dorsal/arxiv
View SchemaSteric effects in the dynamics of electrolytes at large applied voltages: I. Double-layer charging
| Authors | Mustafa Sabri Kilic, Martin Z. Bazant, Armand Ajdari |
|---|---|
| Categories | |
| ArXiv ID | physics/0611030 |
| URL | https://arxiv.org/abs/physics/0611030 |
Abstract
The classical Poisson-Boltzmann (PB) theory of electrolytes assumes a dilute solution of point charges with mean-field electrostatic forces. Even for very dilute solutions, however, it predicts absurdly large ion concentrations (exceeding close packing) for surface potentials of only a few tenths of a volt, which are often exceeded, e.g. in microfluidic pumps and electrochemical sensors. Since the 1950s, several modifications of the PB equation have been proposed to account for the finite size of ions in equilibrium, but in this two-part series, we consider steric effects on diffuse charge dynamics (in the absence of electro-osmotic flow). In this first part, we review the literature and analyze two simple models for the charging of a thin double layer, which must form a condensed layer of close-packed ions near the surface at high voltage. A surprising prediction is that the differential capacitance typically varies non-monotonically with the applied voltage, and thus so does the response time of an electrolytic system. In PB theory, the capacitance blows up exponentially with voltage, but steric effects actually cause it to decrease above a threshold voltage where ions become crowded near the surface. Other nonlinear effects in PB theory are also strongly suppressed by steric effects: The net salt adsorption by the double layers in response to the applied voltage is greatly reduced, and so is the tangential "surface conduction" in the diffuse layer, to the point that it can often be neglected compared to bulk conduction (small Dukhin number).
{
"annotation_id": "ca9484a7-c4d9-4414-b5b8-3956a39d142f",
"date_created": "2026-03-02T18:01:13.866000Z",
"date_modified": "2026-03-02T18:01:13.866000Z",
"file_hash": "545c0b6d3edafc19e34a4395c5bcce5931d29ed5e3e9b1947b19e92ccda41080",
"private": false,
"record": {
"abstract": "The classical Poisson-Boltzmann (PB) theory of electrolytes assumes a dilute\nsolution of point charges with mean-field electrostatic forces. Even for very\ndilute solutions, however, it predicts absurdly large ion concentrations\n(exceeding close packing) for surface potentials of only a few tenths of a\nvolt, which are often exceeded, e.g. in microfluidic pumps and electrochemical\nsensors. Since the 1950s, several modifications of the PB equation have been\nproposed to account for the finite size of ions in equilibrium, but in this\ntwo-part series, we consider steric effects on diffuse charge dynamics (in the\nabsence of electro-osmotic flow). In this first part, we review the literature\nand analyze two simple models for the charging of a thin double layer, which\nmust form a condensed layer of close-packed ions near the surface at high\nvoltage. A surprising prediction is that the differential capacitance typically\nvaries non-monotonically with the applied voltage, and thus so does the\nresponse time of an electrolytic system. In PB theory, the capacitance blows up\nexponentially with voltage, but steric effects actually cause it to decrease\nabove a threshold voltage where ions become crowded near the surface. Other\nnonlinear effects in PB theory are also strongly suppressed by steric effects:\nThe net salt adsorption by the double layers in response to the applied voltage\nis greatly reduced, and so is the tangential \"surface conduction\" in the\ndiffuse layer, to the point that it can often be neglected compared to bulk\nconduction (small Dukhin number).",
"arxiv_id": "physics/0611030",
"authors": [
"Mustafa Sabri Kilic",
"Martin Z. Bazant",
"Armand Ajdari"
],
"categories": [
"physics.chem-ph"
],
"title": "Steric effects in the dynamics of electrolytes at large applied voltages: I. Double-layer charging",
"url": "https://arxiv.org/abs/physics/0611030"
},
"schema_id": "dorsal/arxiv",
"source": {
"execution_id": "c4b6b94b-7a16-49f2-a5a3-6717ab74d88c",
"id": "arXiv Dataset IDs",
"type": "Model",
"variant": "snapshot-2026-03-01",
"version": "0.1.0"
},
"user_id": 1000002
}