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Marcel Mibus, Giovanni Zangari
The electrowetting-on-dielectric behavior of Cytop/Tantalum oxide (TaOx) bilayers is studied by measuring their response vs applied voltage and under prolonged periodic cycling, below and above the threshold voltage VT corresponding to the breakdown field for the oxide. TaOx exhibits symmetric solid state I-V characteristics, with electronic conduction dominated by Schottky, Poole-Frenkel emission; conduction is attributed to oxygen vacancies (6 × 10(16) cm(-3)), resulting in large currents at low bias. Electrolyte/Metal Oxide/Metal I-V characteristics show oxide degradation at (<5 V) cathodic bias; anodic bias in contrast results in stable characteristics until reaching the anodization voltage, where the oxide thickens, leading eventually to breakdown and oxygen production at the electrode...
November 17, 2017: ACS Applied Materials & Interfaces
G Bonfante, T Roux-Marchand, M-C Audry-Deschamps, L Renaud, P Kleimann, A Brioude, M Maillard
We explored polarization mechanisms at the interface between a dielectric material (an electrolyte) and an insulating liquid, during electrowetting actuation. Native surface charge density due to hydrophobic coating has been measured as an offset voltage for which the contact angle is at its minimum. Surface charge densities as low as 0.023 mC m(-2) have been measured using this method, demonstrating that electrowetting can be used as a probe to measure native surface charge density. This effect strongly differs depending on the kind of polarization and is at the origin of major discrepancies between alternative and direct polarization during electrowetting actuation...
November 6, 2017: Physical Chemistry Chemical Physics: PCCP
Alper Tunga Celebi, Murat Barisik, Ali Beskok
Motivated by electrowetting-based flow control in nano-systems, water transport in graphene nano-channels is investigated as a function of the applied electric field. Molecular dynamics simulations are performed for deionized water confined in graphene nano-channels subjected to opposing surface charges, creating an electric field across the channel. Water molecules respond to the electric field by reorientation of their dipoles. Oxygen and hydrogen atoms in water face the anode and cathode, respectively, and hydrogen atoms get closer to the cathode compared to the oxygen atoms near the anode...
October 28, 2017: Journal of Chemical Physics
Ying-Jia Li, Brian P Cahill
An electrowetting-on-dielectric (EWOD) electrode was developed that facilitates the use of low alternating voltages (≤5 VAC). This allows online investigation of the frequency dependence of electrowetting by means of impedance spectroscopy. The EWOD electrode is based on a dielectric bilayer consisting of an anodic tantalum pentoxide (Ta2O5) thin film (d = 59.35 nm) with a high relative permittivity (εd = 26.3) and a self-assembled hydrophobic silane monolayer. The frequency dependence of electrowetting was studied using an aqueous μL-sized sessile droplet on the planar EWOD electrode in oil...
November 2, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Lei Li, Rong-Ying Yuan, Jin-Hui Wang, Qiong-Hua Wang
We report an electrically controlled optofluidic zoom system which can achieve a large continuous zoom change and high-resolution image. The zoom system consists of an optofluidic zoom objective and a switchable light path which are controlled by two liquid optical shutters. The proposed zoom system can achieve a large tunable focal length range from 36mm to 92mm. And in this tuning range, the zoom system can correct aberrations dynamically, thus the image resolution is high. Due to large zoom range, the proposed imaging system incorporates both camera configuration and telescope configuration into one system...
September 18, 2017: Optics Express
Alireza Ousati Ashtiani, Hongrui Jiang
We demonstrate an electrowetting-based liquid optical phase shifter. The phase shifter consists of two immiscible liquid layers with different refractive indices. Sandwiched between the two liquids is a rigid membrane that moves freely along the optical axis and supported by a compliant surround. When applied with a pressure, the thicknesses of both liquid layers change, which induces a difference in optical path, resulting in a phase shift. A miniaturized electrowetting-based actuator is used to produce hydraulic pressure...
April 2017: Journal of Microelectromechanical Systems
Andrej Berg, Christine Peter, Karen Johnston
The structure and dynamics of water at gold surfaces are important for a variety of applications, including lab on a chip and electrowetting. Classical molecular dynamics (MD) simulations are frequently used to investigate systems with water-gold interfaces, such as biomacromolecules in gold nanoparticle dispersions, but the accuracy of the simulations depends on the suitability of the force field. Density functional theory (DFT) calculations of a water molecule on gold were used as a benchmark to assess force field accuracy...
