Ionic cloud distribution close to a charged surface in the presence of salt

¹  Laboratory of Physics and Helsinki Institute of Physics, Helsinki University of Technology P.O. Box 1100, FI-02015 HUT, Espoo, Finland, EU
²  Memphys Center for Biomembrane Physics, Department of Physics and Chemistry, University of Southern Denmark - Campusvej 55, DK-5230 Odense M, Denmark, EU
³  Department of Physics, and Department of Chemistry and Biochemistry, University of California Santa Barbara, CA 93106, USA
⁴  Laboratory of Physical and Structural Biology, National Institutes of Health - Bldg. 9, Bethesda, MD 20892-0924, USA
⁵  Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana - SI-1000, Ljubljana, Slovenia, EU
⁶  Department of Theoretical Physics, J. Stefan Institute - SI-1000, Ljubljana, Slovenia, EU
⁷  Institute of Physics, Tampere University of Technology - P.O. Box 692, FI-33101 Tampere, Finland, EU

Corresponding author: olli.punkkinen@tkk.fi

Received: 28 December 2007
Accepted: 25 March 2008

Abstract

Despite its importance, the understanding of ionic cloud distribution close to a charged macroion under physiological salt conditions has remained very limited especially for strongly coupled systems with, for instance, multivalent counterions. Here we present a formalism that predicts both counterion and coion distributions in the vicinity of a charged macroion for an arbitrary amount of added salt and in both limits of mean field and strong coupling. The distribution functions are calculated explicitly for ions next to an infinite planar charged wall. We present a schematic phase diagram identifying different physical regimes in terms of electrostatic coupling parameter and bulk salt concentration.