Regular microstructures in gel-surfactant complexes: Influence of water content and comparison with the surfactant structure in water

Interaction of slightly crosslinked hydrogels of poly(diallyldimethylammonium chloride) (PDADMACI) and of copolymer DADMACl/acrylamide (AAm) with sodium dodecylsulfate (SDS) and sodium dodecylbenzenesulfate (SDBS) results in significant shrinking of the gels due to the formation of polymer-surfactant complexes. Jump-wise transitions in the collapsed state were observed for the networks with the content of cationic groups 100 and 75 mol %. The structure of complexes was studied by means of X-ray scattering method. The scattering curves for collapsed gels, where most chloride anions were replaced by anions of SDS, show a set of well-pronounced narrow diffraction maxima. Fully charged ''wet'' complexes studied at the equilibrium swelling conditions exhibit high degree of ordering, which diminishes upon drying with the simultaneous transition from hexagonal to lamellar type of ordering. In contrast to this, for DADMACl/AAm copolymer gels (75 mol % of DADMACl monomers in the initial polymerization mixture) the ordering is less pronounced in the ''wet'' state and becomes more perfect upon drying. The SDS aqueous solutions of the same concentration in the absence of gel do not show such high degree of ordering, while the system of SDS/neutral AAm gel exhibits lamellar ordering typical for low-temperature phases of SDS solutions. (C) 1996 John Wiley & Sons, Inc.