Tomaž Urbič, Marija Bešter Rogač and Andrej Jamnik
Faculty of Chemistry and Chemical Technology, University of Ljubljana,
Aškerčeva 5, 1000 Ljubljana, Slovenia
Jernej Stare
National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia
 

Abstract
A theoretical study of small angle X-ray scattering on model rodlike polyelec-
trolytes containing a mixture of univalent (Li + ) and divalent (Sr 2+ ) counte-
rions is presented. Scattering functions, based on the electron density con-
trast relative to solvent, were computed. The distribution of the excess elec-
tron density around the polyion was determined by numerical solving of the
Poisson-Boltzmann (PB) equation within the cell model. For the systems
containing only one kind of counterions analytical solutions of the PB equa-
tion were also used. Such amodel can be applied to rigid polymeric entities
with rodlike shape, the entities being either individual polymers or small con-
stituents of otherwise exible polymers. We studied the in uence of both the
polyion and its ionic atmosphere on the scattering function. As expected, the
contribution of the polyion to the scattering function is signicant while the
contribution of the ionic atmosphere increases with increasing the fraction of
strontium ions with a higher contrast in electron density against the solvent.