Issue
EPL
Volume 79, Number 4, August 2007
Article Number 48002
Number of page(s) 6
Section Interdisciplinary Physics and Related Areas of Science and Technology
DOI http://dx.doi.org/10.1209/0295-5075/79/48002
Published online 23 July 2007
EPL, 79 (2007) 48002
DOI: 10.1209/0295-5075/79/48002

Electrostatic interactions of asymmetrically charged membranes

Dan Ben-Yaakov1, Yoram Burak2, David Andelman1, 3 and S. A. Safran3

1  Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University - Ramat Aviv, Tel Aviv 69978, Israel
2  Kavli Institute for Theoretical Physics, University of California - Santa Barbara, CA 93106, USA
3  Department of Materials and Interfaces, Weizmann Institute of Science - Rehovot 76100, Israel


received 7 May 2007; accepted in final form 20 June 2007; published August 2007
published online 23 July 2007

Abstract
We predict the nature (attractive or repulsive) and range (exponentially screened or long-range power law) of the electrostatic interactions of oppositely charged, planar plates as a function of the salt concentration and surface charge densities (whose absolute magnitudes are not necessarily equal). An analytical expression for the crossover between attractive and repulsive pressure is obtained as a function of the salt concentration. This condition reduces to the high-salt limit of Parsegian and Gingell where the interaction is exponentially screened and to the zero salt limit of Lau and Pincus in which the important length scales are the inter-plate separation and the Gouy-Chapman length. In the regime of low salt and high surface charges we predict -for any ratio of the charges on the surfaces- that the attractive pressure is long-ranged as a function of the spacing. The attractive pressure is related to the decrease in counter-ion concentration as the inter-plate distance is decreased. Our theory predicts several scaling regimes with different scaling expressions for the pressure as a function of salinity and surface charge densities. The pressure predictions can be related to surface force experiments of oppositely charged surfaces that are prepared by coating one of the mica surfaces with an oppositely charged polyelectrolyte.

PACS
82.70.-y - Disperse systems; complex fluids.
61.20.Qg - Structure of associated liquids: electrolytes, molten salts, etc..

© Europhysics Letters Association 2007