H-1 and H-2 NMR studies of poly(acrylate) and poly(sodium styrenesulfonate) interactions with cationic surfactant micelles

Anionic polyelectrolyte interactions with mixed cationic/zwitterionic surfactant micelles have been investigated using H-1 NMR and H-2 NMR. The degree of electrostatic complex formation could be quantified separately, simultaneously, and independently for the cationic surfactant cetyltrimethylammonium bromide and the zwitterionic surfactant hexadecylphosphocholine via the intensity changes produced in the quaternary methyl proton resonances in the H-1 NMR spectrum of mixtures of the two surfactants. The overall anion:cation charge ratio regulated the degree of complex formation, independent of the cationic/zwitterionic surfactant ratio. The maximum degree of complex formation always occurred at a 1:1 ratio of polyelectrolyte anionic to surfactant cationic charge. The nature of the cationic surfactant's counterion was irrelevant. Poly(acrylate) (PA), a relatively flexible polyelectrolyte, produced phase-separated complexes resistant to redissolution, while poly(sodium styrenesulfonate) (PSSS), a relatively stiff polyelectrolyte, produced complexes which readily redissolved. The H-1 NMR resonance intensity changes were parallelled by upfield shifts in the resonance frequencies, consistent with an enhanced shielding arising from close proximity of the anionic groups of the polyelectrolytes to the cationic groups of the surfactants. H-2 NMR of specifically deutero labeled surfactants contained within such phase-separated complexes revealed that complexes formed by PA displayed only anisotropic molecular motions of the surfactants, while complexes formed by PSSS displayed isotropic molecular motions of the surfactants. The results are consistent with a more compact complex being produced by more flexible polyelectrolytes.