An analytical solution is derived for the microchannel
flow of viscoelastic fluids by combined electroosmosis
and pressure gradient forcing. The viscoelastic
fluid is described by the Phan-Thien¿Tanner model with
due account for the near-wall layer depleted of macromolecules.
This skimming layer is wider than the electric
double layer (EDL) and leads to an enhanced flow rate
relative to that of the corresponding uniform concentration
flow case. The derived solution allows a detailed investigation
of the flow characteristics due to the combined
effects of fluid rheology, forcing strengths ratio, skimming
layer thickness and relative rheology of the two fluids. In
particular, when the EDL is much thinner than the skimming
layer and simultaneously the viscosity of the Newtonian
fluid inside this layer is much lower than that of the
fluid outside, the flow is dominated by the characteristics of
the Newtonian fluid. Outside these conditions, proper
account of the various fluid layers and their properties must
be considered for an accurate prediction of the flow characteristics.
The analytical solution remains valid for the
flow driven by a pressure gradient and its streaming
potential, which is determined in the appendix.
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