Showing papers on "Electrowetting published in 2009"
TL;DR: In this article, an ambient light display based on electrofluidic control of coloured pigment fluids is reported, which provides a direct view of brilliantly coloured pigment dispersions, with a white light reflectivity of 55%.
Abstract: Conventional electrowetting displays reconfigure the contact angle of a coloured oil film on a planar hydrophobic surface. We report on electrofluidic displays, in particular a three-dimensional microfluidic display device that provides a direct view of brilliantly coloured pigment dispersions. Electromechanical pressure is used to pull the aqueous dispersion from a reservoir of small viewable area ( 90%). The hydrophobic channel and reservoir respectively impart a small or large radius of curvature on the dispersion. Therefore, with no voltage, Young–Laplace pressure forces the dispersion to retract into the reservoir. Preliminary prototypes exhibit ∼55% white reflectance, and future development points towards a reflectance of ∼85%. Uniquely, compared to electrowetting pixels, the electrofluidic pixels reduce the visible area of the coloured fluid by an additional two to three times (improving contrast), are potentially bistable, are as thin as ∼15 µm (giving potential for rollable displays), and can be miniaturized without increased operating voltage. An ambient light display based on electrofluidic control of coloured pigment fluids is reported. Electromechanical pressure is used to move the pigment from a reservoir to the entire surface of a pixel on a timescale of tens of milliseconds. The display has a white light reflectivity of 55%.
251 citations
TL;DR: In this article, a detailed description of the drop shape and the (singular) distribution of the electric field in the vicinity of the contact line has been provided for dynamic electrowetting.
Abstract: Electrowetting is a versatile tool for manipulating typically submillimetre-sized drops in various microfluidic applications. In recent years the microscopic understanding of the electrowetting effect has substantially improved leading to a detailed description of the drop shape and the (singular) distribution of the electric field in the vicinity of the contact line. Based on these findings, novel quantitative models of contact angle saturation, the most important and longstanding fundamental problem in the field, have recently been developed. Future challenges arise in the context of dynamic electrowetting: neither the translational motion of drops nor the generation of internal flow patterns are currently well understood.
182 citations
TL;DR: In this article, a hydrodynamic scaling model of droplet actuation in an electrowetting-on-dielectric (EWD) actuator is presented that takes into account the effects of contact angle hysteresis, drag from the filler fluid, and change in the actuation force while a droplet traverses a neighboring electrode.
Abstract: A hydrodynamic scaling model of droplet actuation in an electrowetting-on-dielectric (EWD) actuator is presented that takes into account the effects of contact angle hysteresis, drag from the filler fluid, drag from the solid walls, and change in the actuation force while a droplet traverses a neighboring electrode. Based on this model, the threshold voltage, VT, for droplet actuation is estimated as a function of the filler medium of a scaled device. It is shown that scaling models of droplet splitting and liquid dispensing all show a similar scaling dependence on [t/er(d/L)]1/2, where t is insulator thickness and d/L is the aspect ratio of the device. It is also determined that reliable operation of a EWD actuator is possible as long as the device is operated within the limits of the Lippmann–Young equation. The upper limit on applied voltage, Vsat, corresponds to contact-angle saturation. The minimum 3-electrode splitting voltages as a function of aspect ratio d/L < 1 for an oil medium are less than Vsat. However, for an air medium the minimum voltage for 3-electrode droplet splitting exceeds Vsat for d/L ≥ 0.4. EWD actuators were fabricated to operate with droplets down to 35pl. Reasonable scaling results were achieved.
157 citations
TL;DR: A general digital microfluidic platform capable of manipulating both dielectric and conductive droplets was demonstrated, and DEP and EWOD, selectively generated by applying different signals on the same dielectic-covered electrodes, were used to drive silicone oil and water droplets.
