Nanoscale supramolecular structures in the gels of poly(diallyldimethylammonium chloride) interacting with sodium dodecyl sulfate

A highly ordered supramolecular structure is formed in the polyelectrolyte−surfactant complex between the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic network of poly(diallyldimethylammonium chloride) (PDADMACl). From small-angle X-ray scattering (SAXS), the complexes between PDADMACl and SDS were shown to exhibit a hexagonal type of microstructure which is different from that of pure SDS. A d spacing of 3.7 nm corresponding to the interdistance between SDS aggregates in the gel network was obtained. The intensity of the diffraction peaks and the degree of order increased with increasing initial SDS concentration and charge content of the PDADMACl gels. The diffraction peaks were broadened when the concentration of SDS in the external solution phase was higher than its critical micelle concentration (cmc). The SAXS profiles were unexpectedly independent of the degree of cross-linking of the PDADMACl gels in the range of 0.5−2%.