J. Phys. II France
Volume 7, Numéro 3, March 1997
Page(s) 449 - 458
DOI: 10.1051/jp2:1997137
J. Phys. II France 7 (1997) 449-458

Structure of Weakly Charged Polyelectrolyte Brushes: Monomer Density Profiles

O.V. Borisov1 and E.B. Zhulina2

1  Max-Plank-Institut für Polymerforschung, Postfach 3148, 55021 Mainz, Germany
2  University of Pittsburgh, Materials Science and Engineering Department, Pittsburgh PA 15261, USA

(Received 10 May 1996, revised 27 September 1996, accepted 9 December 1996)

The internal structure (the monomer density profiles) of weakly charged polyelectrolyte brushes of different morphologies has been analyzed on the basis of the self-consistent-field approach. In contrast to previous studies based on the local electroneutrality approximation valid for sufficiently strongly charged or densely grafted ("osmotic") brushes we consider the opposite limit of sparse brushes which are unable to retain the counterions inside the brush. We have shown that an exact analytical solution of the SCF-equations is available in the case of a planar brush. In contrast to Gaussian monomer density profile known for "osmotic" polyelectrolyte brushes we have found that weakly charged brushes are characterized by constant monomer density. At the same time free ends of grafted polyions are distributed throughout the brush. Thus, the structural cross-over between polyelectrolyte "mushrooms" and dense brush regimes is established.

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