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Ge T, Hu W, Zhang Z, He X, Wang L, Han X, Dai Z. Open and closed microfluidics for biosensing. Mater Today Bio 2024; 26:101048. [PMID: 38633866 PMCID: PMC11022104 DOI: 10.1016/j.mtbio.2024.101048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2023] [Revised: 04/01/2024] [Accepted: 04/03/2024] [Indexed: 04/19/2024] Open
Abstract
Biosensing is vital for many areas like disease diagnosis, infectious disease prevention, and point-of-care monitoring. Microfluidics has been evidenced to be a powerful tool for biosensing via integrating biological detection processes into a palm-size chip. Based on the chip structure, microfluidics has two subdivision types: open microfluidics and closed microfluidics, whose operation methods would be diverse. In this review, we summarize fundamentals, liquid control methods, and applications of open and closed microfluidics separately, point out the bottlenecks, and propose potential directions of microfluidics-based biosensing.
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Affiliation(s)
- Tianxin Ge
- Guangdong Provincial Key Laboratory of Sensing Technology and Biomedical Instrument, School of Biomedical Engineering, Shenzhen Campus of Sun Yat-sen University, Sun Yat-sen University, No.66, Gongchang Road, Guangming District, Shenzhen, Guangdong, 518107, PR China
| | - Wenxu Hu
- Guangdong Provincial Key Laboratory of Sensing Technology and Biomedical Instrument, School of Biomedical Engineering, Shenzhen Campus of Sun Yat-sen University, Sun Yat-sen University, No.66, Gongchang Road, Guangming District, Shenzhen, Guangdong, 518107, PR China
| | - Zilong Zhang
- Guangdong Provincial Key Laboratory of Sensing Technology and Biomedical Instrument, School of Biomedical Engineering, Shenzhen Campus of Sun Yat-sen University, Sun Yat-sen University, No.66, Gongchang Road, Guangming District, Shenzhen, Guangdong, 518107, PR China
| | - Xuexue He
- Guangdong Provincial Key Laboratory of Sensing Technology and Biomedical Instrument, School of Biomedical Engineering, Shenzhen Campus of Sun Yat-sen University, Sun Yat-sen University, No.66, Gongchang Road, Guangming District, Shenzhen, Guangdong, 518107, PR China
| | - Liqiu Wang
- Department of Mechanical Engineering, The Hong Kong Polytechnic University, 999077, Hong Kong, PR China
| | - Xing Han
- Guangdong Provincial Key Laboratory of Sensing Technology and Biomedical Instrument, School of Biomedical Engineering, Shenzhen Campus of Sun Yat-sen University, Sun Yat-sen University, No.66, Gongchang Road, Guangming District, Shenzhen, Guangdong, 518107, PR China
| | - Zong Dai
- Guangdong Provincial Key Laboratory of Sensing Technology and Biomedical Instrument, School of Biomedical Engineering, Shenzhen Campus of Sun Yat-sen University, Sun Yat-sen University, No.66, Gongchang Road, Guangming District, Shenzhen, Guangdong, 518107, PR China
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2
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Gilinsky SD, Jung DN, Futia GL, Zohrabi M, Welton TA, Supekar OD, Gibson EA, Restrepo D, Bright VM, Gopinath JT. Tunable liquid lens for three-photon excitation microscopy. BIOMEDICAL OPTICS EXPRESS 2024; 15:3285-3300. [PMID: 38855666 PMCID: PMC11161341 DOI: 10.1364/boe.516956] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/27/2023] [Revised: 03/28/2024] [Accepted: 04/06/2024] [Indexed: 06/11/2024]
Abstract
We demonstrate a novel electrowetting liquid combination using a room temperature ionic liquid (RTIL) and a nonpolar liquid, 1-phenyl-1-cyclohexene (PCH) suitable for focus-tunable 3-photon microscopy. We show that both liquids have over 90% transmission at 1300 nm over a 1.1 mm pathlength and an index of refraction contrast of 0.123. A lens using these liquids can be tuned from a contact angle of 133 to 48° with applied voltages of 0 and 60 V, respectively. Finally, a three-photon imaging system including an RTIL electrowetting lens was used to image a mouse brain slice. Axial scans taken with an electrowetting lens show excellent agreement with images acquired using a mechanically scanned objective.
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Affiliation(s)
- Samuel D. Gilinsky
- Department of Electrical, Computer, and Energy Engineering, University of Colorado Boulder, Boulder, Colorado 80309, USA
| | - Diane N. Jung
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, Colorado 80309, USA
| | - Greg L. Futia
- Department of Bioengineering, University of Colorado Anschutz Medical Campus, Aurora, Colorado 80045, USA
| | - Mo Zohrabi
- Department of Electrical, Computer, and Energy Engineering, University of Colorado Boulder, Boulder, Colorado 80309, USA
| | - Tarah A. Welton
- Department of Bioengineering, University of Colorado Anschutz Medical Campus, Aurora, Colorado 80045, USA
| | - Omkar D. Supekar
- Department of Electrical, Computer, and Energy Engineering, University of Colorado Boulder, Boulder, Colorado 80309, USA
| | - Emily A. Gibson
- Department of Bioengineering, University of Colorado Anschutz Medical Campus, Aurora, Colorado 80045, USA
| | - Diego Restrepo
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, Colorado 80045, USA
| | - Victor M. Bright
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, Colorado 80309, USA
| | - Juliet T. Gopinath
- Department of Electrical, Computer, and Energy Engineering, University of Colorado Boulder, Boulder, Colorado 80309, USA
- Department of Physics, University of Colorado Boulder, Boulder, Colorado 80309, USA
- Materials Science and Engineering Program, University of Colorado Boulder, Boulder, Colorado 80309, USA
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3
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Wu R, Ji X, Ma Q, Paulsen BD, Tropp J, Rivnay J. Direct quantification of ion composition and mobility in organic mixed ionic-electronic conductors. SCIENCE ADVANCES 2024; 10:eadn8628. [PMID: 38657078 PMCID: PMC11042751 DOI: 10.1126/sciadv.adn8628] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2024] [Accepted: 03/19/2024] [Indexed: 04/26/2024]
Abstract
Ion transport in organic mixed ionic-electronic conductors (OMIECs) is crucial due to its direct impact on device response time and operating mechanisms but is often assessed indirectly or necessitates extra assumptions. Operando x-ray fluorescence (XRF) is a powerful, direct probe for elemental characterization of bulk OMIECs and was used to directly quantify ion composition and mobility in a model OMIEC, poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS), during device operation. The first cycle revealed slow electrowetting and cation-proton exchange. Subsequent cycles showed rapid response with minor cation fluctuation (~5%). Comparison with optical-tracked electrochromic fronts revealed mesoscale structure-dependent proton transport. The calculated effective ion mobility demonstrated thickness-dependent behavior, emphasizing an interfacial ion transport pathway with a higher mobile ion density. The decoupling of interfacial effects on bulk ion mobility and the decoupling of cation and proton migration elucidate ion transport in conventional and emerging OMIEC-based devices and has broader implications for other ionic conductors writ large.
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Affiliation(s)
- Ruiheng Wu
- Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
| | - Xudong Ji
- Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208, USA
| | - Qing Ma
- DND-CAT, Synchrotron Research Center, Northwestern University, Evanston, IL 60208, USA
| | - Bryan D. Paulsen
- Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208, USA
| | - Joshua Tropp
- Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208, USA
| | - Jonathan Rivnay
- Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208, USA
- Department of Material Science and Engineering, Northwestern University, Evanston, IL 60611, USA
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4
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Louge MY, Wang Y. Statistical Mechanics of Electrowetting. ENTROPY (BASEL, SWITZERLAND) 2024; 26:276. [PMID: 38667830 PMCID: PMC11049600 DOI: 10.3390/e26040276] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2024] [Revised: 03/19/2024] [Accepted: 03/21/2024] [Indexed: 04/28/2024]
Abstract
We derive the ab initio equilibrium statistical mechanics of the gas-liquid-solid contact angle on planar periodic, monodisperse, textured surfaces subject to electrowetting. To that end, we extend an earlier theory that predicts the advance or recession of the contact line amount to distinct first-order phase transitions of the filling state in the ensemble of nearby surface cavities. Upon calculating the individual capacitance of a cavity subject to the influence of its near neighbors, we show how hysteresis, which is manifested by different advancing and receding contact angles, is affected by electrowetting. The analysis reveals nine distinct regimes characterizing contact angle behavior, three of which arise only when a voltage is applied to the conductive liquid drop. As the square voltage is progressively increased, the theory elucidates how the drop occasionally undergoes regime transitions triggering jumps in the contact angle, possibly changing its hysteresis, or saturating it at a value weakly dependent on further voltage growth. To illustrate these phenomena and validate the theory, we confront its predictions with four data sets. A benefit of the theory is that it forsakes trial and error when designing textured surfaces with specific contact angle behavior.
