Multiphysics Simulation of Ion Concentration Polarization Induced by Nafion Film in Microfluidic Devices

Abstract

In this work, multiphysics simulation is performed to investigate not only the polarization of ionic concentration but analyte pre-concentration both in microfluidic dual-channel and single-channel devices. Corresponding experimental research shows inherent shortcomings of explaining the complex physical mechanisms of ion concentration polarization (ICP) and pre-concentration since it is difficult to directly measure ionic concentrations, velocity field and electric field strength that are critical to understand the working mechanisms. To simulate ICP phenomena, fully coupled Navier-Stokes, Nernst-Planck and Poisson equations are solved by using a commercially available multiphysics simulation tool (COMSOL multiphysics V4.3a). The simulation of dual-channel ICP (DC-ICP) is performed to validate boundary conditions and simulation settings by comparing the simulation results with experimental ones obtained from the same group and from other literature. The high electrophoresis mobility of proton inside a nanoporous membrane is numerically proved to be necessary to induce ICP in a single-channel ICP (SC-ICP) device. Boundary conditions and domain properties for simulation are improved to provide faster calculation and more accurate results than previous simulation work. The consistency between simulation results and experimental results for a DC-ICP device provides the validity of the simulation, a better understanding on the pre-concentration and nonlinear vortex flow, which are obtained from the results of velocity field, ionic concentration distribution and electric field strength. To my best knowledge, the pre-concentration and nonlinear vortex flow in a SC-ICP device is simulated in this work for the first time, whose characteristics shows a good agreement with experimental results and expectation very well, providing a reliable insight into the multiphysical mechanisms in SC-ICP. The future work would be to optimize the pre-concentration of analytes and demonstrate 3D vortex flows in a SC-ICP device.