Rectification of bipolar nanopores in multivalent electrolytes: effect of charge inversion and strong ionic correlations

Bipolar nanopores have powerful rectification properties due to the asymmetry in the charge pattern on the wall of the nanopore. In particular, bipolar nanopores have positive and negative surface charges along the pore axis. Rectification is strong if the radius of the nanopore is small compared to...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2020-09, Vol.22 (34), p.1933-1945
Main Authors: Fertig, Dávid, Valiskó, Mónika, Boda, Dezsö
Format: Article
Language:English
Subjects:
Computer simulation
Correlation
Depletion
Electrolytes
Porosity
Surface charge
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Summary:Bipolar nanopores have powerful rectification properties due to the asymmetry in the charge pattern on the wall of the nanopore. In particular, bipolar nanopores have positive and negative surface charges along the pore axis. Rectification is strong if the radius of the nanopore is small compared to the screening length of the electrolyte so that both cations and anions have depletion zones in the respective regions. The depths of these depletion zones is sensitive to sign of the external voltage. In this work, we are interested in the effect of the presence of strong ionic correlations (both between ions and between ions and surface charge) due to the presence of multivalent ions and large surface charges. We show that strong ionic correlations cause leakage of the coions, a phenomenon that is absent in mean field theories. In this modeling study, we use both the mean-field Poisson-Nernst-Planck (PNP) theory and a particle simulation method, Local Equilibrium Monte Carlo (LEMC), to show that phenomena such as overcharging and charge inversion cannot be reproduced with PNP, while LEMC is able to produce nonmonotonic dependence of currents and rectification as a function of surface charge strength. The conductance properties of bipolar nanopores change non-monotonically with surface charge in the presence of multivalent ions due to charge inversion.
ISSN:1463-9076
1463-9084
DOI:10.1039/d0cp03237a