The distribution of counterions around polyacrylate chains analyzed by anomalous small-angle X-ray scattering

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

Corresponding author: guenter.goerigk@desy.de

Received: 18 September 2003
Accepted: 18 February 2004

Abstract

The distribution of counterions around negatively charged sodium polyacrylate chains () in aqueous solution was studied by anomalous small-angle X-ray scattering. Different ratios of the concentrations of 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 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 and a distance between neighbouring pearls close to 60 could be established for the collapsed state of the  chains.