Effect of Polyion Charge Density on the Morphology of Nanostructures in Polyelectrolyte−Surfactant Complexes

The poly(acrylate) (PA)/surfactant and poly(methacrylic acid) (PMA)/surfactant complexes were investigated by synchrotron X-ray scattering at various degrees of neutralization, α, of the polyion and at a fixed surfactant to polyion charge ratio. At low α-values, the surfactant organizes into polymer-induced micelles that are attracted by the polymer through hydrophobic interactions. This is followed by a formation of a Pm3n cubic structure at higher α-values as a consequence of very strong electrostatic attractions between the polyion and charged surfactant aggregates. From the position of the maxima in the scattering curves, the characteristic distance d was obtained. In PA/surfactant complexes, d varies linearly with α. This is an indication of a smooth expansion of the PA chain upon neutralization. In PA/dodecylpyridinium chloride (DPC) solutions, d increases from 30.2 A at α = 0 to 36.6 A at α = 1, and correspondingly d increases from 44.1 to 51 A in the PA/CPC case. The d-value at α = 0 almost matche...