Investigation of structures in polyelectrolyte/surfactant complexes by X-ray scattering

Structural investigation in systems of anionic polyelectrolytes and dodecyl - (DPC) and cetylpyridinium chlorides (CPC were performed at various surfac tant to polyelectrolyte (S/P) ratios using synchrotron X-ray scattering. Th e polyelectrolytes used were sodium poly(styrenesulfonate) (NaPSS), poly(ac rylate) (NaPA), and poly(methacrylate) (NaPMA). From the Bragg peaks emergi ng in the scattering curves, different types of organization of the surfact ant in conjunction with the polyion are proposed. They depend on the surfac tant chain length, on the polyelectrolyte chemistry, and on the S/P value:. (1) NaPSS/DPC tall S/P values), NaPSS/CPC (S/P < 1), and NaPA(NaPMA)/DPC ( S/P < 1) complexes produced a micellelike organization of the surfactant al ong the polyion chain. The NaPSS-induced micelle is smaller in size than th e ordinary one because of the inclusion of the aromatic rings on the PSS ch ain into the hydrophobic interior of the micelle. The size of the ordered e lements in complexes with the hydrophilic NaPA and NaPMA corresponds to the radius of an ordinary globular micelle together with the thickness of the polyelectrolyte chain that surrounds it. (2) In NaPSS/CPC precipitate (SIP I), a hexagonal phase is observed with a unit cell parameter equal to 39.5 Angstrom. (3) The multiple reflections in the scattering curves of NaPA(NaP MA)/DPC complexes with S/P greater than or equal to 1 and of NaPA(NaPMA)/CP C ones for all S/P values point to some cubic structure. The cell constants of these mesophases correspond approximately to 2.5 diameters of a globula r surfactant micelle. (4) In addition to a cubic phase, a well-pronounced h exagonal phase with a unit cell parameter of 40.5 Angstrom develops in the NaPA/CPC case with SIP greater than or equal to 1.