Attraction between like-charge surfaces in polar mixtures

Department of Chemical Engineering and The Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev - 84105 Beer-Sheva, Israel

^a tsori@bgu.ac.il

Received: 26 April 2011
Accepted: 16 June 2011

Abstract

We examine the force between two charged surfaces immersed in aqueous mixtures having a coexistence curve. For a homogeneous water-poor phase, as the distance between the surfaces is decreased, a water-rich phase condenses at a distance D_t in the range 1–100 nm. At this distance the osmotic pressure can become negative leading to a long-range attraction between the surfaces. The osmotic pressure vanishes at a distance D_e<D_t, representing a very deep metastable or globally stable energetic state. We give analytical and numerical results for D_t and D_e on the Poisson-Boltzmann level.