1
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Gilinsky SD, Zohrabi M, Lim WY, Supekar OD, Bright VM, Gopinath JT. Fabrication and characterization of a two-dimensional individually addressable electrowetting microlens array. OPTICS EXPRESS 2023; 31:30550-30561. [PMID: 37710595 PMCID: PMC10544957 DOI: 10.1364/oe.497992] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Revised: 08/08/2023] [Accepted: 08/11/2023] [Indexed: 09/16/2023]
Abstract
We demonstrate a two-dimensional, individually tunable electrowetting microlens array fabricated using standard microfabrication techniques. Each lens in our array has a large range of focal tunability from -1.7 mm to -∞ in the diverging regime, which we verify experimentally from 0 to 75 V for a device coated in Parylene C. Additionally, each lens can be actuated to within 1% of their steady-state value within 1.5 ms. To justify the use of our device in a phase-sensitive optical system, we measure the wavefront of a beam passing through the center of a single lens in our device over the actuation range and show that these devices have a surface quality comparable to static microlens arrays. The large range of tunability, fast response time, and excellent surface quality of these devices open the door to potential applications in compact optical imaging systems, transmissive wavefront shaping, and beam steering.
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Affiliation(s)
- Samuel D. Gilinsky
- Department of Electrical, Computer and Energy Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Mo Zohrabi
- Department of Electrical, Computer and Energy Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Wei Yang Lim
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Omkar D. Supekar
- Department of Electrical, Computer and Energy Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Victor M. Bright
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Juliet T. Gopinath
- Department of Electrical, Computer and Energy Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
- Department of Physics, University of Colorado Boulder, Boulder, CO 80309, USA
- Materials Science and Engineering Program, University of Colorado Boulder, Boulder, CO 80309, USA
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2
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Dwivedi RK, Muralidhar K. Contact line dynamics of a water drop spreading over a textured surface in the electrowetting-on-dielectric configuration. Phys Rev E 2022; 106:045111. [PMID: 36397474 DOI: 10.1103/physreve.106.045111] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Accepted: 10/10/2022] [Indexed: 06/16/2023]
Abstract
Modeling the electrowetting process of a liquid droplet placed on a hydrophobic surface in an ambient environment has several challenges over and above those of basic spreading [F. Mugele, Soft Matter 5, 3377 (2009)10.1039/b904493k]. At an external voltage below the value that causes contact angle saturation, transient spreading is augmented by contact angle reduction defined by the Young-Lippmann equation. In addition, the macroscopic equilibrium contact angle and, therefore, the spreading rate could be altered by the surface hysteresis. Beyond the saturation point, spreading reveals additional features of higher complexity [Q. Vo and T. Tran, J. Fluid Mech. 925, A19 (2021)10.1017/jfm.2021.677]. These details have been examined from experiments as well as numerical simulation in the present work. Below the saturation point, the contact angle model of Dwivedi et al. [Phys. Rev. Fluids 7, 034002 (2022)10.1103/PhysRevFluids.7.034002] with the correction related to the electric field is seen to be applicable. Beyond saturation, the experimentally determined instantaneous contact angle distribution shows two distinct functionalities with respect to the contact line velocity. The first prevails from the onset of spreading until the spreading factor attains a peak value. The second trend is initiated with the retraction of the contact line. Except for differences in parametric values, the form of the contact angle model remains unchanged. Simulations in the postsaturation regime are shown to match experimental data in terms of the transient spreading factor, drop shapes, and the instantaneous contact angle. The role of the ground wire is found to be important and the three-phase contact line formed on it has been included in simulations. Spreading dynamics of the droplet have also been studied when the ground wire is kept at a distance of 40 μm from the apex of the drop. Simulations as well as experiments, show the propagation of a capillary wave between the ground wire and the three-phase contact line. For spreading over an uncoated polydimethylsiloxane (PDMS) surface, the contact line is trapped at local pinning sites, leading to additional distortions in the instantaneous shapes acquired by the interface.
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Affiliation(s)
- Raghvendra Kumar Dwivedi
- Department of Mechanical Engineering Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - K Muralidhar
- Department of Mechanical Engineering Indian Institute of Technology Kanpur, Kanpur 208016, India
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3
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Xiao K, Wu CX. Droplet dynamics driven by electrowetting. Phys Rev E 2022; 105:064609. [PMID: 35854554 DOI: 10.1103/physreve.105.064609] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2022] [Accepted: 05/31/2022] [Indexed: 06/15/2023]
Abstract
Even though electrowetting-on-dielectric (EWOD) is a useful strategy in a wide array of biological and engineering processes with numerous droplet-manipulation applications, there is still a lack of complete theoretical interpretation on the dynamics of electrowetting. In this paper we present an effective theoretical model and use the Onsager variational principle to successfully derive general dynamic shape equations for electrowetting droplets in both the overdamped and underdamped regimes. It is found that the spreading and retraction dynamics of a droplet on EWOD substrates can be fairly well captured by our model, which agrees with previous experimental results very well in the overdamped regime. We also confirm that the transient dynamics of EW can be characterized by a timescale independent of liquid viscosity, droplet size, and applied voltage. Our model provides a complete fundamental explanation of EW-driven spreading dynamics, which is important for a wide range of applications, from self-cleaning to novel optical and digital microfluidic devices.
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Affiliation(s)
- Ke Xiao
- Department of Physics and Fujian Provincial Key Laboratory for Soft Functional Materials Research, College of Physical Science and Technology, Xiamen University, Xiamen 361005, People's Republic of China and Wenzhou Institute, University of Chinese Academy of Sciences, Wenzhou 325016, People's Republic of China
| | - Chen-Xu Wu
- Department of Physics and Fujian Provincial Key Laboratory for Soft Functional Materials Research, College of Physical Science and Technology, Xiamen University, Xiamen 361005, People's Republic of China
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4
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Ahmad I, Pathak M, Kaleem Khan M. Transient evolution of electrowetting induced oscillating droplets on hydrophobic substrates. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.118704] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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5
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Trampolining of Droplets on Hydrophobic Surfaces Using Electrowetting. MICROMACHINES 2022; 13:mi13030345. [PMID: 35334639 PMCID: PMC8953513 DOI: 10.3390/mi13030345] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Revised: 02/15/2022] [Accepted: 02/16/2022] [Indexed: 11/25/2022]
Abstract
Droplet detachment from solid surfaces is an essential part of many industrial processes. Electrowetting is a versatile tool for handling droplets in digital microfluidics, not only on plain surface but also in 3-D manner. Here, we report for the first time droplet trampolining using electrowetting. With the information collected by the real-time capacitor sensing system, we are able to synchronize the actuation signal with the spreading of the droplet upon impacting. Since electrowetting is applied each time the droplet impacts the substrate and switched off during recoiling of the droplet, the droplet gains additional momentum upon each impact and is able to jump higher during successive detachment. We have modelled the droplet trampolining behavior with a periodically driven harmonic oscillator, and the experiments showed sound agreement with theoretical predictions. The findings from this study will offer valuable insights to applications that demands vertical transportation of the droplets between chips arranged in parallel, or detachment of droplets from solid surfaces.
