Finite double layer and non-Newtonian power-law effects on electrokinetic diffusioosmotic flows in parallel plate microchannels

Abstract

Diffusioosmotic flows of electrolytic non-Newtonian power-law liquids in parallel plate microchannels are theoretically investigated by considering the finite thickness of the interfacial electrical double layers. Semi-analytical or numerical solutions to the shear stress, flow velocity, effective viscosity, and volume flow rate are obtained as functions of the spatial coordinate, half channel width to Debye length ratio, interfacial zeta potential, diffusivity difference parameter, and the power-law flow behavior index. The border curves of zero flow rate obtained herein delineating the parametric regimes in which the non-Newtonian diffusioosmotic flow rate is directed towards downstream or upstream are distributed differently on the zeta potential versus diffusivity difference parameter map as compared to those obtained using thin double layer theory. As compared to Newtonian liquids, the rheology of dilatant and pseudoplastic liquids respectively enlarges and reduces the parametric regimes in which flow rate towards downstream occurs, which is a result exactly opposite to that obtained based on the thin double layer theory reported in recent literature.