Abstract
► Coplanar dual-frequency EWOD used as an actuator in a microsystem. ► Liquid surface detection at laser wavelength scale in a microsystem. ► Laser interferometry used at drop apex. ► Contact line friction coefficient identified from apex motion and vibrations model. Here is presented an interferometry technique to quantify damping of electrowetting induced shape oscillations of a sessile microdrop. This characterization method and its devoted chip can be inserted into a microsystem to quantify contact line friction and hence surface ageing in digital electrowetting applications (lab-on-chips, microfluidic lenses and displays). Here, the contact line friction is proposed as a criteria to distinguish sensor surfaces contaminated by adsorbed bio-molecules.
Highlights
Microsystems using droplet microfluidics are subject to a major challenge: how to circumvent contact line friction, which opposes itself to drop motion, and, obviously, how to characterize it? The aim of this paper is to deliver a surface degradation analysis based on wetting abilities, which can be inserted into micro-systems such as lab-on-a-chips [1], microfluidic optical lenses [2] or display technologies [3]
The transduction mechanism used for quantifying the contact line friction is the transient regime of decaying, sessile droplet shape oscillations, initially induced by electrowetting on dielectrics (EWOD)
EWOD is a technology commonly used in digital lab-on-a-chips, for drop motion, mixing enhancement, break-up/ coalescence of drops, aliquoting and other basic manipulations
Summary
Microsystems using droplet microfluidics are subject to a major challenge: how to circumvent contact line friction, which opposes itself to drop motion, and, obviously, how to characterize it? The aim of this paper is to deliver a surface degradation analysis based on wetting abilities, which can be inserted into micro-systems such as lab-on-a-chips [1], microfluidic optical lenses [2] or display technologies [3]. The transduction mechanism used for quantifying the contact line friction is the transient regime of decaying, sessile droplet shape oscillations, initially induced by electrowetting on dielectrics (EWOD). The interferometry signal, which is frequencymodulated by the velocity of the interface, is related to the amplitude of the drop oscillation This point is of prior importance: even small amplitudes, down to the order of several times the laser wavelength of 532 nm, may be detected with a nice precision. One full period of the interferometry signal corresponds to the displacement of the interface over an optical path of one wavelength The novelty of this approach is the combination of a facile in situ analysis of droplet shape oscillations, with a fast and highly accurate measurement by laser interferometry, even for small amplitudes
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