Comicellization of polystyrene-block-poly(ethylene oxide) with cationic and anionic surfactants in aqueous solutions: Indications and limits

Interaction of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) with catio nic and anionic surfactants was studied using light scattering, sedimentati on in ultracentrifuge, and H-1 NMR. The complex structure of the mixed solu tion containing hybrid micelles, micellar clusters, and supermicellar aggre gates was confirmed by independent experiments. By proton NMR, addition of anionic surfactant, sodium dodecyl sulfate (SDS), to PS-b-PEO solution resu lts in loosening the micelle cores and an increase of the PS molecular mobi lity in the presence of surfactant. At the same time, incorporation of SDS into the block copolymer solution leads to noticeable broadening of the sig nals related to methylene protons of the surfactant, which can be assigned to a decrease of mobility of surfactant alkyl chains "immobilized" on the P S cores. These data along with ultracentrifugation of hybrid solutions cont aining PS-b-PEO and surfactant at various concentrations prove that comicel lization occurs and mixed micelles are formed. However, this phenomenon is observed up to a certain limiting concentration of the surfactant. In the c ase of cetyl pyridinium chloride (CPC), increase of surfactant loading up t o 0.05 mol/L results in the solutions containing CPC micelles along with hy brid micellar clusters and supermicellar aggregates.