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Polyelectrolyte adsorption: Chemical and electrostatic interactions Adi Shafir* and David Andelman

Summary: Polyelectrolyte adsorption: Chemical and electrostatic interactions
Adi Shafir* and David Andelman
School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University,
Ramat Aviv, Tel Aviv 69978, Israel
(Received 3 December 2003; revised manuscript received 24 August 2004; published 28 December 2004)
Mean-field theory is used to model polyelectrolyte adsorption and the possibility of overcompensation of
charged surfaces. For charged surfaces that are also chemically attractive, the overcharging is large in high salt
conditions, amounting to 2040 % of the bare surface charge. However, full charge inversion is not obtained in
thermodynamical equilibrium for physical values of the parameters. The overcharging increases with addition
of salt, but does not have a simple scaling form with the bare surface charge. Our results indicate that a more
evolved explanation is needed in order to understand polyelectrolyte multilayer buildup. For strong polymer-
repulsive surfaces, we derive simple scaling laws for the polyelectrolyte adsorption and overcharging. We show
that the overcharging scales linearly with the bare surface charge, but its magnitude is very small in comparison
to the surface charge. In contrast with the attractive surface, here the overcharging is found to decrease
substantially with addition of salt. In the intermediate range of weak repulsive surfaces, the behavior with
addition of salt crosses over from increasing overcharging (at low ionic strength) to a decreasing one (at high
ionic strength). Our results for all types of surfaces are supported by full numerical solutions of the mean-field
DOI: 10.1103/PhysRevE.70.061804 PACS number(s): 82.35.Gh, 82.35.Rs, 61.41. e


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


Collections: Materials Science; Physics