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Description:
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Mixing of fluids at the microscale poses a variety of challenges , many of which
arise from the fact that molecular diffusion is the dominant transport mechanism in the
laminar flow regime . The unfavorable combination of low Reynolds numbers and high
Pà ©clet numbers implies that cumbersomely long microchannels are required to achieve
efficient levels of micromixing . Although considerable progress has been made toward
overcoming these limitations (e .g . , exploiting chaotic effects ) , many techniques employ
intricate 3 -D flow networks whose complexity can make them difficult to build and
operate . In this research , we show that enhanced micromixing can be achieved using
topologically simple and easily fabricated planar 2 -D microchannels by simply
introducing curvature and changes in width in a prescribed manner . This 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 conduitâ  s cross -sectional area . We characterize these effects using top -view imaging of aqueous streams labeled with tracer dyes and
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 , scalable , and can be straightforwardly integrated as generic
components in a variety of lab -on -a -chip systems . |