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Affiliation(s)
- Michel Y. Louge
- Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA;
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5
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Zhu Z, Zhu J, Chang C, Qi C, Zhu Z, Zhao H, Zhang D, Zeng XC, Wang C. Tunable Surface Wettability via Terahertz Electrowave Controlled Vicinal Subnanoscale Water Layer. NANO LETTERS 2024; 24:3243-3248. [PMID: 38427592 DOI: 10.1021/acs.nanolett.4c00248] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/03/2024]
Abstract
Achieving timely, reversible, and long-range remote tunability over surface wettability is highly demanded across diverse fields, including nanofluidic systems, drug delivery, and heterogeneous catalysis. Herein, using molecular dynamic simulations, we show, for the first time, a theoretical design of electrowetting to achieve remotely controllable surface wettability via using a terahertz wave. The key idea driving the design is the unique terahertz collective vibration identified in the vicinal subnanoscale water layer, which is absent in bulk water, enabling efficient energy transfer from the terahertz wave to the rotational motion of the vicinal subnanoscale water layer. Consequently, a frequency-specific alternating terahertz electric field near the critical strength can significantly affect the local hydrogen-bonding network of the contact water layer on the solid surface, thereby achieving tunable surface wettability.
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Affiliation(s)
- Zhi Zhu
- College of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
| | - Junquan Zhu
- College of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
| | - Chao Chang
- Innovation Laboratory of Terahertz Biophysics, National Innovation Institute of Defense Technology, Beijing 100071, China
- School of Physics, Peking University, Beijing 100871, China
| | - Chonghai Qi
- School of Physical and Intelligent Engineering, Jining University, Qufu 273155, China
| | - Zhongjie Zhu
- Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, China
| | - Hongwei Zhao
- Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, China
| | - Dengsong Zhang
- International Joint Laboratory of Catalytic Chemistry, College of Sciences, Shanghai University, Shanghai 200444, China
| | - Xiao Cheng Zeng
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong
| | - Chunlei Wang
- International Joint Laboratory of Catalytic Chemistry, College of Sciences, Shanghai University, Shanghai 200444, China
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6
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Rogier F, Shao W, Guo Y, Zhuang L, Kegel WK, Groenewold J. Deformation of confined liquid interfaces by inhomogeneous electric fields and localized particle forces. J Colloid Interface Sci 2024; 657:830-840. [PMID: 38086246 DOI: 10.1016/j.jcis.2023.11.099] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Revised: 11/13/2023] [Accepted: 11/16/2023] [Indexed: 01/02/2024]
Abstract
HYPOTHESIS Oil-water interfaces that are created by confining a certain amount of oil in a square shaped pixel (∼200 x 200 μm2 with a height of ∼10 μm) topped by a layer of water, have a curvature that depends on the amount of oil that happens to be present in the confining area. Under the application of an electric field normal to the interface, the interface will deform due to inhomogeneities in the electric field. These inhomogeneities are expected to arise from the initial curvature of the meniscus, from fringe fields that emerge at the confining pixel walls and, if applicable, from interfacially adsorbed particles. MODELING AND EXPERIMENTS We model the shape of the confined oil-water interface invoking capillarity and electrostatics. Furthermore, we measure the initial curvature by tracking the position of interfacially adsorbed particles depending on sample tilt. FINDINGS We found that the pixels exhibited meniscus curvature radii ranging from 0.6-7 mm. The corresponding model based minimum oil film thicknesses range between 0.7 and 9 μm. Furthermore, the model shows that the initial meniscus curvature can increase up to 76 percent relative to the initial curvature by the electric field before the oil film becomes unstable. The pixel wall and particles are shown to have minimal impact on the interface deformation.
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Affiliation(s)
- Faranaaz Rogier
- Van 't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, University Utrecht, Padualaan 8, Utrecht, 3584 CH, the Netherlands.
| | - Wan Shao
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, PR China; National Center for International Research on Green Optoelectronics, South China Normal University, Guangzhou 510006, PR China
| | - Yuanyuan Guo
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, PR China; National Center for International Research on Green Optoelectronics, South China Normal University, Guangzhou 510006, PR China
| | - Lei Zhuang
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, PR China; National Center for International Research on Green Optoelectronics, South China Normal University, Guangzhou 510006, PR China
| | - Willem K Kegel
- Van 't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, University Utrecht, Padualaan 8, Utrecht, 3584 CH, the Netherlands.
| | - Jan Groenewold
- Van 't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, University Utrecht, Padualaan 8, Utrecht, 3584 CH, the Netherlands.
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7
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Nie P, Jiang X, Zheng X, Guan D. Manipulation of Contact Angle Hysteresis at Electrified Ionic Liquid-Solid Interfaces. PHYSICAL REVIEW LETTERS 2024; 132:044002. [PMID: 38335359 DOI: 10.1103/physrevlett.132.044002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2022] [Revised: 03/27/2023] [Accepted: 01/02/2024] [Indexed: 02/12/2024]
Abstract
Room-temperature ionic liquids (RTILs) are intriguing fluids that have drawn much attention in applications ranging from tribology and catalysis to energy storage. With strong electrostatic interaction between ions, their interfacial behaviors can be modulated by controlling energetics of the electrified interface. In this work, we report atomic-force-microscope measurements of contact angle hysteresis (CAH) of a circular contact line formed on a micron-sized fiber, which is coated with a thin layer of conductive film and intersects an RTIL-air interface. The measured CAH shows a distinct change by increasing the voltage U applied on the fiber surface. Molecular dynamics simulations were performed to illustrate variations of the solidlike layer in the RTIL adsorbed at the electrified interface. The integrated experiments and computations demonstrate a new mechanism to manipulate the CAH by rearrangement of interfacial layers of RTILs induced by the surface energetics.
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Affiliation(s)
- Pengcheng Nie
- State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
- School of Engineering Science, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xikai Jiang
- State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
| | - Xu Zheng
- State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
| | - Dongshi Guan
- State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
- School of Engineering Science, University of Chinese Academy of Sciences, Beijing 100049, China
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8
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Liao J, Majidi C, Sitti M. Liquid Metal Actuators: A Comparative Analysis of Surface Tension Controlled Actuation. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024; 36:e2300560. [PMID: 37358049 DOI: 10.1002/adma.202300560] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2023] [Revised: 06/09/2023] [Indexed: 06/27/2023]
Abstract
Liquid metals, with their unique combination of electrical and mechanical properties, offer great opportunities for actuation based on surface tension modulation. Thanks to the scaling laws of surface tension, which can be electrochemically controlled at low voltages, liquid metal actuators stand out from other soft actuators for their remarkable characteristics such as high contractile strain rates and higher work densities at smaller length scales. This review summarizes the principles of liquid metal actuators and discusses their performance as well as theoretical pathways toward higher performances. The objective is to provide a comparative analysis of the ongoing development of liquid metal actuators. The design principles of the liquid metal actuators are analyzed, including low-level elemental principles (kinematics and electrochemistry), mid-level structural principles (reversibility, integrity, and scalability), and high-level functionalities. A wide range of practical use cases of liquid metal actuators from robotic locomotion and object manipulation to logic and computation is reviewed. From an energy perspective, strategies are compared for coupling the liquid metal actuators with an energy source toward fully untethered robots. The review concludes by offering a roadmap of future research directions of liquid metal actuators.
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Affiliation(s)
- Jiahe Liao
- Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569, Stuttgart, Germany
| | - Carmel Majidi
- Robotics Institute, Mechanical Engineering, Carnegie Mellon University, 5000 Forbes Ave, Pittsburgh, PA, 15213, USA
| | - Metin Sitti
- Physical Intelligence Department, Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569, Stuttgart, Germany
- Institute for Biomedical Engineering, ETH Zürich, Zürich, 8092, Switzerland
- School of Medicine, College of Engineering, Koç University, Istanbul, 34450, Turkey
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9
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Guo Y, Guo H, He D, Sun J, Chen W, Song Y, Zhou G. Development of Cyclic Tetrasiloxane Polymer as a High-Performance Dielectric and Hydrophobic Layer for Electrowetting Displays. ACS APPLIED MATERIALS & INTERFACES 2023; 15:46470-46482. [PMID: 37738528 DOI: 10.1021/acsami.3c08188] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/24/2023]
Abstract
Cyclic tetrasiloxane polymer (CTP) has recently garnered interest as a hydrophobic material with unique properties. This study aims to enhance the dielectric constant of CTP films by introducing excess Si-H groups and to explore the impact of synthesis and processing conditions on the resulting properties. The film demonstrates high hydrophobicity, with contact angles of 107° in air and 165° in n-decane, along with a notable dielectric constant of 5.1°. Furthermore, the CTP film displays reversible electrowetting behavior with low contact angle hysteresis (2°) and possesses good transparency (∼99%) and thermal stability. As such, the CTP film has significant potential as a material for the electric wetting of hydrophobic dielectric layers and may serve as a promising alternative in electrowetting applications.