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6
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Energy harvesting performance of an EDLC power generator based on pure water and glycerol mixture: analytical modeling and experimental validation. Sci Rep 2021; 11:23426. [PMID: 34873254 PMCID: PMC8648766 DOI: 10.1038/s41598-021-02964-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Accepted: 11/25/2021] [Indexed: 11/13/2022] Open
Abstract
A liquid droplet oscillating between two plane electrodes was visualized, and the electrical power generation based on the reverse-electrowetting-on-dielectric (REWOD) phenomenon was measured. For the upper plate, a hydrophobic surface treated by PTFE was used, and the lower plate was tested using the hydrophilic surface properties of ITO glass. To analyze the dynamic behavior of an oscillating liquid bridge, a modeling study was carried out using the phase field method based on the finite element method. The dynamic contact angle of the oscillating liquid bridge was modeled based on advancing and receding contact angles. The variable interfacial areas between the liquid and solid surfaces were calculated and agreed well with the experimental results within a 10% error band. Furthermore, experimental and analytical studies were carried out to examine the REWOD energy harvesting characteristics of the glycerol-water mixtures in various concentrations. As a result, the peak voltage output was obtained at a specific concentration of the glycerol mixture, and the power density of the oscillating liquid bridge at this point was up to 2.23 times higher than that of pure water.
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7
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Yada S, Allais B, van der Wijngaart W, Lundell F, Amberg G, Bagheri S. Droplet Impact on Surfaces with Asymmetric Microscopic Features. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:10849-10858. [PMID: 34469168 PMCID: PMC8447403 DOI: 10.1021/acs.langmuir.1c01813] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The impact of liquid drops on a rigid surface is central in cleaning, cooling, and coating processes in both nature and industrial applications. However, it is not clear how details of pores, roughness, and texture on the solid surface influence the initial stages of the impact dynamics. Here, we experimentally study drops impacting at low velocities onto surfaces textured with asymmetric (tilted) ridges. We found that the difference between impact velocity and the capillary speed on a solid surface is a key factor of spreading asymmetry, where the capillary speed is determined by the friction at a moving three-phase contact line. The line-friction capillary number Caf = μfV0/σ (where μf,V0, and σ are the line friction, impact velocity, and surface tension, respectively) is defined as a measure of the importance of the topology of surface textures for the dynamics of droplet impact. We show that when Caf ≪ 1, the droplet impact is asymmetric; the contact line speed in the direction against the inclination of the ridges is set by line friction, whereas in the direction with inclination, the contact line is pinned at acute corners of the ridges. When Caf ≫ 1, the geometric details of nonsmooth surfaces play little role.
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Affiliation(s)
- Susumu Yada
- Department
of Engineering Mechanics, Royal Institute
of Technology, 100 44 Stockholm, Sweden
| | | | | | - Fredrik Lundell
- Department
of Engineering Mechanics, Royal Institute
of Technology, 100 44 Stockholm, Sweden
| | - Gustav Amberg
- Department
of Engineering Mechanics, Royal Institute
of Technology, 100 44 Stockholm, Sweden
- Södertörn
University, 141 89 Stockholm, Sweden
| | - Shervin Bagheri
- Department
of Engineering Mechanics, Royal Institute
of Technology, 100 44 Stockholm, Sweden
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8
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Jung GS, Won YH. Compact and fast depth sensor based on a liquid lens using chromatic aberration to improve accuracy. OPTICS EXPRESS 2021; 29:15786-15801. [PMID: 33985273 DOI: 10.1364/oe.425191] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Accepted: 05/02/2021] [Indexed: 06/12/2023]
Abstract
Depth from defocus (DFD) obtains depth information using two defocused images, making it possible to obtain a depth map with high resolution equal to that of the RGB image. However, it is difficult to change the focus mechanically in real-time applications, and the depth range is narrow because it is inversely proportional to the depth accuracy. This paper presents a compact DFD system based on a liquid lens that uses chromatic aberration for real-time application and depth accuracy improvement. The electrical focus changing of a liquid lens greatly shortens the image-capturing time, making it suitable for real-time applications as well as helping with compact lens design. Depth accuracy can be improved by dividing the depth range into three channels using chromatic aberration. This work demonstrated the improvement of depth accuracy through theory and simulation and verified it through DFD system design and depth measurement experiments of real 3D objects. Our depth measurement system showed a root mean square error (RMSE) of 0.7 mm to 4.98 mm compared to 2.275 mm to 12.3 mm in the conventional method, for the depth measurement range of 30 cm to 70 cm. Only three lenses are required in the total optical system. The response time of changing focus by the liquid lens is 10 ms, so two defocused images for DFD can be acquired within a single frame period of real-time operations. Lens design and image processing were conducted using Zemax and MATLAB, respectively.
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9
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Kumar S, Ram R, Sarkar A, DasGupta S, Chakraborty S. Rapid determination of erythrocyte sedimentation rate (ESR) by an electrically driven blood droplet biosensor. BIOMICROFLUIDICS 2020; 14:064108. [PMID: 33312329 PMCID: PMC7710385 DOI: 10.1063/5.0026332] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2020] [Accepted: 11/13/2020] [Indexed: 05/10/2023]
Abstract
In healthcare practice, the sedimentation rate of red blood cells (erythrocytes) is a widely used clinical parameter for screening of several ailments such as stroke, infectious diseases, and malignancy. In a traditional pathological setting, the total time taken for evaluating this parameter varies typically from 1 to 2 h. Furthermore, the volume of human blood to be drawn for each test, following a gold standard laboratory technique (alternatively known as the Westergren method), varies from 4 to 5 ml. Circumventing the above constraints, here we propose a rapid (∼1 min) and highly energy efficient method for the simultaneous determination of hematocrit and erythrocyte sedimentation rate (ESR) on a microfluidic chip, deploying electrically driven spreading of a tiny drop of blood sample (∼8 μl). Our unique approach estimates these parameters by correlating the same with the time taken by the droplet to spread over a given radius, reproducing the results from more elaborate laboratory settings to a satisfactory extent. Our novel methodology is equally applicable for determining higher ranges of ESR such as high concentration of bilirubin and samples corresponding to patients with anemia and patients with some severe inflammation. Furthermore, the minimal fabrication steps involved in the process, along with the rapidity and inexpensiveness of the test, render the suitability of the strategy in extreme point-of-care settings.
