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

We present a study of the clustering counterion of iodine counterions around a cationic rodlike polyelectrolyte in aqueous solution. The novel synthetic polyelectrolyte used here has a poly( p -phenylene) backbone and can be considered as rodlike in good approximation. The correlation of the counterions with the macroion in aqueous solution is determined by small-angle x-ray scattering which is mainly sensitive to the I¯ counterions. The measured intensities agree with the prediction of the Poisson-Boltzmann cell model if radius of the macroion is treated as an adjustable parameter. The small value of radius of the macroion found here shows that the cell model underestimates the correlation of the counterions to the macroion.