Supramolecular structures in aqueous solutions of rigid polyelectrolytes with monovalent and divalent counterions

Dodecyl-substituted poly(p-phenylene) sulfonates (PPPS), which are models of rodlike polyelectrolytes, form cylindrical micelles in aqueous solutions. The effect of different counterions on the association behavior of PPPS in water is investigated by isotropic and anisotropic dynamic light scattering. PPPS of M-W,M-p = 21 x 10(3) g/mol forms micelles of a weight-average length of 600-700 nm and 15-20 individual chains per cross section in very dilute solution. The exact values are depending on whether H+ or Na+ serves as counterion and whether neutral salt is present or not. The form factor of the formed objects can be analyzed in terms of a weakly bending rod (Koyama's form factor). Micelles of the same polymer in the presence of Ca-2(+) or Ba-2(+) exhibit approximately the same length but have around 50 chains per cross section; they are interpreted as defined bundles of a few micelles exhibiting on average the shape of a weakly bending rod. The inferred structures are supported by images of transmission electron microscopy.