thin films on substrates. The suspension will partially evaporate in the spray. The solid content of the suspension, the graphene oxide, undergoes folding and crumpling as the spray droplet size decreases due to solvent evaporation. Too little evaporation at close spraying distances will result in coffee-stain type of effects. We have shown the possibility to control the microstructure of the graphene oxide thin films by optimization of the spraying distance. The increased control in the electrowriting methods will allow us to create structures of supercapacitors for energy storage. We will use these methods to evaluate the possible electrical energy storage possible through microstructure optimization.

A perfect dielectric model was incorporated into the OpenFOAM® software and used for investigation and, possibly, improvements of electrohydrodynamic calculations. Two different sets of numerical simulations were analyzed, in which two different fluids were present. The first set was one-dimensional, while in the second, a drop of one fluid was surrounded by the other fluid. It is shown that oscillations and possibly artificial generation of a curl of the electric field strength can be observed at applying certain expressions or calculation strategies, which can be thus abandoned. Usage of dynamic meshes, at least those present in the used software, and of limiters for the gradient of the electric field strength can lead to large numerical errors. It is also shown that usage of certain cell face values could improve the results. An electric Courant number was derived by dimensional analysis, and it could be suggested for future calculations. Conclusions made in this paper are expected to be transferable to other more complicated models., Model idealnog dielektrika je uključen u programski paket OpenFOAM® (OpenFOAM Foundation, UK) i korišćen za ispitivanje i moguće poboljšavanje elektrohidrodinamičkih proračuna. Analizirana su dva različita seta numeričkih simulacija, u kojima su bila modelovana dva različita fluida. Prvi set je bio jednodimenzionalan dok je u drugom setu kap jednog fluida bila okružena drugim fluidom. U radu je pokazano da se određeni izrazi ili strategije izračunavanja mogu odbaciti usled pojave oscilacija i mogućeg veštačkog stvaranja rotora jačine električnog polja. Korišćenje pokretnih mreža, barem onih prisutnih u programskom paketu OpenFOAM®, i limitera za gradijent jačine električnog polja mogu dovesti do velikih numeričkih grešaka. Takođe je pokazano da bi korišćenje određenih vrednosti sa površi ćelija moglo poboljšati rezultate. Izraz za električni Kuronov broj je izveden dimenzionom analizom i mogao bi se preporučiti za buduće proračune. Očekuje se da su zaključci iz ovog rada prenosivi na druge, komplikovanije modele.

Flow electrification constitutes a significant hazard to operational safety in industry and for this reason it has been studied in detail over the years. It is generally accepted that the impact of turbulence on the electrification of liquids is of paramount importance. More specifically, at sufficiently high Reynolds numbers and for low-conductivity liquids such as hydrocarbons, the thickness of the hydrodynamic boundary layer can become comparable to that of the electrical double layer. This can lead to increased charge diffusion towards the bulk of the flow and, subsequently, flow electrification. However, quantitative information of the underpinning mechanisms of this phenomenon is still lacking. In this paper we present a computational framework for the study of electrification of liquid flows via numerical simulations. In the first part of the paper, we present the governing equations and describe the proposed algorithm and its implementation in pafiX, which is a computational tool for the simulation of fluid flows related to explosion protection. In the second part, we present results from numerical tests that we performed in order to access the efficiency of the proposed computational framework.

The first droplet produced by a low-conductivity pendant/sessile droplet subject to a strong electric field is particularly important at the fundamental level because, in contrast to steady electrospray phenomena, its ejection entails complex charge relaxation and electrokinetic processes. Besides, it is technologically relevant because of its very small diameter and large electric charge per unit volume. In this work, we present an experimental technique to measure with unprecedented accuracy the diameter of the droplet and to determine for the first time its electric charge. We discuss both the advantages of our technique over possible alternatives and the limitations of the method. The proposed method is applied to two alcohols with electrical conductivities of the order of a few lS/m. The high sensitivity of our experimental technique allows us to determine the influence of both the magnitude and the polarity of the applied voltage on the size and charge of the ejected droplet. The electric charge of the first-emitted droplet lies in the interval 0:51 q=qR 0:66 (qR is the Rayleigh limit of charge) for the two liquids analyzed. These experimental values are slightly larger than those obtained from theoretical predictions. The value of q=qR for the first droplet is very relevant because it can be regarded as an upper bound of those of the droplets subsequently emitted in the cone-jet mode of electrospray.

