Measurement of surfactant properties using a circular capillary wave field

Saylor, J. R.; Szeri, Andrew J.; Foulks, G. P.

doi:10.1007/s003480000119

Cited by 31 publications

(34 citation statements)

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“…As a result, a second TCW is excited by the vertically moving apex, which travels radially outwards down to the contact line. 15,20 In steady conditions, a resonance mechanism between these two TCW is therefore expected: drop deformation is observed to be the largest at the drop apex and the contact line, which behave as the antinodes of a resulting standing capillary wave.…”

Section: Oscillating Ewod-induced Streaming Flow In Air As Ambiementioning

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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Section: Oscillating Ewod-induced Streaming Flow In Air As Ambiementioning

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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“…The theory of surfactant-laden meniscus waves in a cylindrical geometry, developed by Bock (1991), Saylor, Szeri & Foulks (2000) and Picard & Davoust (2006), proceeds from the treatment of two-dimensional travelling gravity-capillary waves in a Cartesian geometry (Lucassen-Reynders & Lucassen 1970). In this theory, the fluid motion in the incompressible bulk is modelled with the linearized Navier-Stokes equations, and the vertical and horizontal displacements of the surface satisfy the surface stress and kinematic boundary conditions.…”

Section: Introductionmentioning

confidence: 99%

Spatiotemporal measurement of surfactant distribution on gravity–capillary waves

2015

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Materials adsorbed onto the surface of a fluid -for instance, crude oil, biogenic slicks or industrial/medical surfactants -will move in response to surface waves. Owing to the difficulty of non-invasive measurement of the spatial distribution of a molecular monolayer, little is known about the dynamics that couple the surface waves and the evolving density field. Here, we report measurements of the spatiotemporal dynamics of the density field of an insoluble surfactant driven by gravity-capillary waves in a shallow cylindrical container. Standing Faraday waves and travelling waves generated by the meniscus are superimposed to create a non-trivial surfactant density field. We measure both the height field of the surface using moiré imaging, and the density field of the surfactant via the fluorescence of NBD-tagged phosphatidylcholine, a lipid. Through phase averaging stroboscopically acquired images of the density field, we determine that the surfactant accumulates on the leading edge of the travelling meniscus waves and in the troughs of the standing Faraday waves. We fit the spatiotemporal variations in the two fields using an ansatz consisting of a superposition of Bessel functions, and report measurements of the wavenumbers and energy damping factors associated with the meniscus and Faraday waves, as well as the spatial and temporal phase shifts between them. While these measurements are largely consistent for both types of waves and both fields, it is notable that the damping factors for height and surfactant in the meniscus waves do not agree. This raises the possibility that there is a contribution from longitudinal waves in addition to the gravity-capillary waves.

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“…2 We believe that the model proposed in this paper could also be successfully applied to the case of an interface functionalised with probe molecules designed to capture dissolved target molecules. This configuration also applies to small interfacial rheometres based on a small liquid bath being subjected to vertical vibrations [11][12][13].…”

Section: Model System and Aimsmentioning

confidence: 98%

“…A careful study of (12) shows Table 2 for each of the previous sorption laws listed in Table 1. A condensed form of (12) writes: …”

Section: The Adsorption Isotherm Linearisedmentioning

confidence: 99%

Transient aging of a liquid–gas interface stretched by standing waves: On the interplay of chemical kinetics

Picard

Davoust

2008

Journal of Colloid and Interface Science

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Measurement of surfactant properties using a circular capillary wave field

Cited by 31 publications

References 0 publications

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

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

Spatiotemporal measurement of surfactant distribution on gravity–capillary waves

Transient aging of a liquid–gas interface stretched by standing waves: On the interplay of chemical kinetics

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