Rf. Ismagilov et al., Experimental and theoretical scaling laws for transverse diffusive broadening in two-phase laminar flows in microchannels, APPL PHYS L, 76(17), 2000, pp. 2376-2378
This letter quantifies both experimentally and theoretically the diffusion
of low-molecular-weight species across the interface between two aqueous so
lutions in pressure-driven laminar flow in microchannels at high Peclet num
bers. Confocal fluorescent microscopy was used to visualize a fluorescent p
roduct formed by reaction between chemical species carried separately by th
e two solutions. At steady state, the width of the reaction-diffusion zone
at the interface adjacent to the wall of the channel and transverse to the
direction of flow scales as the one-third power of both the axial distance
down the channel (from the point where the two streams join) and the averag
e velocity of the flow, instead of the more familiar one-half power scaling
which was measured in the middle of the channel. A quantitative descriptio
n of reaction-diffusion processes near the walls of the channel, such as de
scribed in this letter, is required for the rational use of laminar flows f
or performing spatially resolved surface chemistry and biology inside micro
channels and for understanding three-dimensional features of mass transport
in shearing flows near surfaces. (C) 2000 American Institute of Physics. [
S0003-6951(00)02616-4].