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Transverse transport of solutes between co-flowing pressure-driven streams for microfluidic studies of diffusion/reaction processes

J.-B. Salmon, A. Ajdari — J. Appl. Phys. 101, (2007) 074902

publié le , mis à jour le

We consider a situation commonly encountered in microfluidics : two streams of miscible liquids are
brought at a junction to flow side by side within a microchannel, allowing solutes to diffuse from
one stream to the other and possibly react. We focus on two model problems : (i) the transverse
transport of a single solute from a stream into the adjacent one, (ii) the transport of the product of
a diffusion-controlled chemical reaction between solutes originating from the two streams. Our
description is made general through a nondimensionalized formulation that incorporates both the
parabolic Poiseuille velocity profile along the channel and thermal diffusion in the transverse
direction. Numerical analysis over a wide range of the streamwise coordinate x reveal different
regimes. Close to the top and the bottom walls of the microchannel, the extent of the diffusive zone
follows three distinct power law regimes as x is increased, characterized, respectively, by the
exponents 1/2, 1/3, and 1/2. Simple analytical arguments are proposed to account for these results.

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