Small‐angle x‐ray scattering of κ‐carrageenan based systems: Sols, gels, and blends with carob galactomannan

Abstract

Abstract 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, κ‐carrageenan in the sol and in the gel states, and κ‐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 K‐carrageenan in the / 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 K‐carrageenan concentration in close agreement with what is expected for wormlike polyelectrolyte in semidilute solution. In the case of k‐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 carobgalactomannan in κ‐carrageenan gels induced dramatic structural changes. As the galactomannan concentration increased, the correlation peak tended to vanish. In contrast, no change in the 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 κ‐carrageenan double helices. © 1995 John Wiley & Sons, Inc.