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Affiliation(s)
- Sumit Kumar
- Advanced Technology Development Centre, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India
| | - Rishi Ram
- Department of Mechanical Engineering, Indian Institute of Technology (BHU), Varanasi, Uttar Pradesh 221005, India
| | | | | | - Suman Chakraborty
- Author to whom correspondence should be addressed:. Telephone: +913222282990. Fax: +913222282278
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10
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Wang Q, Xu M, Wang C, Gu J, Hu N, Lyu J, Yao W. Actuation of a Nonconductive Droplet in an Aqueous Fluid by Reversed Electrowetting Effect. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:8152-8164. [PMID: 32571027 DOI: 10.1021/acs.langmuir.0c01161] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Manipulation of a conductive droplet by electrowetting has been a popular topic in microfluidics whereby wettability of the droplet on a solid surface is increased by applying a voltage between the conductive droplet and the insulated surface. However, the opposite phenomenon, e.g., decreasing the wettability of a nonconductive droplet and increasing its contact angle (CA) by the reversed electrowetting (REW) effect, has been scarcely reported. Such a process involves not only the transient dynamics of droplet dewetting but also a critical condition for droplet detachment from the adhesive surface. In this work, actuation of a nonconductive droplet in an aqueous surrounding fluid by REW is studied experimentally. Silicone oil is used for the actuated droplet, and filtered water is used as the surrounding fluid. The solid substrate is made of a glass substrate coated with an indium tin oxide (ITO) film and then deposited by a dielectric layer of Parylene C. Potential difference is applied between the substrate and the surrounding fluid, eliminating the disturbance from the top needle on the motion of the droplet. Three different regimes are identified in the full range of operation. An underactuated regime occurs at low applied voltages, in which the CA of the droplet shows a monotonic increase with the increase of voltage (V). The friction coefficient of the contact line decreases with V before the CA saturation (Vs) but shows little change when V > Vs. At high voltages, the contact line of the sessile droplet is contracted excessively by REW. The droplet shows oscillation, and it refers to the overactuated regime. A combined time scale is proposed, and it verifies that the viscous dissipation of the contact line and liquid inertia show comparable contributions in the droplet dynamics. At sufficiently high voltages, the droplet is rejected completely from the surface. A critical equation for the threshold voltage of droplet detachment is built, and its validity is confirmed by experimental results.
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Affiliation(s)
- Qinggong Wang
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, No. 104 Youyi Road, Haidian District, Beijing 100094, China
| | - Meng Xu
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, No. 104 Youyi Road, Haidian District, Beijing 100094, China
- Jilin Province S&T Innovation Center for Physical Simulation and Security of Water Resources and Electric Power Engineering, Changchun Institute of Technology, No. 395 Kuanping Road, Chaoyang District, Changchun 130012, China
| | - Chao Wang
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, No. 104 Youyi Road, Haidian District, Beijing 100094, China
| | - Junping Gu
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, No. 104 Youyi Road, Haidian District, Beijing 100094, China
- Key Laboratory for Thermal Science and Powder Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
| | - Nan Hu
- Jilin Province S&T Innovation Center for Physical Simulation and Security of Water Resources and Electric Power Engineering, Changchun Institute of Technology, No. 395 Kuanping Road, Chaoyang District, Changchun 130012, China
| | - Junfu Lyu
- Key Laboratory for Thermal Science and Powder Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
| | - Wei Yao
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, No. 104 Youyi Road, Haidian District, Beijing 100094, China
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Burkhart CT, Maki KL, Schertzer MJ. Coplanar Electrowetting-Induced Droplet Detachment from Radially Symmetric Electrodes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:8129-8136. [PMID: 32551661 DOI: 10.1021/acs.langmuir.0c01015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
This work demonstrates electrowetting-induced droplet detachment in air from coplanar electrodes using a single voltage pulse. It also presents two models to predict when this detachment will occur. Previous works approximated the minimum energy for detachment based on (i) adhesion work at the solid-liquid interface and (ii) interfacial energy changes along all three interfaces in the system. This investigation updates those models to include changes in gravitational potential energy during detachment and provides validation by testing predicted detachment thresholds against experimental observations. Droplets of varying volume were ejected from electrowetting devices with (i) radially symmetric four-part coplanar electrodes and (ii) single electrodes with a ground wire inserted directly into the droplet. All experiments were performed in air. Incorporation of gravitational potential energy improves predictions for critical electrowetting number and captures the observed increase in applied voltage required with increased droplet volume. These new models will be of particular benefit in three-dimensional digital microfluidics applications that manipulate droplets in air.
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Affiliation(s)
- Collin T Burkhart
- Mechanical Engineering, Rochester Institute of Technology, 76 Lomb Memorial Drive, Rochester, New York 14623, United States
| | - Kara L Maki
- School of Mathematical Sciences, Rochester Institute of Technology, 76 Lomb Memorial Drive, Rochester, New York 14623, United States
| | - Michael J Schertzer
- Mechanical Engineering, Rochester Institute of Technology, 76 Lomb Memorial Drive, Rochester, New York 14623, United States
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12
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Bansal S, Sen P. Electrowetting based local sensing of liquid properties using relaxation dynamics of stretched liquid interface. J Colloid Interface Sci 2020; 568:8-15. [PMID: 32086011 DOI: 10.1016/j.jcis.2020.02.035] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 02/10/2020] [Accepted: 02/11/2020] [Indexed: 10/25/2022]
Abstract
HYPOTHESIS Monitoring progression of biochemical processes is required for medical and industrial applications. Spatiotemporal changes in fluid properties can be measured to determine progress of biochemical processes like blood coagulation. Localised electrowetting-on-dielectric (EWOD) actuates a part of droplet contact line, allowing local measurement of fluid properties without inducing bulk fluid motion, which is unlike full droplet oscillation-based techniques. EXPERIMENTS In this work, narrow electrodes (50-450 μm) were used to actuate a portion of drop interface. Dynamics of interface actuation and relaxation was used to estimate the local visco-elastic properties of the droplet. FINDINGS For local interface motion, theory predicts a generic dispersion relation ω=cqn. In agreement with theory, decay time was found to be proportional to viscosity and inversely proportional to surface tension. Interface displacement remained almost constant for different viscosities, but it decreased with increase in surface tension. Capability to measure spatiotemporal dynamics of chemical process was demonstrated for sugar dissolution in a droplet of water. For full droplet oscillation-based techniques, the induced bulk flows adversely affect the monitored process. Localised EWOD reduces bulk flows in the sample. So, this technique was applied to study blood coagulation dynamics, enlightening the future prospect of developing biomedical sensors.
