Electrowetting on dielectric driven droplet resonance and mixing enhancement in parallel-plate configuration

Chen, Hsin-Chien; Lai, Mei-Feng

doi:10.1063/1.3673258

Cited by 26 publications

(16 citation statements)

References 31 publications

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“…In millimeter-sized systems, this flow is short lived, decaying within hundreds of microseconds, and the following dynamics are governed only by diffusion [23]. Previous studies of mixing driven by free-surface movement [24][25][26] have shown that free-surface dynamics can be effective in enhancing mixing within the enclosed liquid, even under conditions where molecular diffusion is negligible. However, the success of such chaotic advection-driven mixing or stirring relies on repeated stretching and folding of the "interface" between the two liquids being mixed.…”

Section: Introductionmentioning

confidence: 99%

Mixing and internal dynamics of droplets impacting and coalescing on a solid surface

et al. 2013

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The coalescence and mixing of a sessile and an impacting liquid droplet on a solid surface are studied experimentally and numerically in terms of lateral separation and droplet speed. Two droplet generators are used to produce differently colored droplets. Two high-speed imaging systems are used to investigate the impact and coalescence of the droplets in color from a side view with a simultaneous gray-scale view from below. Millimeter-sized droplets were used with dynamical conditions, based on the Reynolds and Weber numbers, relevant to microfluidics and commercial inkjet printing. Experimental measurements of advancing and receding static contact angles are used to calibrate a contact angle hysteresis model within a lattice Boltzmann framework, which is shown to capture the observed dynamics qualitatively and the final droplet configuration quantitatively. Our results show that no detectable mixing occurs during impact and coalescence of similar-sized droplets, but when the sessile droplet is sufficiently larger than the impacting droplet vortex ring generation can be observed. Finally we show how a gradient of wettability on the substrate can potentially enhance mixing.

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Section: Introductionmentioning

confidence: 99%

Mixing and internal dynamics of droplets impacting and coalescing on a solid surface

et al. 2013

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“…This permits to induce shape oscillations of a sessile drop which in return generates a Stokes drift along its liquid surface. Subsequently, oscillating EWOD has been proposed as a mixing promoter in two popular configurations of electrowetting: the parallel-plate 7,8 and needle [9][10][11][12] configurations.…”

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confidence: 99%

Coplanar electrowetting-induced stirring as a tool to manipulate biological samples in lubricated digital microfluidics. Impact of ambient phase on drop internal flow pattern

et al. 2013

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Oscillating electrowetting on dielectrics (EWOD) with coplanar electrodes is investigated in this paper as a way to provide efficient stirring within a drop with biological content. A supporting model inspired from Ko et al. [Appl. Phys. Lett. 94, 194102 (2009)] is proposed allowing to interpret oscillating EWOD-induced drop internal flow as the result of a current streaming along the drop surface deformed by capillary waves. Current streaming behaves essentially as a surface flow generator and the momentum it sustains within the (viscous) drop is even more significant as the surface to volume ratio is small. With the circular electrode pair considered in this paper, oscillating EWOD sustains toroidal vortical flows when the experiments are conducted with aqueous drops in air as ambient phase. But when oil is used as ambient phase, it is demonstrated that the presence of an electrode gap is responsible for a change in drop shape: a pinch-off at the electrode gap yields a peanut-shaped drop and a symmetry break-up of the EWOD-induced flow pattern. Viscosity of oil is also responsible for promoting an efficient damping of the capillary waves which populate the surface of the actuated drop. As a result, the capillary network switches from one standing wave to two superimposed traveling waves of different mechanical energy, provided that actuation frequency is large enough, for instance, as large as the one commonly used in electrowetting applications (f $ 500 Hz and beyond). Special emphasis is put on stirring of biological samples. As a typical application, it is demonstrated how beads or cell clusters can be focused under flow either at mid-height of the drop or near the wetting plane, depending on how the nature of the capillary waves is (standing or traveling), and therefore, depending on the actuation frequency (150 Hz-1 KHz).

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“…In this regard, Paik et al have demonstrated droplet mixing using EWOD by fusing drops and then moving them back and forth on a linear array of electrodes [34]. Recently, Lee et al demonstrated mixing in electrowetting droplets in a sandwiched configuration by driving them at different resonant and at alternating driving frequencies [35].…”

Section: Discussionmentioning

confidence: 98%

Electrowetting-driven oscillating drops sandwiched between two substrates

et al. 2013

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Drops sandwiched between two substrates are often found in lab-on-chip devices based on digital microfluidics. We excite azimuthal oscillations of such drops by periodically modulating the contact line via ac electrowetting. By tuning the frequency of the applied voltage, several shape modes can be selected one by one. The frequency of the oscillations is half the frequency of the contact angle modulation by electrowetting, indicating a parametric excitation. The drop response to sinusoidal driving deviates substantially from sinusoidal behavior in a "stop and go" fashion. Although our simple theoretical model describes the observed behavior qualitatively, the resonances appear at lower frequencies than expected. Moreover, the oscillations produce a nonperiodic fluid transport within the drop with a typical velocity of 1 mm/s. In digital microfluidic devices, where the typical drop size is less than 1 mm, this flow can result in very fast mixing on the spot.

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Electrowetting on dielectric driven droplet resonance and mixing enhancement in parallel-plate configuration

Cited by 26 publications

References 31 publications

Mixing and internal dynamics of droplets impacting and coalescing on a solid surface

Mixing and internal dynamics of droplets impacting and coalescing on a solid surface

Coplanar electrowetting-induced stirring as a tool to manipulate biological samples in lubricated digital microfluidics. Impact of ambient phase on drop internal flow pattern

Electrowetting-driven oscillating drops sandwiched between two substrates

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