 
Summary: Electrochimica Acta 46 (2000) 221229
Adsorption of large ions from an electrolyte solution: a
modified PoissonBoltzmann equation
I. Borukhov a,1
, D. Andelman b,
*, H. Orland c
a
Unite´ mixte de Recherche CNRS/Elf Atochem (UMR 167), 95 rue Danton, B.P. 108, 92303 Le6alloisPerret Cedex, France
b
School of Physics and Astronomy, Raymond and Be6erly Sackler Faculty of Exact Sciences, Tel A6i6 Uni6ersity,
69978 Ramat A6i6, Israel
c
Ser6ice de Physique The´orique, CESaclay, 91191 GifsurY6ette Cedex, France
Received 12 January 2000
Abstract
The behavior of electrolyte solutions close to a charged surface is studied theoretically. A modified PoissonBoltz
mann 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 PoissonBoltzmann equation can be obtained from a
meanfield 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