Abstract: A general digital (droplet-based) microfluidic platform based on the study of dielectric droplet manipulation by dielectrophoresis (DEP) and the integration of DEP and electrowetting-on-dielectric (EWOD) is reported. Transporting, splitting, and merging dielectric droplets are achieved by DEP in a parallel-plate device, which expands the fluids of digital microfluidics from merely being conductive and aqueous to being non-conductive. In this work, decane, hexadecane, and silicone oil droplets were successfully transported in a 150 microm-high gap between two parallel plates by applying a DC voltage above threshold voltages. Non-volatile silicone oil droplets with viscosities of 20 and 50 cSt were studied in more detail in parallel-plate geometries with spacings of 75 microm, 150 microm, and 225 microm. The threshold voltages and the required driving voltages to achieve droplet velocities up to 4 mm/s in the different circumstances were measured. By adding a dielectric layer on the driving electrodes of the tested parallel-plate device, a general digital microfluidic platform capable of manipulating both dielectric and conductive droplets was demonstrated. DEP and EWOD, selectively generated by applying different signals on the same dielectric-covered electrodes, were used to drive silicone oil and water droplets, respectively. Concurrent transporting silicone oil and water droplets along an electrode loop, merging water and oil droplets, and transporting and separating the merged water-in-oil droplet were performed.
152 citations
TL;DR: The general utility of the model is that it can be used to predict the operating conditions needed to actuate particular liquids in devices of known geometry, and to optimize the design and operating conditions to enable movement of virtually any liquid.
Abstract: Both conducting and insulating liquids can be actuated in two-plate droplet ("digital") microfluidic devices. Droplet movement is accomplished by applying a voltage across electrodes patterned beneath the dielectric-coated top and bottom plates. This report presents a general electromechanical model for calculating the forces on insulating and conducting liquids in two-plate devices. The devices are modeled as an equivalent circuit in which the dielectric layers and ambient medium (air or oil) are described as capacitors, while the liquid being actuated is described as a resistor and capacitor in parallel. The experimental variables are the thickness and dielectric constant of each layer in the device, the gap between plates, the applied voltage and frequency, and the conductivity of the liquid. The model has been used to calculate the total force acting on droplets of liquids that have been studied experimentally, and to explain the relative ease with which liquids of different conductivities can be actuated. The contributions of the electrowetting (EW) and dielectrophoretic (DEP) forces to droplet actuation have also been calculated. While for conductive liquids the EW force dominates, for dielectric liquids, both DEP and EW contribute, and the DEP force may dominate. The general utility of the model is that it can be used to predict the operating conditions needed to actuate particular liquids in devices of known geometry, and to optimize the design and operating conditions to enable movement of virtually any liquid.
116 citations
TL;DR: In this paper, the possibility of effective control of the wetting properties of a nanostructured surface consisting of arrays of amorphous carbon nanoparticles capped on carbon nanotubes using the electrowetting technique is demonstrated.
Abstract: The possibility of effective control of the wetting properties of a nanostructured surface consisting of arrays of amorphous carbon nanoparticles capped on carbon nanotubes using the electrowetting technique is demonstrated. By analyzing the electrowetting curves with an equivalent circuit model of the solid/liquid interface, the long-standing problem of control and monitoring of the transition between the "slippy" Cassie state and the "sticky" Wenzel states is resolved. The unique structural properties of the custom-designed nanocomposites with precisely tailored surface energy without using any commonly utilized low-surface-energy (e.g., polymer) conformal coatings enable easy identification of the occurrence of such transition from the optical contrast on the nanostructured surfaces. This approach to precise control of the wetting mode transitions is generic and has an outstanding potential to enable the stable superhydrophobic capability of nanostructured surfaces for numerous applications, such as low-friction microfluidics and self-cleaning.
114 citations
TL;DR: It is proposed that in regions where the electric field strength locally exceeds the material breakdown strength, the dielectric locally switches to a conductor.
Abstract: Electrowetting on dielectric (EWOD) is simulated by solving the equations of capillary electrohydrostatics, by the Galerkin/finite element method. Aiming to provide reliable predictions of the voltage dependence of the apparent contact angle, close to or beyond the saturation limit, special attention is given in the treatment of the dielectric properties of the solid dielectric where the liquid sits. It is proposed that in regions where the electric field strength locally exceeds the material breakdown strength, the dielectric locally switches to a conductor. Without using any fitting parameter, the implementation of the proposed phenomenological idea realized a surprising matching of published experimental data concerning materials ranging from SiO2 to Parylene N and Teflon. Charge trapping is naturally connected to the field-induced transition, and its distribution as well as its dependence on the applied voltage is calculated.
