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. Goerigk31 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
Matthias.Ballauff@chemie.uni-karlsruhe.de
(Received: 27 July 2001 and Received in final form 27 March 2002)
Abstract
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
. 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
