Principles of Microfluidic Actuation by Modulation of Surface Stresses

Darhuber, Anton A.; Troian, Sandra M.

doi:10.1146/annurev.fluid.36.050802.122052

Cited by 440 publications

(351 citation statements)

References 130 publications

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“…This approach has been developed by electrowetting or other surface actuation techniques for several years. 10 However, interfacing such a twodimensional device with a microchannel system for drop formation and preconditioning would bridge the gap between microchannel-based systems and digital microfluidics on surfaces, thus taking advantage of the qualities of both approaches.…”

Section: Summary and Discussionmentioning

confidence: 99%

Dynamics of microfluidic droplets

2010

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This critical review discusses the current understanding of the formation, transport, and merging of drops in microfluidics. We focus on the physical ingredients which determine the flow of drops in microchannels and recall classical results of fluid dynamics which help explain the observed behaviour. We begin by introducing the main physical ingredients that differentiate droplet microfluidics from single-phase microfluidics, namely the modifications to the flow and pressure fields that are introduced by the presence of interfacial tension. Then three practical aspects are studied in detail: (i) The formation of drops and the dominant interactions depending on the geometry in which they are formed.(ii) The transport of drops, namely the evaluation of drop velocity, the pressure-velocity relationships, and the flow field induced by the presence of the drop. (iii) The fusion of two drops, including different methods of bridging the liquid film between them which enables their merging.

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Section: Summary and Discussionmentioning

confidence: 99%

Dynamics of microfluidic droplets

2010

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“…Ref. [14] and references therein). These surface forces become dominant 1 over body forces at small scales, as the ratio of surface to volume becomes large.…”

Section: Introductionmentioning

confidence: 99%

An optical toolbox for total control of droplet microfluidics

2007

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The use of microfluidic drops as microreactors hinges on the active control of certain fundamental operations, such as droplet formation, transport, division and fusion. Recent work has demonstrated that local heating from a focused laser can apply a thermocapillary force on a liquid interface sufficient to block the advance of a droplet in a microchannel (Baroud et al., Phys. Rev. E. V 75, p.046302). Here, we demonstrate the usefulness of this optical approach by implementing the operations mentioned above, without the need for any special microfabrication or moving parts. Building blocks such as a droplet valve, sorter, fuser, or divider are shown, as is the combination of a valve and fuser using a single laser spot.

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“…Recently these approaches have acquired increasing immediacy with the emergence of droplet-based microfluidics, for which there have been many proposals for fluid actuation based on the manipulation of surface stresses. 8 The generation of a net force by thermocapillary flow was first demonstrated by Young et al on air bubbles located between the anvils of a machinist's micrometer. 1 The anvils were held at different temperatures, leading to a thermocapillary flow along the surface of the bubble which also induced a flow from the hot to the cold regions in the external fluid.…”

Section: Introductionmentioning

confidence: 99%

Laser-Induced Force on a Microfluidic Drop: Origin and Magnitude

Verneuil

Cordero

Gallaire³

et al. 2009

Langmuir

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The localized heating produced by a tightly focused infrared laser leads to surface tension gradients at the interface of microfluidic drops covered with surfactants, resulting in a net force on the drop whose origin and magnitude are the focus of this paper. First, by colocalization of the surfactant micelles with a fluorescent dye, we demonstrate that the heating alters their spatial distribution, driving the interface out of equilibrium. This soluto-capillary effect opposes and overcomes the purely thermal dependence of the surface tension, leading to reversed interfacial flows. As the surface of the drop is set into motion, recirculation rolls are created outside and inside the drop that we measure using time-resolved micro-Particle Image Velocimetry. Second, the net force produced on the drop is measured using an original microfluidic design. For a drop 300 µm-long and 100 µm wide we obtain a force of 180 † Laboratoire d'Hydrodynamique (LadHyX), Ecole Polytechnique, 91128 Palaiseau, France ‡ Laboratoire J.A. Dieudonné, Université de Nice Sophia-Antipolis, 06108 Nice, France § Current address:Department of Physics, University of Pennsylvania, Philadelphia, PA 1 Emilie Verneuil et al.Laser-induced force on a drop nN for a laser power of 100 mW. This micro-dynanometer further shows that the magnitude of the heating, which is determined by the laser power and its absorption in the water, sets the magnitude of the net force on the drop. On the other hand, the dynamics of the force generation is limited by the time scale for heating which has independently been measured to be τ Θ = 4 ms. This time scale sets the maximum velocity that the drops can have and still be blocked, by requiring that the interface passes the laser spot in a time longer than τ Θ . The maximum velocity is measured at U max = 0.7 mm/s for our geometric conditions. Finally, a scaling model is derived that describes the blocking force in a confined geometry as the result of the viscous stresses produced by the shear between the drop and the lateral walls.

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Principles of Microfluidic Actuation by Modulation of Surface Stresses

Cited by 440 publications

References 130 publications

Dynamics of microfluidic droplets

Dynamics of microfluidic droplets

An optical toolbox for total control of droplet microfluidics

Laser-Induced Force on a Microfluidic Drop: Origin and Magnitude

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