111 citations
TL;DR: The first complete description of the electrowetting display fabrication process is given in this paper, which includes materials selection, purification, and all fabrication steps from substrate selection to sealing.
Abstract: Electrowetting displays provide a high white state reflectance of >50% and have attracted substantial world-wide interest, yet are primarily an industrially led effort with few details on preferred materials and fabrication processes. Reported herein is the first complete description of the electrowetting display fabrication process. The description includes materials selection, purification and all fabrication steps from substrate selection to sealing. Challenging materials and fabrication processes include dielectric optimization, fluoropolymer selection, hydrophilic grid patterning, liquid dosing, dye purification and liquid ionic content. The process described herein has produced pixel arrays that were switched at <15 V on active-matrix backplanes, and which have individual sub-pixel areas of <50 × 150 µm2. The majority of fabrication processes can conform to liquid-crystal style manufacturing equipment, and therefore can be readily adopted by many display practitioners. Also presented are additional tips and techniques, such as controlling the onset of oil film break-up in an electrowetting display. This paper should enable anyone skilled in displays or microfabrication to quickly and successfully set up research and fabrication of electrowetting displays.
110 citations
01 Jan 2009
TL;DR: The possibility of effective control of the wetting properties of a nanostructured surface consisting of arrays of amorphous carbon nanoparticles capped on carbon nanotubes using the electrowetting technique is demonstrated and has an outstanding potential to enable the stable superhydrophobic capability of nanstructured surfaces for numerous applications, such as low-friction microfluidics and self-cleaning.
Abstract: Thepossibilityofeffectivecontrolofthewettingpropertiesofananostructuredsurfaceconsisting of arrays of amorphous carbon nanoparticles capped on carbon nanotubes using the electrowetting technique is demonstrated. By analyzing the electrowetting curves with an equivalent circuit model of the solid/liquid interface, the long-standing problem of control and monitoring of the transition between the "slippy" Cassie state and the "sticky" Wenzel states is resolved. The unique structural properties of the custom-designed nanocomposites with precisely tailored surface energy without using any commonly utilized low-surface-energy (e.g., polymer) conformal coatings enable easy identification of the occurrence of such transition from the optical contrastonthenanostructuredsurfaces.Thisapproachtoprecisecontrolofthewettingmodetransitionsisgeneric and has an outstanding potential to enable the stable superhydrophobic capability of nanostructured surfaces for numerous applications, such as low-friction microfluidics and self-cleaning.
108 citations
TL;DR: The improvements to the experimental set-up and procedure allow to reveal the two lens regimes which exhibit different optical properties, which could be of great interest to the field of micro-optics thanks to the possibility to achieve focus tuning without moving parts and thus favouring the miniaturization of the optical systems.
Abstract: A special class of tunable liquid microlenses is presented here. The microlenses are generated by an electrowetting effect under an electrode-less configuration and they exhibit two different regimes that are named here as separated lens regime (SLR) and wave-like lens regime (WLR). The lens effect is induced by the pyroelectricity of polar dielectric crystals, as was proved in principle in a previous work by the same authors (S. Grilli et al., Opt. Express 16, 8084, 2008). Compared to that work, the improvements to the experimental set-up and procedure allow to reveal the two lens regimes which exhibit different optical properties. A digital holography technique is used to reconstruct the transmitted wavefront during focusing and a focal length variation in the millimetre range is observed. The tunability of such microlenses could be of great interest to the field of micro-optics thanks to the possibility to achieve focus tuning without moving parts and thus favouring the miniaturization of the optical systems.
103 citations
TL;DR: Electrowetting devices often utilize aqueous solutions with ionic surfactants and inorganic salts to modify the electrowetting response, and more detailed current-voltage investigations reveal less dielectric failure for the larger size ions.
