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Micromachines
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Advances in Electrowetting Devices
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Advances in Electrowetting Devices

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "E：Engineering and Technology".

Deadline for manuscript submissions: closed (31 March 2022) | Viewed by 10918

Special Issue Editors

Dr. Iftekhar Khan

E-Mail Website
Guest Editor
Future Technologies, Engineering, Electrical and Telecoms, College of VE, RMIT University, 115 Queensberry Street, Carlton, VIC 3053, Australia
Interests: microfluidics; optofluidics; beam steering; MEMS device; electrowetting; lab on a chip; renewable and sustainable energy technologies
Dr. Sung-Yong Park

E-Mail Website
Guest Editor
Department of Mechanical Engineering, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA
Interests: microfluidics; optofluidics; interfacial science; biofluidics; biophotonics; biological sensors; water/air quality detection; lab on a chip; energy harvesting; solar energy collection and indoor lighting; multi-physics computational simulation; micro/nano fabrication
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Electrowetting has emerged as a new technique with many applications, such as micro-drop generation, manipulation and actuation, sensor, clinical diagnosis, e-paper and electronic display, energy harvesting, beam steering, liquid lenses, and many more. Despite the wide range of application opportunities, the commercialisation of electrowetting still faces several challenges, such as charge trapping, oil backflow, contact line instability, dielectric breakdown, reliability in repetitive loading, etc.

This Special Issue aims to inform researchers on the recent advancement of the application of electrowetting techniques, fundamental explanation of related phenomena, development of new material and/or process, and solution to the challenges of the commercialisation of electrowetting devices. This Special Issue is also interested in showcasing a new and novel field of electrowetting application. The Special Issue will accept diverse forms of contributions, including research papers, communications, methods, and review articles representing the state-of-the-art in electrowetting.

Dr. Iftekhar Khan
Dr. Sung-Yong Park
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Electrowetting
  • EWOD
  • Contact line modulation
  • AC electrowetting
  • Liquid lens
  • Droplet manipulation
  • Adaptive beam steering
  • Laser beam steering
  • Electrowetting display
  • Biosensors
  • Clinical diagnosis
  • Dielectric material
  • Optofluidics
  • Microfluidics
  • MEMS

Published Papers (5 papers)