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Affiliation(s)
- Yuanyuan Guo
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology and Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China
- Shenzhen Guohua Optoelectronics Tech., Co., Ltd., Shenzhen 518110, China
- Academy of Shenzhen Guohua Optoelectronics, Shenzhen 518110, China
| | - Hao Guo
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology and Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China
| | - Dinggui He
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology and Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China
| | - Jiaqi Sun
- University of Chinese Academy of Sciences, Ningbo Institute of Materials Technology and Engineering, Ningbo 315201, China
| | - Wangqiao Chen
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology and Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China
| | - Yujie Song
- University of Chinese Academy of Sciences, Ningbo Institute of Materials Technology and Engineering, Ningbo 315201, China
| | - Guofu Zhou
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology and Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China
- Shenzhen Guohua Optoelectronics Tech., Co., Ltd., Shenzhen 518110, China
- Academy of Shenzhen Guohua Optoelectronics, Shenzhen 518110, China
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10
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Bhatt B, Mukhopadhyay S, Khare K. Frequency-Dependent Dewetting of Thin Liquid Films Using External ac Electric Field. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:13512-13520. [PMID: 37707358 DOI: 10.1021/acs.langmuir.3c01537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/15/2023]
Abstract
The stability of thin liquid films on a surface can be controlled by using external stimuli, such as an electric field, temperature, or light, by manipulating the total excess free energy of the system. It has been previously shown that thin lubricating films on slippery surfaces can be destabilized via the spinodal mechanism using an external electric field, which returns to the original stable configuration upon the electric field. However, the role of the frequency of the applied ac electric field is not clear, which is the main topic of study in this report. When an ac electric field of fixed voltage and varying frequency is applied across thin lubricating films of slippery surfaces, a different dewetting behavior is observed. Characteristic length and time scales of dewetting depend strongly on the frequency of the applied voltage, which is primarily due to the change in the dielectric behavior of the lubricating fluid. In addition, the interplay of various time scales involved in the dewetting process also depends on the frequency.
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Affiliation(s)
- Bidisha Bhatt
- Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Soumik Mukhopadhyay
- Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Krishnacharya Khare
- Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016, India
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11
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Goel S, Pillai DS. Electrokinetic Thin-Film Model for Electrowetting: The Role of Bulk Charges. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:13076-13089. [PMID: 37656921 DOI: 10.1021/acs.langmuir.3c01421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/03/2023]
Abstract
The electrowetting behavior of a charge-carrying sessile droplet is relevant to applications such as point-of-care diagnostics. Often biomedical assays involve droplets that contain charged molecules such as dissolved ions, proteins, and DNA. In this work, we develop a reduced-order electrokinetic model for electrowetting of such a charge-carrying droplet under a parallel-plate electrode configuration. An inertial-lubrication model based on the weighted residual integral boundary layer (WRIBL) technique is used to obtain evolution equations that describe the spatiotemporal evolution of the fluid-air interface and the depth-integrated flow rate. The solutions to the evolution equations are obtained numerically by using the spectral collocation method. We investigate the role of domain and surface charges, characterized by the Debye length, on droplet wetting. Under low relaxation timescales, both droplet deformation and wetting alteration under an AC field are shown to be equivalent to that under a root-mean-square (RMS) DC field. We show that an electrolytic sessile droplet can exhibit a larger deformation in comparison to the two asymptotic limits of a perfect conductor and a perfect dielectric droplet, corresponding, respectively, to very low and high Debye lengths. The effects of several other parameters such as the inherent equilibrium wettability, permittivity ratio, and electric field strength are also investigated.
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Affiliation(s)
- Shreyank Goel
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, Uttar Pradesh, India
| | - Dipin S Pillai
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, Uttar Pradesh, India
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12
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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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13
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Coelho BJ, Pinto JV, Martins J, Rovisco A, Barquinha P, Fortunato E, Baptista PV, Martins R, Igreja R. Parylene C as a Multipurpose Material for Electronics and Microfluidics. Polymers (Basel) 2023; 15:polym15102277. [PMID: 37242852 DOI: 10.3390/polym15102277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Revised: 04/28/2023] [Accepted: 05/05/2023] [Indexed: 05/28/2023] Open
Abstract
Poly(p-xylylene) derivatives, widely known as Parylenes, have been considerably adopted by the scientific community for several applications, ranging from simple passive coatings to active device components. Here, we explore the thermal, structural, and electrical properties of Parylene C, and further present a variety of electronic devices featuring this polymer: transistors, capacitors, and digital microfluidic (DMF) devices. We evaluate transistors produced with Parylene C as a dielectric, substrate, and encapsulation layer, either semitransparent or fully transparent. Such transistors exhibit steep transfer curves and subthreshold slopes of 0.26 V/dec, negligible gate leak currents, and fair mobilities. Furthermore, we characterize MIM (metal-insulator-metal) structures with Parylene C as a dielectric and demonstrate the functionality of the polymer deposited in single and double layers under temperature and AC signal stimuli, mimicking the DMF stimuli. Applying temperature generally leads to a decrease in the capacitance of the dielectric layer, whereas applying an AC signal leads to an increase in said capacitance for double-layered Parylene C only. By applying the two stimuli, the capacitance seems to suffer from a balanced influence of both the separated stimuli. Lastly, we demonstrate that DMF devices with double-layered Parylene C allow for faster droplet motion and enable long nucleic acid amplification reactions.
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Affiliation(s)
- Beatriz J Coelho
- CENIMAT|i3N, Department of Materials Science, NOVA School of Science and Technology, Campus de Caparica, NOVA University of Lisbon and CEMOP/UNINOVA, 2829-516 Caparica, Portugal
- UCIBIO, I4HB, Department of Life Sciences, NOVA School of Science and Technology, Campus de Caparica, NOVA University of Lisbon, 2829-516 Caparica, Portugal
| | - Joana V Pinto
- CENIMAT|i3N, Department of Materials Science, NOVA School of Science and Technology, Campus de Caparica, NOVA University of Lisbon and CEMOP/UNINOVA, 2829-516 Caparica, Portugal
| | - Jorge Martins
- CENIMAT|i3N, Department of Materials Science, NOVA School of Science and Technology, Campus de Caparica, NOVA University of Lisbon and CEMOP/UNINOVA, 2829-516 Caparica, Portugal
| | - Ana Rovisco
- CENIMAT|i3N, Department of Materials Science, NOVA School of Science and Technology, Campus de Caparica, NOVA University of Lisbon and CEMOP/UNINOVA, 2829-516 Caparica, Portugal
| | - Pedro Barquinha
- CENIMAT|i3N, Department of Materials Science, NOVA School of Science and Technology, Campus de Caparica, NOVA University of Lisbon and CEMOP/UNINOVA, 2829-516 Caparica, Portugal
| | - Elvira Fortunato
- CENIMAT|i3N, Department of Materials Science, NOVA School of Science and Technology, Campus de Caparica, NOVA University of Lisbon and CEMOP/UNINOVA, 2829-516 Caparica, Portugal
| | - Pedro V Baptista
- UCIBIO, I4HB, Department of Life Sciences, NOVA School of Science and Technology, Campus de Caparica, NOVA University of Lisbon, 2829-516 Caparica, Portugal
| | - Rodrigo Martins
- CENIMAT|i3N, Department of Materials Science, NOVA School of Science and Technology, Campus de Caparica, NOVA University of Lisbon and CEMOP/UNINOVA, 2829-516 Caparica, Portugal
| | - Rui Igreja
- CENIMAT|i3N, Department of Materials Science, NOVA School of Science and Technology, Campus de Caparica, NOVA University of Lisbon and CEMOP/UNINOVA, 2829-516 Caparica, Portugal
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14
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Liu D, Cao Q, Piao Z, Li L. Confinement Dynamics of Nanodroplets between Two Surfaces: Effects of Wettability and Electric Field. Chemphyschem 2022; 23:e202200184. [PMID: 35986551 DOI: 10.1002/cphc.202200184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Revised: 08/15/2022] [Indexed: 01/04/2023]
Abstract
The electrowetting effect and related applications of tiny droplets have aroused widespread research interest. In this work, we report molecular dynamics simulations of confinement dynamics of nanodroplets under different droplet-surface interactions and surface distances under an external electric field. So far, the effect of the surface-droplet interactions on electric field-induced dynamics behaviors of droplets in confined spaces has not been extensively studied. Our results show that in the absence of electric field there is a critical value of surface wettability for the shape transition of droplets. Above this value, the droplet is divided into small droplets adhered on the bottom and top surfaces; below this value, the droplets are detached from the surfaces. When an external electric field is applied parallel to the surfaces, the droplet spreads on the surface along the direction of the electric field. It was found that the surface separation significantly influences the transition of the droplet shape. The steady morphology of the droplets under the electric field depends on the surface-droplet interaction and surface separation. We explore the underlying mechanism causing the morphological transition through analyzing the molecular interactions, the number of interracial molecules and the interaction force between the droplets and surfaces. These results provide basic insights into the molecular interactions of nanodroplets under different confined environments, and clues for applications of confined nanodroplets under the control of electric field.