The first droplet produced by a low-conductivity pendant/sessile droplet subject to a strong electric field is particularly important at the fundamental level because, in contrast to steady electrospray phenomena, its ejection entails complex charge relaxation and electrokinetic processes. Besides, it is technologically relevant because of its very small diameter and large electric charge per unit volume. In this work, we present an experimental technique to measure with unprecedented accuracy the diameter of the droplet and to determine for the first time its electric charge. We discuss both the advantages of our technique over possible alternatives and the limitations of the method. The proposed method is applied to two alcohols with electrical conductivities of the order of a few lS/m. The high sensitivity of our experimental technique allows us to determine the influence of both the magnitude and the polarity of the applied voltage on the size and charge of the ejected droplet. The electric charge of the first-emitted droplet lies in the interval 0:51 q=qR 0:66 (qR is the Rayleigh limit of charge) for the two liquids analyzed. These experimental values are slightly larger than those obtained from theoretical predictions. The value of q=qR for the first droplet is very relevant because it can be regarded as an upper bound of those of the droplets subsequently emitted in the cone-jet mode of electrospray.

Near-field electrospinning (NFES) is an additive manufacturing technique that allows for both high-resolution 3D structures and a wide variety of printed materials. Typically, a high electric field between a nozzle, the spinneret, and the substrate creates a mu m-sized jet of a supplied liquid material. With mm distances between spinneret and sample, it is possible to have a fair control of the lateral placement of the deposited material. The placement is, however, distributed by various electrostatic phenomena, and this is one of the present challenges in developing NFES into a more versatile technique. In this paper, a higher degree of control in NFES placement was achieved through manipulation of the electric field direction, using an auxiliary steering electrode. The position of a polycaprolactone plastic jet was determined in real-time with a camera attached to a stereo microscope. The measured position was used to calculate an applied potential to the steering electrode to guide the plastic jet to the desired position. The placement accuracy was measured both at the substrate and during flight using the camera and microscope. The higher control was revealed through the deposition of plastic fibers in a pattern with decreasing separation, with and without the active steering electrode enabled. It is in the authors' opinion that the fabrication of dense structures could be possible with further refinement of the technique.

The first droplet produced by a low-conductivity pendant/sessile droplet subject to a strong electric field is particularly important at the fundamental level because, in contrast to steady electrospray phenomena, its ejection entails complex charge relaxation and electrokinetic processes. Besides, it is technologically relevant because of its very small diameter and large electric charge per unit volume. In this work, we present an experimental technique to measure with unprecedented accuracy the diameter of the droplet and to determine for the first time its electric charge. We discuss both the advantages of our technique over possible alternatives and the limitations of the method. The proposed method is applied to two alcohols with electrical conductivities of the order of a few lS/m. The high sensitivity of our experimental technique allows us to determine the influence of both the magnitude and the polarity of the applied voltage on the size and charge of the ejected droplet. The electric charge of the first-emitted droplet lies in the interval 0:51 q=qR 0:66 (qR is the Rayleigh limit of charge) for the two liquids analyzed. These experimental values are slightly larger than those obtained from theoretical predictions. The value of q=qR for the first droplet is very relevant because it can be regarded as an upper bound of those of the droplets subsequently emitted in the cone-jet mode of electrospray.

Near-field electrospinning (NFES) is an additive manufacturing technique that allows for both high-resolution 3D structures and a wide variety of printed materials. Typically, a high electric field between a nozzle, the spinneret, and the substrate creates a mu m-sized jet of a supplied liquid material. With mm distances between spinneret and sample, it is possible to have a fair control of the lateral placement of the deposited material. The placement is, however, distributed by various electrostatic phenomena, and this is one of the present challenges in developing NFES into a more versatile technique. In this paper, a higher degree of control in NFES placement was achieved through manipulation of the electric field direction, using an auxiliary steering electrode. The position of a polycaprolactone plastic jet was determined in real-time with a camera attached to a stereo microscope. The measured position was used to calculate an applied potential to the steering electrode to guide the plastic jet to the desired position. The placement accuracy was measured both at the substrate and during flight using the camera and microscope. The higher control was revealed through the deposition of plastic fibers in a pattern with decreasing separation, with and without the active steering electrode enabled. It is in the authors' opinion that the fabrication of dense structures could be possible with further refinement of the technique.

