Effects of alkaline metal salts on viscosity of gellan aqueous solutions

Effects of alkaline metal salts on zero-shear viscosity (eta(0)) of gellan aqueous solutions were investigated. The temperature (T) dependence curves of eta(0) showed a steep change due to the coil-helix transition of the gellan molecules. The transition temperature (T-Tr) depended on the salt concentration while it was independent of the cationic species. At temperatures higher than T-Tr, eta(0) decreased with increasing salt concentration. At temperatures lower than T-Tr, T-eta(0) curves at various salt concentrations produced a kind of envelope corresponding to the T-eta(0) curve for gellan with double-helical conformation. The addition of alkaline salts enhanced the aggregate formation at temperatures lower than T-Tr, rand 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 T-a, both T-Tr and T-a were not affected by the type of halogens, Cl-, Br- and I-.