October 26, 2017: Journal of Chemical Theory and Computation
Caroline Duc, Alexis Vlandas, George G Malliaras, Vincent Senez
Conducting polymers demonstrate an interesting ability to change their wettability at ultralow voltage (<1 V). While the conducting hydrogel poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) is increasingly used as an interface with biology partly thanks to its mechanical properties, little is known about the electrical control of its wettability. We rely on the captive bubble technique to study this hydrogel property under relevant conditions (fully immerged). We here report that the wettability variations of PEDOT:PSS are driven by an electrowetting phenomenon in contrast to other conducting polymers which are thought to undergo wettability changes due to oxido-reduction reactions...
October 11, 2017: Journal of Physical Chemistry. B
Hal R Holmes, Karl F Böhringer
Anisotropic ratchet conveyors (ARC) are a type of digital microfluidic system. Unlike electrowetting based systems, ARCs transport droplets through a passive, micro-patterned surface and applied orthogonal vibrations. The mechanics of droplet transport on ARC devices has yet to be as well characterized and understood as on electrowetting systems. In this work, we investigate how the design of the ARC substrate affects the droplet response to vibrations and perform the first characterization of transport velocity on ARC devices...
September 14, 2017: Advances in Colloid and Interface Science
Shubhi Bansal, Prosenjit Sen
Manipulating droplets of biological fluids in an electrowetting on dielectric (EWOD)-based digital microfluidic platform is a significant challenge because of biofouling and surface contamination. This problem is often addressed by operating in an oil environment. We study an alternate configuration of sessile compound droplets having an aqueous core surrounded by a smaller oil shell. In contrast to the conventional EWOD platform, an open digital microfluidic platform enabled by the core-shell configuration will allow electrical, mechanical, or optical probes to get unrestricted access to the droplet, thus enabling highly flexible and dynamically reconfigurable lab-on-chip systems...
October 17, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Alar Ainla, Mahiar M Hamedi, Firat Güder, George M Whitesides
This paper describes electrically-activated fluidic valves that operate based on electrowetting through textiles. The valves are fabricated from electrically conductive, insulated, hydrophobic textiles, but the concept can be extended to other porous materials. When the valve is closed, the liquid cannot pass through the hydrophobic textile. Upon application of a potential (in the range of 100-1000 V) between the textile and the liquid, the valve opens and the liquid penetrates the textile. These valves actuate in less than 1 s, require low energy (≈27 µJ per actuation), and work with a variety of aqueous solutions, including those with low surface tension and those containing bioanalytes...
August 15, 2017: Advanced Materials
Carlos E Clement, Dongyue Jiang, Si Kuan Thio, Sung-Yong Park
We present a dip-coatable, high-capacitance ion gel dielectric for scalable fabrication of three-dimensional (3D) electrowetting-on-dielectric (EWOD) devices such as an n × n liquid prism array. Due to the formation of a nanometer-thick electric double layer (EDL) capacitor, an ion gel dielectric offers two to three orders higher specific capacitance (c ≈ 10 μF/cm²) than that of conventional dielectrics such as SiO₂. However, the previous spin-coating method used for gel layer deposition poses several issues for 3D EWOD device fabrication, particularly when assembling multiple modules...
January 5, 2017: Materials
Daniel R Martin, Dmitry V Matyushov
Complex I is a part of the respiration energy chain converting the redox energy into the cross-membrane proton gradient. The electron-transfer chain of iron-sulfur cofactors within the water-soluble peripheral part of the complex is responsible for the delivery of electrons to the proton pumping subunit. The protein is porous to water penetration and the hydration level of the cofactors changes when the electron is transferred along the chain. High reaction barriers and trapping of the electrons at the iron-sulfur cofactors are prevented by the combination of intense electrostatic noise produced by the protein-water interface with the high density of quantum states in the iron-sulfur clusters caused by spin interactions between paramagnetic iron atoms...
July 14, 2017: Scientific Reports
Mark W Rutland
It is an honour to be charged with providing the concluding remarks for a Faraday Discussion. As many have remarked before, it is nonetheless a prodigious task, and what follows is necessarily a personal, and probably perverse, view of a watershed event in the Chemical Physics of Electroactive materials. The spirit of the conference was captured in a single sentence during the meeting itself."It is the nexus between rheology, electrochemistry, colloid science and energy storage". The current scientific climate is increasingly dominated by a limited number of global challenges, and there is thus a tendency for research to resemble a football match played by 6 year olds, where everyone on the field chases the (funding) ball instead of playing to their "discipline"...