Near-field electrospinning (NFES) is an additive manufacturing technique that allows for both high-resolution 3D structures and a wide variety of printed materials. Typically, a high electric field between a nozzle, the spinneret, and the substrate creates a mu m-sized jet of a supplied liquid material. With mm distances between spinneret and sample, it is possible to have a fair control of the lateral placement of the deposited material. The placement is, however, distributed by various electrostatic phenomena, and this is one of the present challenges in developing NFES into a more versatile technique. In this paper, a higher degree of control in NFES placement was achieved through manipulation of the electric field direction, using an auxiliary steering electrode. The position of a polycaprolactone plastic jet was determined in real-time with a camera attached to a stereo microscope. The measured position was used to calculate an applied potential to the steering electrode to guide the plastic jet to the desired position. The placement accuracy was measured both at the substrate and during flight using the camera and microscope. The higher control was revealed through the deposition of plastic fibers in a pattern with decreasing separation, with and without the active steering electrode enabled. It is in the authors' opinion that the fabrication of dense structures could be possible with further refinement of the technique.

Near-field electrospinning (NFES) is an additive manufacturing technique that allows for both high-resolution 3D structures and a wide variety of printed materials. Typically, a high electric field between a nozzle, the spinneret, and the substrate creates a mu m-sized jet of a supplied liquid material. With mm distances between spinneret and sample, it is possible to have a fair control of the lateral placement of the deposited material. The placement is, however, distributed by various electrostatic phenomena, and this is one of the present challenges in developing NFES into a more versatile technique. In this paper, a higher degree of control in NFES placement was achieved through manipulation of the electric field direction, using an auxiliary steering electrode. The position of a polycaprolactone plastic jet was determined in real-time with a camera attached to a stereo microscope. The measured position was used to calculate an applied potential to the steering electrode to guide the plastic jet to the desired position. The placement accuracy was measured both at the substrate and during flight using the camera and microscope. The higher control was revealed through the deposition of plastic fibers in a pattern with decreasing separation, with and without the active steering electrode enabled. It is in the authors' opinion that the fabrication of dense structures could be possible with further refinement of the technique.

Near-field electrospinning (NFES) is an additive manufacturing technique that allows for both high-resolution 3D structures and a wide variety of printed materials. Typically, a high electric field between a nozzle, the spinneret, and the substrate creates a mu m-sized jet of a supplied liquid material. With mm distances between spinneret and sample, it is possible to have a fair control of the lateral placement of the deposited material. The placement is, however, distributed by various electrostatic phenomena, and this is one of the present challenges in developing NFES into a more versatile technique. In this paper, a higher degree of control in NFES placement was achieved through manipulation of the electric field direction, using an auxiliary steering electrode. The position of a polycaprolactone plastic jet was determined in real-time with a camera attached to a stereo microscope. The measured position was used to calculate an applied potential to the steering electrode to guide the plastic jet to the desired position. The placement accuracy was measured both at the substrate and during flight using the camera and microscope. The higher control was revealed through the deposition of plastic fibers in a pattern with decreasing separation, with and without the active steering electrode enabled. It is in the authors' opinion that the fabrication of dense structures could be possible with further refinement of the technique.

The first droplet produced by a low-conductivity pendant/sessile droplet subject to a strong electric field is particularly important at the fundamental level because, in contrast to steady electrospray phenomena, its ejection entails complex charge relaxation and electrokinetic processes. Besides, it is technologically relevant because of its very small diameter and large electric charge per unit volume. In this work, we present an experimental technique to measure with unprecedented accuracy the diameter of the droplet and to determine for the first time its electric charge. We discuss both the advantages of our technique over possible alternatives and the limitations of the method. The proposed method is applied to two alcohols with electrical conductivities of the order of a few lS/m. The high sensitivity of our experimental technique allows us to determine the influence of both the magnitude and the polarity of the applied voltage on the size and charge of the ejected droplet. The electric charge of the first-emitted droplet lies in the interval 0:51 q=qR 0:66 (qR is the Rayleigh limit of charge) for the two liquids analyzed. These experimental values are slightly larger than those obtained from theoretical predictions. The value of q=qR for the first droplet is very relevant because it can be regarded as an upper bound of those of the droplets subsequently emitted in the cone-jet mode of electrospray.

Flow electrification constitutes a significant hazard to operational safety in industry and for this reason it has been studied in detail over the years. It is generally accepted that the impact of turbulence on the electrification of liquids is of paramount importance. More specifically, at sufficiently high Reynolds numbers and for low-conductivity liquids such as hydrocarbons, the thickness of the hydrodynamic boundary layer can become comparable to that of the electrical double layer. This can lead to increased charge diffusion towards the bulk of the flow and, subsequently, flow electrification. However, quantitative information of the underpinning mechanisms of this phenomenon is still lacking. In this paper we present a computational framework for the study of electrification of turbulent liquid flows via numerical simulations. In the first part of the paper, we present the governing equations and describe the proposed algorithm and its implementation in pafiX, which is a computational tool for the simulation of fluid flows related to explosion protection. In the second part, we present results from numerical tests that we performed in order to access the efficiency of the proposed computational framework.