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Research

22 pages, 5898 KiB  
Article
Influence of the Ground Electrode on the Dynamics of Electrowetting
by Iftekhar Khan, Stefania Castelletto and Gary Rosengarten
Micromachines 2023, 14(2), 348; https://doi.org/10.3390/mi14020348 - 30 Jan 2023
Cited by 1 | Viewed by 1405
Abstract
The ability to manipulate a liquid meniscus using electrowetting has many applications. In any electrowetting design, at least two electrodes are required: one forms the field to change the contact angle and the other functions as a ground electrode. The contribution of the [...] Read more.
The ability to manipulate a liquid meniscus using electrowetting has many applications. In any electrowetting design, at least two electrodes are required: one forms the field to change the contact angle and the other functions as a ground electrode. The contribution of the ground electrode (GE) to the dynamics of electrowetting has not yet been thoroughly investigated. In this paper, we discovered that with a bare ground electrode, the contact angle of a sessile drop increases instead of decreases when a direct current (DC) voltage varying from zero to the threshold voltage is applied. This phenomenon is opposite to what occurs when the GE is coated with a dielectric, where the contact-angle change follows the Lippmann–Young equation above the threshold voltage of electrowetting. However, this behaviour is not observed with either a dielectric-coated electrode using direct current (DC) or a bare ground electrode using alternating current (AC) voltage electrowetting. This study explains this phenomenon with finite element simulation and theory. From previous research work, the ground electrode configuration is inconsistent. In some studies, the ground electrode is exposed to water; in other studies, the ground electrode is covered with dielectric. This study identified that an exposed ground electrode is not required in electrowetting. Moreover, this research work suggests that for applications where precise control of the contact angle is paramount, a dielectric-coated ground electrode should be used since it prevents the increase in the contact angle when increasing the applied potential from zero to the threshold voltage. This study also identified that contact angle hysteresis is lower with a Cytop-coated ground electrode and DC voltage than with a bare ground electrode using AC or DC voltages. Full article
(This article belongs to the Special Issue Advances in Electrowetting Devices)
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13 pages, 12344 KiB  
Article
Trampolining of Droplets on Hydrophobic Surfaces Using Electrowetting
by Zhantao Wang, Xiaojuan Liu, Li Wang, Cunlu Zhao, Danfeng Zhou and Jiazheng Wei
Micromachines 2022, 13(3), 345; https://doi.org/10.3390/mi13030345 - 22 Feb 2022
Cited by 3 | Viewed by 2009
Abstract
Droplet detachment from solid surfaces is an essential part of many industrial processes. Electrowetting is a versatile tool for handling droplets in digital microfluidics, not only on plain surface but also in 3-D manner. Here, we report for the first time droplet trampolining [...] Read more.
Droplet detachment from solid surfaces is an essential part of many industrial processes. Electrowetting is a versatile tool for handling droplets in digital microfluidics, not only on plain surface but also in 3-D manner. Here, we report for the first time droplet trampolining using electrowetting. With the information collected by the real-time capacitor sensing system, we are able to synchronize the actuation signal with the spreading of the droplet upon impacting. Since electrowetting is applied each time the droplet impacts the substrate and switched off during recoiling of the droplet, the droplet gains additional momentum upon each impact and is able to jump higher during successive detachment. We have modelled the droplet trampolining behavior with a periodically driven harmonic oscillator, and the experiments showed sound agreement with theoretical predictions. The findings from this study will offer valuable insights to applications that demands vertical transportation of the droplets between chips arranged in parallel, or detachment of droplets from solid surfaces. Full article
(This article belongs to the Special Issue Advances in Electrowetting Devices)
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18 pages, 9450 KiB  
Article
BiowareCFP: An Application-Agnostic Modular Reconfigurable Cyber-Fluidic Platform
by Georgi Tanev, Winnie E. Svendsen and Jan Madsen
Micromachines 2022, 13(2), 249; https://doi.org/10.3390/mi13020249 - 02 Feb 2022
Viewed by 1608
Abstract
Microfluidic biochips have been in the scientific spotlight for over two decades, and although technologically advanced, they still struggle to deliver on the promise for ubiquitous miniaturization and automation for the biomedical sector. One of the most significant challenges hindering the technology transfer [...] Read more.
Microfluidic biochips have been in the scientific spotlight for over two decades, and although technologically advanced, they still struggle to deliver on the promise for ubiquitous miniaturization and automation for the biomedical sector. One of the most significant challenges hindering the technology transfer is the lack of standardization and the resulting absence of a common infrastructure. Moreover, microfluidics is an interdisciplinary field, but research is often carried out in a cross-disciplinary manner, focused on technology and component level development rather than on a complete future-proof system. This paper aims to raise awareness and facilitate the next evolutionary step for microfluidic biochips: to establish a holistic application-agnostic common microfluidic architecture that allows for gracefully handling changing functional and operational requirements. Allowing a microfluidic biochip to become an integrated part of a highly reconfigurable cyber-fluidic system that adopts the programming and operation model of modern computing will bring unmatched degrees of programmability and design reusability into the microfluidics field. We propose a three-tier architecture consisting of fluidic, instrumentation, and virtual systems that allows separation of concerns and promotes modularity. We also present BiowareCFP as a platform-based implementation of the outlined concepts. The proposed cyber-fluidic architecture and the BiowareCFP facilitate the integration between the virtual and the fluidic domains and pave the way for seamless integration between the cyber-fluidic and biological systems. Full article
(This article belongs to the Special Issue Advances in Electrowetting Devices)
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13 pages, 2916 KiB  
Article
Optical Dielectrophoretic (DEP) Manipulation of Oil-Immersed Aqueous Droplets on a Plasmonic-Enhanced Photoconductive Surface
by Si Kuan Thio and Sung-Yong Park
Micromachines 2022, 13(1), 112; https://doi.org/10.3390/mi13010112 - 11 Jan 2022
Cited by 4 | Viewed by 2715
Abstract
We present a plasmonic-enhanced dielectrophoretic (DEP) phenomenon to improve optical DEP performance of a floating electrode optoelectronic tweezers (FEOET) device, where aqueous droplets can be effectively manipulated on a light-patterned photoconductive surface immersed in an oil medium. To offer device simplicity and cost-effectiveness, [...] Read more.
We present a plasmonic-enhanced dielectrophoretic (DEP) phenomenon to improve optical DEP performance of a floating electrode optoelectronic tweezers (FEOET) device, where aqueous droplets can be effectively manipulated on a light-patterned photoconductive surface immersed in an oil medium. To offer device simplicity and cost-effectiveness, recent studies have utilized a polymer-based photoconductive material such as titanium oxide phthalocyanine (TiOPc). However, the TiOPc has much poorer photoconductivity than that of semiconductors like amorphous silicon (a-Si), significantly limiting optical DEP applications. The study herein focuses on the FEOET device for which optical DEP performance can be greatly enhanced by utilizing plasmonic nanoparticles as light scattering elements to improve light absorption of the low-quality TiOPc. Numerical simulation studies of both plasmonic light scattering and electric field enhancement were conducted to verify wide-angle scattering light rays and an approximately twofold increase in electric field gradient with the presence of nanoparticles. Similarly, a spectrophotometric study conducted on the absorption spectrum of the TiOPc has shown light absorption improvement (nearly twofold) of the TiOPc layer. Additionally, droplet dynamics study experimentally demonstrated a light-actuated droplet speed of 1.90 mm/s, a more than 11-fold improvement due to plasmonic light scattering. This plasmonic-enhanced FEOET technology can considerably improve optical DEP capability even with poor-quality photoconductive materials, thus providing low-cost, easy-fabrication solutions for various droplet-based microfluidic applications. Full article
(This article belongs to the Special Issue Advances in Electrowetting Devices)
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15 pages, 2538 KiB  
Article
Static and Dynamic Optical Analysis of Micro Wrinkle Formation on a Liquid Surface
by Antariksh Saxena, Costas Tsakonas, David Chappell, Chi Shing Cheung, Andrew Michael John Edwards, Haida Liang, Ian Charles Sage and Carl Vernon Brown
Micromachines 2021, 12(12), 1583; https://doi.org/10.3390/mi12121583 - 19 Dec 2021
Cited by 1 | Viewed by 2212
Abstract
A spatially periodic voltage was used to create a dielectrophoresis induced periodic micro wrinkle deformation on the surface of a liquid film. Optical Coherence Tomography provided the equilibrium wrinkle profile at submicron accuracy. The dynamic wrinkle amplitude was derived from optical diffraction analysis [...] Read more.
A spatially periodic voltage was used to create a dielectrophoresis induced periodic micro wrinkle deformation on the surface of a liquid film. Optical Coherence Tomography provided the equilibrium wrinkle profile at submicron accuracy. The dynamic wrinkle amplitude was derived from optical diffraction analysis during sub-millisecond wrinkle formation and decay, after abruptly increasing or reducing the voltage, respectively. The decay time constant closely followed the film thickness dependence expected for surface tension driven viscous levelling. Modelling of the system using numerical solution of the Stokes flow equations with electrostatic forcing predicted that wrinkle formation was faster than decay, in accord with observations. Full article
(This article belongs to the Special Issue Advances in Electrowetting Devices)
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