Mass transfer enhancement and surface functionalization in digital microfluidics using AC electrowetting: the smaller, the better

Theisen, Johannes; Davoust, Laurent

doi:10.1007/s10404-014-1536-2

Cited by 15 publications

(12 citation statements)

References 35 publications

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“…The values of the Peclet and Damköhler numbers (Pe ∼ 10 6 , Da ∼ 10 −4 , see e.g. [9]) suggest that convection acts on shorter time scales than diffusion and adsorption, which confirms again that the influence of drop internal flows can not be neglected. Isoconcentration contours, as calculated from numerical simulations of BSA chemical transport, clearly demonstrate that a large concentration gradient arises near the contact line for high modes 4 and 6, while for mode 2, the most significant gradients are observed a little further to the center of the drop.…”

Section: Dca Experiments With Oscillating Ewodsupporting

confidence: 58%

“…2). And the numerical calculations of drop flow patterns [7] show that, in contrast to mode n=2 for which the vortices are observed throughout the drop, the vortices observed at high mode, n=6, concentrate within the Stuart layer standing along the drop surface with a steady corner eddy located near the contact line [9]. This could explain why the efficiency of stirring-enhanced surface ageing might be higher for modes 4 and 6; a point which is in line with the presented measurements.…”

Section: Dca Experiments With Oscillating Ewodmentioning

confidence: 93%

“…To support this physical interpretation, transient diffusive and convective transports of BSA molecules are calculated by taking into account drop streaming and adsorption at the solid substrate ( [9]). The large value of the finiteness number, ε 0 ∼ 10, means that the drop behaves as a semi-infinite system [10].…”

Section: Dca Experiments With Oscillating Ewodmentioning

confidence: 99%

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Biosensing at Drop Scale Assisted by Electrowetting at Moderate Frequency

Davoust¹,

Theisen²

2015

Procedia Engineering

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This paper addresses surface ageing of a functionalized substrate in digital microfluidics. A model system based on bovine serum albumin (BSA)-laden sessile drop is selected. AC ElectroWetting-On-Dielectrics (EWOD), increasingly used in digital micro-systems for medical assays, is implemented in coplanar configuration. The small frequency required by EWOD actuation (f =100 -1000 Hz) enables shape oscillations of the latter sessile drop and internal streaming. As demonstrated from dynamic contact angle (DCA) imaging, adsorption of BSA at the solid substrate is promoted under EWOD, as also shown from the time-dependent solid-liquid surface pressure. For an oscillating mode, n = 6, our numerical simulations show that corner eddies located near the oscillating contact line yield an efficient molecular renewal. In this way, oscillating EWOD could be used purposely as a tool to speed up label-free detection from DCA measurements.

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Section: Dca Experiments With Oscillating Ewodsupporting

confidence: 58%

Section: Dca Experiments With Oscillating Ewodmentioning

confidence: 93%

Section: Dca Experiments With Oscillating Ewodmentioning

confidence: 99%

See 1 more Smart Citation

Biosensing at Drop Scale Assisted by Electrowetting at Moderate Frequency

Davoust¹,

Theisen²

2015

Procedia Engineering

Self Cite

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“…If R s ≫ 1, then the typical length scale of the streaming vortices is δ s ≈ δ/ε. This is better known as the Stuart length scale . Here, .…”

Section: Resultsmentioning

confidence: 99%

Evaporation–Oscillation Driven Assembly: Microtailoring the Spatial Ordering of Particles in Sessile Droplets

et al. 2018

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This work explores the physical mechanism that can be used to control the final residual pattern of nanoparticles obtained from an evaporating-oscillating sessile droplet. To that end, the substrate is vibrated in the vertical direction with a constant amplitude, while the frequency of excitation is varied. It is found that evaporation progressively shifts the mode number of the oscillating droplet to lower values, while the oscillations enhance the rate of solvent loss, causing a reduction in the droplet lifetime. The coupling between evaporation and oscillation drives the internal flow through two distinct regimes. Initially, oscillation leads to inner flow recirculation, which delays the evaporation driven edge deposition of particles. Subsequently at lower modes, caused by solvent depletion, the effect of oscillation is weakened, which allows evaporation-driven flow to gain prominence and thus transport the dispersed particles to the contact line. We demonstrate here how this delay in particle migration can be controlled to engineer morphological changes in not just the resulting macroscopic aspect of the deposit but also its microstructure. We especially focus on the relatively unexplored microstructural pattern of deposits from evaporating−oscillating droplets. Using scanning electron micrograph and Voronoi tessellation of the final deposit, we show unique spatial variation in particle ordering at macro−micro length scales. Thus, droplet oscillation tunes the spatial extent of the particle ordering crucial in applications like photonic crystals and photonic glass.

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“…Data on mechanical-oscillation-induced flows are scarce in the literature. The generated flows are time-averaged streaming from an oscillating two-phase interface. , As such, they both originate from the solid substrate and the wavy (liquid–vapor) interface (Figure a). Hence, a double boundary layer exists at each of these locations .…”

Section: Effect Of External Stimulimentioning

confidence: 99%

Engineering Interfacial Processes at Mini-Micro-Nano Scales Using Sessile Droplet Architecture

et al. 2018

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Evaporating sessile functional droplets act as the fundamental building block that controls the cumulative outcome of many industrial and biological applications such as surface patterning, 3D printing, photonic crystals, and DNA sequencing, to name a few. Additionally, a drying single sessile droplet forms a high-throughput processing technique using low material volume which is especially suitable for medical diagnosis. A sessile droplet also provides an elementary platform to study and analyze fundamental interfacial processes at various length scales ranging from macroscopically observable wetting and evaporation to microfluidic transport to interparticle forces operating at a nanometric length scale. As an example, to ascertain the quality of 3D printing we must understand the fundamental interfacial processes at the droplet scale. In this article, we review the coupled physics of evaporation flow-contact-line-driven particle transport in sessile colloidal droplets and provide methodologies to control the same. Through natural alterations in droplet vaporization, one can change the evaporative pattern and contact line dynamics leading to internal flow which will modulate the final particle assembly in a nontrivial fashion. We further show that control over particle transport can also be exerted by external stimuli which can be thermal, mechanical oscillations, vapor confinement (walled or a fellow droplet), or chemical (surfactant-induced) in nature. For example, significant augmentation of an otherwise evaporation-driven particle transport in sessile droplets can be brought about simply through controlled interfacial oscillations. The ability to control the final morphologies by manipulating the governing interfacial mechanisms in the precursor stages of droplet drying makes it perfectly suitable for fabrication-, mixing-, and diagnostic-based applications.

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Mass transfer enhancement and surface functionalization in digital microfluidics using AC electrowetting: the smaller, the better

Cited by 15 publications

References 35 publications

Biosensing at Drop Scale Assisted by Electrowetting at Moderate Frequency

Biosensing at Drop Scale Assisted by Electrowetting at Moderate Frequency

Evaporation–Oscillation Driven Assembly: Microtailoring the Spatial Ordering of Particles in Sessile Droplets

Engineering Interfacial Processes at Mini-Micro-Nano Scales Using Sessile Droplet Architecture

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