Nanostructure formation in polyelectrolyte-surfactant complexes

A phase transition to the collapsed state in slightly cross-linked positively charged gels of poly(diallyldimethylammonium chloride) (PDADMAC) interacting with n-alkyl sulfates (octyl(SOS), nonyl (SNS), decyl (SDCS), undecyl (SUS), and dodecyl (SDS) sulfates) in aqueous solution has been investigated. studied polyelectrolyte-surfactant complexes (PSC) exhibited the formation of pronounced crystalline nanostructures. The poly(diallyldimethylammonium chloride) gel-SOS, -SNS, -SDCS, -SUS, and -SDS PSC's were studied at different temperatures. The gel-SOS complex, which does not otherwise exhibit crystallinity, was successfully crystallized at approximately -6 degrees C and formed the same type of cubic lattice as the gel-SNS and gel-SDCS complexes. Corresponding gel-SNS and gel-SDCS complexes, while crystalline at room temperatures, could be melted at higher temperatures (62 and similar to 70 degrees C for gel-SDCS and gel-SNS complexes, respectively) and displayed a structure similar to that of the gel-SOS complex at room temperatures. After cooling, imperfect crystals of gel-SDCS complex were obtained. Gel complexes of mixed SDCS-SDS surfactants were also studied with small-angle X-ray scattering (SAXS). It was observed that the mixed surfactants crystallized together forming a multitude of crystalline structures gradually changing from cubic (SDCS) to hexagonal (SDS) as the composition of the mixture was changed from SDCS to SDS. Anionic linear polymer-cationic surfactant complexes were also used to show that the crystalline structure formation was due a combination of electrostatic and hydrophobic interactions and therefore should not be affected by the charge polarity. The crystalline structure formation was observed in acrylamide-hydroxamate acrylate copolymer/cetylpyridinium bromide complexes.