Mixing and charge transfer in a nanofluidic system due to a patterned surface

In this work, electroosmotic flow mixing enhancement is investigated in a sufficiently long nano-channel with a rectangular nonconducting obstacle mounted on the lower wall with heterogeneous surface electrical potential. A linear pressure drop is observed above the region of patch potential to form a recirculating zone. Formation of vortical flow due to the combined effect of enhanced surface area, heterogeneity in surface potential and external electric field is discussed. A numerical method is adopted based on a finite volume approach to solve the governing coupled Nernst-Planck, Navier-Stokes and Maxwell's equations to describe ion transport, electrical potential distribution and their impact on flow field. It is observed that an increment in patch potential strength and block height increases the species concentration gradient and surface area, respectively, which enhances the diffusive flux resulting in better mixing performance.