Abstract: Electrowetting devices often utilize aqueous solutions with ionic surfactants and inorganic salts to modify the electrowetting response. It has been observed in low-voltage electrowetting devices (thin dielectric, <12 V) that a frequent onset of dielectric failure (electrolysis) occurs with use of ionic solutes such as potassium chloride (KCl) or sodium dodecyl sulfate. More detailed current-voltage investigations reveal less dielectric failure for the larger size ions. Specifically, improved resistance to failure is seen for surfactant ions carrying a long alkane chain. Therefore, a catanionic surfactant (in which both ions are amphiphilic) was custom synthesized, and elimination of dielectric failure was observed in both negative and positive voltage. Because water is a small molecule that easily penetrates dielectrics, further experiments were performed to show that dielectric failure can also be eliminated by use of larger size polar molecules such as propylene glycol. In addition to these results, important parameters such as conductivity and interfacial tensions are reported.
TL;DR: In this paper, the authors describe the modeling and simulation of planar electrowetting on dielectric devices that move fluid droplets by modulating surface tension effects with a focus on including the relevant boundary phenomena.
Abstract: This work describes the modeling and simulation of planar electrowetting on dielectric devices that move fluid droplets by modulating surface tension effects. The fluid dynamics are modeled by Hele-Shaw type equations with a focus on including the relevant boundary phenomena. Specifically, we include contact angle saturation and a contact line force threshold model that can account for hysteresis and pinning effects. These extra boundary effects are needed to make reasonable predictions of the correct shape and time scale of liquid motion. Without them the simulations can predict droplet motion that is much faster than in experiments (up to 10–20 times faster). We present a variational method for our model, and a corresponding finite element discretization, which is able to handle surface tension, conservation of mass, and the nonlinear contact line pinning in a straightforward and numerically robust way. In particular, the contact line pinning is captured by a variational inequality. We note that all the...
21 Dec 2009-Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems
TL;DR: In this article, the fundamental building blocks of typical electrowetting-on-dielectric (EWOD) actuation and their importance in the EWOD mechanism are introduced and reviewed, respectively.
Abstract: The fundamental building blocks of typical electrowetting-on-dielectric (EWOD) actuation and their importance in the EWOD mechanism are introduced and reviewed, respectively. The emphasis in this experimental study of EWOD is on dielectric materials, upon which the performance of EWOD devices is heavily dependent. Dielectric breakdown of several typical polymeric and inorganic insulators employed as dielectrics for EWOD has been analytically investigated, which is forced to occur between the electrodes and conductive liquids under certain threshold potential. The electric breakdown occurring in both dielectric layer and surrounding medium (air or silicon oil) has been studied to build up a mathematical model of breakdown voltage as a function of dielectric thickness. Contact angle measurement of some polymeric materials and self-assembled monolayer using pure water has been carried out to demonstrate the contact angle tunability and reversibility, respectively, upon EWOD actuation.
TL;DR: In this article, a microfluidic platform for the formation and electrical measurement of lipid bilayer membranes was presented, where two or more aqueous droplets surrounded by a lipid-containing organic phase were manipulated into contact to form a bilayer at their interface.
Abstract: We present a microfluidic platform for the formation and electrical measurement of lipid bilayer membranes. Using electrowetting on dielectric (EWOD), two or more aqueous droplets surrounded by a lipid-containing organic phase were manipulated into contact to form a lipid bilayer at their interface. Thin-film Ag/AgCl electrodes integrated into the device enabled electrical measurement of membrane formation and the incorporation of gramicidin channels of two bilayers in parallel.
TL;DR: In this article, a programmable electrowetting micropump has been realized to dispense and manipulate droplets in 2D with up to 1000 addressable electrodes and electronics built underneath.
Abstract: Microfluidic systems are part of an emerging technology which deals with minute amounts of liquids (biological samples and reagents) on a small scale. They are fast, compact and can be made into a highly integrated system to deliver sample purification, separation, reaction, immobilization, labelling, as well as detection, thus are promising for applications such as lab-on-a-chip and handheld healthcare devices. Miniaturized micropumps typically consist of a moving-part component, such as a membrane structure, to deliver liquids, and are often unreliable, complicated in structure and difficult to be integrated with other control electronics circuits. The trend of new-generation micropumps is moving-part-free micropumps operated by advanced techniques, such as electrokinetic force, surface tension/energy, acoustic waves. This paper reviews the development and advances of relevant technologies, and introduces electrowetting-on-dielectrics and acoustic wave-based microfluidics. The programmable electrowetting micropump has been realized to dispense and manipulate droplets in 2D with up to 1000 addressable electrodes and electronics built underneath. The acoustic wave-based microfluidics can be used not only for pumping, mixing and droplet generation but also for biosensors, suitable for single-mechanism-based lab-on-a-chip applications.