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Affiliation(s)
- Dandan Liu
- College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou, 310014, P.R. China.,College of Information Science and Engineering, Jiaxing University, Jiaxing, 314001, P.R. China
| | - Qianqian Cao
- College of Information Science and Engineering, Jiaxing University, Jiaxing, 314001, P.R. China
| | - Zhongyu Piao
- College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou, 310014, P.R. China
| | - Lujuan Li
- College of Information Science and Engineering, Jiaxing University, Jiaxing, 314001, P.R. China
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15
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He X, Li J, Guan Y, Wang Z. Nanodroplet Wetting and Electrowetting Behavior on Liquid-infused Surfaces: A Molecular Simulation Study. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.121157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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16
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Rosenholm JB. Characterization of molecule clustering and liquid transport at nearly ideal solid surfaces. Adv Colloid Interface Sci 2022; 307:102733. [PMID: 35872441 DOI: 10.1016/j.cis.2022.102733] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Revised: 07/06/2022] [Accepted: 07/08/2022] [Indexed: 11/29/2022]
Abstract
Vapor adsorption, mobility, two-dimensional (monolayer formation) and three-dimensional (multilayer formation) clustering is evaluated. Two-dimensional vapor diffusion is compared to results obtained from molecular kinetic (MK) model fits. Three-dimensional clustering results in condensation of multimolecular vapor layers to thin films. Thin films are characte-rized by line tension and liquid spreading by hydrodynamic (HD) models. Although it is experimentally shown that steady-state wetting ranges are intersected by a chaotic slip-stick range, MK and HD models are combined to molecular hydrodynamic (MH) models with the aim to cover this slip-stick range. The results of MK, HD and MH model fits are, however rather poor (unphysical results). Thin film (α-phase) models are compared to thick film (β-phase) models. In order to improve model designs, established phenomenological relation-ships known from irreversible thermodynamics are presented. Forced wetting, expressed as generalized fluxes can be made dependent on multiple generalized conjugate forces which enables identification of dominant interactions to be introduced in future improved transport models.
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Affiliation(s)
- Jarl B Rosenholm
- Physical Chemistry, Laboratory of Molecular Science and Engineering, Aurum, Henriksgatan 2, 20500 Åbo (Turku), Finland.
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17
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Xiang Y, Fulmek P, Platz D, Schmid U. Temperature Dependence of Water Contact Angle on Teflon AF1600. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:1631-1637. [PMID: 35048705 PMCID: PMC8812120 DOI: 10.1021/acs.langmuir.1c03202] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 01/04/2022] [Indexed: 06/14/2023]
Abstract
In this work, we investigate the change of contact angle (CA) of a water droplet during evaporation on a Teflon AF1600 surface in the temperature range between 20 and 80 °C under standard laboratory conditions. An almost constant initial CA and a significant increase of the stabilized CA have been observed. The results reveal a temperature-dependent CA change, mainly due to water adsorption on the solid surface. Soaking experiments indicate that besides adsorption, a temperature-independent friction-like force contributes to the pinning of triple-line and therefore to the CA change. We propose an adsorption coverage parameter and a friction-like force to describe the CA change. Furthermore, we describe a reproducible process to produce smooth and homogeneous Teflon AF1600 thin films, minimizing the influence of roughness and local heterogeneity on the CA.
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19
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Abstract
The surface wettability of catalysts is typically controlled via surface treatments that promote catalytic performance. Here we report on potential-regulated hydrophobicity/hydrophilicity at cobalt-based oxide interfaces with an alkaline solution. The switchable wetting of single particles, directly related to their activity and stability towards the oxygen evolution reaction, was revealed by electrochemical liquid-phase transmission electron microscopy. Analysis of the movement of the liquid in real time revealed distinctive wettability behaviour associated with specific potential ranges. At low potentials, an overall reduction of the hydrophobicity of the oxides was probed. Upon reversible reconstruction towards the surface oxyhydroxide phase, electrowetting was found to cause a change in the interfacial capacitance. At high potentials, the evolution of molecular oxygen, confirmed by operando electron energy-loss spectroscopy, was accompanied by a globally thinner liquid layer. This work directly links the physical wetting with the chemical oxygen evolution reaction of single particles, providing fundamental insights into solid–liquid interfacial interactions of oxygen-evolving oxides. ![]()
Surface treatments can tune catalysts’ wettability, which can be used to promote their catalytic performance. Now, a potential-dependent dynamic wetting behaviour of cobalt-based oxide catalysts is identified before and during the oxygen evolution reaction.
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20
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Wang Q, Li L, Gu J, Zhang C, Lyu J, Yao W. Manipulation of a Nonconductive Droplet in an Aqueous Fluid with AC Electric Fields: Droplet Dewetting, Oscillation, and Detachment. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:12098-12111. [PMID: 34519514 DOI: 10.1021/acs.langmuir.1c01934] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Electrowetting (EW) is an effective method for droplet manipulation in microfluidics. In traditional EW, a conductive droplet is actuated, which spreads on a solid substrate. Recently, we considered an opposite phenomenon of droplet actuation in EW: inducing nonconductive droplet dewetting and detaching from the substrate. An oil/water system is used in which the oil droplet (nonconductive) is actuated on a flat substrate in surrounding water (conductive) by EW. In this work, alternating current (AC) electric fields are applied to EW, and the transient dynamics of droplet dewetting, oscillation, and detachment with the AC signals are investigated. The droplet is not in contact with electrodes, and it dances freely on the substrate. Experiments are performed in a wide range of voltages and AC frequencies. To demonstrate the droplet dynamics, we divide the full process of droplet manipulation into three distinguishable periods, that is, an initiating period, a steady oscillation period, and a detaching condition. Transient droplet dewetting is considered in the initiating period, and we obtain the distribution of the contact line friction factor. In steady oscillation, the oscillation resonance is verified from the oscillating amplitude of the contact line. Different periodical features are found for the droplet dancing at the resonance frequencies and departure from resonance. The droplet is detached at high voltages, and we provide a map for the detachable and nondetachable zones. The voltage is the dominant factor determining the droplet detachment; however, the AC frequency has notable influences on the critical voltage. The detachment is promoted when the AC frequency is within the region of the oscillation resonance (e.g., 20 < f < 75 Hz). In this region, the detaching process is not monotonic but instead, the droplet rebounds by several times before it is completely detached.
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Affiliation(s)
- Qinggong Wang
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
| | - Long Li
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
| | - Junping Gu
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
| | - Ce Zhang
- Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China
| | - Junfu Lyu
- Key Laboratory for Thermal Science and Power 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, Beijing 100094, China
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21
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Granda R, Plog J, Li G, Yurkiv V, Mashayek F, Yarin AL. Evolution and Shape of Two-Dimensional Stokesian Drops under the Action of Surface Tension and Electric Field: Linear and Nonlinear Theory and Experiment. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:11429-11446. [PMID: 34559540 DOI: 10.1021/acs.langmuir.1c01015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The creeping-flow theory describing evolution and steady-state shape of two-dimensional ionic-conductor drops under the action of surface tension and the subcritical (in terms of the electric Bond number) electric field imposed in the substrate plane is developed. On the other hand, the experimental data are acquired for drops impacted or softly deposited on dielectric surfaces of different wettability and subjected to an in-plane subcritical electric field. Even though the experimental situation involves viscous friction of drops with the substrates and wettability-driven motion of the contact line, the comparison to the theory reveals that it can accurately describe the steady-state drop shape on a non-wettable substrate. In the latter case, the drop is sufficiently raised above the substrate, which diminishes the three-dimensional effects, making the two-dimensional description (lacking the no-slip condition at the substrate and wettability-driven motion of the contact line) relevant. Accordingly, it is demonstrated how the subcritical electric field deforms the initially circular drops until an elongated steady-state configuration is reached. In particular, the surface tension tends to round off the non-circular drops stretched by the electric Maxwell stresses imposed by the electrodes. A more pronounced substrate wettability leads to more elongated steady-state configurations observed experimentally than those predicted by the two-dimensional theory. The latter cases reveal significant three-dimensional effects in the electrically driven drop stretching. In the supercritical electric fields (corresponding to the supercritical electric Bond numbers), the electrical stretching of drops predicted by the present linearized two-dimensional theory results in splitting into two separate droplets. This scenario is corroborated by the predictions of the fully nonlinear results for similar electrically stretched bubbles in the creeping-flow regime available in the literature as well as by the present experimental results on a substrate with slip.
