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Soft Matter and Biological Physics

Eur. Phys. J. E 1, 203-214

Beyond Poisson-Boltzmann: Fluctuation effects and correlation functions

R.R. Netz1 - H. Orland2

1 Max-Planck-Institut für Kolloid- und Grenzflächenforschung, 14424 Potsdam, Germany
2 Service de Physique Théorique, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France


Received 8 February 1999 and Received in final form 15 May 1999

We formulate the exact non-linear field theory for a fluctuating counter-ion distribution in the presence of a fixed, arbitrary charge distribution. The Poisson-Boltzmann equation is obtained as the saddle-point of the field-theoretic action, and the effects of counter-ion fluctuations are included by a loop-wise expansion around this saddle point. The Poisson equation is obeyed at each order in this loop expansion. We explicitly give the expansion of the Gibbs potential up to two loops. We then apply our field-theoretic formalism to the case of a single impenetrable wall with counter ions only (in the absence of salt ions). We obtain the fluctuation corrections to the electrostatic potential and the counter-ion density to one-loop order without further approximations. The relative importance of fluctuation corrections is controlled by a single parameter, which is proportional to the cube of the counter-ion valency and to the surface charge density. The effective interactions and correlation functions between charged particles close to the charged wall are obtained on the one-loop level.

82.70.-y Disperse systems - 61.20.Qg Structure of associated liquids: electrolytes, molten salts, etc. - 82.45.+z Electrochemistry and electrophoresis

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