  In fully-developed pressure-driven flow, the spreading of a dissolved solute
is enhanced in the flow direction due to transverse velocity variations in a
phenomenon now commonly referred to as Taylor-Aris dispersion. It is well
understood that the characteristics of the dispersion are sensitive to the
channel's cross-sectional geometry. Here we demonstrate a method for
manipulation of dispersion in a single rectangular microchannel via controlled
deformation of its upper wall. Using a rapidly prototyped multi-layer
microchip, the channel wall is deformed by a controlled pressure source
allowing us to characterize the dependence of the dispersion on the deflection
of the channel wall and overall channel aspect ratio. For a given channel
aspect ratio, an optimal deformation to minimize dispersion is found,
consistent with prior numerical and theoretical predictions. Our experimental
measurements are also compared directly to numerical predictions using an
idealized geometry.
