Nanostructures of polyelectrolyte gel-surfactant complexes

Small-angle X-ray scattering was used to investigate the nanostructures of complexes formed by slightly crosslinked anionic copolymer gels of poly(sod ium methacrylate-co-N-isopropylacrylamide) [P(MAA/NIPAM)] with cetyltrimeth ylammonium bromide (CTAB), and didodecyldimethylammonium bromide (DDAB), re spectively, at room temperature (similar to 23 degrees C). Several highly o rdered supramolecular structures were observed in the polyelectrolyte gel-s urfactant complexes. In P(MAA/NIPAM)-CTA systems, in sequence with decreasi ng charge density of the P(MAA/NIPAM) copolymer chains, structures of the P m3n space group cubic, face-centered cubic close packing of spheres, and he xagonal close packing of spheres were determined at a charge content of gre ater than or equal to 75, 67, and 50%, respectively. The spheres and rods i n these structures were the spherical and cylindrical micelles formed by th e self-assembly of CTA cations with their paraffin chains inside. Both the aggregation number and the size of the micelles decreased with a decreasing charge density of the copolymer chains. In the P(MAA/ NIPAM)-DDA systems, the bilayer lamellar structures formed at charge contents greater than or e qual to 75% transferred to bicontinuous cubic structures of the Ia3d space group at charge contents of 50-67%. The rods in the Ia3d cubic structures w ere formed by the self-assembly of double-tailed DDA cations with polar moi eties inside. The formation of these highly ordered structures were driven by both electrostatic and hydrophobic interactions of the charged copolymer chains/surfactants and the surfactants/surfactants inside the charged gels . The structures became less ordered by further decreasing the charge conte nt of the P(MAA/NIPAM) chains. (C) 1999 John Wiley & Sons, Inc.