Tissue engineering and cell-based therapy approaches require artificial scaffolds as extracellular matrix (ECM) and three-dimensional (3D) environment for clinically relevant cells to attach, be metabolically active and proliferate. Moreover, these constructs must possess mechanical and physical-chemical properties matched with certain implantation site. If all the required conditions are met, a tissue-engineered construct is considered as functional and will regenerate or replace the damaged tissue after implantation. In this work, we give a short overview of so-called electrohydrodynamic approach (EHD), e.g. with an application of electric field, to fabricate nano- and microstructured porous polymeric networks. This includes the application of electrospinning (networks) and electrospraying (micro- and macrospheres) to produce scaffolds and semipermeable hydrogel structures as a basis for tissue engineering and cell-based therapies.

We apply fluctuating hydrodynamics to strong electrolyte mixtures to compute the concentration corrections for chemical potential, diffusivity, and conductivity. We show these corrections to be in agreement with the limiting laws of Debye, Hückel, and Onsager. We compute explicit corrections for a symmetric ternary mixture and find that the co-ion Maxwell-Stefan diffusion coefficients can be negative, in agreement with experimental findings.

As a potential alternative of traditional heat transfer enhancement technology, ionic wind has drawn great attention. In this study, a direct comparison of the ionic wind devices with needle-mesh and needle-fin electrodes is carried out experimentally. The ionic characteristics and cooling performances of two electrode types here are tested and quantitatively analyzed by calculating the empirical correlations defining the relationship between electrohydrodynamics and heat transfer. The results indicate that the electrode gap d and the number of needle electrodes N are the main factors of ionic characteristics such as current, velocity and efficiency. And the results of heat transfer show that the needle-fin configuration has a superior performance, which has made a temperature drop from 54.5 °C to 39.1 °C with the low power consumption of 0.85 W. An empirical correlation for calculating the Nu-Re relation in the case is developed, which reflects that the ionic wind is a fluid with thinner boundary layer and stronger convection. In addition, the heat transferred by the fins in the ionic wind device is more than twice that of the convection on the plate surface. Finally, the feasibility and advantages of using fins as collector electrodes are confirmed. © 2018 Elsevier Ltd

As a potential alternative of traditional heat transfer enhancement technology, ionic wind has drawn great attention. In this study, a direct comparison of the ionic wind devices with needle-mesh and needle-fin electrodes is carried out experimentally. The ionic characteristics and cooling performances of two electrode types here are tested and quantitatively analyzed by calculating the empirical correlations defining the relationship between electrohydrodynamics and heat transfer. The results indicate that the electrode gap d and the number of needle electrodes N are the main factors of ionic characteristics such as current, velocity and efficiency. And the results of heat transfer show that the needle-fin configuration has a superior performance, which has made a temperature drop from 54.5 °C to 39.1 °C with the low power consumption of 0.85 W. An empirical correlation for calculating the Nu-Re relation in the case is developed, which reflects that the ionic wind is a fluid with thinner boundary layer and stronger convection. In addition, the heat transferred by the fins in the ionic wind device is more than twice that of the convection on the plate surface. Finally, the feasibility and advantages of using fins as collector electrodes are confirmed. © 2018 Elsevier Ltd

Charge injection and generation mechanisms under intense electric fields (up to 10(9)Vm(-1)) in mineral oil are assessed experimentally and numerically. For this, current-voltage characteristics under positive and negative polarities are measured in a needle-plane configuration using sharp needles (with tip radius R-tip <= 1.1 mu m). In addition, a state of the art electro-hydrodynamic (EHD) model is implemented to calculate the contribution of the different mechanisms on the high-field conduction currents in the liquid. In order to evaluate exclusively the contribution of field emission, experiments are also performed in vacuum. It is found that neither field emission nor field ionisation can explain the conduction currents measured in mineral oil. It is proposed that field molecular ionisation, as described by Zener tunnelling model for solids, and electron impact ionisation are the processes dominating the generation of excess electron-ion pairs in mineral oil under positive and negative polarity, respectively. It is also shown that Zener molecular ionisation alone grossly overestimates the measured currents when parameters previously suggested in the literature for mineral oil are used. Preliminary model parameters for these mechanisms that best fit the conduction currents measured in mineral oil are presented and discussed., QC 20190423

