Investigations of rodlike polyelectrolytes in solution by small-angle x-ray scattering

We present a study of the clustering counterion of iodine counterions aroun d a cationic rodlike polyelectrolyte in aqueous solution. The novel synthet ic polyelectrolyte used here has a poly(p-phenylene) backbone and can be co nsidered as rodlike in good approximation. The correlation of the counterio ns with the macroion in aqueous solution is determined by small-angle x-ray scattering which is mainly sensitive to the I- counterions. The measured i ntensities agree with the prediction of the Poisson-Boltzmann cell model if radius of the macroion is treated as an adjustable parameter. The small va lue of radius of the macroion found here shows that the cell model underest imates the correlation of the counterions to the macroion.