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Affiliation(s)
- Rafael Granda
- Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, 842 West Taylor Street, Chicago, Illinois 60607-7022, United States
| | - Jevon Plog
- Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, 842 West Taylor Street, Chicago, Illinois 60607-7022, United States
| | - Gen Li
- Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, 842 West Taylor Street, Chicago, Illinois 60607-7022, United States
| | - Vitaliy Yurkiv
- Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, 842 West Taylor Street, Chicago, Illinois 60607-7022, United States
| | - Farzad Mashayek
- Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, 842 West Taylor Street, Chicago, Illinois 60607-7022, United States
| | - Alexander L Yarin
- Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, 842 West Taylor Street, Chicago, Illinois 60607-7022, United States
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22
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Zhang BX, Wang SL, He X, Yang YR, Wang XD. Dynamic spreading of a water nanodroplet on a nanostructured surface in the presence of an electric field. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.116039] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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23
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Controlling the breakup of toroidal liquid films on solid surfaces. Sci Rep 2021; 11:8120. [PMID: 33854150 PMCID: PMC8046813 DOI: 10.1038/s41598-021-87549-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Accepted: 03/26/2021] [Indexed: 11/09/2022] Open
Abstract
The breakup of a slender filament of liquid driven by surface tension is a classical fluid dynamics stability problem that is important in many situations where fine droplets are required. When the filament is resting on a flat solid surface which imposes wetting conditions the subtle interplay with the fluid dynamics makes the instability pathways and mode selection difficult to predict. Here, we show how controlling the static and dynamic wetting of a surface can lead to repeatable switching between a toroidal film of an electrically insulating liquid and patterns of droplets of well-defined dimensions confined to a ring geometry. Mode selection between instability pathways to these different final states is achieved by dielectrophoresis forces selectively polarising the dipoles at the solid-liquid interface and so changing both the mobility of the contact line and the partial wetting of the topologically distinct liquid domains. Our results provide insights into the wetting and stability of shaped liquid filaments in simple and complex geometries relevant to applications ranging from printing to digital microfluidic devices.
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24
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Kovalchuk NM, Simmons MJ. Surfactant-mediated wetting and spreading: Recent advances and applications. Curr Opin Colloid Interface Sci 2021. [DOI: 10.1016/j.cocis.2020.07.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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25
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Guan Y, Tu J, Li B, Fu J, Zhu M, Chen X, Zhou C. Stripped Electrode Based Electrowetting-on-Dielectric Digital Microfluidics for Precise and Controllable Parallel Microdrop Generation. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:9540-9550. [PMID: 32698587 DOI: 10.1021/acs.langmuir.0c01543] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Microdrop generation with excellent controllability and volume precision is of paramount significance for a large variety of microfluidic applications. In this work, we propose a new configuration comprising only stripped electrodes of rectangular shape for the closed electrowetting-on-dielectric digital microfluidic (EWOD DMF) system and investigate its parallel microdrop generation outcomes via a numerical approach. The microfluidic droplet motion is solved by a finite-volume scheme on a fixed computational domain. The numerical model is verified by an experimental study of microdrop production from an EWOD DMF device with three different electrode designs. After model verification, we examine the influences of the equilibrium contact angle and the spacing of the microchannel on stripped electrode based microdrop generation outcomes and discover five different regimes including the phenomena of satellite droplet formation and separation cessation. Despite the various generation outcomes, the daughter droplet size is found to vary linearly with a dimensionless EWOD parameter κ*. More importantly, for all successful generations, the deviation of the daughter droplet size from that of the stripped electrode is smaller than 3.5%, which even reaches zero in proper conditions. This new configuration can be utilized as a convenient alternative for electrowetting-induced parallel microdrop production with excellent precision and controllability.
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Affiliation(s)
- Yin Guan
- School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, People's Republic of China
| | - Jiyue Tu
- School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, People's Republic of China
| | - Baiyun Li
- School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, People's Republic of China
| | - Jingwei Fu
- School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, People's Republic of China
| | - Mengnan Zhu
- School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, People's Republic of China
| | - Xiyang Chen
- School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, People's Republic of China
| | - Cheng Zhou
- School of Business Administration, Hubei University of Economics, Wuhan, Hubei 430205, People's Republic of China
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26
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Statistical modeling of electrowetting-induced droplet coalescence for condensation applications. Colloids Surf A Physicochem Eng Asp 2020. [DOI: 10.1016/j.colsurfa.2020.124874] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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27
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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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28
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Designing Micro Bulge Structure with Uniform PS Microspheres for Boosted Dielectric Hydrophobic Blend Films. Polymers (Basel) 2020; 12:polym12030574. [PMID: 32143490 PMCID: PMC7182817 DOI: 10.3390/polym12030574] [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: 01/14/2020] [Revised: 02/28/2020] [Accepted: 03/03/2020] [Indexed: 11/16/2022] Open
Abstract
In this paper, homogeneous polystyrene (PS) microspheres with controllable sizes of 40 nm, 80 nm, and 120 nm were synthesized by controlling the temperature of solvothermal method. In order to explore the effect of PS microspheres on dielectric-hydrophobic properties of the composite films, the composite films containing polystyrene, Polydimethylsiloxane, and P(VDF-TrFE) with high dielectric and hydrophobicity were successfully prepared by a simple and feasible solution blending method. The dielectric constant and hydrophobicity of composite films were boosted by increasing the mass fraction of PS content and decreasing the size of PS due to the enhanced interfacial polarization and the uniform surface micro bulge structure. Meanwhile, the composite films maintain a low loss tangent. Typically, the dielectric constant with 5 wt.% 40 nm PS reached to 29 at 100Hz, which is 4 times that of PDMS/P(VDF-TrFE) (mass ratio: 2/3). Otherwise, the largest the contact angle of 126° in the same composition was remarkably larger than the pure PDMS/P(VDF-TrFE) (110°). These improved properties have more potential applications in the electric wetting devices.
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29
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Löwe JM, Hinrichsen V, Roisman IV, Tropea C. Behavior of charged and uncharged drops in high alternating tangential electric fields. Phys Rev E 2020; 101:023102. [PMID: 32168636 DOI: 10.1103/physreve.101.023102] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2019] [Accepted: 01/07/2020] [Indexed: 06/10/2023]
Abstract
The interaction of drops and electric fields occurs in many applications like electrowetting, electrospinning, atomization, but also causes unwanted effects like the aging of high-voltage composite insulators. Water drops are influenced by electric fields due to the polar properties of the water molecules. The behavior of the drops depends on several parameters like the orientation and strength of the electric field, drop volume, and frequency of the applied field. In addition, electric charges can influence the behavior of drops significantly. However, the impact of electric charges, including the interaction with the drop as well as the electric field strength, is far from being well understood. In this work, the impact of electric charges on the behavior of single sessile drops is investigated experimentally under well-defined conditions. The effects of the drop volume, electric field strength, field frequency, and electric charge of the drop are studied. The necessary amount of charge to change the behavior of drops, depending on the applied electric field and drop volume, is determined and different drop behavior regimes are identified. Depending on the boundary conditions, the drop oscillates with the same or double the frequency of the applied voltage. The different regimes are investigated for the first three oscillation modes. The obtained results will help to improve the understanding and to manipulate the behavior of uncharged and charged drops in strong electric fields.
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Affiliation(s)
- Jens-Michael Löwe
- High-Voltage Laboratories, Technische Universität Darmstadt, Darmstadt 64283, Germany
| | - Volker Hinrichsen
- High-Voltage Laboratories, Technische Universität Darmstadt, Darmstadt 64283, Germany
| | - Ilia V Roisman
- Institute of Fluid Mechanics and Aerodynamics, Technische Universität Darmstadt, Darmstadt 64283, Germany
| | - Cameron Tropea
- Institute of Fluid Mechanics and Aerodynamics, Technische Universität Darmstadt, Darmstadt 64283, Germany
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Mazuruk K, Volz MP. Electric field effect on the contact angle for non-wetting drops. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:395002. [PMID: 31239408 DOI: 10.1088/1361-648x/ab2c8f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
A microscopic model is formulated concerning the electrowetting of an electrically conducting drop on a dielectric substrate. The interaction energy between the drop and substrate includes both van der Waals attractive forces and Born repulsive forces resulting in an equilibrium gap. An augmented Young-Laplace equation is derived and used as the basis for calculations of wetting phenomena both with and without an applied voltage. In the absence of an electric field, a well-defined Young's angle is established at a distance from the meniscus incipience that is less than 100 times the equilibrium gap. An expression for Young's angle is determined showing its dependence on material properties of the system. With an electric field applied, the meniscus angle changes continuously from the three-phase line (TPL), where it is near zero, until after a distance of at least ten times the thickness of the dielectric where the Lippmann angle is established. Therefore, the initial angle is not the Lippmann angle and care must be taken in the interpretation of measurements of an apparent contact angle.
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Affiliation(s)
- K Mazuruk
- University of Alabama in Huntsville, Huntsville, AL 35899, United States of America
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31
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Torabi M, Hemeda AA, Palko JW, Feng Y, Cao Y, Ma Y. Modes and break periods of electrowetting liquid bridge. Phys Rev E 2019; 100:033102. [PMID: 31640039 DOI: 10.1103/physreve.100.033102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Indexed: 06/10/2023]
Abstract
In this paper, we propose a microscale liquid oscillator using electrowetting-on-dielectric (EWOD). Specifically, a mesoscale liquid bridge (LB) between two horizontal surfaces with EWOD is considered. When EWOD is applied, the solid surface becomes more hydrophilic, and hence the contact angle (CA) is reduced. Following the activation of EWOD, the LB can remain connected or it can break into either symmetric or asymmetric shapes depending on the initial liquid volume and wettability of the two surfaces. The LB dynamics activated by EWOD is studied using the multibody dissipative particle dynamics (MDPD) method. Our numerical results show that the behavior of an LB under EWOD can be interpreted via three modes. In the first mode, the LB does not break after applying EWOD. In the second mode, the LB breaks and does not reform. The third mode happens when, depending on the interplay of the volume of the liquid and CA manipulation, the LB continuously breaks, recoils, and reforms. For asymmetric cases, it was observed that the LB may completely detach from one surface and may not reform. It was also observed that decreasing the wettability of a surface, for cases with a continuous breaking and reformation behavior, increases the connecting time interval and decreases the breaking time interval in one break-reform cycle. The results provided in this investigation facilitate fundamental understanding of LB dynamics and their application for the design of microscale liquid oscillators using EWOD.
