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

Abstract

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...

Scaling for rectification of bipolar nanopores as a function of a modified Dukhin number: the case of 1:1 electrolytes

“…For the diffusion coefficient profile, D i (r), we use a piecewise constant function, where the value in the baths is 1.334 × 10 −9 m 2 s −1 for both ionic species, while it is the tenth of that inside the pore, D pore i , as in our earlier works. 12,13,17,24,26,51 These particular choices do not qualitatively affect our conclusions.…”

“…This is more apparent for multivalent electrolytes where ionic correlations are strong (data not shown). 26 Here, we are restricted to the question of why changing σ, H, or U has similar effects on rectification for a given value of c and R. To answer this question, we need to examine more detailed results provided by the simulations, e.g., concentration, electrical potential, and electrochemical potential profiles.…”

“…It has already been realized and discussed in numerous several publications of ours 26,[69][70][71][72][73][74][75] that the conductance of the pore is better described by the reciprocal of the concentration than the concentration itself as soon as the resistance of the pore is determined by the low-resistance elements of the consecutive segments of the pore along the z-axis that are considered as resistors connected in series. This approach works if there are so deep depletion zones in the pore that the importance of the peaks are dwarfed compared to them.…”

“…Coions, however, can also be excluded from wide pores if the screening length of the electrolyte is large enough compared to the radius of the pore. 13,17,24,26,[74][75][76][77][78][79] An elegant quantification of this idea is the slope conductance approach 69,70,72 in which we assume that the chemical potential is constant in the radial dimension (µ i (z, r) ≈ µ i (z)) inside the pore. The current carried by an ionic species i, I i , is computed from the crosssectional integral of j i (z, r), inside the pore.…”

“…study, 26 where a non-monotonic σ-dependence of rectification was observed for electrolytes containing multivalent ions (2:2, 2:1, 3:1). This behavior is caused by strong ionic correlations resulting in charge inversion, overcharging, and anion leakage.…”