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Affiliation(s)
- Shubhi Bansal
- Centre for Nano Science and Engineering (CeNSE), Indian Institute of Science, Bangalore, India; University of Sussex, UK.
| | - Prosenjit Sen
- Centre for Nano Science and Engineering (CeNSE), Indian Institute of Science, Bangalore, India
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13
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Shin D, Kim C, Koo G, Hyub Won Y. Depth plane adaptive integral imaging system using a vari-focal liquid lens array for realizing augmented reality. OPTICS EXPRESS 2020; 28:5602-5616. [PMID: 32121777 DOI: 10.1364/oe.384697] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Accepted: 01/29/2020] [Indexed: 06/10/2023]
Abstract
Augmented reality (AR) is an interactive experience of a real-world environment where the objects that reside in the real world are enhanced by computer-generated perceptual information. Despite its attractive features, AR has not become popular because of the visual fatigue that many people face when they experience it. Many methods have been introduced to solve this visual fatigue problem and one of these methods is an integral imaging system that provides images almost continuous viewpoints and full parallax. However, the integral imaging system, which uses a lens array with a fixed focal length, has limited depth of focus (DOF) range. As a result, images that are outside of the DOF range become distorted. In this paper, a vari-focal liquid lens array was fabricated and the optical characteristics of the lens array were evaluated. Using the vari-focal liquid lens array, the DOF range was extended and high-resolution images are realized without restriction of depth range in an AR system.
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14
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Ye X, Hou J, Cai D. Novel reversibly switchable wettability of superhydrophobic-superhydrophilic surfaces induced by charge injection and heating. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2019; 10:840-847. [PMID: 31019871 PMCID: PMC6466678 DOI: 10.3762/bjnano.10.84] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Accepted: 03/14/2019] [Indexed: 06/09/2023]
Abstract
Reversibly switching wettability between superhydrophobicity and superhydrophilicity has attracted widespread interest because of its important applications. In this work, we propose a reversible superhydrophobic-superhydrophilic conversion induced by charge injection and heating. Different from the conventional electrowetting phenomenon caused by the accumulation of solid-liquid interfacial charges, we discovered a phenomenon where charge injection and accumulation at the solid surface results in a sharp increase in wettability. The wettability of a sprayed SiO2 nanoparticle coating on a glass slide was shown to change from superhydrophobic to superhydrophilic by charge injection and heating, and the superhydrophobicity was restored by heating, verifying a reversible superhydrophobic-superhydrophilic conversion. The influence of voltage, temperature, and time on the coating wettability and its durability under reversible conversion have been studied.
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Affiliation(s)
- Xiangdong Ye
- School of Mechanical and Electrical Engineering, Shaanxi Key Laboratory of Nano Materials and Technology, Xi’an University of Architecture and Technology, Xi’an 710055, China
| | - Junwen Hou
- School of Mechanical and Electrical Engineering, Shaanxi Key Laboratory of Nano Materials and Technology, Xi’an University of Architecture and Technology, Xi’an 710055, China
| | - Dongbao Cai
- School of Mechanical and Electrical Engineering, Shaanxi Key Laboratory of Nano Materials and Technology, Xi’an University of Architecture and Technology, Xi’an 710055, China
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15
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Ruiz-Gutiérrez É, Ledesma-Aguilar R. Lattice-Boltzmann Simulations of Electrowetting Phenomena. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:4849-4859. [PMID: 30869524 DOI: 10.1021/acs.langmuir.9b00098] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
When a voltage difference is applied between a conducting liquid and a conducting (solid) electrode, the liquid is observed to spread on the solid. This phenomenon, generally referred to as electrowetting, underpins a number of interfacial phenomena of interest in applications that range from droplet microfluidics to optics. Here, we present a lattice-Boltzmann method that can simulate the coupled hydrodynamics and electrostatics equations of motion of a two-phase fluid as a means to model the electrowetting phenomena. Our method has the advantage of modeling the electrostatic fields within the lattice-Boltzmann algorithm itself, eliminating the need for a hybrid method. We validate our method by reproducing the static equilibrium configuration of a droplet subject to an applied voltage and show that the apparent contact angle of the drop depends on the voltage following the Young-Lippmann equation up to contact angles of ≈50°. At higher voltages, we observe a saturation of the contact angle caused by the competition between electric and capillary stresses, similar to previous experimental observations. We also study the stability of a dielectric film trapped between a conducting fluid and a solid electrode and find a good agreement with analytical predictions based on lubrication theory. Finally, we investigate the film dynamics at long times and report observations of film breakup and entrapment similar to previously reported experimental results.
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Affiliation(s)
- Élfego Ruiz-Gutiérrez
- Smart Materials and Surfaces Laboratory , Northumbria University , Ellison Building, Ellison Place , Newcastle upon Tyne NE1 8ST , U.K
| | - Rodrigo Ledesma-Aguilar
- Smart Materials and Surfaces Laboratory , Northumbria University , Ellison Building, Ellison Place , Newcastle upon Tyne NE1 8ST , U.K
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16
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Kamihoriuchi B, Otsuka Y, Takeuchi A, Iwata F, Matsumoto T. Visualization of Sampling and Ionization Processes in Scanning Probe Electrospray Ionization Mass Spectrometry. ACTA ACUST UNITED AC 2019; 7:S0078. [PMID: 31840014 PMCID: PMC6863452 DOI: 10.5702/massspectrometry.s0078] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2018] [Accepted: 12/25/2018] [Indexed: 02/05/2023]
Abstract
Ambient sampling and ionization techniques based on direct liquid extraction and electrospray ionization are of great value for rapid analysis and mass spectrometry imaging. Scanning probe electrospray ionization (SPESI) enables the sampling and ionization of analyte molecules in a solid material using a liquid bridge and electrospray, respectively, from a single capillary probe. To further improve SPESI, it is essential to understand the dynamic behavior of nanoliter volumes of liquids during sampling and ionization. In this study, the dynamic formation and breakage of the liquid bridge and the subsequent electrospray ionization were investigated by measuring the displacement of the capillary probe using a new optical technique. Measurements revealed that both the time from the formation of the liquid bridge to its breakage and the time from the breakage of the liquid bridge to the detection of analyte ions were correlated with the physical properties of the solvent. It was also found that both of these times were positively correlated with the flow rate. These results will not only lead to the improvement of sampling and ionization efficiencies but also afford a greater understanding of the physicochemical properties of charged nanoliter volumes of liquids.