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Affiliation(s)
- Mohsen Torabi
- School of Engineering, University of California, Merced, California 95343, USA
| | - Ahmed A Hemeda
- School of Engineering, University of California, Merced, California 95343, USA
- Aerospace Engineering Department, Cairo University, 12613 Egypt
| | - James W Palko
- School of Engineering, University of California, Merced, California 95343, USA
| | - Yu Feng
- Harbin Institute of Technology, Shenzhen, Guangdong 518055, People's Republic of China
| | - Yong Cao
- Harbin Institute of Technology, Shenzhen, Guangdong 518055, People's Republic of China
| | - Yanbao Ma
- School of Engineering, University of California, Merced, California 95343, USA
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32
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Dong H, Liu Y, Zhou Y, Liu T, Li M, Yang Z. Mechanism investigation of coalescence behaviors of conducting droplets by molecular dynamics simulations. Colloids Surf A Physicochem Eng Asp 2019. [DOI: 10.1016/j.colsurfa.2019.03.014] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Yang J, Wang D, Liu H, Li L, Chen L, Jiang HR, Deng X. An electric-field-dependent drop selector. LAB ON A CHIP 2019; 19:1296-1304. [PMID: 30849148 DOI: 10.1039/c8lc01403e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Drop manipulation on hydrophobic surfaces is of importance in lab-on-a-chip applications. Recently, superhydrophobic surface-assisted lab-on-a-chips have attracted significant attention from researchers due to their advantages of contamination resistance and low adhesion between the drop and the surface during manipulation. However, control over both static and dynamic interactions between a drop and a superhydrophobic surface has been rarely achieved. In this study, we designed an electric-field-dependent liquid-dielectrophoresis force to manipulate a drop on a superhydrophobic surface. This type of control has been found to be fast in response, bio-friendly, convenient, repeatable, and energy efficient. Moreover, the adhesion force and rebounding for both the static and the dynamic interactions between the drop and the surface under an electric field have been explored. It was found that the adhesion force could be reversibly tuned three-fold without breaking the Cassie-Baxter state. Rebounding experiments showed a close to linear relation between energy dissipation and the applied voltage. This relation was used to tune the on-demand behaviors of a drop on a surface in a proof-of-concept experiment for drop sorting. This electric-field-dependent drop manipulation may have potential applications in digital microfluidics, micro-reactors and advanced lab-on-a-drop platforms.
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Affiliation(s)
- Jinlong Yang
- Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu, China.
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34
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Aydogan Gokturk P, Ulgut B, Suzer S. AC Electrowetting Modulation of Low-Volatile Liquids Probed by XPS: Dipolar vs Ionic Screening. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:3319-3326. [PMID: 30768276 DOI: 10.1021/acs.langmuir.8b04099] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
X-ray photoelectron spectroscopic (XPS) data have been recorded for a low-molecular-weight poly(ethylene glycol) microliter-sized sessile liquid drops sitting on a dielectric covered planar electrode while imposing a ±6 V square-wave actuation with varying frequencies between 10-1 and 105 Hz to tap into the information derivable from (AC) electrowetting. We show that this time-varying XPS spectra reveal two distinct behaviors of the device under investigation, below and above a critical frequency, measured as ∼70 Hz for the liquid poly(ethylene glycol) with a 600 Da molecular weight. Below the critical frequency, the liquid complies faithfully to the applied bias, as determined by the constant shift in the binding energy position of the XPS peaks representative of the liquid throughout its entire surface. The liquid completely screens the applied electrical field and the entire potential drop takes place at the liquid/dielectric interface. However, for frequencies above the critical value, the resistive component of the system dominates, resulting in the formation of equipotential surface contours, which are derived from the differences in the positions of the twinned O 1s peaks under AC application. This critical frequency is independent of the size of the liquid drop, and the amplitude of the excitation, but increases when ionic moieties are introduced. The XP spectra under AC actuation is also faithfully simulated using an equivalent circuit model consisting of only resistors and capacitors and using an electrical circuit simulation software. Moreover, a mimicking device is fabricated and its XP spectra are recorded using the Sn 3d peaks of the solder joints at different points on the circuit to confirm the reliability of the measured and simulated AC behaviors of the liquid. These new findings indicate that in contrast to direct current case, XPS measurements under variable frequency AC actuation reveal (through differences in the frequency response) information related to the chemical makeup of the liquid(s) and brings the laboratory-based XPS as a powerful complimentary arsenal to electrochemical analyses of liquids and their interfaces.
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Affiliation(s)
| | - Burak Ulgut
- Department of Chemistry , Bilkent University , Bilkent , 06800 Ankara , Turkey
| | - Sefik Suzer
- Department of Chemistry , Bilkent University , Bilkent , 06800 Ankara , Turkey
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35
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Yan Z, Jin M, Li Z, Zhou G, Shui L. Droplet-Based Microfluidic Thermal Management Methods for High Performance Electronic Devices. MICROMACHINES 2019; 10:mi10020089. [PMID: 30691049 PMCID: PMC6412277 DOI: 10.3390/mi10020089] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Revised: 01/11/2019] [Accepted: 01/14/2019] [Indexed: 12/02/2022]
Abstract
Advanced thermal management methods have been the key issues for the rapid development of the electronic industry following Moore’s law. Droplet-based microfluidic cooling technologies are considered as promising solutions to conquer the major challenges of high heat flux removal and nonuniform temperature distribution in confined spaces for high performance electronic devices. In this paper, we review the state-of-the-art droplet-based microfluidic cooling methods in the literature, including the basic theory of electrocapillarity, cooling applications of continuous electrowetting (CEW), electrowetting (EW) and electrowetting-on-dielectric (EWOD), and jumping droplet microfluidic liquid handling methods. The droplet-based microfluidic cooling methods have shown an attractive capability of microscale liquid manipulation and a relatively high heat flux removal for hot spots. Recommendations are made for further research to develop advanced liquid coolant materials and the optimization of system operation parameters.
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Affiliation(s)
- Zhibin Yan
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China.
- National Center for International Research on Green Optoelectronics, South China Normal University, Guangzhou 510006, China.
- Defense Key Disciplines Lab of Novel Micro-Nano Devices and System Technology, Chongqing University, Chongqing, 400044, China.
| | - Mingliang Jin
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China.
- National Center for International Research on Green Optoelectronics, South China Normal University, Guangzhou 510006, China.
| | - Zhengguang Li
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China.
- National Center for International Research on Green Optoelectronics, South China Normal University, Guangzhou 510006, China.
| | - Guofu Zhou
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China.
- National Center for International Research on Green Optoelectronics, South China Normal University, Guangzhou 510006, China.
- Shenzhen Guohua Optoelectronics Technology Co., Ltd., Shenzhen 518110, China.
- Academy of Shenzhen Guohua Optoelectronics, Shenzhen 518110, China.
| | - Lingling Shui
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China.
- National Center for International Research on Green Optoelectronics, South China Normal University, Guangzhou 510006, China.
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36
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Bifunction-Integrated Dielectric Nanolayers of Fluoropolymers with Electrowetting Effects. MATERIALS 2018; 11:ma11122474. [PMID: 30563169 PMCID: PMC6316971 DOI: 10.3390/ma11122474] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/19/2018] [Revised: 11/29/2018] [Accepted: 11/30/2018] [Indexed: 11/16/2022]
Abstract
Fluoropolymers play an essential role in electrowetting (EW) systems. However, no fluoropolymer possesses the desirable properties of both hydrophobicity and dielectric strength. In this study, for the first time, we report the integration of two representative fluoropolymers-namely, Teflon AF (AF 1600X) and Cytop (Cytop 809A)-into one bifunctionalized dielectric nanolayer. Within this nanolayer, both the superior hydrophobicity of Teflon AF and the excellent dielectric strength of Cytop were able to be retained. Each composed of a 0.5 μm Cytop bottom layer and a 0.06 μm Teflon AF top layer, the fabricated composite nanolayers showed a high withstand voltage of ~70 V (a dielectric strength of 125 V/μm) and a high water contact angle of ~120°. The electrowetting and dielectric properties of various film thicknesses were also systemically investigated. Through detailed study, it was observed that the thicker Teflon AF top layers produced no obvious enhancement of the Cytop/Teflon AF stack.
