Microchannel flow with patchwise and periodic surface heterogeneity

Surface heterogeneity is present in a variety of electrokinetic transport phenomena. It is desirable to understand the synergetic effects of the electrical double layer field and the surface heterogeneity on electrokinetic flow in microchannels. In this paper, a 3D, finite element based, numerical model for pressure-driven flow through microchannels with an arbitrary but periodic patchwise heterogeneous surface pattern has been developed. The model is based on a simultaneous solution to the Nernst-Planck, Poisson, and Navier-Stokes equations to determine the local ionic concentration, the double layer distribution, and the flow field. The presence of a heterogeneous patch is shown to induce flow in all three coordinate directions, including a circulation pattern perpendicular to the main flow axis. The strength of this circulation region is found to be proportional to Reynolds number and double layer thickness. While at low Reynolds number (i.e., Re < 1) the double layer distribution is diffusion dominated, significant convective effects are observed at higher Reynolds number leading to a deviation from the classical Poisson-Boltzmann distribution. The combined effect of the 3D flow field and disturbed double layer region on measurable quantities such as the streaming potential is discussed.