SMALL-ANGLE X-RAY-SCATTERING OF KAPPA-CARRAGEENAN BASED SYSTEMS - SOLS, GELS, AND BLENDS WITH CAROB GALACTOMANNAN

Small-angle x-ray scattering using a synchroton x-ray monochromatic radiation was carried out to investigate the structure of different polysaccharides in aqueous medium: carob galactomannan, kappa-carrageenan in the sol and in the gel states, and kappa-carrageenan-carob galactomannan mixed systems. Experiments performed on a 0.2% carob galactomannan solutions confirmed that this polysaccharide behaved as a neutral polymer in a good solvent. For kappa-carrageenan in the sol state, either in the sodium form or in the cesium form, a maximum in the scattering curve was evidenced. Position and height of this maximum changed with kappa-carrageenan concentration in close agreement with what is expected fro wormlike polyelectrolyte in semidilute solution. In the case of kappa-carrageenan in the gel state, in the cesium form, scattering curves also exhibited a maximum at an intermediate Q value. The position of this correlation peak did not change with concentration while its intensity increased. This effect was ascribed to a packing of rodlike structures by analogy with a suspension of colloidal elongated particles. This local structure could be viewed as bundles of parallel double helices. Addition of carob galactomannan in kappa-carrageenan gels induced dramatic structural changes. As the galactomannan concentration increased, the correlation peak tended to vanish. IN contrast, no change int eh cross-sectional radius of gyration was noticed. This phenomenon suggested a screening effect of the galactomannan, resulting in a loss of the correlation between the kappa-carrageenan double helices. (C) 1995 John Wiley & Sons, Inc.