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The present study deals with the effect of ionic advection on electroosmoticflow over charge modulated surfaces in a generalized paradigm when theclassically restrictive "weak field" limit may be relaxed. Going beyond thecommonly portrayed weak field limit (i.e, the externally applied electric fieldis over-weighed by the surface-induced electrical potential, towards chargedistribution in an electrified wall-adhering layer) for electroosmotictransport, we numerically solve the coupled full set of Poisson-Nernst-Planck(PNP) and Navier-Stokes equations, in a semi-infinite domain, bounded at thebottom by a charged wall. Further, in an effort to obtain deeper physicalinsight, we solve the simplified forms of the relevant governing equations forlow surface potential in two separate asymptotic limits: (i) a regularperturbation solution for Low Ionic Peclet number (Pe), where Pe is employed asthe gauge function and (ii) a matched asymptotic solution for O(1) Pe in theThin Electric Double Layer (EDL) limit. We demonstrate that reasonably goodagreement is observed between the analytical and numerical solutions. Ouranalysis reveals that the primary effect of Pe on the flow is to slow down the"free stream velocity", adding to the periodicity of the flow, while it alsoinduces significant changes in the overall potential. We further show that theelectrical double layer thickness strongly dictates the "free stream velocity",and a simple Smoluchowski type of slip boundary condition cannot be used, ifthe effect of advection is taken into account. These results can be ofsignificant importance in designing microfluidic and nanofluidic systems withsurface charge modulation.

Effect of Ionic Advection on Electroosmosis over Charge Modulated Surfaces: Beyond the Weak Field Limit