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J Colloid Interface Sci. 2015 Sep 15;454:187-91. doi: 10.1016/j.jcis.2015.05.018. Epub 2015 May 16.

The interaction of electric field and hydrostatic pressure in an electrical double layer: A simple "first principle" model that accounts for the finite sizes of counterions.

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N.N. Semenov Institute of Chemical Physics RAS, Kosygina 4, 119991 Moscow, Russian Federation. Electronic address:


A simple model describing the influence of ion size in the electrical double layer (EDL) near a highly charged plane is proposed here. This model is based on the Poisson-Boltzmann equation with a single additional term representing the mechanical response of bulky ions to hydrostatic pressure. This pressure is produced by Coulomb forces, and increases to several kilobars in the vicinity of a highly charged plane. Numerical simulations demonstrate close packing as a limit for counterion concentrations. Differential capacity reaches maximum at 0.1-0.3V and remains reasonably small in wide range of potentials.


Electrical double layer; Gouy–Chapman model; Hydrostatic pressure; Ion size effect; Poisson–Boltzmann equation


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