 
Summary: Effect of Polyelectrolyte Adsorption on Intercolloidal Forces
Itamar Borukhov, David Andelman,*, and Henri Orland
School of Physics and Astronomy, Raymond and BeVerly Sackler Faculty of Exact Sciences,
TelAViV UniVersity, RamatAViV 69978, TelAViV, Israel, and SerVice de Physique The´orique,
CESaclay, 91191 GifsurYVette Cedex, France
ReceiVed: January 5, 1999§
The behavior of polyelectrolytes between charged surfaces immersed in semidilute solutions is investigated
theoretically. A continuum mean field approach is used for calculating numerically concentration profiles
between two electrodes held at a constant potential. A generalized contact theorem relates the intersurface
forces to the concentration profiles. The numerical results show that overcompensation of the surface charges
by adsorbing polyelectrolytes can lead to effective attraction between equally charged surfaces. Simple scaling
arguments enable us to characterize qualitatively the intersurface interactions as a function of the fraction of
charged monomers p and the salt concentration cb. In the lowsalt regime, we find strong repulsion at short
distances, where the polymers are depleted from the intersurface gap, followed by strong attraction when the
two adsorbed layers overlap. The magnitude of this attraction scales as p1/2
and its dominant length scale is
proportional to a/p1/2
, where a is the monomer size. At larger distances, the two adsorbing surfaces interact
via a weak electrostatic repulsion. For strong polyelectrolytes at high salt concentration, the polymer contribution
to attraction at short distances scales as p/cb
