STRUCTURAL-CHANGE OF GELLAN HYDROGEL INDUCED BY ANNEALING

Structural change of gellan hydrogels induced by annealing was investigated by small angle X-ray scattering measurement. The scattering profiles of gellan in the gel and sol slates were analyzed by the cross-sectional Guinier plot assuming rod-like molecular structure. The diameter of molecules annealed at 365 K was obtained from the radius of gyration of the rod cross section. The diameter decreased from 1.2 nm to 0.5 nm by 5 min annealing and then increased to 1.5 nm. The former value of 0.5 nm was attributed to the diameter of a single double-helix molecule and the latter of 1.5 nm to the diameter of the hexagonal packing of six hydrated double-helix molecules. It is suggested that the junction zone of gellan is organized by the aggregation of the four basic units of hexagonal rods and that the size and stability of the junction zone are influenced by annealing at the temperature in the sol state.