Detaching droplets in immiscible fluids from a solid substrate with the help of electrowetting

Hong, Jiwoo; Lee, Sang Joon

doi:10.1039/c4lc01049c

Cited by 37 publications

(46 citation statements)

References 52 publications

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“…The experimental setup, shown in Figure 3, is similar to that described by Hong and Lee 12 and consists of a water droplet in a silicone oil bath placed on a conducting substrate coated with a thin dielectric layer. The substrates used in the present work are glass slides covered in a 120-160 µm thick film of indium tin oxide (ITO).…”

Section: A Experiments Setupmentioning

confidence: 99%

“…The same physical mechanism has been applied in single-droplet, non-coalescence based, capillary-to-inertial energy conversion by melting-initiated 9,10 and electrowetting-actuated a) Author to whom correspondence should be addressed. Electronic mail: bush@math.mit.edu drop ejection, [11][12][13][14] for uses in micro-fabrication, droplet transfer across surfaces, and controlled dewetting of superhydrophobic surfaces. 15 However, these studies are primarily experimental, and the field is lacking a detailed physical model capable of predicting jumping behavior.…”

Section: Introductionmentioning

confidence: 99%

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Electrically induced drop detachment and ejection

et al. 2016

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A deformed droplet may leap from a solid substrate, impelled to detach through the conversion of surface energy into kinetic energy that arises as it relaxes to a sphere. Electrowetting provides a means of preparing a droplet on a substrate for lift-off. When a voltage is applied between a water droplet and a dielectric-coated electrode, the wettability of the substrate increases in a controlled way, leading to the spreading of the droplet. Once the voltage is released, the droplet recoils, due to a sudden excess in surface energy, and droplet detachment may follow. The process of drop detachment and lift-off, prevalent in both biology and micro-engineering, has to date been considered primarily in terms of qualitative scaling arguments for idealized superhydrophobic substrates. We here consider the eletrically-induced ejection of droplets from substrates of finite wettability and analyze the process quantitatively. We compare experiments to numerical simulations and analyze how the energy conversion efficiency is affected by the applied voltage and the intrinsic contact angle of the droplet on the substrate. Our results indicate that the finite wettability of the substrate significantly affects the detachment dynamics, and so provide new rationale for the previously reported large critical radius for drop ejection from micro-textured substrates.

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Section: A Experiments Setupmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Electrically induced drop detachment and ejection

et al. 2016

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“…A projection method similar to Sussman, Smereka, and Osher [28] and Sussman et al [27] is used to solve (11). First, the projection operator is defined as…”

Section: Computational Fluid Dynamics Approachmentioning

confidence: 99%

“…Rewriting the Navier-Stokes equation in (11) as u t = N (u, t) − ∇p/ρ, the projection applied to both sides gives u t = P (N (u, t), t), because P (∇p/ρ, t) = 0. Taking a cross-product of ρP (N (u, t), t) then gives Thus, the pressure has been removed from (11) to give u t = ∇ × Ψ, where Ψ = Ψk is obtained by the above equation. Taking a cross-product of ρP (N (u, t), t) then gives Thus, the pressure has been removed from (11) to give u t = ∇ × Ψ, where Ψ = Ψk is obtained by the above equation.…”

Section: Computational Fluid Dynamics Approachmentioning

confidence: 99%

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A Curvature-Augmented, REA Approach to the Level Set Method

Vogl¹

2016

SIAM J. Sci. Comput.

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When solving a moving interface problem, the interface can be tracked using a variety of methods. The level set method captures the interface as an isocontour of a scalar level set function. The method has many advantages, including the ability to express many geometric quantities, such as the interface curvature, as derivatives of the level set. However, the numerically constructed level set function may not be smooth enough to compute the required derivatives. Furthermore, the method overall is known for having a high sensitivity to numerical dissipation. The former of these two shortfalls is addressed by augmenting the traditional level set equations with an explicitly tracked interface curvature. The curvature is then updated alongside the level set through an additional advection equation. The latter shortfall is addressed by combining a new velocity extension, that better maintains the signed-distance property of the level set, with a reconstruct-evolve-average approach to advancing the advection equations. The new approach is shown to have less mass loss (numerical dissipation) and better accuracy than comparable level set approaches. Three scenarios are investigated: an interface moving according to an external velocity field, an interface moving according to the interface curvature (mean-curvature flow), and the air-water interface of a water drop moving according to the curvature-dependent fluid velocity (surface-tension driven flow). point on the interface. Thus, the gradient of the SDLS is neither too shallow to see large movements in interface positions from small perturbations in the level set value nor too steep to influence truncation errors when taking derivatives of the level set. In general, there is not a closed-form expression for the SDLS of an arbitrary interface. Thus, it is numerically constructed using a reinitialization process. There are two main variations of reinitialization: PDE-based reinitialization, developed by Peng et al. [21], and the fast marching method (FMM) reinitialization, developed by Sethian [26]. PDE-based reinitialization obtains the SDLS by solving a timedependent PDE, whose steady state solution is the SDLS. In theory, one can get arbitrarily close to the SDLS by evolving the PDE further and further in time. In practice, however, the combination of a smooth signum function and numerical errors from each iteration can cause the zero contour to move during the reinitialization process, leading to errors in the interface location.FMM reinitialization, on the other hand, computes the SDLS by marching signeddistance values out from the interface. This typically involves first using high-order interpolation near the interface to seed the values, then solving the Eikonal equation in a directional fashion. While this method is generally less computationally costly and less prone to movement of the zero contour than that of PDE-based reinitialization, the resulting SDLS is usually less smooth. This can be an issue, for example, if the interface velocity depends on the curva...

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Bubble Control, Levitation, and Manipulation Using Dielectrophoresis

Brown

Edwards

Roberts

et al. 2020

Adv Materials Inter

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Bubbles attached to surfaces are ubiquitous in nature and in industry. However, bubbles are problematic in important technologies, including causing damage to the operation of microfluidic devices and being parasitic during heat transfer processes, so considerable efforts have been made to develop mechanical and electrical methods to remove bubbles from surfaces. In this work, liquid dielectrophoresis is used to force a captive air bubble to detach away from an inverted solid surface and, crucially, the detached bubble is then held stationary in place below the surface at a distance controlled by the voltage. In this “levitated” state, the bubble is separated from the surface by liquid layer with a voltage‐selected thickness at which the dielectrophoresis force exactly counterbalances the gravitational buoyancy force. The techniques described here provide exceptional command over repeatable cycles of bubble detachment, levitation, and reattachment. A theoretical analysis is presented that explains the observed detachment–reattachment hysteresis in which bubble levitation is maintained with voltages in an order of magnitude lower than those used to create detachment. The precision surface bubble removal and control concepts are relevant to situations such as nucleate boiling and microgravity environments and offer an approach toward “wall‐less” bubble microfluidic devices.

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Detaching droplets in immiscible fluids from a solid substrate with the help of electrowetting

Cited by 37 publications

References 52 publications

Electrically induced drop detachment and ejection

Electrically induced drop detachment and ejection

A Curvature-Augmented, REA Approach to the Level Set Method

Bubble Control, Levitation, and Manipulation Using Dielectrophoresis

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