As a potential alternative of traditional heat transfer enhancement technology, ionic wind has drawn great attention. In this study, a direct comparison of the ionic wind devices with needle-mesh and needle-fin electrodes is carried out experimentally. The ionic characteristics and cooling performances of two electrode types here are tested and quantitatively analyzed by calculating the empirical correlations defining the relationship between electrohydrodynamics and heat transfer. The results indicate that the electrode gap d and the number of needle electrodes N are the main factors of ionic characteristics such as current, velocity and efficiency. And the results of heat transfer show that the needle-fin configuration has a superior performance, which has made a temperature drop from 54.5 °C to 39.1 °C with the low power consumption of 0.85 W. An empirical correlation for calculating the Nu-Re relation in the case is developed, which reflects that the ionic wind is a fluid with thinner boundary layer and stronger convection. In addition, the heat transferred by the fins in the ionic wind device is more than twice that of the convection on the plate surface. Finally, the feasibility and advantages of using fins as collector electrodes are confirmed. © 2018 Elsevier Ltd

We apply fluctuating hydrodynamics to strong electrolyte mixtures to compute the concentration corrections for chemical potential, diffusivity, and conductivity. We show these corrections to be in agreement with the limiting laws of Debye, Hückel, and Onsager. We compute explicit corrections for a symmetric ternary mixture and find that the co-ion Maxwell-Stefan diffusion coefficients can be negative, in agreement with experimental findings.

Enabling a future full of insect-scale robots will require progress on a huge number of fronts, one of which is the development of mobility platforms designed to operate beyond the scaling frontier of commercially available solutions. The vast majority of researchers seeking to create functional centimeter-scale flying robots have turned towards biomimetic propulsion mechanisms, specifically flapping wings. In this work I take a very different tack, investigating a propulsion mechanism with no natural analogue --- electrohydrodynamic thrust. Electrohydrodynamics (EHD), specifically in the context of corona discharge based systems, has been a long studied and, until relatively recently, often poorly understood phenomenon. The beginning of this dissertation focuses on the theoretical underpinnings of the thrust mechanism. The bulk of my work has focused on developing proof of concept demonstrators for EHD at the meso-scale. Starting with rapidly prototyped materials and quickly moving to microfabricated electrodes, a series of prototypes elucidate the potential for EHD to yield high thrust-to-weight ratio fliers. Initial demonstrations have been backed up by more rigorous investigations of electrode geometric and density effects. Quadrotor systems begin to suffer from decreased performance at and below the centimeter scale, especially with regards to increasing demands on durability of rotory components (which may not exist at scale), efficiency of available DC motors, and propeller figures of merit. Simply replacing the rotors with EHD thrusters, however, allows us to sidestep some of the unfavorable scaling laws of propeller-based propulsion while maintaining the ability to transfer domain knowledge from the rich world of quadcopter design and control. Demonstrating repeatable takeoff and rudimentary (open-loop) attitude control is trivial with external power supplied to the simple quad-thruster design. Through a combination of design and methodology (e.g., with reg

While a liquid is dripping out of a capillary tube, there is a possibility to affect the characteristics of the exiting flow in certain ways. One of the ways already used is by introducing an electric field that can be used to change the average droplet diameter and the droplet size distribution. This process is called electrospraying, while the theory behind it is sometimes called electrohydrodynamics (EHD). This phenomenon has been investigated for more than a hundred years both empirically and theoretically. In this paper, a review of the available literature and the empirical and theoretical findings is presented. A new classification of the electrospray modes had to be given to include all the different modes mentioned by different authors. The necessary pieces of the equipment and their different types are also given.

Chitosan particles loaded with the antigen ovalbumin (OVA) and the adjuvant Quil-A were produced by electrospray, using mixtures of water/ethanol/acetic acid as a solvent. Three different chitosans designed as HMC+70, HMC+85, and HMC+90 (called as 705010, 855010, and 905010) were tested and its efficacy to be used in oral vaccine delivery applications was investigated. The morphology, size, and zeta potential of the produced particles were investigated, together with the encapsulation efficiency and release of OVA from the three chitosan formulations. Moreover, the mucoadhesion and cytotoxicity of the chitosan microparticles was examined. All the three formulations with OVA and Quil-A were in the micrometer size range and had a positive zeta potential between 46 and 75 mV. Furthermore, all the three formulations displayed encapsulation efficiencies above 80% and the release of OVA over a period of 80 h was observed to be between 38 and 47%. None of the developed formulations exhibited high mucoadhesive properties, either cytotoxicity. The formulation prepared with HMC+70, OVA, and Quil-A had the highest stability within 2 h in buffer solution, as measured by dynamic light scattering. The electrosprayed formulation consisting of HMC+70 with OVA and Quil-A showed to be the most promising as an oral vaccine system.

