J. Phys. II France
Volume 6, Numéro 11, November 1996
Page(s) 1607 - 1613
DOI: 10.1051/jp2:1996151
J. Phys. II France 6 (1996) 1607-1613

Structure of Salt-free Linear Polyelectrolytes in the Debye-Hückel Approximation

Mark J. Stevens1 and Kurt Kremer2

1  MS 1111, Sandia National Laboratory, Albuquerque, NM 87185, USA
2  Max Planck Institut für Polymerforschung, Postfach 3148, 55021 Mainz, Germany

(Received 6 May 1996, revised 21 June 1996, accepted 31 July 1996)

We examine the effects of the common Debye-Hückel approximation used in theories of polyelectrolytes. Molecular dynamics simulations using the Debye-Hückel pair potential of salt-free polyelectrolytes have been performed. The results of these simulations are compared to earlier "Coulomb" simulations which explicitly treated the counterions. We report here the comparisons of the osmotic pressure, the end-to-end distance and the single chain structure factor. In the dilute regime the Debye-Hückel chains are more elongated than the Coulomb chains implying that the counterion screening is stronger than the Debye-Hückel prediction. Like the Coulomb chains the Debye-Hückel chains contract significantly below the overlap density in contradiction to all theories. Entropy thus plays an important and sorely neglected role in theory.

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