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Affiliation(s)
- Bui Kamihoriuchi
- Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Yoichi Otsuka
- Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Aya Takeuchi
- Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Futoshi Iwata
- Faculty of Engineering, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8561, Japan
| | - Takuya Matsumoto
- Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
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Zohrabi M, Lim WY, Cormack RH, Supekar OD, Bright VM, Gopinath JT. Lidar system with nonmechanical electrowetting-based wide-angle beam steering. OPTICS EXPRESS 2019; 27:4404-4415. [PMID: 30876059 PMCID: PMC6410924 DOI: 10.1364/oe.27.004404] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Revised: 01/07/2019] [Accepted: 01/07/2019] [Indexed: 05/27/2023]
Abstract
A light detection and ranging (lidar) system with ±90° of steering based on an adaptive electrowetting-based prism for nonmechanical beam steering has been demonstrated. Electrowetting-based prisms provide a transmissive, low power, and compact alternative to conventional adaptive optics as a nonmechanical beam scanner. The electrowetting prism has a steering range of ±7.8°. We demonstrate a method to amplify the scan angle to ±90° and perform a one-dimensional scan in a lidar system.
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Affiliation(s)
- Mo Zohrabi
- Department of Electrical, Computer, and Energy Engineering, University of Colorado, Boulder, Colorado 80309,
USA
| | - Wei Yang Lim
- Department of Mechanical Engineering, University of Colorado Boulder, Colorado 80309,
USA
| | - Robert H. Cormack
- Department of Electrical, Computer, and Energy Engineering, University of Colorado, Boulder, Colorado 80309,
USA
| | - Omkar D. Supekar
- Department of Mechanical Engineering, University of Colorado Boulder, Colorado 80309,
USA
| | - Victor M. Bright
- Department of Mechanical Engineering, University of Colorado Boulder, Colorado 80309,
USA
| | - Juliet T. Gopinath
- Department of Electrical, Computer, and Energy Engineering, University of Colorado, Boulder, Colorado 80309,
USA
- Department of Physics, University of Colorado, Boulder, Colorado 80309,
USA
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18
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Wu L, Han Y, Zhang Q, Zhao S. Effect of external electric field on nanobubbles at the surface of hydrophobic particles during air flotation. RSC Adv 2019; 9:1792-1798. [PMID: 35516131 PMCID: PMC9059776 DOI: 10.1039/c8ra08935c] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Accepted: 01/02/2019] [Indexed: 12/11/2022] Open
Abstract
In this paper, the effect of external electric field on nanobubbles adsorbed on the surface of hydrophobic particles during air flotation was studied by molecular dynamics simulations. The gas density distribution, diffusion coefficient, viscosity, and the change of the angle and number distribution of hydrogen bonds in the system with different amounts of gas molecules were calculated and compared with the results without an external electric field. The results show that the external electric field can make the size of the bubbles smaller. The diffusion coefficient of the gas increases and the viscosity of the system decreases when the external electric field is applied, which contribute to the reduction of the size of the nanobubbles. At the same time, comparing with the results under no external electric field, the angle of hydrogen bonding under the external electric field will increase, and the proportion of water molecules containing more hydrogen bonds will reduce, which further explains the reason why the external electric field reduces the viscosity. The conclusions of this paper demonstrate at the micro level that the external electric field can enhance the efficiency of air-floating technology for the separation of hydrophobic particles, which may provide meaningful theoretical guidance for the application and optimization of electric field-enhanced air-floating technology in practice.
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Affiliation(s)
- Leichao Wu
- Measurement Technology and Instrumentation Key Laboratory of Hebei Province, School of Electrical Engineering, Yanshan University Qinhuangdao 066004 P. R. China
| | - Yong Han
- Measurement Technology and Instrumentation Key Laboratory of Hebei Province, School of Electrical Engineering, Yanshan University Qinhuangdao 066004 P. R. China
| | - Qianrui Zhang
- Measurement Technology and Instrumentation Key Laboratory of Hebei Province, School of Electrical Engineering, Yanshan University Qinhuangdao 066004 P. R. China
| | - Shuai Zhao
- Measurement Technology and Instrumentation Key Laboratory of Hebei Province, School of Electrical Engineering, Yanshan University Qinhuangdao 066004 P. R. China
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19
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Lim WY, Supekar OD, Zohrabi M, Gopinath JT, Bright VM. Liquid Combination with High Refractive Index Contrast and Fast Scanning Speeds for Electrowetting Adaptive Optics. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:14511-14518. [PMID: 30411903 DOI: 10.1021/acs.langmuir.8b02849] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Electrowetting adaptive optical devices are versatile, with applications ranging from microscopy to remote sensing. The choice of liquids in these devices governs its tuning range, temporal response, and wavelength of operation. We characterized a liquid system, consisting of 1-phenyl-1-cyclohexene and deionized water, using both lens and prism devices. The liquids have a large contact angle tuning range, from 173 to 60°. Measured maximum scanning angle was realized at ±13.7° in a two-electrode prism, with simulation predictions of ±18.2°. The liquid's switching time to reach 90° contact angle from rest, in a 4 mm diameter device, was measured at 100 ms. Steady-state scanning with a two-electrode prism showed linear and consistent scan angles of ±4.8° for a 20 V differential between the two electrodes, whereas beam scanning using the liquid system achieved ±1.74° at 500 Hz for a voltage differential of 80 V.
