Eur. Phys. J. E 4, 131-142
Small-angle X-ray scattering from salt-free solutions of star-branched polyelectrolytes
M. Heinrich1, M. Rawiso1, J.G. Zilliox1, P. Lesieur2 and J.P. Simon31 Institut Charles Sadron, CNRS-ULP, 6 rue Boussingault, 67083 Strasbourg Cedex, France
2 Laboratoire pour l'Utilisation du Rayonnement Electromagnétique, Bât. 209 D, Centre Universitaire Paris-Sud, 91405 Orsay Cedex, France
3 Laboratoire de Thermodynamique et Physico-Chimie Métallurgiques, CNRS-INPG-UJF, BP 75, 38402 Saint Martin d'Hères Cedex, France
rawiso@ics.u-strasbg.fr
(Received 14 May 1999 and Received in final form 15 March 2000)
Abstract
The dispersion state of sodium-sulphonated polystyrene
(NaPSS) star-branched polyelectrolytes was investigated in
salt-free aqueous solutions, by use of the small-angle X-ray
scattering technique. With respect to polystyrene (PS)
star-branched polymers of identical functionality, the ordering
phenomenon occurring in the neighborhood of the overlap
concentration c* is reinforced and observed in a larger range
of concentrations. Moreover, the degree of order is no longer
maximum at c* and is improved as the concentration decreases. The
dispersion state is then mainly controlled by the electrostatic
interaction. A crystalline order should therefore be achieved
with stars of lower functionality, provided the electrostatic
interaction is added to the osmotic repulsion.
On the other hand, unusual scattering patterns are measured for
aqueous solutions of NaPSS star polyelectrolytes. Indeed, a
diffuse scattering is revealed at high angles, in addition to the
regular diffraction rings related to preferred interstar
distances. It is similar to the broad scattering peak produced by
semidilute solutions of NaPSS linear polyelectrolytes and
associated to the electrostatic correlation hole within the
isotropic model. In the dilute regime (c< c*), it is just an
intramolecular characteristic and represents the electrostatic
repulsion between arms belonging to the same star. In the
semidilute regime (c> c*), it also reflects the electrostatic
repulsion between arms of distinct stars. So, as the
concentration increases, it is mainly caused by the
interpenetration of NaPSS stars. Such an observation is in
agreement with the composite structure earlier proposed by Daoud
and Cotton for star semidilute solutions. For c> c*,
NaPSS star aqueous solutions can therefore be pictured as
effective stars immersed in a matrix formed by the overlap of the
arm ends. With respect to the dilute regime, the effective stars
are smaller; the higher the concentration the smaller the size.
61.25.Hq - Macromolecular and polymer solutions.
82.70.-y - Disperse systems.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001