Ion transport in a pH-regulated conical nanopore filled with a power-law fluid

Extending previous electrokinetic analyses based on a Newtonian fluid to power-law fluids, we investigate the behaviors of the ion current rectification (ICR) and the ion selectivity S of a conical nanopore having a pH-regulated surface. The bulk salt concentration Cbulk, the solution pH, and the power-law index n are examined in detail for their influences on these behaviors. We show that the ICR ratio for the case where pH is lower than the isoelectric point (IEP) of the nanopore surface is different both quantitatively and qualitatively from that for the case where pH > IEP. The relative magnitude of the ICR ratio as n varies depends largely on the level of Cbulk. In contrast, S (pH IEP), where | S | decreases with increasing Cbulk and/or decreasing n. In addition, S is very sensitive to n, for example, a decrease of n from 1.0 (Newtonian fluid) to 0.9 (pseudoplastic fluid) can yield a 245% increase in S at Cbulk = 100 mM. Implying that the performance of ion separation can be improved by tuning the fluid viscosity. Mechanisms are proposed for explaining the observed behaviors in the ICR ratio.