SANS INVESTIGATION OF SUPRAMOLECULAR ASSEMBLIES CONSTRUCTED IN AQUEOUS ALKYLDIMETHYLAMINE OXIDE SOLUTIONS WITH ORGANIC ADDITIVES

SANS investigations were carried out for supramolecular assemblies con structed in aqueous alkyldimethylamine oxide (C(n)DAO) solutions with organic additives. The SANS intensities of aqueous C(12)DAO solutions mixed with sodium dodecyl sulfate (SDS) were analyzed on the basis of the rescaled mean spherical approximation. The aggregation numbers and axial ratios of prolate ellipsoidal micelles were maximum at equimola r mixing. Similar behavior was also observed for the pH of the solutio ns. This non-ideality is caused by the ion-pair formation between prot onated C(12)DAO and anionic SDS. The electrostatic repulsive interacti on was dominant in solutions without salt rather than in solutions wit h 50 mM NaCl. The structure of supramolecular assemblies consisting of C(12)DAO changed drastically with the addition of cinnamic acid. Vesi cles were formed at a mixing molar fraction X (=[cinnamic acid]/([cinn amic acid] + [C(n)DAO])) above 0.3. While C(16)DAO were associated int o a lamellar structure in water, those mixed with cinnamic acid at X=0 .17 formed rodlike micelles which had a cross-sectional radius consist ent with the molecular length. Vesicles were also constructed above X= 0.3. The bilayer thickness of C(n)DAO vesicles and the C(16)DAO lamell ar structure, evaluated from quantitative analyses of SANS data, was t hinner than that estimated from the molecular length. The molecular ar rangement in bilayers was estimated. In the L(1) phase, where the hexa nol content is lowest in the C(12)DAO/hexanol/water ternary system, gl obular particles were constructed. The analysis including the contribu tion of polydispersity was applied for the SANS data. The particle con centration distribution as a function of particle size displayed a bim odal profile, indicating the coexistence of small micelles and microem ulsions.