The efficacy of chitosan (CS) to be used as drug delivery carrier has previously been reported. However, limited work has been pursued to produce stable and mucoadhesive CS electrosprayed particles for oral drug delivery, which is the aim of this study. Various CS types with different molecular weight (MW), degree of deacetylation (DD), and degree of polymerization (DP) were assessed. In addition, the effect of the solvent composition was also investigated. Results showed that stable CS electrosprayed particles can be produced by dissolving 3% w/v of low MW CS in mixtures of aqueous acetic acid and ethanol (50/50% v/v). The stable CS particles displayed diameters of approximately 1 μm as determined by dynamic light scattering. The zeta potential of these particles was found to be approximately 40 mV confirming the mucoadhesion properties of these CS electrosprayed particles and its potential to be used as drug delivery carrier.

We analyze the effects of an externally applied electric field on thermal fluctuations for a binary electrolyte fluid. We show that the fluctuating Poisson-Nernst-Planck (PNP) equations for charged multispecies diffusion coupled with the fluctuating fluid momentum equation result in enhanced charge transport via a mechanism distinct from the well-known enhancement of mass transport that accompanies giant fluctuations. Although the mass and charge transport occurs by advection by thermal velocity fluctuations, it can macroscopically be represented as electrodiffusion with renormalized electric conductivity and a nonzero cation-anion diffusion coefficient. Specifically, we predict a nonzero cation-anion Maxwell-Stefan coefficient proportional to the square root of the salt concentration, a prediction that agrees quantitatively with experimental measurements. The renormalized or effective macroscopic equations are different from the starting PNP equations, which contain no cross-diffusion terms, even for rather dilute binary electrolytes. At the same time, for infinitely dilute solutions the renormalized electric conductivity and renormalized diffusion coefficients are consistent and the classical PNP equations with renormalized coefficients are recovered, demonstrating the self-consistency of the fluctuating hydrodynamics equations. Our calculations show that the fluctuating hydrodynamics approach recovers the electrophoretic and relaxation corrections obtained by Debye-Huckel-Onsager theory, while elucidating the physical origins of these corrections and generalizing straightforwardly to more complex multispecies electrolytes. Finally, we show that strong applied electric fields result in anisotropically enhanced "giant" velocity fluctuations and reduced fluctuations of salt concentration.

[EN] Airblast atomization is commonly used to atomize fuel in aircraft engines. An annular liquid sheet is atomized by the shear forces exerted by the co-flowing air stream. Nevertheless, this technique is less effective in some specific cases, e.g. when the external air flow velocity is relatively low. Electrohydrodynamic (EHD) atomization can constitute a solution in these cases. It consists of applying an electric field between two electrodes and electrically charging the passing carburant. This phenomenon will create instabilities within the liquid, provoking therefore its atomization. The main objective is therefore to electrically atomize a liquid sheet without the application of an external air flow like in airblast atomizers. This paper presents a novel actuator, based on dielectric barrier injection, used to induce instabilities within a plane liquid sheet of fuel similar to the annular sheet in aircraft engines. The behaviour of this atomizer was described in previous works. Several modes were observed, sometimes leading to a complete atomization, or just inducing instabilities and oscillating the liquid sheet. In the present study, only the cases where the liquid sheet is completely atomized are investigated. Images were recorded with the help of a high speed camera. Primary atomization is only studied, secondary atomization being neglected. The properties of the spray obtained by EHD atomization are investigated thoroughly, namely the breakup length, the mesh size, the drople t diameter, the droplet count, etc.

[EN] Airblast atomization is commonly used to atomize fuel in aircraft engines. An annular liquid sheet is atomized by the shear forces exerted by the co-flowing air stream. Nevertheless, this technique is less effective in some specific cases, e.g. when the external air flow velocity is relatively low. Electrohydrodynamic (EHD) atomization can constitute a solution in these cases. It consists of applying an electric field between two electrodes and electrically charging the passing carburant. This phenomenon will create instabilities within the liquid, provoking therefore its atomization. The main objective is therefore to electrically atomize a liquid sheet without the application of an external air flow like in airblast atomizers. This paper presents a novel actuator, based on dielectric barrier injection, used to induce instabilities within a plane liquid sheet of fuel similar to the annular sheet in aircraft engines. The behaviour of this atomizer was described in previous works. Several modes were observed, sometimes leading to a complete atomization, or just inducing instabilities and oscillating the liquid sheet. In the present study, only the cases where the liquid sheet is completely atomized are investigated. Images were recorded with the help of a high speed camera. Primary atomization is only studied, secondary atomization being neglected. The properties of the spray obtained by EHD atomization are investigated thoroughly, namely the breakup length, the mesh size, the drople t diameter, the droplet count, etc.

