Multiphysics Simulation of Ion Concentration Polarization Induced by Nanoporous Membranes in Dual Channel Devices

Abstract

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.

Multiphysics Simulation of Ion Concentration Polarization Induced by a Surface-Patterned Nanoporous Membrane in Single Channel Devices

“…It is noted that our previous simulation results of DC-ICP devices offered the same conclusion of the effect of the charge density on ICP being insignificant in low-EPM conditions. 22 To simulate ICP phenomena more accurately, we assumed a high EPM condition (3×) and repeated the simulations under the same electric potential (5 V) and the membrane charge densities of −0.1, −0.25, −0.5, −0.75, and −1.0 mM. Figure 4c shows the distribution of ion concentrations that drops sharply down to 0.1 mM near the membrane, with the lowest concentration at nearly 0.01 mM along the interface between the membrane and the solution.…”

“…22 In addition, we found that the variation of the EPM of counterions in the nanoporous membrane makes a greater impact on the strength of ICP than the charge density of the membrane. However, DC-ICP devices are unique in that ions are forced to penetrate through the nanoporous membrane, isolating two channels so that it is necessary to study other general models for comprehensive understanding of ICP phenomena.…”

“…22 A fine mesh size (∼10 nm) was applied to the interface between the microchannel and the nanoporous membrane due to the local existence of a space charge layer. A slip boundary condition was applied to the interface for the Navier−Stokes equation because the exact simulation of the fluid flow inside the nanoporous membrane seemed to be currently impossible and its contribution to the perm-selectivity in the membrane could be compensated for by using a high EPM of counterions in the membrane.…”

Ion transport and selectivity in biomimetic nanopores with pH-tunable zwitterionic polyelectrolyte brushes

“…12 Among them, pH-tunable biomimetic nanopores, nanosized pores in solid-state membranes modified with pH-regulated polyelectrolyte (PE) brushes, have attracted more attention due to their potential applications in diverse fields, including energy transduction, 1 ionic gates, 2-5 ionic pumps, 6 nanofluidic diodes 7,8 and biosensors, 9 to name a few. Recent studies strongly suggest that as the size of pores is narrowed to the thickness of electric double layer (EDL), unique ion transport properties, not observed in microscale pores, emerge, such as ion selectivity, 13,14 ion concentration polarization (ICP), [15][16][17] and ion concentration rectification (ICR). Recent studies strongly suggest that as the size of pores is narrowed to the thickness of electric double layer (EDL), unique ion transport properties, not observed in microscale pores, emerge, such as ion selectivity, 13,14 ion concentration polarization (ICP), [15][16][17] and ion concentration rectification (ICR).…”

Ion Concentration Polarization by Bifurcated Current Path

“…In order to describe ICP phenomenon above the protruded nanoporous membrane, we established a numerical model which was based on the three-layer model suggested by Rubinstein and Zaltzman 42 for saving computational costs 43, 44 . The computational domain was depicted in Fig.…”