Europhys. Lett.
Volume 66, Number 3, May 2004
Page(s) 331 - 337
Section General
Published online 01 April 2004
Europhys. Lett., 66 (3) , pp. 331-337 (2004)
DOI: 10.1209/epl/i2003-10215-y

The distribution of $\chem{Sr^{2+}}$ counterions around polyacrylate chains analyzed by anomalous small-angle X-ray scattering

G. Goerigk1, R. Schweins2, K. Huber3 and M. Ballauff4

1  Institut für Festkörperforschung, Forschungszentrum Jülich Postfach 1913, D-52425, Germany
2  Institut Laue-Langevin, Large Scale Structures Group B.P. 156, F-38042 Grenoble CEDEX 9, France
3  Universität-GH Paderborn, Fachbereich 13 Chemie und Chemietechnik Warburger Str. 100, D-33098 Paderborn, Germany
4  Universität Karlsruhe, Polymer-Institut Kaiserstr. 12/PF 6980, D-76128 Karlsruhe, Germany

(Received 18 September 2003; accepted in final form 18 February 2004)

The distribution of $\chem{Sr}$ counterions around negatively charged sodium polyacrylate chains ( $\chem{NaPA}$) in aqueous solution was studied by anomalous small-angle X-ray scattering. Different ratios of the concentrations of $\chem{SrCl_2/[NaPA]}$ reveal dramatic changes in the scattering curves. At the lower ratio the scattering curves indicate a coil-like behavior, while at the higher ratio the scattering curves are contracted to smaller q-values, caused by the collapse of the $\chem{NaPA}$ coil. The form factor of the scattering contribution of the counterions was separated and analyzed. For the scattering curves of the collapsed chains, this analysis agrees with the model of a pearl necklace, consisting of collapsed sphere-like subdomains which are connected by stretched chain segments. An averaged radius of the pearls of 19 $\un{nm}$ and a distance between neighbouring pearls close to 60 $\un{nm}$ could be established for the collapsed state of the $\chem{NaPA}$ chains.

07.85.Qe - Synchrotron radiation instrumentation.
61.10.Eq - X-ray scattering (including small-angle scattering).
82.35.Rs - Polyelectrolytes.

© EDP Sciences 2004