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Discrete aqueous solvent effects and possible attractive forces and D. Andelmanb)

Summary: Discrete aqueous solvent effects and possible attractive forces
Y. Buraka)
and D. Andelmanb)
School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences,
Tel Aviv University, Tel Aviv 69 978, Israel
Received 11 July 2000; accepted 18 October 2000
We study discrete solvent effects on the interaction of two parallel charged surfaces in ionic aqueous
solution. These effects are taken into account by adding a bilinear nonlocal term to the free energy
of Poisson≠Boltzmann theory. We study numerically the density profile of ions between the two
plates, and the resulting interplate pressure. At large plate separations the two plates are decoupled
and the ion distribution can be characterized by an effective Poisson≠Boltzmann charge that is
smaller than the nominal charge. The pressure is thus reduced relative to Poisson≠Boltzmann
predictions. At plate separations below 20 Ň the pressure is modified considerably, due to the
solvent mediated short-range attraction between ions in the system. For high surface charges this
contribution can overcome the mean-field repulsion giving rise to a net attraction between the plates.
© 2001 American Institute of Physics. DOI: 10.1063/1.1331569
Aqueous ionic solutions are abundant in biological and
chemical systems. Often they play a prominent role in deter-
mining the properties of charged macromolecules that are


Source: Andelman, David - School of Physics and Astronomy, Tel Aviv University


Collections: Materials Science; Physics