Angstrom-scale ionic streaming when electrical double-layer concept fails

TL;DR

This study reveals that ionic streaming conductance at the Angstrom scale depends on pressure and channel size, challenging traditional electrical double-layer models and highlighting the role of Coulomb interactions and counterion dynamics.

Contribution

It uncovers pressure-dependent ionic streaming conductance at Angstrom-scale channels and introduces a stochastic model to explain the transition from nonlinear to linear regimes.

Findings

Streaming conductance becomes pressure dependent in Angstrom channels.

A threshold pressure is needed for streaming current to emerge.

The phenomenon weakens and disappears as channel radius exceeds 2 nm.

Abstract

A knowledge gap exists for flows and transport phenomena at the Angstrom scale when the Poisson Nernst Planck equation based on the concept of electrical double layer (EDL) fails. We discovered that streaming conductance becomes pressure dependent in Angstrom channels using latent track membranes. The streaming current emerges only when the applied pressure exceeds a threshold value, which is inconsistent with the existing knowledge as a constant. With increasing channel size, we found that the pressure dependent streaming conductance phenomenon weakens and vanishes into a constant streaming conductance regime when the mean channel radius exceeds 2 nm. The effective surface potential derived from the stream conductance that divides conduction anomalously increases as the channel narrows. We suspect the pressure dependent streaming current is due to the reinforced Coulomb interaction between counterions and deprotonated carboxyl groups at the surface, which is close to the ion channel but different from the electrified 2D materials. The streaming current emerged due to hydrodynamic friction when the counterions were released from the surface. We approximated the stochastic process of counterion dissociation by 1D Kramer escape theory framework and defined the Damkohler Number to describe the transition from nonlinear streaming conductance regime to linear regime as functions of applied pressure and channel radius and well explained the enhanced effective surface potential in confinement.