Charge-Coupled Transient Model for Electrowetting

Castañer, Luís; Virgilio, Vito di; Bermejo, Sandra

doi:10.1021/la102777m

Cited by 12 publications

(27 citation statements)

References 38 publications

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“…However, CA saturation is a problem not well explained yet. Extensive hypotheses have been proposed in the literature with the EW experiments, covering the models of zero interfacial tension, 48,49 dielectric breakdown, 42,44,50 contact line instability, 51,52 gas ionization or insulating fluid charging, 53 minimization of the electrostatic energy, 16 tailor cone, 41 and even material deficiency. 54 The present experimental study is still not able to explain the CA saturation at a microscopic level; however, our experimental observation may provide some further indication of the CA saturation phenomenon.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

Actuation of a Nonconductive Droplet in an Aqueous Fluid by Reversed Electrowetting Effect

Wang

et al. 2020

Langmuir

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Manipulation of a conductive droplet by electrowetting has been a popular topic in microfluidics whereby wettability of the droplet on a solid surface is increased by applying a voltage between the conductive droplet and the insulated surface. However, the opposite phenomenon, e.g., decreasing the wettability of a nonconductive droplet and increasing its contact angle (CA) by the reversed electrowetting (REW) effect, has been scarcely reported. Such a process involves not only the transient dynamics of droplet dewetting but also a critical condition for droplet detachment from the adhesive surface. In this work, actuation of a nonconductive droplet in an aqueous surrounding fluid by REW is studied experimentally. Silicone oil is used for the actuated droplet, and filtered water is used as the surrounding fluid. The solid substrate is made of a glass substrate coated with an indium tin oxide (ITO) film and then deposited by a dielectric layer of Parylene C. Potential difference is applied between the substrate and the surrounding fluid, eliminating the disturbance from the top needle on the motion of the droplet. Three different regimes are identified in the full range of operation. An underactuated regime occurs at low applied voltages, in which the CA of the droplet shows a monotonic increase with the increase of voltage (V). The friction coefficient of the contact line decreases with V before the CA saturation (V s) but shows little change when V > V s. At high voltages, the contact line of the sessile droplet is contracted excessively by REW. The droplet shows oscillation, and it refers to the overactuated regime. A combined time scale is proposed, and it verifies that the viscous dissipation of the contact line and liquid inertia show comparable contributions in the droplet dynamics. At sufficiently high voltages, the droplet is rejected completely from the surface. A critical equation for the threshold voltage of droplet detachment is built, and its validity is confirmed by experimental results.

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Section: ■ Materials and Methodsmentioning

confidence: 99%

Actuation of a Nonconductive Droplet in an Aqueous Fluid by Reversed Electrowetting Effect

Wang

et al. 2020

Langmuir

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“…In all those appli-47 cations a thin electrode layer, a dielectric and a hydrophobic layer electrode unbalances the surface tension equilibrium leading to 54 movement of the triple line [9][10][11]. This is schematically shown 55 in Fig.…”

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confidence: 99%

EWOD using nonaqueous liquids

Ahmadi

Bermejo

Castañer

2015

Microelectronic Engineering

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“…In the case of the transport of the 100 mM KCl droplet, the applied electrical voltage ( V ) results in the reduction of the dielectric surface–droplet interfacial tension, above the activated electrode pad . Since the hydrophobic dielectric film takes a finite time to get charged , after the activation of an electrode pad, a time-averaged form of the corresponding transient electrical driving force for the droplet, due to such electrocapillarity-induced solid–liquid interfacial tension gradient between the activated and ground electrodes, is considered here. The transient electrical driving force is averaged over the time period ( t c = 2.3 RC ) in which saturation in dielectric charging is effectively attained, on considering an equivalent RC circuit.…”

Section: Results and Discussionmentioning

confidence: 99%

Dynamics of Electrically Modulated Colloidal Droplet Transport

et al. 2015

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Electrically actuated transport dynamics of colloidal droplets, on a hydrophobic dielectric film covering an array of electrodes, is studied here. Specifically, the effects of the size and electrical properties (zeta-potential) of the colloidal particles on such transport characteristics are investigated. For the colloidal droplets, the application of an electrical voltage leads to additional attenuation of the local dielectric-droplet interfacial tension. This is due to the electrically triggered enhanced colloidal particle adsorption at the dielectric-droplet interface, in the immediate vicinity of the droplet three-phase contact line (TPCL). The extent of such interfacial particle adsorption, and hence, the extent of the consequential reduction in the interfacial tension, is dictated by the combined effects of the three-phase contact line spreading, particle size, the interfacial electrostatic interaction between the colloidal particles (if charged) and the charged dielectric surface above the activated electrode, and the interparticle electrostatic repulsion. The electrical driving force of varying magnitude, stemming from this altered solid-liquid interfacial tension gradient in the presence of the colloidal particles, culminates in different droplet transport velocity and droplet transfer frequency for different colloidal droplets. We substantiate the inferences from our experimental results by a quasi-steady state force balance model for colloidal droplet transport. We believe that the present work will provide an accurate framework for determining the optimal design and operational parameters for digital microfluidic chips handling colloidal droplets, as encountered in a plethora of applications.

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Charge-Coupled Transient Model for Electrowetting

Cited by 12 publications

References 38 publications

Actuation of a Nonconductive Droplet in an Aqueous Fluid by Reversed Electrowetting Effect

Actuation of a Nonconductive Droplet in an Aqueous Fluid by Reversed Electrowetting Effect

EWOD using nonaqueous liquids

Dynamics of Electrically Modulated Colloidal Droplet Transport

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