Patent•
14 May 2009TL;DR: In this paper, the droplet meniscus is used to assist in the magnetic collection and positioning of magnetic particles or beads during droplet microfluidic operations, and chemical additives are used to reduce the adhesion of MBs to surfaces.
Abstract: Methods of utilizing magnetic particles or beads (MBs) in droplet-based (or digital) microfluidics are disclosed The methods may be used in enrichment or separation processes A first method employs the droplet meniscus to assist in the magnetic collection and positioning of MBs during droplet microfluidic operations The sweeping movement of the meniscus lifts the MBs off the solid surface and frees them from various surface forces acting on the MBs A second method uses chemical additives to reduce the adhesion of MBs to surfaces Both methods allow the MBs on a solid surface to be effectively moved by magnetic force Droplets may be driven by various methods or techniques including, for example, electrowetting, electrostatic, electromechanical, electrophoretic, dielectrophoretic, electroosmotic, thermocapillary, surface acoustic, and pressure
TL;DR: It is demonstrated that low contact angle of oil on the hydrophobic surfaces is a key parameter to obtain a low hysteresis system, below 2 degrees, useful for many applications from liquid lenses to displays and laboratory-on-a-chip.
Abstract: This study focuses on electrowetting using two immmiscible liquids on a dielectric coating. It is demonstrated that low contact angle of oil on the hydrophobic surfaces is a key parameter to obtain a low hysteresis system, below 2°. On the basis of these results, three aspects of the wetting properties have been studied: the influence of the surface hydrophobic properties, the design of the liquids according to the hydrophobic surface, and a graphical method to solve the Bartell-Osterhof equation and predict the wetting properties of two liquids on a surface. These results define clear design rules to obtain a low hysteresis system, useful for many applications from liquid lenses to displays and laboratory-on-a-chip.
TL;DR: It is suggested that the high-frequency flow originated mainly from the electrothermal effect, in which electrical charge is generated due to the gradient of electrical conductivity and permittivity, which is induced by the Joule heating of fluid medium.
Abstract: In ac electrowetting, hydrodynamic flows occur within a droplet. Two distinct flow patterns were observed, depending on the frequency of the applied electrical signal. The flow at low-frequency range was explained in terms of shape oscillation and a steady streaming process in conjunction with contact line oscillation. The origin of the flow at high-frequency range has not yet been explained. We suggest that the high-frequency flow originated mainly from the electrothermal effect, in which electrical charge is generated due to the gradient of electrical conductivity and permittivity, which is induced by the Joule heating of fluid medium. To support our argument, we analyzed the flow field numerically while considering the electrical body force generated by the electrothermal effect. We visualized the flow pattern and measured the flow velocity inside the droplet. The numerical results show qualitative agreement with experimental results with respect to electric field and frequency dependence of flow velocity. The effects of induced-charge electro-osmosis, natural convection, and the Marangoni flow are discussed.
TL;DR: In this paper, the authors pointed the way toward exciting applications for laser radar, 3D displays, adaptive camouflage, electronic paper, retroreflector communication and lab-on-a-chip.
Abstract: Electrowetting devices can now be formed in arrays covering thousands of square centimeters of glass. New research is pointing the way toward exciting applications for laser radar, 3D displays, adaptive camouflage, electronic paper, retroreflector communication and lab-on-a-chip.
TL;DR: The contact line dynamics of sessile water droplets, 1.1-1.6 mm in radius, spread by electrowetting in air are reported, showing the effect of contact angle hysteresis in form of stick-slip motion.
Abstract: We report the contact line dynamics of sessile water droplets, 1.1−1.6 mm in radius, spread by electrowetting in air. Coplanar electrodes patterned on the substrate allow a true sessile condition with no wire into the droplet. The frequency response of the droplets is studied using 25 VAC ranging from 10 to 205 Hz. The effect of contact angle hysteresis is seen in form of stick-slip motion. A model developed provides a good match to the experimental result. Step response is studied with voltages in the range of 20−80 VDC. Two regimes of motion are observed. In the first regime, local flows cause the contact line speed to increase and reach a maximum while the contact angle is still changing. Global flows in the second regime cause the contact line to move with a reduced speed and attain the spherical shape pertaining to the new equilibrium contact angle. A model is used to describe the motion.
