Multivortex micromixing

Abstract

The ability to mix liquids in microchannel networks is fundamentally important in the design of nearly every miniaturized chemical and biochemical analysis system. Here, we show that enhanced micromixing can be achieved in topologically simple and easily fabricated planar 2D microchannels by simply introducing curvature and changes in width in a prescribed manner. This goal is accomplished by harnessing a synergistic combination of (i) Dean vortices that arise in the vertical plane of curved channels as a consequence of an interplay between inertial, centrifugal, and viscous effects, and (ii) expansion vortices that arise in the horizontal plane due to an abrupt increase in a conduit's cross-sectional area. We characterize these effects by using confocal microscopy of aqueous fluorescent dye streams and by observing binding interactions between an intercalating dye and double-stranded DNA. These mixing approaches are versatile and scalable and can be straightforwardly integrated as generic components in a variety of lab-on-a-chip systems.Dean flow ͉ expansion vortex ͉ microfluidics ͉ lab on a chip A lthough microf luidic mixing is a key process in a host of miniaturized analysis systems (1-7), it continues to pose challenges owing to constraints associated with operating in an unfavorable laminar f low regime dominated by molecular diffusion and characterized by a combination of low Reynolds numbers (Re ϭ Vd͞v Ͻ Ͻ 100, where V is the f low velocity, d is a length scale associated with the channel diameter, and v is the f luid kinematic viscosity) and high Péclet numbers (Pe ϭ Vd͞D Ͼ 100, where D is the molecular diffusivity). The relatively large discrepancy between convective and diffusive timescales implies that in a straight smooth-walled microchannel, the downstream distances over which liquids must travel to become fully intermixed (⌬y m ϳ Vd 2 ͞D ϭ Pe ϫ d) can be on the order of several centimeters. These mixing lengths are generally prohibitively long and often negate many of the benefits of miniaturization.A wide variety of micromixing approaches have been explored (8, 9), most of which can be broadly classified as either ''active'' (involving input of external energy) or ''passive'' (harnessing the inherent hydrodynamic structure of specific flow fields to mix fluids in the absence of external forces). Passive designs are often desirable in applications involving sensitive species (e.g., biological samples) because they do not impose strong mechanical, electrical, or thermal agitation. Examples of passive micromixing approaches that have been widely investigated include the following: (i) ''split-and-recombine'' strategies where the streams to be mixed are divided or split into multiple channels and redirected along trajectories that allow them to be subsequently reassembled as alternating lamellae yielding exponential reductions in interspecies diffusion length and time scales (4, 10-12); and (ii) ''chaotic'' strategies where transverse flows are passively generated that continuously expand interfacial...

Engineering fluid flow using sequenced microstructures

“…C ontrol of fluid streams is useful in biological processing [1][2][3] , chemical reaction control 4,5 , and creating structured materials [6][7][8] ; however, general strategies to engineer the cross-sectional form and motion of fluid streams have been limited. Strategies to mix fluids 1,9,10 and control particles 11,12 using engineered systems exist, often relying on chaotic fluid transformations as an effective tool 13,14 to disrupt sustained regions of order in the flow 10,15 .…”

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Lateral migration of dual droplet trains in a double spiral microchannel

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Micropillar sequence designs for fundamental inertial flow transformations

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