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20
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Accelerated spreading of inviscid droplets prompted by the yielding of strongly elastic interfacial films. Colloids Surf A Physicochem Eng Asp 2018. [DOI: 10.1016/j.colsurfa.2018.06.026] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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21
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LUO F, HONG G, WANG T, JIA L, CHEN JY, SUO L, PEI XB, WAN QB. Static and dynamic evaluations of the wettability of commercial vinyl polysiloxane impression materials for artificial saliva. Dent Mater J 2018; 37:818-824. [PMID: 29962413 DOI: 10.4012/dmj.2017-290] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- Feng LUO
- State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University
| | - Guang HONG
- Liaison Center for Innovative Dentistry, Graduate School of Dentistry, Tohoku University
| | - Tong WANG
- State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University
| | - Lingling JIA
- State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University
| | - Jun-Yu CHEN
- State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University
| | - Lai SUO
- State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University
| | - Xi-Bo PEI
- State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University
| | - Qian-Bing WAN
- State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University
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22
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Vo Q, Tran T. Contact line friction of electrowetting actuated viscous droplets. Phys Rev E 2018; 97:063101. [PMID: 30011486 DOI: 10.1103/physreve.97.063101] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Indexed: 11/07/2022]
Abstract
We examine the contact line friction coefficient of viscous droplets spreading and retracting on solid surfaces immersed in ambient oil. By using the electrowetting effect, we generate a surface tension imbalance to drive the spreading and the retracting motion of the three-phase contact line (TCL). We show that neither the driving force intensity nor TCL direction significantly influences the friction coefficient. Instead, the friction coefficient depends equivalently on the viscosity of liquid droplets and the surrounding oil. We derive and experimentally verify a transient timescale that can be used to characterize both the spreading and retracting dynamics.
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Affiliation(s)
- Quoc Vo
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore
| | - Tuan Tran
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore
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23
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Vo Q, Su H, Tran T. Universal Transient Dynamics of Electrowetting Droplets. Sci Rep 2018; 8:836. [PMID: 29339769 PMCID: PMC5770462 DOI: 10.1038/s41598-018-19167-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2017] [Accepted: 12/15/2017] [Indexed: 11/09/2022] Open
Abstract
Droplet spreading on substrates by electrowetting exhibits either of the two transient behaviours: one characterised by contact line oscillation, and the other one by slow spreading dynamics. The transition between these behaviours remains elusive due to the current limited understanding of the spreading dynamics on the hydrodynamical and electrical properties of electrowetting systems. To understand this transition we propose a model capturing the transition's occurrence based on both the hydrodynamical and electrical parameters. We derive the critical viscosity at which the transition occurs and reveal its subtle and often hidden dependence on the electrowetting dynamics. We find and experimentally verify that the condition for minimization of droplets' actuation time is only achieved at the transition. Particularly, the transition time as a function of damping ratio exhibits the general feature of Kramers' reaction-rate theory.
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Affiliation(s)
- Quoc Vo
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore, Singapore
| | - Haibin Su
- Institute of Advanced Studies, Nanyang Technological University, 60 Nanyang View, 639673, Singapore, Singapore
| | - Tuan Tran
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore, Singapore.
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24
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Supekar OD, Zohrabi M, Gopinath JT, Bright VM. Enhanced Response Time of Electrowetting Lenses with Shaped Input Voltage Functions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:4863-4869. [PMID: 28431469 DOI: 10.1021/acs.langmuir.7b00631] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Adaptive optical lenses based on the electrowetting principle are being rapidly implemented in many applications, such as microscopy, remote sensing, displays, and optical communication. To characterize the response of these electrowetting lenses, the dependence upon direct current (DC) driving voltage functions was investigated in a low-viscosity liquid system. Cylindrical lenses with inner diameters of 2.45 and 3.95 mm were used to characterize the dynamic behavior of the liquids under DC voltage electrowetting actuation. With the increase of the rise time of the input exponential driving voltage, the originally underdamped system response can be damped, enabling a smooth response from the lens. We experimentally determined the optimal rise times for the fastest response from the lenses. We have also performed numerical simulations of the lens actuation with input exponential driving voltage to understand the variation in the dynamics of the liquid-liquid interface with various input rise times. We further enhanced the response time of the devices by shaping the input voltage function with multiple exponential rise times. For the 3.95 mm inner diameter lens, we achieved a response time improvement of 29% when compared to the fastest response obtained using single-exponential driving voltage. The technique shows great promise for applications that require fast response times.
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Affiliation(s)
- Omkar D Supekar
- Department of Mechanical Engineering and §Department of Electrical, Computer, and Energy Engineering, University of Colorado , Boulder, Colorado 80309, United States
| | - Mo Zohrabi
- Department of Mechanical Engineering and §Department of Electrical, Computer, and Energy Engineering, University of Colorado , Boulder, Colorado 80309, United States
| | - Juliet T Gopinath
- Department of Mechanical Engineering and §Department of Electrical, Computer, and Energy Engineering, University of Colorado , Boulder, Colorado 80309, United States
| | - Victor M Bright
- Department of Mechanical Engineering and §Department of Electrical, Computer, and Energy Engineering, University of Colorado , Boulder, Colorado 80309, United States
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25
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Nita S, Do-Quang M, Wang J, Chen YC, Suzuki Y, Amberg G, Shiomi J. Electrostatic cloaking of surface structure for dynamic wetting. SCIENCE ADVANCES 2017; 3:e1602202. [PMID: 28275725 PMCID: PMC5325542 DOI: 10.1126/sciadv.1602202] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2016] [Accepted: 01/27/2017] [Indexed: 05/05/2023]
Abstract
Dynamic wetting problems are fundamental to understanding the interaction between liquids and solids. Even in a superficially simple experimental situation, such as a droplet spreading over a dry surface, the result may depend not only on the liquid properties but also strongly on the substrate-surface properties; even for macroscopically smooth surfaces, the microscopic geometrical roughness can be important. In addition, because surfaces may often be naturally charged or electric fields are used to manipulate fluids, electric effects are crucial components that influence wetting phenomena. We investigate the interplay between electric forces and surface structures in dynamic wetting. Although surface microstructures can significantly hinder spreading, we find that electrostatics can "cloak" the microstructures, that is, deactivate the hindering. We identify the physics in terms of reduction in contact-line friction, which makes the dynamic wetting inertial force dominant and insensitive to the substrate properties.
