H-1 AND H-2 NMR-STUDIES OF POLY(ACRYLATE) AND POLY(SODIUM STYRENE-SULFONATE) 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 sepa rately, simultaneously, and independently for the cationic surfactant cetyltrimethylammonium bromide and the zwitterionic surfactant hexadec ylphosphocholine via the intensity changes produced in the quaternary methyl proton resonances in the H-1 NMR spectrum of mixtures of the tw o surfactants. The overall anion:cation charge ratio regulated the deg ree of complex formation, independent of the cationic/zwitterionic sur factant ratio. The maximum degree of complex formation always occurred at a 1:1 ratio of polyelectrolyte anionic to surfactant cationic char ge. 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(sodiu m styrenesulfonate) (PSSS), a relatively stiff polyelectrolyte, produc ed complexes which readily redissolved. The H-1 NMR resonance intensit y changes were parallelled by upfield shifts in the resonance frequenc ies, consistent with an enhanced shielding arising from close proximit y of the anionic groups of the polyelectrolytes to the cationic groups of the surfactants. H-2 NMR of specifically deutero labeled surfactan ts contained within such phase-separated complexes revealed that compl exes formed by PA displayed only anisotropic molecular motions of the surfactants, while complexes formed by PSSS displayed isotropic molecu lar motions of the surfactants. The results are consistent with a more compact complex being produced by more flexible polyelectrolytes.