TL;DR: In this paper, the fabrication and demonstration of an array of >12 000 switchable liquid microlenses, each ~300 mum in diameter and switchable through plano-concave to planoconvex.
Abstract: Reported is the fabrication and demonstration of an array of >12 000 switchable liquid microlenses, each ~300 mum in diameter and switchable through plano-concave to plano-convex. Electrowetting is used to modulate the contact angle of an aqueous/oil liquid system over a range of 100deg, resulting in a switchable dioptric range of -360 m-1 to 230 m-1. Compared to previous reports of single 2-6 mm electrowetting lenses, the fabrication process reported herein reduces the individual lenslet size by ~10times. To dose liquids into large arrays of these small liquid lenslets, a scalable self-assembled dosing process was developed. The completed liquid lens array has a fill factor of 50% which can be extended to >80%.
TL;DR: In this article, the authors investigated electrowetting of several room temperature ionic liquids having in common the cation or the anion on poly(tetrafluoroethylene) (PTFE) and found the typical behavior of aqueous salt solutions: symmetric parabolic curves of contact angle versus (positive and negative) applied voltage, at low voltages, and contact angle saturation after a threshold voltage.
Abstract: In this work, electrowetting of several room temperature ionic liquids having in common the cation or the anion, [EMIM][EtSO4], [EMPy][EtSO4], [EMIM][NTf2], [BMIM][BF4], [BMIM][TFA], and [OMIM][BF4], on poly(tetrafluoroethylene) (PTFE) was investigated. The typical behavior of aqueous salt solutions was found: symmetric parabolic curves of contact angle versus (positive and negative) applied voltage, at low voltages, and contact angle saturation after a threshold voltage. Furthermore, the contact angle did not recover its initial value when the voltage decreased, and this irreversibility was found even at low voltages. The dependence of the contact angle with the applied voltage is generally described by the Young−Lippmann equation before contact angle saturation. In contrast, the Langevin function as well as a modified form of the Young−Lippmann equation were found to fit the experimental electrowetting curves in the whole range of voltages. A correlation between the electrowetting behavior and the surfa...
TL;DR: This article presents a multichannel droplet-based surface plasmon resonance platform that comprises a digital electrowetting-on-dielectric (EWOD) microfluidic device coupled to surface plAsmon resonance imaging (SPRi) to increase the capability of existing SPRi technology.
Abstract: This article presents a multichannel droplet-based surface plasmon resonance platform. The platform comprises a digital electrowetting-on-dielectric (EWOD) microfluidic device coupled to surface plasmon resonance imaging (SPRi). SPRi is now a well-established detection technique that enables in-situ monitoring of multiple reactions occurring at the surface of the chip without the use of labels. Currently, the limiting factor in the application of SPRi for high-throughput applications is the flow-cell technology which relies on sequential sample processing within the continuous fluid flow. An original solution compared to the continuous flow-cell technology is proposed to increase the capability of existing SPRi technology. A parallel SPRi detection of different samples on the surface is achieved using the array-based digital microfluidic device.
TL;DR: In this article, a tunable, high-reflectivity optofluidic device based on self-assembly of anisotropic functionalized hexagonal micromirrors (Janus tiles) on the surface of an oil droplet to create a concave liquid mirror is described.
Abstract: In this paper, we describe a tunable, high-reflectivity optofluidic device based on self-assembly of anisotropically functionalized hexagonal micromirrors (Janus tiles) on the surface of an oil droplet to create a concave liquid mirror. The liquid mirror is deposited on a patterned transparent electrode that allows the focal length and axial position to be electrically controlled. The mirror is mechanically robust and retains its integrity even at high levels of vibrational excitation of the interface. The use of reflection instead of refraction overcomes the limited available refractive-index contrast between pairs of density-matched liquids, allowing stronger focusing than is possible for a liquid lens of the same geometry. This approach is compatible with optical instruments that could provide novel functionality-for example, a dynamic 3D projector, i.e., a light source which can scan an image onto a moving, nonplanar focal surface. Janus tiles with complex optical properties can be manufactured using our approach, thus potentially enabling a wide range of novel optical elements.
