(703g) Electrostatic Funnel, Ionic Concentration Polarization, and Diffusion Limited Ionic Transport in Charged Membranes

In this presentation, we will explore the characteristics of a phenomenon we have termed “Electrostatic Funnel” (EF) and its interplay with ion concentration polarization and diffusion-limited ionic transport, both well-established concepts in the field.

The EF is a non-equilibrium phenomenon that occurs as a manifestation of charge conservation at the boundary where charged membranes interface with their adjacent solutions. This scenario typically presents a disparity in the concentration of charge carriers on either side of the membrane, leading to a conductivity mismatch at this junction. Contrary to expectations, this mismatch cannot be corrected by merely accelerating the ions in the solution to maintain current continuity, as that would deplete the charge carriers neutralizing the membrane's interior. Instead, an electrostatic potential is droped at the membrane's entrance, creating an “Electrostatic Funnel.” This mechanism effectively adjusts the ion concentration from the diluted external reservoir to the levels necessary for membrane neutralization. Remarkably, it achieves current continuity not by increasing the velocity of charge carriers but by augmenting their concentration. The influence of the EF thus hinges on various factors, including the electrolyte concentration in the reservoir, the membrane's charge density, and ratio of the ionic current sustained by the membrane and the reservoir.

Our findings also reveal that while the EF enhances the “effective” cross-sectional area of the membrane pores, it simultaneously creates a depletion zone of ions within. This latter effect, known as ionic concentration polarization, is recognized for its negative impact on the maximum current a membrane can support, constrained by diffusion-limited transport mechanisms.