TY - JOUR

T1 - Adsorption of large ions from an electrolyte solution

T2 - A modified Poisson-Boltzmann equation

AU - Borukhov, I.

AU - Andelman, D.

AU - Orland, H.

N1 - Funding Information:
We wish to thank N. Cuvillier and F. Rondelez for sharing with us their experimental results prior to publication and for fruitful discussions. We also benefited from discussions and correspondence with H. Diamant, M.E. Fisher, C. Holm. A.A. Kornyshev, R. Netz, P. Sens and M. Urbakh. Partial support from the US-Israel Binational Foundation (BSF) under grant No. 98-00429, and the Israel Science Foundation founded by the Israel Academy of Sciences and Humanities — Centers of Excellence Program is gratefully acknowledged. One of us (HO) would like to thank the Sackler Institute of Solid State Physics (Tel Aviv University) for a travel grant. IB gratefully acknowledges the support of the Chateaubriand postdoctoral fellowship.

PY - 2000/11/1

Y1 - 2000/11/1

N2 - The behavior of electrolyte solutions close to a charged surface is studied theoretically. A modified Poisson-Boltzmann equation that takes into account the volume excluded by the ions in addition to the electrostatic interactions is presented. In a formal lattice gas formalism the modified Poisson-Boltzmann equation can be obtained from a mean-field approximation of the partition function. In an alternative phenomenological approach, the same equation can be derived by including the entropy of the solvent molecules in the free energy. In order to visualize the effect of steric repulsion, a simple case of a single, highly charged, flat surface is discussed. This situation resembles recent adsorption experiments of large ions onto a charged monolayer. A simple criterion for the importance of the steric effects is expressed in terms of the surface charge density and the size of the ions. It is shown that when these effects are important a saturated layer is formed near the surface. A modified Grahame equation relating the ion concentration at the surface to the surface charge density is obtained.

AB - The behavior of electrolyte solutions close to a charged surface is studied theoretically. A modified Poisson-Boltzmann equation that takes into account the volume excluded by the ions in addition to the electrostatic interactions is presented. In a formal lattice gas formalism the modified Poisson-Boltzmann equation can be obtained from a mean-field approximation of the partition function. In an alternative phenomenological approach, the same equation can be derived by including the entropy of the solvent molecules in the free energy. In order to visualize the effect of steric repulsion, a simple case of a single, highly charged, flat surface is discussed. This situation resembles recent adsorption experiments of large ions onto a charged monolayer. A simple criterion for the importance of the steric effects is expressed in terms of the surface charge density and the size of the ions. It is shown that when these effects are important a saturated layer is formed near the surface. A modified Grahame equation relating the ion concentration at the surface to the surface charge density is obtained.

UR - http://www.scopus.com/inward/record.url?scp=0034315255&partnerID=8YFLogxK

U2 - 10.1016/S0013-4686(00)00576-4

DO - 10.1016/S0013-4686(00)00576-4

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AN - SCOPUS:0034315255

SN - 0013-4686

VL - 46

SP - 221

EP - 229

JO - Electrochimica Acta

JF - Electrochimica Acta

IS - 2-3

ER -