Multiphysics simulation of ion concentration polarization induced by nanoporous membranes in dual channel devices

Many microfluidic devices have been utilizing ion concentration polarization (ICP) phenomena by using a permselective, nanoporous membrane with electric fields for a variety of preconcentration applications. However, numerical analyses on the ICP phenomena have not drawn sufficient attention, although they are an intriguing and interdisciplinary research area. In this work, we propose a 2-D model and present numerical simulation results on the ICP, which were obtained by solving three coupled governing equations: Nernst-Planck, Navier-Stokes, and Poisson. With improved boundary conditions and assumptions, we demonstrated that the simulation results not only are consistent with other experimental results but also make it possible to thoroughly understand the ICP phenomena. In addition, we demonstrated that the preconcentration of analytes can be simulated and quantified in terms of concentration enhancement factors (CEFs) that were related to many factors, such as ionic concentration distribution, electric fields, and flow fields including vortex flows across the membrane. Furthermore, we demonstrated that a high electrophoretic mobility (EPM) of counterions in the membrane plays the most important role in producing accurate simulation results while the effect of the charge density of the membrane is relatively insignificant. Hence, it is believed that the model and simulation results would provide good guidelines to better develop microfluidic preconcentration devices based on the ICP phenomena.