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Affiliation(s)
- Satoshi Nita
- Department of Mechanical Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Minh Do-Quang
- Department of Mechanics, Linné FLOW Centre, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Jiayu Wang
- Department of Mechanical Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Yu-Chung Chen
- Department of Mechanical Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Yuji Suzuki
- Department of Mechanical Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Gustav Amberg
- Department of Mechanics, Linné FLOW Centre, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Junichiro Shiomi
- Department of Mechanical Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
- Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Tokyo, Japan
- Corresponding author.
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26
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Sinha S, Padia V, Bae KI, Chen G, Das S. Effect of electric double layer on electro-spreading dynamics of electrolyte drops. Colloids Surf A Physicochem Eng Asp 2017. [DOI: 10.1016/j.colsurfa.2016.11.031] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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27
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Yu J, Kwon H, Park HS, Hong S, Choi Y. Femtoliter scale quantitative injection control by experimental and theoretical modeling. Biomed Eng Lett 2016. [DOI: 10.1007/s13534-016-0228-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
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28
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Xie G, He F, Liu X, Si L, Guo D. Sessile multidroplets and salt droplets under high tangential electric fields. Sci Rep 2016; 6:25002. [PMID: 27121926 PMCID: PMC4848563 DOI: 10.1038/srep25002] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Accepted: 04/08/2016] [Indexed: 11/24/2022] Open
Abstract
Understanding the interaction behaviors between sessile droplets under imposed high voltages is very important in many practical situations, e.g., microfluidic devices and the degradation/aging problems of outdoor high-power applications. In the present work, the droplet coalescence, the discharge activity and the surface thermal distribution response between sessile multidroplets and chloride salt droplets under high tangential electric fields have been investigated with infrared thermography, high-speed photography and pulse current measurement. Obvious polarity effects on the discharge path direction and the temperature change in the droplets in the initial stage after discharge initiation were observed due to the anodic dissolution of metal ions from the electrode. In the case of sessile aligned multidroplets, the discharge path direction could affect the location of initial droplet coalescence. The smaller unmerged droplet would be drained into the merged large droplet as a result from the pressure difference inside the droplets rather than the asymmetric temperature change due to discharge. The discharge inception voltages and the temperature variations for two salt droplets closely correlated with the ionization degree of the salt, as well as the interfacial electrochemical reactions near the electrodes. Mechanisms of these observed phenomena were discussed.
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Affiliation(s)
- Guoxin Xie
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
| | - Feng He
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
| | - Xiang Liu
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
| | - Lina Si
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.,School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China
| | - Dan Guo
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
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29
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Hong SJ, Hong J, Seo HW, Lee SJ, Chung SK. Fast Electrically Driven Capillary Rise Using Overdrive Voltage. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:13718-13724. [PMID: 26641954 DOI: 10.1021/acs.langmuir.5b02921] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Enhancement of response speed (or reduction of response time) is crucial for the commercialization of devices based on electrowetting (EW), such as liquid lenses and reflective displays, and presents one of the main challenges in EW research studies. We demonstrate here that an overdrive EW actuation gives rise to a faster rise of a liquid column between parallel electrodes, compared to a DC EW actuation. Here, DC actuation is actually a simple applied step function, and overdrive is an applied step followed by reduction to a lower voltage. Transient behaviors and response time (i.e., the time required to reach the equilibrium height) of the rising liquid column are explored under different DC and overdrive EW actuations. When the liquid column rises up to a target height by means of an overdrive EW, the response time is reduced to as low as 1/6 of the response time using DC EW. We develop a theoretical model to simulate the EW-driven capillary rise by combining the kinetic equation of capillary flow (i.e., Lucas-Washburn equation) and the dynamic contact angle model considering contact line friction, contact angle hysteresis, contact angle saturation, and the EW effect. This theoretical model accurately predicts the outcome to within a ± 5% error in regard to the rising behaviors of the liquid column with a low viscosity, under both DC EW and overdrive actuation conditions, except for the early stage (<about 20 ms).
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Affiliation(s)
- Sung Jin Hong
- Department of Mechanical Engineering, Myongji University , Yongin, Gyeonggido 17058, South Korea
| | - Jiwoo Hong
- Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH) , San 31, Hyoja-dong, Pohang 790-784, South Korea
| | - Hee Won Seo
- Department of Mechanical Engineering, Myongji University , Yongin, Gyeonggido 17058, South Korea
| | - Sang Joon Lee
- Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH) , San 31, Hyoja-dong, Pohang 790-784, South Korea
| | - Sang Kug Chung
- Department of Mechanical Engineering, Myongji University , Yongin, Gyeonggido 17058, South Korea
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30
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Liu Y, Liang YE, Sheng YJ, Tsao HK. Ultralow voltage irreversible electrowetting dynamics of an aqueous drop on a stainless steel surface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:3840-3846. [PMID: 25730308 DOI: 10.1021/acs.langmuir.5b00411] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The electrowetting dynamics of a water drop on a stainless steel surface in air is investigated under ultralow voltages. The spreading behavior can be classified into three regimes. The drop expands slowly in regime I, but the spreading accelerates quite rapidly in regime II. The spreading becomes insignificant in regime III. The experimental results are compared to the equilibrium shapes acquired by Surface Evolver simulations. The good agreement between them indicates that the slow electrowetting dynamics can be considered to be a quasi-equilibrium process. The influences of the electric field and drop size on the spreading dynamics are examined. The variation of both the contact angle and base diameter with time in regimes II and III can be well described by the exponential change with a characteristic time, which grows with the drop volume but is inversely proportional to the electric field. A simple model based on the electromechnical mechanism is proposed to explain the spreading dynamics. The exponential change is attributed to ion migration from the bulk of the drop to the contact line. The experimental results agree well with the prediction of our simple theory.
