Sol–Gel transition of alginate solution by the addition of various divalent cations: A rheological study

Several rheological properties of aqueous alginate solution have been investigated in the absence and presence of four divalent cations: Ca, Cu, Mn, and Co. The concentration dependence of viscosity in alginate solution without addition of divalent cations shows a similar behavior to that found for other polysaccharides and synthetic polymers. We have found that for Ca(II) ‐added systems, sol‐gel transition curves for different alginate concentrations can be superimposed over the concentration range of this study by using a normalized parameter. Shear‐thinning behavior has been observed for all the alginate solutions by addition of four divalent cations over sol‐gel transition process. The values of exponent b in the power‐law relation {article}{empty}{document}η ∝ γ{document} were found in the range of −0.3 ∼ −0.6. It is suggested that a considerable portion of divalent cations remains in a cross‐linking state even under shear flow. The results obtained from thixotropy measurements indicate the existence of a major framework formed in the gel‐like and well‐gelled samples, which can be maintained until shear rate (or shear stress) reaches a threshold value.