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37
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Edwards A, Brown C, Newton M, McHale G. Dielectrowetting: The past, present and future. Curr Opin Colloid Interface Sci 2018. [DOI: 10.1016/j.cocis.2017.11.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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38
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Duc C, Vlandas A, Malliaras GG, Senez V. Electrowetting on Immersed Conducting Hydrogel. J Phys Chem B 2017; 121:9947-9956. [PMID: 28930452 DOI: 10.1021/acs.jpcb.7b07971] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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. In addition, we propose a modified electrowetting model to describe the wettability variations of PEDOT:PSS in aqueous solution under ultralow voltage and we show how these variations can be tuned in different ranges of contact angles (above or under 90°) by coating the PEDOT:PSS surface.
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Affiliation(s)
- Caroline Duc
- BioMEMS, Univ. Lille, CNRS, ISEN, UMR 8520 - IEMN , F-59000 Lille, France
| | - Alexis Vlandas
- BioMEMS, Univ. Lille, CNRS, ISEN, UMR 8520 - IEMN , F-59000 Lille, France
| | - George G Malliaras
- Department of Bioelectronics, Ecole Nationale Supérieure des Mines CMP-EMSE, MOC , 13541 Gardanne, France
| | - Vincent Senez
- BioMEMS, Univ. Lille, CNRS, ISEN, UMR 8520 - IEMN , F-59000 Lille, France
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39
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Insight into the Electrical Double Layer of an Ionic Liquid on Graphene. Sci Rep 2017; 7:4225. [PMID: 28652593 PMCID: PMC5484676 DOI: 10.1038/s41598-017-04576-x] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Accepted: 05/24/2017] [Indexed: 11/14/2022] Open
Abstract
Graphene is a promising next-generation conducting material with the potential to replace traditional electrode materials in supercapacitors. Since energy storage in supercapacitors relies on the electrolyte-electrode interface, here we elucidate the interfacial subnanometer structure of a single component liquid composed solely of cations and anions – an ionic liquid- on electrified graphene. We study the effect of applied potential on the interaction between graphene and a silicon tip in an ionic liquid and describe it within the framework of the Derjaguin-Landau-Verwey-Overbeck (DLVO) theory. The energy is stored in an electrical double layer composed of an extended Stern layer, which consists of multiple ion layers over ~2 nanometers, beyond which a diffuse layer forms to compensate the applied potential on graphene. The electrical double layer significantly responds to the applied potential, and it shows the transition from overscreening to crowding of counterions at the interface at the highest applied potentials. It is proposed that surface charging occurs through the adsorption of the imidazolium cation to unbiased graphene (likely due to π-π interactions) and that the surface potential is better compensated when counterion crowding happens. This study scrutinizes the electrified graphene-ionic liquid interface, with implications not only in the field of energy storage, but also in lubrication.
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40
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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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41
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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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42
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Cao Q, Li L, Huang F, Zuo C. Ion-Specific Effects on the Elongation Dynamics of a Nanosized Water Droplet in Applied Electric Fields. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:428-437. [PMID: 27996273 DOI: 10.1021/acs.langmuir.6b04101] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We report an all-atom molecular dynamics study of the structures and dynamics of salty water droplets on a silicon surface under the influence of applied electric field. Our simulation results support ion-specific effects on the elongation dynamics of salty nanodroplets, induced by the field. This feature has not been explored up to now in monovalent salts. Nevertheless, the importance of ion-specific effects is widely confirmed in biological and colloidal systems. In particular, the increase of salt concentration enhances the effect of the nature of ions on the wetting properties of droplets. In the presence of electric field (0.05 V Å-1), a complete spreading is implemented in a short time for different droplets at a concentration of 1 M, and the droplet morphology is stable, observed at long time scales. However, a higher salt concentration of 4 M considerably suppresses the spreading process owing to the increase of surface tension. It was found that the NaCl droplet shows deformation oscillations along the external field, but cannot fully wet the substrate surface. By contrast, the CsCl droplet reaches complete elongation rapidly and adopts a steady strip shape. The KCl droplet undergoes frequent transitions between breakup and connection. Additionally, the droplets can be elongated only when the electric field strength exceeds a threshold value. The dipole orientation of interfacial water and the ionic diffusion exhibit ion-specific dependences, but the hydrogen bond network is scarcely disturbed, excluding a concentration-dependent effect.
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Affiliation(s)
- Qianqian Cao
- College of Mechanical and Electrical Engineering, Jiaxing University , Jiaxing 314001, P.R. China
| | - Lujuan Li
- College of Mechanical and Electrical Engineering, Jiaxing University , Jiaxing 314001, P.R. China
| | - Fengli Huang
- College of Mechanical and Electrical Engineering, Jiaxing University , Jiaxing 314001, P.R. China
| | - Chuncheng Zuo
- College of Mechanical and Electrical Engineering, Jiaxing University , Jiaxing 314001, P.R. China
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43
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Burger B, Rabot R. Design of low hysteresis electrowetting systems in non-aqueous media by the addition of low HLB amphiphilic compounds. Colloids Surf A Physicochem Eng Asp 2016. [DOI: 10.1016/j.colsurfa.2016.06.041] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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44
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Corson LT, Mottram NJ, Duffy BR, Wilson SK, Tsakonas C, Brown CV. Dynamic response of a thin sessile drop of conductive liquid to an abruptly applied or removed electric field. Phys Rev E 2016; 94:043112. [PMID: 27841646 DOI: 10.1103/physreve.94.043112] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Indexed: 06/06/2023]
Abstract
We consider, both theoretically and experimentally, a thin sessile drop of conductive liquid that rests on the lower plate of a parallel-plate capacitor. We derive analytical expressions for both the initial deformation and the relaxation dynamics of the drop as the electric field is either abruptly applied or abruptly removed, as functions of the geometrical, electrical, and material parameters, and investigate the ranges of validity of these expressions by comparison with full numerical simulations. These expressions provide a reasonable description of the experimentally measured dynamic response of a drop of conductive ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate.
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Affiliation(s)
- L T Corson
- Department of Mathematics & Statistics, University of Strathclyde, 26 Richmond Street, Glasgow G1 1XH, United Kingdom
| | - N J Mottram
- Department of Mathematics & Statistics, University of Strathclyde, 26 Richmond Street, Glasgow G1 1XH, United Kingdom
| | - B R Duffy
- Department of Mathematics & Statistics, University of Strathclyde, 26 Richmond Street, Glasgow G1 1XH, United Kingdom
| | - S K Wilson
- Department of Mathematics & Statistics, University of Strathclyde, 26 Richmond Street, Glasgow G1 1XH, United Kingdom
| | - C Tsakonas
- School of Science & Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, United Kingdom
| | - C V Brown
- School of Science & Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, United Kingdom
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45
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Choudhuri JR, Vanzo D, Madden PA, Salanne M, Bratko D, Luzar A. Dynamic Response in Nanoelectrowetting on a Dielectric. ACS NANO 2016; 10:8536-8544. [PMID: 27556934 DOI: 10.1021/acsnano.6b03753] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Droplet spreading at an applied voltage underlies the function of tunable optical devices including adjustable lenses and matrix display elements. Faster response and the enhanced resolution motivate research toward miniaturization of these devices to nanoscale dimensions. The response of an aqueous nanodroplet to an applied field can differ significantly from macroscopic predictions. Understanding these differences requires characterization at the molecular level. We describe the equilibrium and nonequilibrium molecular dynamics simulations of nanosized aqueous droplets on a hydrophobic surface with the embedded concentric electrodes. Constant electrode potential is enforced by a rigorous account of the metal polarization. We demonstrate that the reduction of the equilibrium contact angle is commensurate to, and adjusts reversibly with, the voltage change. For a droplet with O(10) nm diameter, a typical response time to the imposition of the field is of O(10(2)) ps. Drop relaxation is about twice as fast when the field is switched off. The friction coefficient obtained from the rate of the drop relaxation on the nonuniform surface, decreases when the droplet approaches equilibrium from either direction, that is, by spreading or receding. The strong dependence of the friction on the surface hydrophilicity points to the dominance of the liquid-surface friction at the drop's perimeter as described in the molecular kinetic theory. This approach enables correct predictions of trends in dynamic responses associated with varied voltage or substrate material.
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Affiliation(s)
- Jyoti Roy Choudhuri
- Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States
| | - Davide Vanzo
- Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States
| | - Paul Anthony Madden
- Department of Material Science, Oxford University , Park Road, Oxford OX1 3PH, United Kingdom
| | - Mathieu Salanne
- Sorbonne Universités, UPMC Université Paris 06, CNRS, UMR 8234 PHENIX , 75005 Paris, France
- Maison de la Simulation, CEA, CNRS, Université Paris-Sud, UVSQ, Université Paris-Saclay , F-91191 Gif-sur-Yvette, France
| | - Dusan Bratko
- Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States
| | - Alenka Luzar
- Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States
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46
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Sawane YB, Ogale SB, Banpurkar AG. Low Voltage Electrowetting on Ferroelectric PVDF-HFP Insulator with Highly Tunable Contact Angle Range. ACS APPLIED MATERIALS & INTERFACES 2016; 8:24049-24056. [PMID: 27553685 DOI: 10.1021/acsami.6b05958] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We demonstrate a consistent electrowetting response on ferroelectric poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) insulator covered with a thin Teflon AF layer. This bilayer exhibits a factor of 3 enhancement in the contact angle modulation compared to that of conventional single-layered Teflon AF dielectric. On the basis of the proposed model the enhancement is attributed to the high value of effective dielectric constant (εeff ≈ 6) of the bilayer. Furthermore, the bilayer dielectric exhibits a hysteresis-free contact angle modulation over many AC voltage cycles. But the contact angle modulation for DC voltage shows a hysteresis because of the field-induced residual polarization in the ferroelectric layer. Finally, we show that a thin bilayer exhibits contact angle modulation of Δθ (U) ≈ 60° at merely 15 V amplitude of AC voltage indicating a potential dielectric for practical low voltage electrowetting applications. A proof of concept confirms electrowetting based rapid mixing of a fluorescent dye in aqueous glycerol solution for 15 V AC signal.
