Modeling, simulation, and optimization of electrowetting-on-dielectric (EWOD) devices

Wei, Qiuxu; Yao, Wenliang; Gu, Lixin; Fan, Boyu; Gao, Yongjia; Li, Yang; Zhao, Yingying; Che, Chuncheng

doi:10.1063/5.0029790

Cited by 10 publications

(8 citation statements)

References 41 publications

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“…The droplet actuated at 100 V behaves in good agreement with established EWOD theory. 34,44,45 The front contact angle decreases to the minimum saturation angle of around 60°as the droplet moves forward. The rear contact angle decreases slightly as the contact line starts moving, which is well-known as contact angle hysteresis.…”

Section: Resultsmentioning

confidence: 99%

Actuating droplets with electrowetting: Force and dynamics

Hennig,

Cacucciolo,

Shea

2024

Droplet

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Electrowetting on dielectric (EWOD) allows rapid movement of liquid droplets on a smooth surface, with applications ranging from lab‐on‐chip devices to micro‐actuators. The in‐plane force on a droplet is a key indicator of EWOD performance. This force has been extensively modeled but few direct experimental measurements are reported. We study the EWOD force on a droplet using two setups that allow, for the first time, the simultaneous measurement of force and contact angle, while imaging the droplet shape at 6000 frames/s. For several liquids and surfaces, we observe that the force saturates at a voltage of approximately 150 V. Application of voltages of up 2 kV, that is, 10 times higher than is typical, does not significantly increase forces beyond the saturation point. However, we observe that the transient dynamics, localized at the front contact line, do not show saturation with voltage. At the higher voltages, the initial front contact line speed continues to increase, the front contact angle temporarily becomes near zero, creating a thin liquid film, and capillary waves form at the liquid–air interface. When the localized EWOD forces at the contact line exceed the capillary forces, projectile droplets form. Increasing surface tension allows for higher droplet forces, which we demonstrate with mercury.

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Section: Resultsmentioning

confidence: 99%

Actuating droplets with electrowetting: Force and dynamics

Hennig,

Cacucciolo,

Shea

2024

Droplet

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“…The studies on electrode geometry aim to facilitate the speed of droplet manipulation [16,17] or the easiness of the droplet transfer directions, [12] to enable the droplet splitting/joining or to perform dilutions or concentrations of a solution. [18,19] On the other hand, the study of the dielectric layer pursues the understanding of the effects of its thickness, the dielectric constant and the breakdown field [20,21] on the EWOD phenomena. The objective is to achieve a lower actuation voltage, [22] a lower CA, an understanding of the saturation phenomenon, [23][24][25][26] and/or the search for different materials, which can provide more flexibility on the kind of fabrication processes used.…”

Section: Doi: 101002/mame202200193mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Materials and Manufacturing Methods for EWOD Devices: Current Status and Sustainability Challenges

Caro‐Pérez

Casals‐Terré

Roncero

2022

Macro Materials & Eng

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Electrowetting-on-dielectric (EWOD) devices have proven to be effective tools for precise microfluidic manipulation or in liquid lenses that surpass conventional solid lenses in versatility. However, the fabrication of these devices presents many challenges, such as their scalability or the growing concern on their environmental impact due to materials used in their fabrication. This review provides a comprehensive analysis of the materials currently used in the fabrication of EWOD devices and the characteristics they must meet. In addition, a discussion of future challenges in the fabrication of EWOD devices is presented, in particular the environmental problems presented by some of the materials currently in use.

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“…The effect of electric field distribution evaluated from the ES module on drop shape and motion is derived in a coupled manner. The dielectric layer in Figure 2 is specified a thickness of 35 μm with the permittivity of PDMS (Wei et al, 2021;Khanna et al 2020).…”

Section: Dynamic Contact Angle Modelingmentioning

confidence: 99%

Electrically actuated continuous motion of a water droplet over a PDMS-coated surface

Upadhyay

Muralidhar

2022

Preprint

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Electrically actuated continuous motion of a water droplet over PDMS-coated single active electrode is analyzed from detailed modeling and experiments. In an experiment, continuous motion of the droplet is achieved when it is located over an active electrode with a horizontal ground wire placed just above in an open-EWOD configuration. Using a CCD camera, the instantaneous centroid position of the droplet is determined, and its velocity is inferred by numerical differentiation. The edge-detected image is also used to determine the advancing and receding contact angles of the moving drop relative to the substrate. Motion of 2, 6, and 10 µl water droplets for voltages in the range of 170–270 VDC is examined to investigate the effect of drop volume and voltage on drop deformation and velocity. Simulations have been carried out in a two-dimensional coordinate system using COMSOL© Multiphysics with full coupling between the electric field and hydrodynamics. The motion of the droplet is initiated by Young-Lippmann spreading at the three-phase contact line, followed by a nonuniform electric force field distributed between the active electrode and the ground wire localized at the droplet-air interface. The solver evaluates the Maxwell's stress tensor and introduces it as a volumetric electrostatic force in the Navier-Stokes equations. The fully coupled numerical solution shows a good match with experimentally determined drop movement over a silicone oil-coated PDMS layer for which contact line friction is absent. A contact angle model with friction leads to close agreement between simulations and drop motion over a bare PDMS layer. Over both surfaces, continuous motion of the water droplet is seen to be achieved in three stages, namely, initial spreading, acceleration, and attainment of constant speed. Numerical modeling that includes electric field-fluid flow coupling is shown to yield data in conformity with experiments.

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Modeling, simulation, and optimization of electrowetting-on-dielectric (EWOD) devices

Cited by 10 publications

References 41 publications

Actuating droplets with electrowetting: Force and dynamics

Actuating droplets with electrowetting: Force and dynamics

Materials and Manufacturing Methods for EWOD Devices: Current Status and Sustainability Challenges

Electrically actuated continuous motion of a water droplet over a PDMS-coated surface

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