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Soft Matter and Biological Physics

Eur. Phys. J. E 8, 299-309 (2002)
DOI: 10.1140/epje/i2001-10105-8

The distribution of counterions around synthetic rod-like polyelectrolytes in solution

A study by small-angle X-ray scattering and by anomalous small-angle X-ray scattering
B. Guilleaume1, J. Blaul1, M. Ballauff1, M. Wittemann2, M. Rehahn2 and G. Goerigk3

1  Polymer-Institut, Universität Karlsruhe, Kaiserstrasse 12, 76128 Karlsruhe, Germany
2  Institut für Makromolekulare Chemie, Technische Universität Darmstadt, Petersenstrasse 22, 64287 Darmstadt, Germany
3  Institut für Festkörperforschung, Forschungszentrum Jülich, Postfach 1913, 52425 Jülich, Germany


(Received: 27 July 2001 and Received in final form 27 March 2002)

An investigation of the radial distribution of the counterions of a synthetic rodlike polyelectrolyte in aqueous solution is presented. The cationic polyelectrolyte used here has a poly(p-phenylene) backbone. For typical molecular weights the macroion comprises approximately one persistence length (ca. 20 nm) and effects of finite stiffness may be disregarded. Each repeating unit bears four charges which leads to a charge parameter of $\xi = 6.65$. The distribution of the iodide counterions around this highly charged macroion is studied by small-angle X-ray scattering (SAXS) in dilute aqueous solution. These investigations are supplemented by measurements using anomalous small-angle X-ray scattering (ASAXS) that furnishes additional information about the contrast of the macroion. Data taken at high scattering angles give indication for contributions caused by the longitudinal fluctuations of the counterions. After correction for this effect the experimental results are compared to intensities calculated by use of the Poisson-Boltzmann (PB)-cell model. It is found that the PB-cell model describes the corrected data at intermediate and high scattering angles. Deviations at low scattering angle are attributed to the mutual interaction of the rod-like polyelectrolyte that can be described in terms of an effective structure factor. Data taken at lowest scattering angles point to a weak attraction between the rod-like macroions.

82.35.Rs - Polyelectrolytes.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002