Effects of Alkaline Metal Salts on Viscosity of Gellan Aqueous Solutions.

Abstract

Effects of alkaline metal salts on zero-shear viscosity (η0) of gellan aqueous solutions were investigated. The temperature (T) dependence curves of η0 showed a steep change due to the coil-helix transition of the gellan molecules. The transition temperature (TTr) depended on the salt concentration while it was independent of the cationic species. At temperatures higher than TTr, η0 decreased with increasing salt concentration. At temperatures lower than TTr, T-η0 curves at various salt concentrations produced a kind of envelope corresponding to the T-η0 curve for gellan with double-helical conformation. The addition of alkaline salts enhanced the aggregate formation at temperatures lower than TTr, and the efficiency for the aggregate formation depended on the cationic species used. At a fixed salt concentration, the degree of aggregation increased in the order of Cs +>Rb+>K+>Na + >Li. Defining the temperature at which the double helices start to aggregate as Ta, both TTr and Ta were not affected by the type of halogens, Cl −, Br− and I−.