  We discuss experimental investigations on steady streaming flows of dilute
and semi-dilute polymer solutions in microfluidic devices. The effect of
non-Newtonian behavior on steady streaming for different model fluids is
determined by characterizing the evolution of the inner streaming layer as a
function of oscillation frequency using particle tracking velocimetry. We find
that steady streaming velocity profiles in constant-viscosity elastic liquids
are qualitatively similar to those in Newtonian liquids. Steady streaming
velocity profiles in elastic liquids with strong shear thinning, however,
display two unique features: (i) a non-monotonic evolution of the inner
streaming layer with increasing frequency, first growing then decreasing in
width, and (ii) a clear asymmetry in the flow profile at high frequencies.