TL;DR: It was found that the superhydrophobic NWs display different EW behaviors according to their double nanotexturation with varying droplet impalement levels, and a scenario is proposed to explain the unique properties of these surfaces.
Abstract: The paper reports on wetting, electrowetting (EW), and systematic contact angle hysteresis measurements after electrowetting of superhydrophobic silicon nanowire surfaces (NWs). The surfaces consist of C4F8-coated silicon nanowires grown on Si/SiO2 substrate. Different surfaces modulating (i) the dielectric layer thickness and (ii) the nanotexturation were investigated in this study. It was found that the superhydrophobic NWs display different EW behaviors according to their double nanotexturation with varying droplet impalement levels. Some surfaces exhibited a total reversibility to EW with no impalement (contact angle variation of 35 ± 2° at 190 VTRMS with deionized water), whereas other surfaces showed nonreversible behavior to EW with partial droplet impalement. A scenario is proposed to explain the unique properties of these surfaces.
TL;DR: In this article, the authors developed a method to actuate oscillation of a sessile bubble in a fluid to produce steady streaming within the fluid, based on time-periodic control of the wettability of the bubble by electrowetting.
Abstract: We developed a method to actuate oscillation of a sessile bubble in a fluid to produce steady streaming within the fluid. This method is based on time-periodic control of the wettability of the bubble by electrowetting. Jet velocity is proportional to oscillation amplitude and is greatest at natural oscillation frequencies. Analytical and numerical analyses indicate that the jet is produced by steady streaming in the Stokes layer.
Journal Article•
TL;DR: In this paper, a low-voltage micro gripper utilizing a liquid droplet to pick up and release micro-objects is presented, where the lifting force is generated by a liquid bridge formed between the gripper surface and an object.
Abstract: We present a low-voltage microgripper utilizing a liquid droplet to pick up and release micro-objects. Lifting force is generated by a liquid bridge formed between the gripper surface and an object. Electrowetting was used to dynamically change the capillary lifting forces and enable easy object release. The driving voltage was applied to a pair of coplanar interdigitated electrodes, eliminating the need for an electrode on top of the droplet and thus significantly facilitating object manipulation. A barium strontium titanate insulation layer was used to lower the driving voltage. Experiments indicated that the lifting forces can be as high as 213 µN at a driving voltage of 28 V. Experiments also demonstrated a low-voltage, low power consumption soft microgripper by picking up and releasing micro glass beads.
TL;DR: In this paper, a model for electrowetting that combines the Navier-Stokes system for fluid flow, a phase-field model of Cahn-Hilliard type for the movement of the interface, a charge transport equation, and the potential equation of electrostatics is presented.
Abstract: The term electrowetting is commonly used for phenomena where shape and wetting behavior of liquid droplets are changed by the application of electric fields. We develop and analyze a model for electrowetting that combines the Navier–Stokes system for fluid flow, a phase-field model of Cahn–Hilliard type for the movement of the interface, a charge transport equation, and the potential equation of electrostatics. The model is derived with the help of a variational principle due to Onsager and conservation laws. A modification of the model with the Stokes system instead of the Navier– Stokes system is also presented. The existence of weak solutions is proved for several cases in two and three space dimensions, either with non-degenerate or with degenerate electric conductivity vanishing in the droplet exterior. Some numerical examples in two space dimensions illustrate the applicability of the model. 2000 Mathematics Subject Classification: 35D05, 35D10, 35R35, 76M30.
Patent•
06 Mar 2009
TL;DR: In this paper, the authors present methods for manufacturing three-dimensional, bioactive, tissue scaffold fabrications with embedded cells and bioactive materials, such as growth factors, using biomimetic structure modeling, solid free-form fabrication, biocompatible hydrogel material, and electrowetting on dielectric-based multi-microarray printing.
Abstract: Apparatuses and methods for manufacturing three-dimensional, bioactive, tissue scaffold fabrications with embedded cells and bioactive materials, such as growth factors, using biomimetic structure modeling, solid freeform fabrication, biocompatible hydrogel material, and electrowetting on dielectric-based multi-microarray printing.