Flow rate analysis of an EWOD-based device: how important are wetting-line pinning and velocity effects?

    Authors

    R. Shabani;H. J. Cho

    Comments

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    Abbreviated Journal Title

    Microfluid. Nanofluid.

    Keywords

    Droplet; Electrowetting on dielectric; Hysteresis; Dynamic contact; angle; Wetting-line velocity; Pinning; Advancing and receding; wetting-lines; SPIN-ON-GLASSES; ELECTROWETTING ACTUATION; DROPLET TRANSPORT; CONTACT; ANGLES; DYNAMICS; ENERGY; MODEL; SIMULATION; MICROPUMP; Nanoscience & Nanotechnology; Instruments & Instrumentation; Physics, ; Fluids & Plasmas

    Abstract

    An electrowetting on dielectric (EWOD)-based micropump was used as a platform to study the contribution of the pinning and wetting-line velocity effects on its flow rate. In this micropump, a droplet is driven into a microchannel using EWOD to manipulate a meniscus in the channel. An interesting observation was that the shrinking input droplet changes its shape in two modes: (1) in the first mode, droplet contact angle decreases while its wetting area remains constant (pinning) and (2) in the second mode, droplet wetting line recedes while its contact angle changes as a function of its velocity (dynamic contact angle). Unexpectedly, the micropump flow rate was found to be constant in spite of the changes in the droplet radius. The pump performance was studied to unravel the physical concept behind its constant flow rate. A detailed characterization of variation in contact angle due to pinning, wetting-line velocity, and EWOD was carried out. Dynamic contact angles were used to accurately calculate the pressure gradient between the droplet and the meniscus for flow rate estimation. It was shown that neglecting either the wetting-line energy or the velocity effect results in not only a considerable gap between the predicted and the measured flow rates but also an unphysical instability in flow rate analysis. However, when these effects were fully taken into account, an excellent agreement between the predicted and the measured flow rates was obtained.

    Journal Title

    Microfluidics and Nanofluidics

    Volume

    15

    Issue/Number

    5

    Publication Date

    1-1-2013

    Document Type

    Article

    Language

    English

    First Page

    587

    Last Page

    597

    WOS Identifier

    WOS:000326295200002

    ISSN

    1613-4982

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