July 1, 2017: Faraday Discussions
Han Zhang, Qiuping Yan, Qingyu Xu, Changshi Xiao, Xuelei Liang
Patterning micro-structures on highly hydrophobic surface by photolithography is usually inevitable for fabricating devices based on electrowetting effects. The key challenges for such photolithography processes are how to coat photoresist uniformly and maintain the hydrophobicity of the highly hydrophobic surface, which are usually two contradict aspects. Moreover, the patterned microstructure must adhere to the highly hydrophobic surface excellently, which is critical for device application. However, a simple and robust fabrication process that fulfills all the above requirements was seldom reported...
June 21, 2017: Scientific Reports
Zhantao Wang, Dirk van den Ende, Arjen Pit, Rudy Lagraauw, Daniël Wijnperlé, Frieder Mugele
Aqueous sessile drops are launched from a super-hydrophobic surface by electric actuation in an electrowetting configuration with a voltage pulse of variable duration. We show that the jump height, i.e. the amount of energy that is transferred from surface energy to the translational degree of freedom, depends not only on the applied voltage but also in a periodic manner on the duration of the actuation pulse. Specifically, we find that the jump height for a pulse of optimized duration is almost twice as high as the one obtained upon turning off the voltage after equilibration of the drop under electrowetting...
July 19, 2017: Soft Matter
Arun G Banpurkar, Yogesh Sawane, Sandip M Wadhai, C U Murade, Igor Siretanu, D van den Ende, F Mugele
Fluoropolymers are widely used as coatings for their robustness, water-repellence, and chemical inertness. In contact with water, they are known to assume a negative surface charge, which is commonly attributed to adsorbed hydroxyl ions. Here, we demonstrate that a small fraction of these ions permanently sticks to surfaces of Teflon AF and Cytop, two of the most common fluoropolymer materials, upon prolonged exposure to water. Electrowetting measurements carried out after aging in water are used to quantify the density of 'trapped' charge...
July 1, 2017: Faraday Discussions
Andrew C Madison, Matthew W Royal, Frederic Vigneault, Liji Chen, Peter B Griffin, Mark Horowitz, George M Church, Richard B Fair
Electrowetting-on-dielectric (EWD) digital microfluidic laboratory-on-a-chip platforms demonstrate excellent performance in automating labor-intensive protocols. When coupled with an on-chip electroporation capability, these systems hold promise for streamlining cumbersome processes such as multiplex automated genome engineering (MAGE). We integrated a single Ti:Au electroporation electrode into an otherwise standard parallel-plate EWD geometry to enable high-efficiency transformation of Escherichia coli with reporter plasmid DNA in a 200 nL droplet...
September 15, 2017: ACS Synthetic Biology
Vincent Sénéchal, Hassan Saadaoui, Juan Rodriguez-Hernandez, Carlos Drummond
Polymer coatings are commonly used to modify interfacial properties like wettability, lubrication, or biocompatibility. These properties are determined by the conformation of polymer molecules at the interface. Polyelectrolytes are convenient elementary bricks to build smart materials, given that polyion chain conformation is very sensitive to different environmental variables. Here we discuss the effect of an applied electric field on the properties of surfaces coated with poly(acrylic acid) brushes. By combining atomic force microscopy, quartz crystal microbalance, and contact angle experiments, we show that it is possible to precisely tune polyion chain conformation, surface adhesion, and surface wettability using very low applied voltages if the polymer grafting density and environmental conditions (pH and ionic strength) are properly formulated...
May 12, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Nico E A Cousens, Anthony R J Kucernak
Electrowetting-on-dielectric devices typically have operating voltages of 10-20 V. A reduction in the operating voltage could greatly reduce the energy consumption of these devices. Herein, fully reversible one-electrolyte electrowetting of a droplet on a solid metal surface is reported for the first time. A reversible change of 29° for an 800 mV step is achieved. The effects of surface roughness, electrolyte composition, electrolyte concentration and droplet composition are investigated. It was found that there is a dramatic dependence of the reversibility and hysteresis of the system on these parameters, contrary to theoretical predictions...
July 1, 2017: Faraday Discussions
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