The rheological study of the interaction between alkali metal ions and kappa-carrageenan gels

The rheological change in kappa-carrageenan and agarose gels immersed in alkali metal salt solution was studied by the measurement of longitudinal vibrations. The storage modulus of kappa-carrageenan gel increased remarkably by the immersion, while that of agarose gel did not change so much. The reason of this change in kappa-carrageenan was ascribed to the shielding effect of the electrostatic repulsion of sulfate groups by alkali metal ions. As a result of the shielding, the helical structure was thought to become the densely packed state. The difference of the action between the two groups (Li⁺, Na⁺) and (K⁺, Cs⁺) was discussed from the viewpoint that these ions are either structure makers or breakers for the structure of water.