[EN] Airblast atomization is commonly used to atomize fuel in aircraft engines. An annular liquid sheet is atomized by the shear forces exerted by the co-flowing air stream. Nevertheless, this technique is less effective in some specific cases, e.g. when the external air flow velocity is relatively low. Electrohydrodynamic (EHD) atomization can constitute a solution in these cases. It consists of applying an electric field between two electrodes and electrically charging the passing carburant. This phenomenon will create instabilities within the liquid, provoking therefore its atomization. The main objective is therefore to electrically atomize a liquid sheet without the application of an external air flow like in airblast atomizers. This paper presents a novel actuator, based on dielectric barrier injection, used to induce instabilities within a plane liquid sheet of fuel similar to the annular sheet in aircraft engines. The behaviour of this atomizer was described in previous works. Several modes were observed, sometimes leading to a complete atomization, or just inducing instabilities and oscillating the liquid sheet. In the present study, only the cases where the liquid sheet is completely atomized are investigated. Images were recorded with the help of a high speed camera. Primary atomization is only studied, secondary atomization being neglected. The properties of the spray obtained by EHD atomization are investigated thoroughly, namely the breakup length, the mesh size, the drople t diameter, the droplet count, etc.

[EN] Airblast atomization is commonly used to atomize fuel in aircraft engines. An annular liquid sheet is atomized by the shear forces exerted by the co-flowing air stream. Nevertheless, this technique is less effective in some specific cases, e.g. when the external air flow velocity is relatively low. Electrohydrodynamic (EHD) atomization can constitute a solution in these cases. It consists of applying an electric field between two electrodes and electrically charging the passing carburant. This phenomenon will create instabilities within the liquid, provoking therefore its atomization. The main objective is therefore to electrically atomize a liquid sheet without the application of an external air flow like in airblast atomizers. This paper presents a novel actuator, based on dielectric barrier injection, used to induce instabilities within a plane liquid sheet of fuel similar to the annular sheet in aircraft engines. The behaviour of this atomizer was described in previous works. Several modes were observed, sometimes leading to a complete atomization, or just inducing instabilities and oscillating the liquid sheet. In the present study, only the cases where the liquid sheet is completely atomized are investigated. Images were recorded with the help of a high speed camera. Primary atomization is only studied, secondary atomization being neglected. The properties of the spray obtained by EHD atomization are investigated thoroughly, namely the breakup length, the mesh size, the drople t diameter, the droplet count, etc.

[EN] Airblast atomization is commonly used to atomize fuel in aircraft engines. An annular liquid sheet is atomized by the shear forces exerted by the co-flowing air stream. Nevertheless, this technique is less effective in some specific cases, e.g. when the external air flow velocity is relatively low. Electrohydrodynamic (EHD) atomization can constitute a solution in these cases. It consists of applying an electric field between two electrodes and electrically charging the passing carburant. This phenomenon will create instabilities within the liquid, provoking therefore its atomization. The main objective is therefore to electrically atomize a liquid sheet without the application of an external air flow like in airblast atomizers. This paper presents a novel actuator, based on dielectric barrier injection, used to induce instabilities within a plane liquid sheet of fuel similar to the annular sheet in aircraft engines. The behaviour of this atomizer was described in previous works. Several modes were observed, sometimes leading to a complete atomization, or just inducing instabilities and oscillating the liquid sheet. In the present study, only the cases where the liquid sheet is completely atomized are investigated. Images were recorded with the help of a high speed camera. Primary atomization is only studied, secondary atomization being neglected. The properties of the spray obtained by EHD atomization are investigated thoroughly, namely the breakup length, the mesh size, the drople t diameter, the droplet count, etc.