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Affiliation(s)
- Yanna Liu
- †Faculty of Chemical Engineering, Kunming University of Science and Technology, Kunming 650500, China
| | - Yu-En Liang
- ∥Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan 106, R.O.C
| | - Yu-Jane Sheng
- ∥Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan 106, R.O.C
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31
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Hong J, Lee SJ. Detaching droplets in immiscible fluids from a solid substrate with the help of electrowetting. LAB ON A CHIP 2015; 15:900-907. [PMID: 25500988 DOI: 10.1039/c4lc01049c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The detachment (or removal) of droplets from a solid surface is an indispensable process in numerous practical applications which utilize digital microfluidics, including cell-based assay, chip cooling, and particle sampling. When a droplet that is fully stretched by impacting or electrowetting is released, the conversion of stored surface energy to kinetic energy can lead to the departure of the droplet from a solid surface. Here we firstly detach sessile droplets in immiscible fluids from a hydrophobic surface by electrowetting. The physical conditions for droplet detachment depend on droplet volume, viscosity of ambient fluid, and applied voltage. Their critical conditions are determined by exploring the retracting dynamics for a wide range of driving voltages and physical properties of fluids. The relationships between physical parameters and dynamic characteristics of retracting and jumping droplets, such as contact time and jumping height, are also established. The threshold voltage for droplet detachment in oil with high viscosity is largely reduced (~70%) by electrowetting actuations with a square pulse. To examine the applicability of three-dimensional digital microfluidic (3D-DMF) platforms to biological applications such as cell culture and cell-based assays, we demonstrate the detachment of droplets containing a mixture of human umbilical vein endothelial cells (HUVECs) and collagen (concentration of 4 × 10(4) cells mL(-1)) in silicone oil with a viscosity of 0.65 cSt. Furthermore, to complement the technical limitations due to the use of a needle electrode and to demonstrate the applicability of the 3D-DMF platform with patterned electrodes to chemical analysis and synthesis, we examine the transport, merging, mixing, and detachment of droplets with different pH values on the platform. Finally, by using DC and AC electrowetting actuations, we demonstrate the detachment of oil droplets with a very low contact angle (<~13°) in water on a hydrophobic surface.
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Affiliation(s)
- Jiwoo Hong
- Center for Biofluid Flow and Biomimic Research, Department of Mechanical Engineering, Pohang University of Science and Technology, San 31, Hyoja-dong, Pohang 790-784, South Korea.
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32
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Wehking JD, Kumar R. Droplet actuation in an electrified microfluidic network. LAB ON A CHIP 2015; 15:793-801. [PMID: 25435073 DOI: 10.1039/c4lc00934g] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
This work demonstrates that liquid droplet emulsions in a microchannel can be deformed, decelerated and/or pinned by applying a suitable electrical potential. By concentrating a potential gradient at the corners, we show that different droplets can be passively binned by size and on demand in a branched microfluidic device. The deformation, deceleration, squeezing and release of droplets in a three-dimensional numerical simulation are qualitatively verified by experiments in a PDMS microfluidic device. The forces required for pinning or binning a droplet provide a delicate balance between hydrodynamics and the electric field, and are obtained using appropriate non-dimensional parameters.
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33
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Chen L, Bonaccurso E. Electrowetting -- from statics to dynamics. Adv Colloid Interface Sci 2014; 210:2-12. [PMID: 24268972 DOI: 10.1016/j.cis.2013.09.007] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Revised: 09/16/2013] [Accepted: 09/28/2013] [Indexed: 11/16/2022]
Abstract
More than one century ago, Lippmann found that capillary forces can be effectively controlled by external electrostatic forces. As a simple example, by applying a voltage between a conducting liquid droplet and the surface it is sitting on we are able to adjust the wetting angle of the drop. Since Lippmann's findings, electrocapillary phenomena - or electrowetting - have developed into a series of tools for manipulating microdroplets on solid surfaces, or small amounts of liquids in capillaries for microfluidic applications. In this article, we briefly review some recent progress of fundamental understanding of electrowetting and address some still unsolved issues. Specifically, we focus on static and dynamic electrowetting. In static electrowetting, we discuss some basic phenomena found in DC and AC electrowetting, and some theories about the origin of contact angle saturation. In dynamic electrowetting, we introduce some studies about this rather recent area. At last, we address some other capillary phenomena governed by electrostatics and we give an outlook that might stimulate further investigations on electrowetting.
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Affiliation(s)
- Longquan Chen
- Experimental Interface Physics, Center of Smart Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 10, 64287 Darmstadt, Germany
| | - Elmar Bonaccurso
- Experimental Interface Physics, Center of Smart Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 10, 64287 Darmstadt, Germany.
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Lee SJ, Hong J, Kang KH, Kang IS, Lee SJ. Electrowetting-induced droplet detachment from hydrophobic surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:1805-1811. [PMID: 24490590 DOI: 10.1021/la404344y] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Detachment of droplets from solid surfaces is a basic and crucial process in practical applications such as heat transfer and digital microfluidics. In this study, electrowetting actuations with square pulse signals are employed to detach droplets from a hydrophobic surface. The threshold voltage for droplet detachment is obtained both experimentally and theoretically to find that it is almost constant for various droplet volumes ranging from 0.4 to 10 μL. It is also found that droplets can be detached more easily when the width of applied pulse is well-matched to the spreading time (i.e., the time to reach the maximum spread diameter). When the droplet is actuated by a double square pulse, the threshold voltage is reduced by ∼20% from that for a single square pulse actuation. Finally, by introducing an interdigitated electrode system, it is demonstrated that droplets can be detached from the solid bottom surface without using a top needle electrode.
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Affiliation(s)
- Seung Jun Lee
- Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH) , San 31, Hyoja-dong, Pohang 790-784, South Korea
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Mampallil D, Eral HB, Staicu A, Mugele F, van den Ende D. Electrowetting-driven oscillating drops sandwiched between two substrates. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:053015. [PMID: 24329359 DOI: 10.1103/physreve.88.053015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2013] [Indexed: 06/03/2023]
Abstract
Drops sandwiched between two substrates are often found in lab-on-chip devices based on digital microfluidics. We excite azimuthal oscillations of such drops by periodically modulating the contact line via ac electrowetting. By tuning the frequency of the applied voltage, several shape modes can be selected one by one. The frequency of the oscillations is half the frequency of the contact angle modulation by electrowetting, indicating a parametric excitation. The drop response to sinusoidal driving deviates substantially from sinusoidal behavior in a "stop and go" fashion. Although our simple theoretical model describes the observed behavior qualitatively, the resonances appear at lower frequencies than expected. Moreover, the oscillations produce a nonperiodic fluid transport within the drop with a typical velocity of 1 mm/s. In digital microfluidic devices, where the typical drop size is less than 1 mm, this flow can result in very fast mixing on the spot.
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Affiliation(s)
- Dileep Mampallil
- Physics of Complex Fluids, MESA+ Institute, Department of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - H Burak Eral
- Physics of Complex Fluids, MESA+ Institute, Department of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Adrian Staicu
- Physics of Complex Fluids, MESA+ Institute, Department of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Frieder Mugele
- Physics of Complex Fluids, MESA+ Institute, Department of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Dirk van den Ende
- Physics of Complex Fluids, MESA+ Institute, Department of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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