Structural investigations of carrageenan-surfactant systems by synchrotronX-ray scattering

Small-angle X-ray scattering by means of synchrotron radiation was used to study the interaction of kappa- and iota-carrageenan of different molar mas s in the presence of the gel-inducing ions, K+, with the ionic surfactants cetylpyridinium chloride (CPC) and dodecylpyridinium chloride (DPC). This i nteraction resulted in a more or less complete shrinking of the gel and in the formation of ordered periodic structures of the surfactant in conjuncti on with the carrageenan molecules. The influence of the polymer concentrati on for a given surfactant concentration, the content of surfactant for the same concentration of the polysaccharide, the molar mass, and the linear ch arge density of the polymer were all investigated. Decreasing the length of the alkyl chain of the surfactant, increasing the charge density of the po lymer chain, and increasing the polymer concentration for the samples explo red improved the ordering in the carrageenan-surfactant complexes. The stru ctures of the kappa-carrageenan-CPC complexes were investigated as a functi on of temperature during reversible heating-cooling cycles, and it was show n that the addition of the surfactant lead to a more pronounced temperature stability of polymer network. (C) 2000 John Wiley & Sons, me.