Two-dimensional numerical simulations are carried out to evaluate the enhancement of natural convection heat transfer in a dielectric liquid resulting from injection induced annular electro-convection. The liquid is confined between two concentric horizontal cylinders and subjected to the simultaneous actions of a direct current electric field and a thermal gradient. A unipolar injection from the inner cylinder introduces free space charges into the liquid. Numerical results are presented for the configuration of inner to outer diameter ratio of 0.5 and silicon oil as the working medium. It is found that the charge injection may induce a strong radial fluid motion, which consequently augments the heat transfer rate. Due to the linear stability nature of electro-convection, there exists a threshold value of the electric driving parameter, above which the electrical enhancement becomes manifest. In addition, when the electric driving parameter is sufficiently high, the flow is fully dominated by the Coulomb force, and thus heat transfer becomes independent of the thermal driving parameter.

The dynamics of dielectric rigid particles and liquid drops suspended in another liquid medium and subject to a uniform DC electric field, the study of which forms the field of electrohydrodynamics (EHD), has fascinated scientists for decades. This phenomena is described by the much celebrated Melcher-Taylor leaky dielectric model. The model hypothesises development of interfacial charge on the application of an electric field and prescribes a balance between transient charge, jump in normal Ohmic currents due to finite conductivities of the medium and charge convection arising from interfacial velocity. While there have been numerous studies on the dynamics of particles and drops more conducting than the surrounding liquid medium, weakly conducting particles and drops in strong electric fields, known to undergo symmetry-breaking bifurcations leading to steady rotation known as Quincke electrorotation has received much less attention.Recent experiments have reported a decrease in the effective viscosity of particle under Quincke rotation, thereby providing a means to tune the rheological properties of these suspensions. However, existing models based on an isolated particle, valid for dilute suspension, have been shown to be inaccurate as the density of particles increases. Motivated to resolve these discrepancies, we develop a theoretical model to account for electrohydrodynamic interactions between a pair of spherical particles. We then turn our attention to many particles free to roll on an electrode due to Quincke rotation. Using numerical simulations, we show that electrohydrodynamic interactions between particles give rise to collective motion of these colloidal suspensions. We find emergence of a polar liquid state with large vortical structure in circular confinement. Finally, we address the problem of electrohydrodynamics of deformable liquid drops, first studied by Taylor in 1966. We develop a transient small deformation theory for axisymmetric drops while

Two-dimensional numerical simulations are carried out to evaluate the enhancement of natural convection heat transfer in a dielectric liquid resulting from injection induced annular electro-convection. The liquid is confined between two concentric horizontal cylinders and subjected to the simultaneous actions of a direct current electric field and a thermal gradient. A unipolar injection from the inner cylinder introduces free space charges into the liquid. Numerical results are presented for the configuration of inner to outer diameter ratio of 0.5 and silicon oil as the working medium. It is found that the charge injection may induce a strong radial fluid motion, which consequently augments the heat transfer rate. Due to the linear stability nature of electro-convection, there exists a threshold value of the electric driving parameter, above which the electrical enhancement becomes manifest. In addition, when the electric driving parameter is sufficiently high, the flow is fully dominated by the Coulomb force, and thus heat transfer becomes independent of the thermal driving parameter.

The natural convection heat transfer in a highly insulating liquid contained between two horizontal concentric cylinders is shown by two-dimensional numerical simulations to be noticeably enhanced by imposing a direct current electric field. This augmentation of heat transfer is due to the radial flow motion induced by unipolar injection of ions. It is found that there exists a threshold of the electric driving parameter T, above which the heat transfer enhancement due to the electric effect becomes significant. For relatively small T values, the mean Nusselt numbers are closely related to the flow pattern and Rayleigh number Ra. In addition, for sufficiently high T values, the flow is fully dominated by the Coulomb force, and thus the heat transfer rate no long depends on Ra.

This research focuses on the modeling of the liquid-liquid dispersed system, including particular insight on the electrocoalescence (EC) process that occurs during the breaking of double emulsions. The representative system, used in this work, was taken from the pilot plant for solvent extraction of uranium from wet phosphoric acid. The chosen framework required for elucidation of the EC process is based on the electrohydrodynamic (EHD) principles. During the model development it was necessary to consider several theoretical concepts for easier understanding and description of the related events. The first is the concept of entities, and corresponding classification of finely dispersed systems. The second concept is an introduction of almost forgotten basic electrodynamics element the memdiode or memristor as a current controlled device, and corresponding memristive systems. Hence, the conclusions that may be withdrawn from the presented results and findings could enable easier designing of the solutions for a breaking of double emulsions problems, that is, the entrainment problems that may arise in some pilot or industrial plants. Finally, the perspectives and the remaining challenges, considering the here discussed concepts and model based on the EHD principles, are mentioned.