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Affiliation(s)
- Yogesh B Sawane
- Centre for Advanced Studies in Condensed Matter and Solid State Physics, Department of Physics, Savitribai Phule Pune University , Pune-411007, India
| | - Satishchandra B Ogale
- Department of Physics and Centre for Energy Science, Indian Institute of Science Education and Research , Dr. Homi Bhabha Road, Pashan, Pune-411008, India
| | - Arun G Banpurkar
- Centre for Advanced Studies in Condensed Matter and Solid State Physics, Department of Physics, Savitribai Phule Pune University , Pune-411007, India
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47
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Corbett A, Kumar S. Spreading of Thin Droplets of Perfect and Leaky Dielectric Liquids on Inclined Surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:6606-6617. [PMID: 27247998 DOI: 10.1021/acs.langmuir.6b01716] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The spreading of droplets may be influenced by electric fields, a situation that is relevant to applications such as coating, printing, and microfluidics. In this work we study the effects of an electric field on the gravity-driven spreading of two-dimensional droplets down an inclined plane. We consider both perfect and leaky dielectric liquids, as well as perfectly and partially wetting systems. In addition to the effects of electric fields, we examine the use of thermocapillary forces to suppress the growth of the capillary ridge near the droplet front. Lubrication theory is applied to generate a set of coupled partial differential equations for interfacial height and charge, which are then solved numerically with a finite-difference method. Electric fields increase the height of the capillary ridge in both perfect and leaky dielectric droplets due to electrostatic pressure gradients that drive liquid into the ridge. In leaky dielectrics, large interfacial charge gradients in the contact-line region create shear stresses that also enhance ridge growth and the formation of trailing minor ridges. The coalescence of these ridges can significantly affect the long-time thinning rate of leaky dielectric droplets. In partially wetting liquids, electric fields promote the splitting of smaller droplets from the primary droplet near the receding contact line due to the interplay between electrostatic forces and disjoining pressure. Cooling from below and heating from above generates thermocapillary forces that counteract the effects of electric fields and suppress the growth of the capillary ridge. The results of this work have important implications for manipulating the spreading of droplets down inclined surfaces.
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Affiliation(s)
- Andrew Corbett
- Department of Chemical Engineering and Materials Science, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Satish Kumar
- Department of Chemical Engineering and Materials Science, University of Minnesota , Minneapolis, Minnesota 55455, United States
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He T, Jin M, Eijkel JCT, Zhou G, Shui L. Two-phase microfluidics in electrowetting displays and its effect on optical performance. BIOMICROFLUIDICS 2016; 10:011908. [PMID: 26909120 PMCID: PMC4752538 DOI: 10.1063/1.4941843] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2015] [Accepted: 01/29/2016] [Indexed: 05/25/2023]
Abstract
Driving microfluidic flow in micropixels by electrowetting to realize light switches and displays is of both practical and fundamental significance. The electro-optical performance related to microfluidic behavior needs to be clarified to optimize device functions. In this article, the microfluidic performance in electrowetting display devices was categorized according to the oil-water interface shape and response. The oil film movement was divided into vertically "thinning" and transversally "opening," for which the "thinning" process was found the key factor determining the pixel switching speed rather than the "opening" process. Therefore, the breakup point and the oil film thickness were critical, which could be controlled by surface wettability and oil volume. We have also realized a new oil filling method with controllable dosing volume assisted by the microfluidic creation of microdroplets. This study could help quantitatively understand electrowetting display performance in both its theoretical and practical aspects.
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Affiliation(s)
- Tao He
- Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics , South China Normal University, Guangzhou 510006, Guangdong, China
| | - Mingliang Jin
- Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics , South China Normal University, Guangzhou 510006, Guangdong, China
| | - Jan C T Eijkel
- BIOS/Lab-on-a-Chip group, MESA+ Institute for Nanotechnology, University of Twente , Enschede, The Netherlands
| | | | - Lingling Shui
- Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics , South China Normal University, Guangzhou 510006, Guangdong, China
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Pinchasik BE, Steinkühler J, Wuytens P, Skirtach AG, Fratzl P, Möhwald H. From Beetles in Nature to the Laboratory: Actuating Underwater Locomotion on Hydrophobic Surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:13734-13742. [PMID: 26633751 DOI: 10.1021/acs.langmuir.5b03821] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The controlled wetting and dewetting of surfaces is a primary mechanism used by beetles in nature, such as the ladybird and the leaf beetle for underwater locomotion.1 Their adhesion to surfaces underwater is enabled through the attachment of bubbles trapped in their setae-covered legs. Locomotion, however, is performed by applying mechanical forces in order to move, attach, and detach the bubbles in a controlled manner. Under synthetic conditions, however, when a bubble is bound to a surface, it is nearly impossible to maneuver without the use of external stimuli. Thus, actuated wetting and dewetting of surfaces remain challenges. Here, electrowetting-on-dielectric (EWOD) is used for the manipulation of bubble-particle complexes on unpatterned surfaces. Bubbles nucleate on catalytic Janus disks adjacent to a hydrophobic surface. By changing the wettability of the surface through electrowetting, the bubbles show a variety of reactions, depending on the shape and periodicity of the electrical signal. Time-resolved (μs) imaging of bubble radial oscillations reveals possible mechanisms for the lateral mobility of bubbles on a surface under electrowetting: bubble instability is induced when electric pulses are carefully adjusted. This instability is used to control the surface-bound bubble locomotion and is described in terms of the change in surface energy. It is shown that a deterministic force applied normal can lead to a random walk of micrometer-sized bubbles by exploiting the phenomenon of contact angle hysteresis. Finally, bubble use in nature for underwater locomotion and the actuated bubble locomotion presented in this study are compared.
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Affiliation(s)
- Bat-El Pinchasik
- Department of Biomaterials, ‡Department of Theory and Bio-systems, and ⊥Emeritus Group of Interfaces, Max-Planck Institute of Colloids and Interfaces , Golm/Potsdam, D14476 Germany
- Photonics Research Group, IMEC, INTEC Department and ∥Department of Molecular Biotechnology and NB-Photonics, Ghent University , 9000 Ghent, Belgium
| | - Jan Steinkühler
- Department of Biomaterials, ‡Department of Theory and Bio-systems, and ⊥Emeritus Group of Interfaces, Max-Planck Institute of Colloids and Interfaces , Golm/Potsdam, D14476 Germany
- Photonics Research Group, IMEC, INTEC Department and ∥Department of Molecular Biotechnology and NB-Photonics, Ghent University , 9000 Ghent, Belgium
| | - Pieter Wuytens
- Department of Biomaterials, ‡Department of Theory and Bio-systems, and ⊥Emeritus Group of Interfaces, Max-Planck Institute of Colloids and Interfaces , Golm/Potsdam, D14476 Germany
- Photonics Research Group, IMEC, INTEC Department and ∥Department of Molecular Biotechnology and NB-Photonics, Ghent University , 9000 Ghent, Belgium
| | - Andre G Skirtach
- Department of Biomaterials, ‡Department of Theory and Bio-systems, and ⊥Emeritus Group of Interfaces, Max-Planck Institute of Colloids and Interfaces , Golm/Potsdam, D14476 Germany
- Photonics Research Group, IMEC, INTEC Department and ∥Department of Molecular Biotechnology and NB-Photonics, Ghent University , 9000 Ghent, Belgium
| | - Peter Fratzl
- Department of Biomaterials, ‡Department of Theory and Bio-systems, and ⊥Emeritus Group of Interfaces, Max-Planck Institute of Colloids and Interfaces , Golm/Potsdam, D14476 Germany
- Photonics Research Group, IMEC, INTEC Department and ∥Department of Molecular Biotechnology and NB-Photonics, Ghent University , 9000 Ghent, Belgium
| | - Helmuth Möhwald
- Department of Biomaterials, ‡Department of Theory and Bio-systems, and ⊥Emeritus Group of Interfaces, Max-Planck Institute of Colloids and Interfaces , Golm/Potsdam, D14476 Germany
- Photonics Research Group, IMEC, INTEC Department and ∥Department of Molecular Biotechnology and NB-Photonics, Ghent University , 9000 Ghent, Belgium
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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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