Ion Distributions near a Liquid-Liquid Interface

Abstract

Mean field theories of ion distributions, such as the Gouy-Chapman theory that describes the distribution near a charged planar surface, ignore the molecular-scale structure in the liquid solution. The predictions of the Gouy-Chapman theory vary substantially from our x-ray reflectivity measurements of the interface between two electrolyte solutions. Molecular dynamics simulations, which include the liquid structure, were used to calculate the potential of mean force on a single ion. We used this potential of mean force in a generalized Poisson-Boltzmann equation to predict the full ion distributions. These distributions agree with our measurements without any adjustable parameters.

Molecular electrocatalysis at soft interfaces

“…Here, the Gibbs energy of transfer from water to 1,2-DCE of Cl À is equal to 51 AE 4 kJ mol À1 and that of BA + equal to À67 AE 4 kJ mol À1 5 such that the potential window is limited by the transfer of chloride. When using LiSO 4 instead of LiCl, the potential window can be extended, as sulfate ions are more hydrophilic than chloride. All in all, in such a system the potential window is equal to about 1 Volt as shown in Fig.…”

Ion Dynamics in Cationic Lipid Bilayer Systems in Saline Solutions

“…4 The average ion distribution in the vicinity of a charged surface is often described using the Poisson-Boltzmann theory, 5,6 a mean-field approximation treating ions implicitly as an ion cloud. The theory neglects fluctuations and correlations, the finite size of ions, and the discreteness of solvent, and therefore has obvious restrictions; pronounced deviations from its predictions emerge at the limit of high ion concentrations, [7][8][9] as well as in the presence of large surface charge densities or multivalent ions. [10][11][12][13][14] We note that there are a number of theories that go beyond the Poisson-Boltzmann approximation.…”

Electric Double-Layer Structure in Primitive Model Electrolytes: Comparing Molecular Dynamics with Local-Density Approximations

“…ex (8) which, when nondimensionalized by 2qen B , is given by (13) Closing the LDA description requires a form for the excess chemical potentials μẽ x ± , after which the LDA equations can be solved self-consistently by imposing constraints on the electrostatic potential at the charged interface (14) and in the bulk…”

“…Despite these well-known shortcomings, LDA models have been proposed to treat shortranged enthalpic 20 and steric interactions between equisized 21,22 and asymmetric 23 ions for ionic liquids, 24 electrochemical cells, 6,13 and liquid−liquid interfaces. 8,10 We recently showed that all EDLs described by any particular LDA have self-similar scaling and thus collapse onto a single master curve when plotted against suitably derived similarity coordinates. 25 Such similarity coordinates can be derived directly from experimentally or computationally determined EDL profiles, without assuming any particular form for a LDA.…”

“…EDLs play a central role in colloidal 1 and polyelectrolyte science, 2 micro-and nanofluidics, 3 surface conductivity, 4 "blue energy" systems, 5 and in electric double-layer capacitors 6 that store energy electrochemically across the EDL. Detailed ion density profiles within EDLs have been measured experimentally using various techniques and materials, 7 e.g., from X-ray reflectivity measurements of liquid−liquid interfaces 8,9 and Langmuir monolayers. 10 Rational design and engineering of EDL capacitors, 11 electrokinetic flows, 12 or capacitive deionization systems 13−15 require accurate double-layer models of electrolytic and ionic liquid systems.…”